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=Welcome to the OP2102 2010-2011 Exam Feedback Wiki=

Please use the discussion board to ask questions and this page to upload answers of past exam papers. To edit the page, click EDIT in the top right hand corner and start typing or cut and paste your text in. Remember to save your changes after you have finished by clicking save on the toolbar above. Spring Exam questions 1. a) Briefly describe the major componenets of a soft lens multipurpose care solution (8) b) In bullet point form outline the methodology used to assess the antimicrobial activity of a contact lens solution as defined by ISO14729 (7) 2. Decrsibe five different types of corneal staining associated with contact lens wear. For each, explain what causes each pattern of staining typically observed. (15) 3. A new patient attends for a contact lens fitting. During the anterior eye examination you record that the patient has bilateral Grade 3 stapphylococcal blepharitis. a) What is the aetiology (cause) of staph. blepharitis? (2) b) What symptoms might this patient complain of? (4) c) What are the longstanding signs of staph blepharitis? (3) d) How would you manage this patient? (6) 4. Discuss the options for contact lens correction of presbyopia. (15)


 * 4. Water is essential to the function of soft contact lenses. Discuss the influenece that water content has on the physical properties and clinical performance of a soft contact lens. (15)**

Thank you for posting this response, it's a very detailed answer. This is really Paul's area of expertise but I've added a few comments.

Water is an essential property of soft contact lenses. It acts as a plasticiser in hydrogels, causing the material to swell reducing the glassy transition temperature making the lens more flexible. Water content of a lens is determined by a polymers structure and how many hydroxyl groups it contains. Lenses have a wide range of water contents from around 38% to 85%. Water content affects; the mechanical strength, density, refractive index, optical transmission, wettability and dimensional stability and also helps with oxygen transmission, a key factor in lens design. Water content in a lens is especially important to provide metabolites to the cornea, the Dk of a lens is the diffusion coefficient (D) and solubility (k), the Dk of a material can be affected by water content. The water content also can determine what can pass through the lens, for example, lysozyme penetrates high water content lenses. Practically all oxygen diffuses through the lens to the cornea rather than tear exchange.

KE- I would put in the equation here about the equation oxygen permeanility of a lens material = Dk. I know you can't draw on this wiki but it would also be useful to draw the graph showing how Dk increases with increasing WC.

The density of a soft contact lens is dependent on both water content and the monomer composition of a lens. Density decreases with increasing water content, Hydrogels are denser than water and will not float. At 38% water content, density is 1.16g/ml at 75% this reduces to 1.05ml/g. The refractive index of a lens changes as the water content changes. Refractive index decreases as water content increases. This means the refractive index of a len can be used to work out the water content of an unknown lens. At 20% water content the refractive index is 1.46 -1.48 and at 75% 1.37-1.38, the refractive index increases almost linearly as water content decreases. The refractive index of a lens is important to maintain the correct lens power. If a lens dehydrates it can cause the refractive index to change hence causing blurred vision due to a power change. (KE- the change of refractive index from dehydration would only cause a problem in much higher powered lenses) If a lens dehydrates the Dk of the lens will also reduce.

The fact that density and refractive index both decrease with increasing WC highlights the fact that high WC lenses need to be thicker to achieve the same power- this impacts on Dk/t though. Also a high WC lens is difficult to manufacture- therefore they tend to be made thicker for this reason too. Therefore, a thick High WC lens has the same Dk as a thin low water content lens. This is why oxygen transmissibility (Dk/t) is more informative than Dk which is just a property of the lens material rather than the property of a lens itself.

Water acts as a plasticiser in hydrogels, it causes the glassy transition temperature to become reduced. This means that rigid materials can become more rubbery and flexible with the addition of water, an essential property of a soft lens. For example PolyHEMA is a hard brittle material but when water is added it swells to become soft and rubbery. The increased water content does cause the tensile strength of hydrogels to be reduced and to tear more easily than hard lenses meaning they need more frequent replacement than hard lenses. High water content lenses can be less stable, the stability can be improved by cross links and inter-chain forces of the material. Water content therefore has a marked effect on stability of soft lenses.

High WC lenses tend to have more problems with deposition too. Planned replacement or conventional lenses tend to have to be made in mid WC materials, if the WC is too high the lenses become spoiled too quickly and they have to be replaced more frequently which tends to be very expensive.

Contact lenses need to be transparent and give little scatter to give the best optical performance. Contact lenses can become opaque or translucent due to microphase separation of water, creating areas of different refractive indices, and the lens becomes milky in appearance. The lens is therefore required to have a uniform refractive index, and uniform water content. As lenses progressively dehydrate during the day it can cause deposits from the tear film to build up on the lens, contributing to light scatter, it can also cause light scatter and the dryness can cause end of day discomfort. An increase in temperature can also cause the lens to become opaque. Wettability of all soft lenses is good when they are fully hydrated, but the anterior surface of the lens progressively looses water throughout the day, especially in dry or air conditioned places. The wettability is important to maintain the pre-lens tear film (on top of the lens). A wetting angle can be used as a measurement of how well water spreads out over the lens, a wetting angle of 0degrees would mean water could spontaneously, spread out completely, a hydrophilic surface. A low contact angle is better and is a function of the surface free energy. This reduced wettability can cause the end of day discomfort and grittiness. Wettability is liked to water content and rises rapidly upto 30% and then increases slowly thereafter.

Wettability is also important for patient comfort. The more wettable the surface the more comfortable is too.

Dimensional stability of a lens changes as the water content varies. An increase in temperature, such as when the lens hits the eye, encourages water absorbtion and can lead to opaqueness. Water content also varies with pH hence the solution contains a buffer and saline to store, if the water content changes the lens stability ill also change. The water content of a lens also deacrease as tonicity increases, this has a minor effect on the eye. The higher the water content, the more easily it drys out, when a lens drys out it can lead to increased tightness on the cornea.

Water content can be calculated by : = __Weight of water X 100__ Weight of hydrated gel

Water content of a lens is difficult to measure. It is temperature and pH dependant and is also dependant on the nature of the monomers whether they are hydrophilic or hydrophobic. With conventional hydrogels it is the case the with increasing water content the oxygen available to the cornea increases. With silicon hydrogels however the more silicon it contains and therefore less water hence with silicon hydrogels an increased water content does not mean increased oxygen. 3. Your patient complains they are becoming increasingly intolerant to their soft contact lenses. Their eyes are uncomfortable, red and itchy. You suspect this patient might be suffering from contact lens related papillary conjunctivitis. a. What are the causes of this condition? (3) b. What are the signs of this condition? (6) c. What different options are available to manage this patient? (6)

CLIPC is caused by a non-specific immune response which causes the connective tissue of the papillae to become infiltrated with cells associated with the immune response. The reaction could be due to: hypersensitivity to solutions and lens deposits (especially protein deposits); mechanical trauma for example when blinking with a poorly fitting contact lens; Meibomian gland dysfunction or individual susceptibility. It has a higher prevalence in soft lens wearers than RGP wearers, but is continuously decreasing due to the availability of daily disposable lenses and improved care products.

On observation of everted lids with 10-15x magnification, the central tarsal plate may appear red and rough (cobblestone appearance) due to the localised swellings (papillae). Papillae are more numerous in soft lens wearers with a rounded apex and appear in zones 1 and 2. Papillae are flatter and appear in zone 3 for RGP wearers. Vessels may show at the papillae apex when using 40x mag. Severe cases may have conjunctival oedema, excessive mucous and mild ptosis. The cornea may display punctuate staining and superior infiltrates along with limbal redness.

Grade the CLIPC using Efron or CCLRU and record on a diagram of the lid divided into 5 sections. If more than Grade 2 cease lens wear initially. Symptoms will improve quickly but the papillae can take 2 weeks to 6 months to resolve. To avoid recurrence on resumption of CL wear refit with an RGP or another hydrogel. Change the material to reduce deposits; the modulus to reduce lens stiffness, reducing mechanical trauma and increase the replacement frequency to avoid the build up of deposits. Check the compliancy of the patient, reminding them of the appropriate hygiene and care system for example, wash hands, don’t swim, shower or sleep in lenses, rub and rinse on removal and store in a clean case with fresh solution, renew lens case monthly. Reducing the wear time can also help along with controlling and managing MGD. It may be beneficial to advise the use of protein removal tablets and change the solution to a preservative free solution or use a peroxide solution. In severe cases it may be necessary to administer anti-inflammatory treatment.

KE- Thanks for uploading a great answer. This is full of detail and displays a clear understanding of the condition and would be rewarded with a very high mark. I only think there's a small amount of detail missing that could improve the answer really. You could think about adding the following to the anser...

a. CLIPC particularly in response to denatured protein. Native protein is deposited on the lens and then undergoes conformational change becoming denatured. This isn't recognised by the immune system as self so it mediates a non-specific immune response. SiH lenses are known to deposit more denatured protein than standard hydrogels therefore the lens material can be an issue.

b. Observe with direct illumination. Redness and roughness best observed with white light. Fuorescein can be instilled then used with cobalt blue and Wratten filter to help visualise the cobblestone appearance. The superior cornea can be affected by coming into contact with the papillae (as you mentioned- staining, infiltrates and limbal redness). Useful to compare sup lid redness and roughness to inferior lid. Inf lid serves as baseline as not affected by CL wear. If asymmetry noticed may be worth advising patient of importance of compliance before any papillae start to develop. Important to differentially diagnose from follicles observed in follicular conj. Typically, whilst papillae have a central vascular tuft follicles have vesicles on the outside and are whiter than papillae. A detailed history & symptoms can help too- follicular conj caused by a viral infection and is not associated with CL wear. Patients complain of a watery discharge with no mucous and slight irritation rather than itching as associated with CLIPC.

c. The important thing to remember is that you must wait for signs of CLIPC to go before the patient returns to CL wear, otherwise there will be a rebound effect. So the patient must wait until you have seen them and advised it is safe to return to CL wear. Daily disposables may be an ideal modality, thin with low modulus and no problems with solution or deposits.

**10/5/2011** I've added 20 MCQ questions below. These are based on the how to and pathology lectures only- please remember in your exam some of these questions will be from Paul's lectures too though. In the real exam you will have five answer options rather than 4 that you have here.

I've put them on blackboard/VLE too so you can print them out from there if it's easier. I haven't added any answers yet- if you're stuck on anything then perhaps add a question to the discussion board. Please don't put your answers directly on this page as it may ruin it for other people who haven't had a chance to try them yet.

Be careful not to freak yourselves out by having a go and not being able to answer all of them- you still have over a fortnight until the exam so plenty of time for more revision. You may feel it's better to leave them until you've have longer to revise instead.

1. What slit lamp illumination technique is most suited to viewing corneal neovascularisation? a. retroillumination b. parallelepiped c. optic section d. specular reflection
 * OP2102 MCQ’s Part 2**

2. Meibomian glands in the tarsal plate secrete: a. mucin b. sebum c. aqueous d. lipid

3. According to Holden and Mertz, the minimum Dk/t value needed for extended wear is: a. 24 x 10-9 (cm x ml O2 / sec x ml x mmHg) b. 35 x 10-9 (cm x ml O2 / sec x ml x mmHg) c. 87 x 10-9 (cm x ml O2 / sec x ml x mmHg) d. 125 x 10-9 (cm x ml O2 / sec x ml x mmHg)

4. An RGP lens is fitted to the cornea with keratometry readings of 7.95 @ 180 / 7.95 @ 90. Assuming that the contact lens power was equal to the ocular refraction, and knowing that the over-refraction is +0.75DS, what is the BOZR of the lens? a. 8.10 b. 7.95 c. 8.05 d. 7.80

5. A superior epithelial arcuate lesion (SEAL) is most likely to be confused with: a. smile stain b. papillary conjunctivitis c. superior limbic keratoconjunctivitis (SLK) d. 3 & 9 o’clock staining

6. For an eye with the following ocular parameters, what would be your first choice of soft lens BOZR? (Keratometry 7.67 @ 170 / 7.82 @ 80, HVID 12.5mm, Refraction -2.75DS) a. 7.80 b. 7.70 c. 8.60 d. 8.40

7. For the eye described in the previous question (6), what would be your first choice of soft lens diameter? a. 12.5 b. 10.5 c. 14.5 d. 13.5

8. What is NOT a typical symptom of sterile keratitis? a. lacrimation b. foreign body sensation c. worsening on lens removal d. moderate pain

9. A back surface toric RGP lens is required for which of the following keratometry and ocular refraction combination? a. K’s 7.85x180/7.85x90 Refraction -2.00/-0.25x180 b. K’s 7.85x180/7.60x90 Refraction -2.00/-0.25x180 c. K’s 7.85x180/7.15x90 Refraction -2.00/-3.50x180 d. K’s 7.85x180/7.85x90 Refraction -2.00/-1.50x180

10. The log reduction of each bacteria required by the primary criteria of ISO 14729 is: a. 3 b. 1 c. 5 d. 4

11. Demodex brevis mites infest the: a. eyelash follicles b. glands of Zeis c. glands of Moll d. goblet cells

12. According to Harvitt and Bonanno, the minimum Dk/t value needed for no corneal anoxia during open eye conditions is: a. 24 x 10-9 (cm x ml O2 / sec x ml x mmHg) b. 35 x 10-9 (cm x ml O2 / sec x ml x mmHg) c. 87 x 10-9 (cm x ml O2 / sec x ml x mmHg) d. 125 x 10-9 (cm x ml O2 / sec x ml x mmHg)

13. The following RGP lens is fitted in alignment 8.00/9.00/-3.00DS. If the TD needs to be increased by 0.5mm, what BOZR must be ordered to maintain equivalency? a. 8.00 b. 9.50 c. 8.05 d. 7.95

14. Which of the following is NOT a symptom of blepharitis? a. burning b. grittiness c. mucus discharge d. mild photophobia

15. If the visual acuity achieved with a soft lens is worse immediately after a blink, this indicates: a. a tight fitting lens b. a loose fitting lens c. an alignment fitting lens d. has no bearing on the fit of the lens

16. For a contact lens care solution, the function of a chelating agent is to: a. aid removal of tear film proteins b. aid removal lipid deposits c. promote lens wetting d. maintain solution osmolarity

17. Which of the following tear film assessment tests is the least invasive? a. fluorescein tear break-up time b. schirmer strip c. tear prism height d. phenol red thread test

18. For the following soft toric lens prescription (+3.25 / -1.75 x 20), what would be your next lens choice if the lens had rotated and stabilised at 10 degrees left (clockwise)? a. +3.25 / -1.75 x 180 b. +3.25 / -1.75 x 0 c. +3.25 / -1.75 x 30 d. +3.25 / -1.75 x 10

19. A smile stain is NOT typically caused by: a. drying of the post lens tear film b. incomplete blink c. low humidity d. poor insertion and removal technique

20. What is the most identifiable feature of Pseudomonas keratitis? a. dendritic infiltrates b. increased intraocular pressure c. paracentral ring infiltrate d. large fluffy infiltrate

** 08/09 Q4. Describe the signs and symptoms of MGD in a contact lens wearer. Outline your advice to such a patient in terms of management (15). ** MGD is a non inflammatory condition which causes obstruction of the meibomian glands in 20-40% of non CL wearers and 30-50% of CL wearers. The normally clear, oily secretions become semi-solid, toothpaste- like plaques with an increased melting point. This is due to increased keratinisation of the epithelial walls of the meibomian gland ducts which leads to the formation of keratinised epithelial plugs that create a physical blockage restricting the outflow of meibomian oils. MGD is associated with cosmetic use, microbial contamination, anterior blepharitis, excess eye rubbing and secondary to papillary conjunctivitis. Along with the cloudy, yellow, paste-like secretions on expression, signs of MGD include: tear foaming/frothing at the lower tear meniscus; reduced tear break up time indicating tear film instability; corneal staining and in long standing cases may be associated with additional signs such as irregularity, distortion and thickening of the lid margins, slight distension of the glands, mild to moderate papillary hypertrophy, vascular changes and chronic chalazia. The patient will complain of dry, itchy red eyes and contact lens intolerance. The adhesion of waxy dysfunctional meibomian oils to the surface of the contact lens will cause blurred or smeary vision and the lens will dehydrate due to the physical barrier to wetting. MGD can be graded using the Efron scale. If it is more than Grade 2 then lid scrubs must be advocated to clean and remove excess lipid. A warm compress followed by gentle massage may help expression of the glands. Antibiotics could be administered in severe cases and artificial tears may help as a short term solution to promote comfort. It is important to control MGD in CL wear as the reduced tear film stability can cause dry eye and reduce the comfort and wearing time. Corneal staining may cause discomfort and increase the risk of infection. To reduce these CL associated problems it may be necessary to cease lens wear initially until the MGD in controlled. On resuming lens wear increasing replacement frequency and careful cleaning with a surfactant cleaner will reduce the risk of infection and remove lipids which have adhered to the lens. Refitting with a SiH or a low water content lens that is less prone to dehydration may be beneficial if the patient if suffering from dry eye. It may be a good idea to remind the patient of the care and hygiene of contact lenses to further reduce any risk of infection for example, no swimming, showering or sleeping in lenses, wash hands prior to insertion and removal, rub and rinse lenses on removal before storing in fresh solution and renew cases each month.

KE- this is an excellent answer- really well done. You cover everything very concisely and demonstrate you understand the impact of MGD on a CL wearer. I'm really struggling to find any fault here! Have just listed a few, very minor, points below.

I think it would be useful to include a sentance about the function of the meibomian glands- secrete lipid which creates the superficial layer of the tear film which promotes stability and limits evaporation of the aqueous portion of the tear film. The meibomian gland orrifices may appear healthy, it is often only on expression that you can detect the contents of the gland are abnormal.

Just to help you understand the treatment of MGD... Whilst optoms used to recommend home made lid scrubs (like baby shampoo or bicarb of soda) they are often ineffective and patients are often poorly compliant. It is much more worthwhile suggesting a commercially available lid scrub product. The point of the warm compress is to melt the lipid so it can be expressed with massage. We used to recommend hot flannels or even wrapping a hot spoon in a flannel and applying that but they often cool down too quickly to be effective. The best thing is to suggest an eyebag (bag containing flax seeds thats warmed in the microwave) or the blephasteam (steam producing goggles) to deliver sustained, effective heat.

3/5/2011 Hope all the revision is going well. I have put up some comments for the answers that have been submitted. Thanks again for posting them and I hope you all find the comments useful. I'm going to put up a few questions that were in the revision lecture so fell free to upload your answers.

1. What are the risk factors for MK? MK stands for Microbial Keratitis and is caused by a direct infection of a bacteria, fungi or protozoa so as to cause and inflammation reaction. There are many risk factors some are modifiable while others are non-modifiable. Some risk factors are the type of CL that a patient has. For example a EW lens has a higher risk of MK than a daily wear lens. The risk of contracting MK in an EW lens increases by 4-8x. Standard Hydrogel CL also increase the risk of MK with a reduced risk in a SiH lens or even lower risk factor in a RGP. When the patient wears CL's can be a risk factor for MK, such that sleeping in daily disposable lenses increases the risk of MK by 9x. Swimming in CL also increases the risk of MK by a large 17x. This is due to the bacteria's that are found in the swimming pools, such as the Protozoa Acantheomeoba so without proper disinfectant or disposal it can cause MK on the cornea. It has been proven that internet purchase of CL is a risk factor for MK. This is because it usually involve non-compliance as they have not been seen by a optometrist or had a proper aftercare. They then may not clean there lenses properly, so internet purchase rather than in-store purchase increases the risk of MK by 2x.

The non-modifiable risk factors for MK include gender. for example males have an increased risk of MK than females, so a male patient is more at risk. Sometimes poor health is non-modifiable at the time and this can also increases the risk of MK. The time of year is also a risk factor for MK as MK is seen more in the winter months than in the Summer. Smoking also increases the risk of MK, however this can be seen as modifiable as to reduce this elevated risk they should stop smoking.

The main risk factor is non-compliance by CL-wearers. This includes poor hygeine, inadequate lens cleaning, swimming in contact lenses and wearing lenses longer than advised.

KE- a good way to answer this question is to organise it into modifiable risk factors and modifiable risk factors- there is a table in your inflammation and infection lecture. If a patient has many non-modifiable risk factors then it is important to prescribe them the safest lens wearing modality possible (RGP or daily disposable with no EW) to reduce their risks and/or try to get them to have regular aftercares (every 6 months) to be able to monitor them carefully and to try and correct any non-compliance.

2. What are the 4 different measures of the oxygen performance of a contact lens? 1-Dk. This measures the permeablity of a CL, with D=diffusivity which is the ease of movement of molecules across the CL and k=solubility. This is calculated by multiplying the Fatt unite by 0.75 to give a value in Dk form. It is effected by lens thickness and it is important to take into account the boundary effect and the edge effect for lens permeablity. 2-Dk/t. This measures the transmissiblity of a CL when matched against a -3.00 lens. However this value varies across a CL and is different for different lens powers, but is a more useful value when assessing the oxygen performance of a CL. 3-EOP. This measures the Equivalent Oxygen Potential, which relates to the thirst of the cornea, which is created by a graph of known results being compared to an unknown CL. 21% is the optimal value. 4-Oxygen Flux. This measures the oxygen that reaches the cornea per unit of time which is based on Ficks law. This is calculated by the greater the tension the greater the push of oxygen. the Maximum flux is when behind the lens equals the flux infront of the lens. This is the best measure of oxygen performance on a lens, however it is the hardest value to measure.

3. What are the signs of hypoxia in the epithelium, stroma and endothelium?

4. What are the requirements of an ideal lens solution?

5. What are the major components of a contact lens solution and what do they each do?

6. How is a lens care solution efficacy tested?

7. Give 2 examples of a non-invasive tear film assessment test. For each, indicate a brief method and the result you would expect for a patient with dry eye and a normal, healthy patient.

8. Give 2 examples of an invasive tear film assessment test. For each, indicate a brief method and the result you would expect for a patient with dry eye and a normal, healthy patient.

9. List the strategies available for the management of contact lens induced dry eye (CLIDE).

10. Briefly outline 2 different lid conditions and 2 different lash conditions. For each, indicate if this is a contraindication for contact lens wear.

5/4/11 I have uploaded the exam questions for the 2009-2010 OP2102 exams. Feel free to upload your answer and I will add comments and corrections.

Describe the aetiology and management of contact lens induced corneal neovascularisation (15)

Neovascularisation (neovasc) can be described as the formation and extension of vascular cappillaries within and into previously avascular regions of the cornea. Superficial neovasc is the most common of the various forms of contact lens (CL) induced vascular responses. Prevelance of neovasc for PMMA and RGP wearers is less than 0.05%, however is much higher in extended wear soft (especially aphakes due to the think positive lenses). There are numerous different theories as to the aetiology of CL induced neovasc. Theory 1 suggests that chronic hypoxia (lack of oxygen) induces stromal oedems (excessive fluid in the stromal layer).Tight fitting CL's may indent the cornea and restrict venous drainage causing lactic acid accumulation. The oedema causes stromal softening resulting in stromal thinning and/or reducing the physical barrier to vesel penetration. This renders the tissue more susceptible to vessel penetration. Theory 2 involves a factor in the cornea - corneal fibroblasts and lymphocytes - that restrains cell division and migration of vascular cells of the peri-corneal plexus. Corneal neovasc occurs due to substances that inactivate the normally normally present angiogenic inhibitors. The most convincing theory is that corneal neovasc is produced by locally generated vasostimulory factors (most likely free cellular elements, humoral components, epithelial cell factors or extrinsic substances).

Corneal neovasc is extremely serious and on observation should be managed immediately. If grading is between 1 and 2, oxygen concentration to the cornea should be increased by increasing Dk or Dk/t, replacing with RGP's or SiH lenses, changing to daily wear or reducing wear time. Mechanical stimulation should be decreased and exteneded lens wear should be ceased. If the neovasc is higher than grade 2, it may cause a serious threat to vision and CL wear should be ceased immediately. The above steps should be taken, but very careful monitering should take place if the patient wants to resume CL wear at some point in the future. A care system should be derived to minimise toxic/allergic responses, and in extreme cases where vision is lost, keratoplasty may be necessary to restore vision. Cessation of lens wear will halt the progression of vessel infiltration into the cornea but empty ghost vessels will remain for months or years. Resumption of lens wear will result in immediate refilling of the vessels. Thus in advanced cases, long term cessation is indicated until ghost vessels are no longer visible.

KE- this is an excellent answer, well done. I'm struggling to find fault and give you feedback on this answer! I notice you haven't mentioned about the 4th theory- the neural control theory for the aetiology. The other thing is about the management- I would include about careful viewing and grading for the management of neovasc- so measure ingrowth by altering the slit length or width or with the Efron scale. Ideal observation is with direct or indirect retroillumination, 16x mag initially and red-free illumination can help to increase contrast.

Describe the appearance and management of five types of Fluorescein staining that we commonly observe in contact lens wearers. (15)

KE- In the exam I would suggest you draw pictures for each of these- I know it's not easy on this wiki. I would suggest you include if the condition is bilateral and unilateral. Remember this question is not only asking about the appearance but also the management of each type of staining. If you look at the answers below you will notice you haven't always included it. Not providing a full answer is a really common error in exams and highlights the need for you to read the question carefully- perhaps organise each of your 5 answers with an appearance and management sub-heading- but also to re-read the question after you have written your answer to check you have covered everything.

There are 3 main types of dyes used to observe corneal or ocular staining. These are Rose Bengal, which stings on instillation if the epithelium of the cornea is damaged, Lissamine green is used more for conjunctival staining in the assessment of dry eye, Sodium Fluorescein is the most commonly used dye in the assessment of corneal staining and fluoresces green under cobalt blue light. Contrast can be enhanced by using a Wratten filter as it absorbs reflected blue light from the ocular surface. Fluorescein is used to assess ocular surface integrity as it enters damaged epthelial cells. Depth can be assessed by using a thin optic section and extent can be graded with the Efron or CCLRU scale. There can be a number of causes for corneal staining that include; mechanical damage, exposure to certain environments, metabolic causes, toxic, allergic and infectious causes, and the pattern of staining may indicate the cause. There are a number of fluorescein stains that can be commonly observed in contact lens wearers, these include;

3 & 9 o’clock staining – this is common in RGP wearers, lens vaults top lid away from cornea leading to areas of corneal non-wetting in the 3 and 9 o'clock areas. This can also be caused by incomplete or infrequent blinks. In this case refitting to a flatter fitting RGP lens should be considered to prevent this from occurring.

KE- 3 % 9 o'clock staining would often be bilateral and can be very difficult to manage. Initially, lens wear needs to be ceased until the staining has resolved (length of time depends on the depth and extent of staining) then the lens needs to be refitted. Generally increasing the TD can help by increasing the area of coverage by the lens to promote wetting. If it is caused by incomplete blinking then blinking exercises could be beneficial. If there is no resolution by altering the RGP fit refitting with a soft lens could be considered.

Foreign Body staining – this can occur when a foreign body gets caught underneath the contact lens preventing it being flushed from the eye by the lacrimal gland. The patient may have reported difficulty in inseting their lens that morning, also soft lenses can act as a bandage and depress the sensation of the foreign body, so the patient may be unaware of the particle.

KE- This would typically be monocular. In a RGP wearer, the foreign body could have blown into the eye from the environment. If it gets underneath the lens it typically causes characteristic vertical tracks of staining as the lens moves vertically on a blink before it is flushed out by lacrimation. Management would require ensuring the FB has been removed- evert lid and check and check anterior eye to ensure it has not embedded. If it cannot be removed easily refer to Eye Casualty. Lens wear should be ceased until it has resolved (antibiotic drops may be indicated if the staining is particularly deep to reduce the risk of infection), non-preserved artificial tears may help if px very uncomfortable. Check cornea before returning to lens wear to ensure the staining has resolved. Care should taken to make sure the lens has not been damaged- if this is the case it must be replaced before resuming lens wear.

SEAL staining – this is a superior epithelial arcuate lesion, typically mechanical aetiology in soft lens wearers and is more common in SiH wearers due to their higher modulus. Patients with this staining should cease lens wear until the condition improves and if it persists consider a lens refit, or changing to a softer lens.

KE- This is likely to be bilateral although may be asymmetric in appearance. As you said this is caused by mechanical chafing of the cornea by the lens from the inward pressure of the lid. The important thing to mention is the patient needs to be carefully monitored here when they return to lens wear. You need more detail about the lens refit to demonstrate you understand this condition- lower modulus, thinner, steepen fit if excessively flat (flat lens causes more mechanical issues), cease EW or reduce WT's, refit with daily disposable (very thin) or standard hydrogel if no resolution with methods mentioned earlier.

Smile staining – this is due to drying of the tear film behind the contact lens leading to dessication of the inferior cornea, it is usually of arcuate shape on the inferior cornea. If it is due to incomplete blinking the patient should do blinking exercises, if its beacause of lens drying a refit should be considered. Can also be due to dry environment.

KE- This will often be bilateral but may be asymmetric. As you said this is caused by drying of the post lens tear film. It often occurs with relatively high WC, thin lenses. Again, you need more detail about the refit to indicate you understand the condition- this is where you need to put your knowledge of staining and contact lens induced dry eye (CLIDE) together. Refit standard hydrogel with SiH or even RGP. Reduce WC/increase lens thickness, lens with low dehydration tendency (Proclear). If due to environmental then increase the humidity if possible- use of humidifier.

CLPU staining – this is usually the result of a sterile contact lens peripheral ulcer caused by inflammation of the cornea although no direct microbial penetration has occurred.

**KE- you would more detail here for top marks. These is typically a unilateral condition. It is a focal, full thickness epithelial lesion with fluorescein penetration into the stroma causing a distinctive gloe or halo around the ulcer. It is typically located in the peripheral cornea and is 0.1-1.5mm in size. It is often associated with EW and caused by an inflammatory response to bacterial toxins so is often associated with blepharitis. CL wear should be ceased immediately and the patient should be seen later the same day to ensure improvement and rule out MK. Patient should be monitored until resolution. Lenses should be replaced and patient reminded of the importance of hygiene and compliance and risks of EW. Any bleph should be managed with lid scrubs. If a repeated episode occurs EW should be ceased. Increasing replacement frequency can help eg daily disposables.**

1. A soft contact lens wearer presents with unilateral, Grade 3 conjunctival hyperaemia. How do you decide if this is Contact Lens Acute Red Eye (CLARE)? Use bullet points to outline your approach to the diagnosis. (15)
 * Summer Resit Exam**

=** Response 1 **= ==== CLARE is an acute complication of extended soft lens wear. It is an inflammatory response to proteases being released by bacteria trapped under the contact lens. It is sometimes referred to as immobile lens syndrome, tight lens syndrome or contact lens over wear syndrome, although these are less appropriate names. ==== ==== The prevalence of a patient with bulbar conjunctiva hyperaemia with a grade of >2 in non-contact lens wearers is 15% and in RGP lens wearers is 15-20%. Differential diagnosis is required as conjunctival hyperaemia of grade 3 could be a sub-conjunctival haemorrhage or it could be CLARE. ====

To decide whether your patient has CLARE the differential diagnosis should start with a detailed history and symptoms:
==== · Establishing whether the patient has any symptoms and their onset will aid the diagnosis. The onset of CLARE tends to be on waking in the morning, usually the patient presents with a red and severely painful eye which may even have woken them up. They may present with excess tearing and photophobia which is indicative of CLARE. If the patient is asymptomatic then it is more likely to be a sub-conjunctival haemorrhage. ====

· This may outline that the patient is over-wearing their lenses or is wearing extended wear (EW) lenses, which may indicate CLARE.
==== If the patient is wearing their contact lenses, the lens may display little or no movement upon initial examination and debris may be seen trapped beneath the lens. Epithelial staining may be seen following the removal of the lens. ====

A detailed slit lamp examination of the anterior eye should then be performed:
==== · The area of hyperaemia with a sub-conjunctival haemorrhage will be localised and is likely to spare the limbus. Whereas CLARE is more generalised and the hyperaemia occurs at both the conjunctiva and limbus. ====

From the detailed history and symptoms and anterior eye exam, the diagnosis should accurately differentiate between a sub-conjunctival haemorrhage and CLARE.
= Response 2 = ==== Conjunctival hyperaemia or red eye usually refers to hyperaemia of the superficial blood vessels of the conjunctiva, sclera or episclera. Common condition affecting 15% of non-CL wearers, 15-20% of RGP wearers and is even more common in SCL wearers. It can occur due to a number of reasons including conjunctivitis, blepharitis, acute glaucoma, injury, sub-conjunctival haemorrhage, keratitis, airborne contaminants, stress, drug use, dry eye and contact lens induced red eye or CLARE. CLARE is an acute, unilateral, inflammatory response to proteases released by bacteria trapped underneath a contact lens. CLARE is a common condition in contact lens wearers that over wear or sleep in their lenses and in patients wearing extended wear contact lenses. In order to confirm that this patient is suffering from CLARE a practitioner would determine the following; - Is the condition affecting one eye only – CLARE is usually a unilateral condition - Using a slit lamp examine the anterior eye for conjunctival and limbal hyperaemia, corneal infiltrates, AC flare and endothelial bedewing - If the patient has been over wearing or sleeping in their lenses - If the condition is most prevalent in the morning, is painful, causes tearing and photophobia. If the patient is presenting with the above signs and symptoms it is very likely that they are suffering from CLARE. In this case the patient should be advised to cease lens wear immediately and return to the practice later that day to assess whether the condition has improved. Lens wear can be resumed when the infiltrates subside which can take a few weeks. In the meantime the patient should be restricted to wearing daily wear lenses. ====

==== KE These are some really great answers, both with good levels of detail. I think the opening few sentances of each which defines the aetiology and prevalence are particularly well done. This question is about differential diagnosis of CLARE and grade 3 conjunctival hyperaemia which should not be confuced with a sub-conjunctvial haemorrhage. Notice this question doesn't actually ask about the management and treatment of CLARE and conjunctival hyperaemia but I do think it is worth including in your answer that you would see the patient again later the same day to ensure if it is CLARE that it is resolving and ruling out MK. ==== ==== The important thing to consider is this question is essentially asking you to differentially diagnose CLARE and conjunctival hyperaemia and to use bullet points to organise your asnwer. I think the easiest was to construct an answer is to use the following subheadings. ====
 * ==== Aetiology ====
 * History
 * Signs
 * Symptoms

This is a BRIEF ANSWER ONLY, obviously if I was answering it myself in the exam I wouldn't be this brief but I just wanted to get the detail across to you.

> CLARE- acute, unilateral, inflammatory response > Conj hyp- generally bilateral if metabolic, hypoxia, solution toxicity, may be unilateral if infection or sectional if caused by lens defect > CLARE-sudden onset, patient sleeping in lenses overnight or overwearing lenses > Conj hyp- typically chronic if metabolic, hypoxia, toxicity. May have slower onset if infection. > CLARE- conj and limbal hyp, corneal infiltrates near limbus, AC flare, endothelial bedewing > Conj hyp- depends on specific cause, could give few examples eg. toxicity- diffuse corneal staining throughout whole cornea. Bacterial infection- sticky discharge, corneal ulcer etc > CLARE- morning onset, may have been woken by pain, painful red eye, tearing, photophobia...improvement later that same day (ensure not MK) > Conj hyp- typically asmptomatic unless severe such as infection.
 * Aetiology:
 * History (by detailed H&S):
 * Signs (Slit lamp exam):
 * Symptoms (by detailed H&S):

2. Describe the signs, symptoms and management of blepharitis. (15)
==== Blepharitis is an ocular condition characterised by chronic inflammation of the eyelid. The severity and time course of the condition can vary. Onset can be acute resolving without treatment within a few weeks but the condition is usually a long standing or chronic inflammation with varying severity. Early signs of blepharitis include; collarettes (anterior crusting), lid erythema (lid redness), dilated lid margin veins and swelling of the lid margins. Long standing signs of blepharitis include; thickened lid margins, hordeolum on the lid margins, trichiasis, madarosis and poliosis, blocked meibomian glands, corneal staining and saponification of tears by excess fatty acids. The patient will complain of pain, redness and irritation of the lids, a FB sensation, dryness, itching and photophobia. Symptoms can be more prevalent in the morning and be worse than the signs the patient presents with. Contact lens patients usually complain of being unable to wear their lenses for long periods of time or that the lenses are causing even more irritation of the eye. Blepharitis does not directly cause problems with vision; however it can affect the tear film and lead to blurred vision in some cases. The condition can be classified into anterior blepharitis which affects the glands of Zeis and Moll and posterior blepharitis which is an inflammation of the meibomian glands. Anterior blepharitis can be caused by either a staphylococcal infection of the eyelash follicle, leading to collarettes at the base of the lashes and an inflammatory reaction to bacterial exotoxins or an allergic reaction to the bacteria themselves. It can also be caused by a seborrhoeic infection of the glands of Zeis or Moll, resulting in soft greasy scales and greasy and stuck together lashes. Blepharitis can be quite easily managed by applying warm compresses to the eye which will soften the lid margin debris and oils blocking the meibomian glands. The lids can also be washed using lid hygiene products or baby shampoo. In more prevalent cases a topical antibiotic like chloramphenicol can be applied, and in even more severe cases systemic antibiotics or corticosteroids can also be considered. Artificial tears can also be used to provide comfort. ==== ==== KE- a very good answer with lots of detail. The use of a plan for your answer might help the structure here. I would start off with a definition and then explain the 2 forms (staphylococcal and seborrhoeic). Then I would use subheadings for the signs, symptoms and management. It was a good idea to define the signs as early and longstanding but I would also list the different signs for staphylococcal and seborrhoeic bleph here too. Blepharitis is a chronic condition and very difficult to treat. The main management is to improve lid hygiene. This used to be done with home made lid scrubs of baby shampoo or bicarbonate of soda diluted with cooled boiled water but these are often ineffective. It is much better to use commercially available lid scrubs to clean and remove the crusts. The important thing to stress here is this is a chronic condition so treatment will have to be ongoing although the frequency of lid care may be reduced from twice a day to daily or every other day when the bleph is well controlled. ==== ==== To get more marks we would expect you to consider the consequences to a contact lens wearer. The patient is at greater risk of infection, staining, limbal or conjunctiavl hyperaemia or infiltrates due to the increased bacterial load. In severe case CL wear might need to be ceased until the bleph is under good control- the patient should not resume lens wear until you have have given the go ahead (careful grading needed here). This patient might not be suitable for EW due to increased risk of MK or CLARE therefore they should be advised of this. They may have associated dry eye therefore you might need to change lens material (SiH or RGP). Furthermore, the patient should be advised of the need for careful lens cleaning and frequent lens replacement should be advocated, perhaps daily dispoables would be the ideal modality. ====

3. Your patient complains they are becoming increasingly intolerant to their soft contact lenses. Their eyes are uncomfortable, red and itchy. You suspect this patient might be suffering from contact lens related papillary conjunctivitis. a. What are the causes of this condition? (3) b. What are the signs of this condition? (6) c. What different options are available to manage this patient? (6)

4. Discuss the toric contact lens options available for correcting astigmatism. Include in your answer a discussion of the pratitioner problems associated with toric lens fitting, and how these problems are solved through lens design and clinical practice. (15)

__Response 1 __
 * Toric contact lenses can be prescribed for uncorrected astigmatism of 0.75DC or over, or due to induced astigmatism formed by the tear lens. If the patient has a poor tolerence tolerence to a spherical RGP, then only soft toric lenses are apprpriate. Toric lens rescribing is based on 2 assumptions: corneal and lenticular astigmatism. Most corneal astigmatism is transferred thorugh a soft lens to its anterior surface so has little effect on the quality of vision. Soft lenses, when fitted, commonly rotate from their natural postion. This can be problematic with torics, as the axis needs to be accuarte to provide good vision. This is overcome by markings on the lens in the forms of small faint lines to indiciate the bottom of the lens. It is then easy for the practioner to evaluate the rotation and order a change in axis by however much the lens has rotated (If the lens rotates 10 degrees to the left, then subtract 10 degrees from the original axis and the lens should sit to give optimal vision). When considering RGP lenses, corneal and lenticular astigmatism needs to be compared with the patients Rx. Spherical RGP's can correct corneal astigmatism by the tear lens forming along the steeper axis. If the corneal astigmatism is different to the Rx, then a toric RGp should be considered: **
 * Back surface toric lenses have a toroidal back surface but a spherical front surface. If the BOZR is matched to the K readings there may be insufficiant tear exchange so the steeper meridian must be fitted little flat. Front surface torics correct for residual astigmatism when a Px is fitted well with a spherical back optic zone. When a back surface toric induces sufficient uncorrected astigmatism, a bi-toric lens is required. The front surface contains a cyl soely for the correction of induced astigmatism. A bi-toric lens can rotate without visual disturance because the effect of the rotation is counteracted by the equal change in cyl power of the tear lens. This unfortunately cannot be said for the other torics described and stabilisation is necessary to maintain orientation. An effective method is prism ballasting where base down prism os introduced into the lens so it will be heavier at the lens base. Gravity causes the prism to lacate inferiorly hencethe axis is positioned correctly. Truncation involves slicing the bottom of the lens to form a 'shelf' that will rest upon the lower lid and keep the axis alligned. This method is less comfortable that prism ballasting. Dynamic stabilisation involves thinning the lenses superiorly and inferiorly and relies uponthe 'watermelon seed' principle for re-orientation during a blink. **
 * <span style="color: #800080; font-family: 'Comic Sans MS',cursive;">RGP lenses are sometimes tricky to fit and are difficult for the patient to get used to, but they offer excellent visual quality and it is important that Practictioners encourage their use for high astigmatic patients, providing their problems can be solved. **

KE- this can be a very tricky question to answer. This question is asking you to compare the different options (soft torics and RGP torics) for different types of astigmatism (corneal, lenticular, mixed etc). In the revision lecture I got everyone to fill in a table that considerent different Ks and spec Rxs to get you thinking about whether the astigmatism is corneal, lenticular or mixed and then thinking about what type of RGP and soft toric design would be appropriate. I would suggest you have a look at that table to help you form a more descriptive answer to the first part of the question so it includes small diameter RGPs, toric periphery, front and back surface torics and bitorics.

Some things you might also include are that spec astigmatism = corneal astigmatism + lenticular astigmatism and that corneal astigmatism can be calculated from the keratometry readings where a difference of 0.05mm equals 0.25DC. Spectacle astigmatism that isn't derived from the cornea must therefore be lenticular.

Problems that practitioners encounter are that toric lenses rotate off axis- this occurs because the way the lens interacts with the lids and the ocular surface. If a lens stabilises in an off axis position, we can reorder the lens to take into account this rotation based on the LARS and CAAS rules (explain these accronyms in your answer though). ANother problem is the availability of certain parameters- especially for soft lenses. Daily and fortnightly soft toric lenses have a very limited parameter range (cyl power and axis options) compared to monthly or planned replacement lenses. For very high cyl powers it may be necessary to use a conventional lens (made to measure) but these are expensive and must be carefully cleaned. You have mentioned the different stabilisation techniques but it might be worth mentioning that if a patient has a particular problem with one type of lens stabilisation method then it may be worth trying a different lens that utilises a different stabilisationn technique.

<span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">Response 2: (Answer Plan- In the exam I would expand on this but just wanted to see if I was on the right track) <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">Intro <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-What is a toric lens, when would you give a toric CL. (0.75cyl) <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-How it is calculated from K readings, 0.05difference= 0.25DC I would just mention the diff types of astig here- corneal and lentic and that spec astig = corneal astig + lentic astig and to calculate the corneal cyl you measure the corneal curvature and calc from the equation above.

<span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">Options available; <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">Soft- easy to fit, like spherical but toris, use markings to ensure the correct orientation, LARS. take into account the chang of Rx from spectacles to CL Think about adding methods of stabilisation for soft torics here- prism ballast or dynamic stabilisation. Also, it doesn't matter if the astigmatism is corneal or lenticular- as there's no tear lens we just fit the lens based on their spec Rx.

<span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">RGP <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-spheres, tear lens corrects astigmatism when astigmatism is all corneal <span style="color: #008000; font-family: 'Comic Sans MS',cursive;">up until a point though- beyond 2DC (there is too much diff in the Ks and the lens will rock along the steeper meridian, be uncomfortable and decentre) you might need to consider a small diameter or spherical with toric periphery to ensure centration and comfort. <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-torics, done with k's to assess if corneal or lentic <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">back toric-for when all astigmatism is corneal - <span style="color: #008000; font-family: 'Comic Sans MS',cursive;">You typically choose a back surface toric when the you have a toric cornea but no spec astig (in this case the lenticular astig is equal and opposite to the corneal astig thereby cancelling out). If you put a spherical back surface on this cornea the tear lens will correct the corneal astigmatism- beacause this is no longer equal and opposite to the lentic astig it actually ends up inducing unwanted astigmatism.The toric back surface completely aligns with the cornea therefore only a thin spherical tear lens is created- therefore the corneal astigmatism is not corrected. <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">front toric-for when all astigmatism is lenticular - yes, this is true if you have a spherical cornea and the astigmatism in the spec Rx is soley lenticular. <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">bi-toric- when mixture of corneal and lenticular astigmatism- <span style="color: #008000; font-family: 'Comic Sans MS',cursive;">or even a front surface toric- the spherical back surface allows the corneal astigmatism to be corrected with the tear lens, the residual lensticular astigmatism is corrected by the front surface toric. <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">spherical centre with toric periphery- <span style="color: #008000; font-family: 'Comic Sans MS',cursive;">to stablise and cancel out some astigmatism- see above, you would use this to correct higher levels of corneal astigmatism. The tear lens in the spherical part correct the astigmatism. The periphery is made toric to stabilise the fit ie, the steep and flat meridians of the periphral lens align with the steep and flat meridians of the lens. This stops the lens rocking, decentring and being so uncomfortable- which would happen if the periphery was toric too. Your answers above don't really consider the K's and spec Rx and are too simplistic. Have a look at the table we did in the revision lecture and try to think about the importance of the Rx and Ks. Have a look at some of the comments I've made and see if it helps you understand.

<span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">Problems; <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-sphere RGP can induce more astigmatism as they can reveal the lenticular astigmatism so be careful when giving these <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-stabilisation <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-truncations- benefits and the problems, eg sudden change in thickness will be uncomfortable <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-prism ballast- benefits and problems <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-dynamic stabilisation- benefits and problems <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">- double truncation- benefits and problems, if px has a problem with one type of stabilisation technique then try another type. Other problems include rotation (LARS & CAAS rule)- I know you have discussed this above though. Availablity of parameters. Extra expertise required for RGP vs soft

<span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">Conclusion <span style="color: #10c1c1; font-family: 'Comic Sans MS',cursive;">-many options available, more options depending on source of astigmatism with RGP's. main problem is stabilisation but overcome with LARS and stabilisation techniques.

KE- sorry for the slow response, I've only just noticed this. Thanks for posting it- it's a really good idea to organise your thoughts into this kind of plan. Have a look at the comments I've added above.

Response 3 Astigmatism is fairly common in refractive errors, spherical contact lenses may not always be able to give the best results for astigmatic patients, both visually and regarding fit. Toric lenses are available in both RGPs and in soft lenses and an increasing wider range of astigmatic prescriptions are able to be catered for with advancing technology, and at a reasonable price. There are two main classes of astigmatism that need to be corrected for in contact lenses these are ocular (corneal) and lenticular. Corneal astigmatism is measured by measuring the curvature of the cornea with a keratometer, 0.05mm difference between the two meridians equated to 0.25DC of astigmatism. Lenticular astigmatism is any difference between the corneal astigmatism and the spec rx.

To firstly discuss RGP lenses, there are two types of astigmatism need to be corrected for with toric RGP lenses; residual and induced. Residual astigmatism is the uncorrected astigmatism when a spherical lens is on the cornea and there is astigmatism that needs to be corrected by the lens, this is indicated when the astigmatism in the Ks does not match with the spec Rx. Induced astigmatism is when a toric back surface is placed on the cornea and has for example with rule astigmatism but the lens has against rule, that was originally cancelled out by the cornea but now cornea has been corrected it has been induced.

The issue of residual and induced astigmatism is caused by the tear lens. This is formed when a spherical lens is placed on a toric cornea- the lens aligns along the flatter meridian and the tear lens forms along the steeper meridian. The statement about the induced astigmatism above is a bit confused so I'm going to use an example to try and make it clearer. A patient has the following spec Rx -3.00DS and K's 8.00 @ 180 and 7.50 @ 90. This patient has with the rule corneal astigmatism (-2.50x180 calculated from her Ks) but there is no astigmatism in the spec Rx. Her lenticular astigmatism must therefore be equal and opposite (-2.50x90)- so her against the rule lenticular astigmatism cancels out her corneal astigmatism and she doesn't have any astigmatism in her spec Rx.

If we put a spherical RGP lens on this patients eye, the tear lens would correct her corneal astigmatism. This would induce against the rule (lenticular) astigmatism as the corneal cyl has been corrected by the RGP. To avoid this we could use a back surface toric RGP. The meridians of the lens would then match the meridians of the cornea (unlike a spherical back surface) so the tear lens can't correct the corneal astigmatism. Therefore, lenticular astigmatism won't be induced.

Thank you- that is so much clearer, I understand now!

The use of RGP torics is indicated when: Types of RGP torics Front surface toric
 * Spherical lens does not give a good enough VA
 * Spherical lens rocks or does not stabilise
 * Ks dif by ~0.6mm
 * More toric corneal periphery
 * A small diameter spherical doesn’t work (smaller diameter helps correct as usually central cornea more spherical
 * Back surface toric
 * Back surface central and peripheral toriodal radii
 * Front surface spherical
 * Indicated when a toridal cornea and no lenticular astigmatism
 * Follows the principle meridians of the cornea

Bitoric Toric periphery
 * Spherical back surface with a cylinder on the front surface
 * Corrects for lenticular astigmatism and residual astigmatism that is not corrected by the tear lens
 * Best in plus cyl form
 * Not great – consider a soft toric instead
 * Back and front surface toriodal
 * Req when back surface toric produces significant residual astigmatism
 * Spherical BOZR
 * Toric back surface peripheral radii
 * Corneas where the peripheral toricity is significantly dif to spherical centre
 * Front surface usually spherical

RGP torics need to be stabilised to keep the axis in the correct place, there are two main methods for this in RGP, prism ballast and truncation, they can also be combined. This is one of the main problems faced with toric lenses, stabilisation. The types of stabilisation are: Prism Ballast Truncation Soft lenses are often preferred by patients due to comfort issues. The indications for soft toric lenses are: Types include: Toric back surface · Toroidal optical zone = elliptical · Naturally stable position Front surface toric Besides prism ballast, another method of stabilisation can be used for soft lenses known as dynamic stabilisation, this is said to be the most effective technique for stabilising astigmatic lenses. The lens is thinned both superiorly and inferiorly and hence relaying on the watermelon seed effect. This gives a thinner lens design hence good comfort however only upto around 4DC of astigmatism can be corrected for. Lens rotation may occur when the lens is first fitted, this is often a nasal rotation meaning the axis is incorrect. To correct for this error an acronym ‘LARS’ can be used, this means if the lens rotates left, then add the amount of rotation to the new spec, and if the lens rotates right then subtract the amount of rotation from the axis. Response 5: <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">SOFT LENS OPTIONS: <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">There are two types of soft lens toric contract lenses; Prism ballasted (peri-ballast) and Dynamic stabilization (accelerated stabilization designs ASD). Soft toric lenses are usually back surface toric due the draping effect of soft lenses this limits the effect of the correction. This is why the back surface torics are used in conjunction with a stabilization method.
 * ~1.5Δ of base down prism added to the lens
 * Gravity pulls this thicker and heavier area to the bottom
 * Axis is aligned accordingly
 * Watermelon seed principle
 * Not monocular due to differential prism
 * 0.5mm – 1mm cut off the bottom of the lens
 * Allows it to ‘sit’ on the lower lid
 * Can also be double truncated, to have the same effect at the top (less successful)
 * Need to reduce TD (0.5mm if single and 1mm if double)
 * Less comfortable and corneal coverage problems
 * Some back surface torics are thought to align to the cornea hence do not need a method of stabilisation, often used in conjunction with other methods of stabilisation.
 * Over 0.75DC of spec astigmatism
 * Reduced VA which spherical lens
 * Not getting on with RGP toric
 * Can correct corneal and lenticular astigmatism upto ~4.50DC
 * B ack surface can be spherical or aspheric

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">A prism ballast lens is increasingly thicker towards the base of the lens and the reason it works is because the thinner portion of the lens is located under the upper eyelid and the thicker portion is squeezed towards the lower lid. The problem with this is that there is reduced comfort because of the thicker lens and therefore that is a reduced Dk/t. This option also means there will be prism in the optic zone and the orientation is effected by gravity, however this option is preferable for patients with oblique cyls. A modification of this method uses a prism free peri-ballast. This removed the most amount of prism through comfort chamfers and eccentric lenticulation to reduce lens thickness but gives a smaller optic zone. Examples of lenses that use this method are cooper vision biofinity and Bausch and lomb pure vision toric.

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">Thin zones at the top and the bottom of the lens that orientate beneath the lids achieve dynamic stabilization.

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">Dynamic stabilization in the form of accelerated stabilization design (ASD) is used by all Johnson and Johnson toric lenses. This method has proved successful because there is better orientation for patients with tight or high lower lids. There is minimal thickness different giving good comfort and Dk. With this method gravity is less of an issue and better for dynamic activities e.g. sports. The limitation of this lens is that it is limited to a correction of 4.00DC. <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">RGP OPTIONS:
 * <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">• (Spherical)
 * <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">• Spherical centre / toric periphery
 * <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">• Back surface toric
 * <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">• Front surface toric
 * <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">• Bitoric

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">Spherical non toric lenses have a spherical lens surface and the tear lens provides up to -2.00/2.50 corneal astigmatism correction. This is method works best when the total diameter of the lens is kept small.

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">A spherical centre and toric periphery lens has a special BOZR with toric back peripheral radii. It is used to improve fit where corneal astigmatism is corrected by spherical BOZR. It allows for even bearing and clearance at periphery resulting in improved centration and comfort. This is when we need to improve fit of periphery to help match the curvature in the periphery of the cornea.

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">Back surface torics with a spherical front surface. Stabilisation with this method is normally not needed because the radius of the lens aligns with the principle corneal meridians. The fluorescein appearance should be identical to that of the spherical lens on a spherical cornea. The lens will automatically find the curve that it fits best. This method is good for when corneal and lenticular astigmatism is equal and opposite as it would fit better and reduce residual astigmatism. These are simple and provide good patient comfort.

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">Front surface torics have a spherical back surface with a front surface cyl to correct the residual astigmatism. Stabilisation is needed to maintain orientation at correct cyl axis. Typically a prism ballast used (1.5prism) the weight differential causes orientation with base down. This method is comfortable for the patient is good for oblique axes, however due to the thickness of the lens there is a reduced Dk/t. <span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;"> Truncation (single or double) alternative or used in conjunction with prism ballast which can be uncomfortable in comparison to the prism ballast especially if the finish is poor or the lens is too thick. Truncation is ineffective for small total diameters or if the lower lid is below the limbus.

<span style="color: #c320de; font-family: 'Comic Sans MS',cursive; font-size: 12pt; line-height: 115%;">Bitoric lenses have both a front and back surface as a toric. It is used when the other optics leave too much residual astigmatism. The toric back surface deals with the physical fit and the toric front surface for the astigmatism correction. No stabilization is needed with this method.

1. You observe a small, white, hazy spot on the left cornea of a soft contact lens wearer. It has not been recorded previously. How can you determine if this spot is sterile (non-infective) or infective? Use bullet points to outline your approach to the differential diagnosis. (15)
 * Spring Exam**

Microbal Keratitis (MK) is a more serious and even sight threatening condition and is much more severe than sterile keratitis (SK), it is therefore vital that the correct differential diagnosis is made between the two. There are 5 types of sterilte keratitis: asymptomatic infiltrative keratitis (AIK), Asymptomatic infiltrates (AI), Contact lens induced acute red eye (CLARE), Infiltrative keratisis and Contact lens induced peripheral ulcer (CLPU). CLPU is the most similar to MK and care must be taken in the diagnosis. The white hazy spot on the cornea is known as an infiltrate and MK and SK infiltrates have different characteristics when viewed under a slit lamp.The PEDAL acronym is a good place to start in the differential diagnosis but is not the only factor that needs to be considered, a detailed history and symptoms is vital. Pedal stands for Pain, Epithelial defect, Discharge, Anterior chamber involvement and Location.Pain Epithelial Damage Discharge Anterior chamber involvement Location Although the pedal acronym is a good place to start with the differential diagnosis of MK and SK there are other factors that increase the risk of MK: SK has a longer onset and the patient may have noticed a white spot for a while or had some symptoms on or off for a while whereas in MK the patient will suddenly notice the pain and it will be a quick onset. MK also is associated with vision loss and lid swelling that are not associated with SK, and severe redness (vs moderate in SK). The redness of the conjunctiva is also more severe in MK than SK and is more localised in SK.Overall an ultimate differential diagnosis is on a culture of bacteria from a swab taken from the problematic area to identify the offending organism or in the case of SK no direct bacterium, although this is not always 100% conclusive. A practitioner should use all the above steps to identify and from the above it shows the importance of regular monitoring and if there is any uncertainty over the differential diagnosis then referral should be made due to the severity of MK. KE- This is an excellent answer, thank you for posting it. It is very well structured, organised in bullet points as requested (it is surprisingly common how often instructions about the organisation of an exam question are not followed) and has sufficient detail for a mark exceeding 70%. It is important to stress that it is essential for a practitioner to be able to differentially diagnose MK from SK. MK needs urgent referral as the prognosis can depend on the speed of diagnosis and starting treatment. Another important point to mention is practitioner caution- the PEDAL list is not definite so SK needs very careful monitoring to ensure it has not been misdiagnosed. The risk factors you have mentioned are a very good point but it would be a detailed history and symptoms that could help with the differential diagnosis. This could help identify if your patient had exposed themself to these risks and therefore increased the risk of them getting MK. Remember, the cause of MK is not only bacterial- it includes fungi and protozoa. The culture therefore may not only be bacteria but any of theses microbes. Your answer could also be improved by including a short sentance about MK and SK at the start, for example. Sterile keratitis (SK) is an inflammation of the cornea in the absence of direct microbial penetration, infection and replication. Microbial keratitis (MK) is the inflammation of the cornea through direct infection from a microbial agent including bacteria, virus, fungus or protozoa.
 * ====== SK may have varying amounts of pain with the lens in, from being asymptomatic to moderate/severe pain in the sense of a foreign body sensation. If the condition was asymptomatic they may even report seeing a white spot on their cornea. The key here is that the pain stops or greatly impoves on lens removal and continues to reduce throughout the day without lens wear. ======
 * ====== MK will cause excruciating pain and this pain may continue or even become worse after the lens is removed and will also give photophobia. ======
 * ====== In SK the infitrates are said to be a diffuse band of haziness near the limbus, or as focal spots in any region but usually a more peripheral region of the cornea. In SK they are usually subepithelial and if they do extend into the stroma they are in the anterior half. On the slit lamp they are usually of a graining appearance in SK. In CLPU the infiltrate is small 0.5mm – 1mm diameter and is focal with diffuse infiltrates around it. On installation of NaFl the CLPU is seen as a very bright spot and may possible have a bright halo around it. 7 ======
 * ====== The larger the diameter of the infiltrates also increases the chance it being MK. In CLPU the ulcer is usually round, 0.5mm -1mm in diameter and is a focal infiltrate. In MK the defect is usually of irregular shape and is larger over 2mm in diameter in the later stages, in the early stages however it is almost indistinguishable from CLPU. ======
 * ====== No discharge in SK ======
 * ====== Often discharge in MK ======
 * ====== No cells and flare in SK ======
 * ====== Cells and flare in MK ======
 * ====== Hypyon – cells at the bottom of anterior chamber in a band in MK ======
 * ====== SK is usually in the peripheral cornea ======
 * ====== MK is usually more central/mid-peripheral cornea. ======
 * ====== EW in EW lenses increases the patients risk by around 4-8x ======
 * ====== Sleeping in daily lenses on a regular basis increases risk by around 9x ======
 * ====== Standard hydrogels have more of a risk of MK than SIH ======
 * ====== Smoking increases the risk, usually associated with poor hygiene/compliance, increase by 1.6-3x ======
 * ====== Poor health also increases the risk by 2.5x ======
 * ====== Poor hygiene and compliance is a huge risk of MK as it increases the risk of bacteria on the lens, increases by 4.5x ======
 * ====== Men are at an increases risk of MK by 1.4x ======
 * ====== Internet purchases also increase the risk, this is likely to be non-compliance related and not attending aftercares, increase 2.6x ======
 * ====== Swimming in lenses greatly increases the risk by 17.22x ======
 * ====== Season also has an effect, it is more common in late winter e.g march than July, 3.6x more likely in march than july ======
 * ====== Less risk with RGP ======
 * ====== Increased risk of SK with SiH but less risk of MK ======
 * ====== Very occasional EW carries same risk as DW, 6 nights has same risk as 30 nights ======

2. Your patient complains thet are becoming increasingly intolerant to their soft contact lenses. Their eyes are uncomfortable, red and sore. When you examine them you notice they have bilateral limbal hyperaemia,punctate staining on the superior third of the cornea, microcysts and corneal infiltrates. The palpebral conjunctiva appears healthy. a. What is this condition most likely to be? (1) b. What is the cause of this condition and what would be the management of this patient? (6) c. Briefly outline four other causes of limbal hyperaemia in a soft contact lens wearer. (8)

<span style="color: #21796c; font-family: 'Times New Roman',Times,serif; font-size: 110%;">- discard lenses and refit with new ones.
==== <span style="color: #21796c; font-family: 'Times New Roman',Times,serif;">c) physiological or physical stress can cause the vessels along the limbus to dilate, for example if a soft contact lens wearer rubs their eye a lot or is ruthless inserting and removing their lenses. If there is a defect in the contact lens the patient is wearing such as a tear, this can also trigger localised hyperaemia, caused by mechanical stress. An allergic reaction or an infection of some kind may also cause limbal hyperaemia. <span style="color: #21796c; font-family: 'Times New Roman',Times,serif; line-height: 30px;"> Hypoxia can also cause it, since the worse the Dk of the lens the greater the hyperaemia will be. <span style="color: #21796c; font-family: 'Times New Roman',Times,serif; font-size: 110%; line-height: 30px;"> Limbal hyperaemia is also directly <span style="color: #21796c; font-family: 'Times New Roman',Times,serif; line-height: 30px;"> related to soft contact lens dk/t, which is worse with hydrogel contact lenses as opposed to silicone hydrogel due to poorer oxygen transmittability ====

KE- A great answer, thanks for posting it. Your answer for c is a little too brief for full marks though, there are 2 marks available for each cause so make sure you are writing a good sentance or 2 for each to make sure you get all the marks you deserve. An ideal answer needs to indicate why the vessels are dilating (eg in infection dilation of vessels to enable white blood cells to be released). Also is the redness unilateral or bilateral, is it sectorial/localised (in the case of a lens defect) or the the whole limbus (allergic reaction)?

3. A patient has been sleeping in their standars hydrogel lenses (Dk 20, 30% water content) for the last 3 months. a. Describe the corneal epithelial abnormalities you might expect to see in thsi patient. (10) ==== A corneal abnormality such as epithelial microcysts may be visible in this patient. These are vesicles which are 10--50µm in size and are found in the superficial epithelium and they display reversed illumination from the slit lamp. If the microcysts break the surface of the epithelium, fine punctuate staining may also be observed. ==== ==== Corneal staining may also be observed due to the lens being over-worn and therefore dehydrating from its original low water content material. This in turn would decrease the wetting of the cornea under the lens causing an impact on the corneal epithelium integrity. This would likely to be a smile stain from an inferior epithelial arcuate lesion which may be exaggerated by possible incomplete closing of lids when asleep. A superior epithelial arcuate lesion may also occur from the increased hypoxia from wearing a contact lens under a closed eye which appears as 0.1-0.3 wide arcuate stain, 1mm from the superior limbus between 10 and 2 o’clock, often parallel to the limbus. ==== ==== Observed epithelial staining may also indicate to abnormalities in other areas of the cornea which would be expected to be seen from this patient. For example, this patient may also be at risk of infiltrative keratitis or a contact lens peripheral ulcer which can often show focal epithelial staining and affect the whole cornea. ====

KE- This question is checking you understand the effects of low Dk lenses so it is fundamental to mention initially that this patient is likely to be suffering from hypoxia and the impact of insufficient corneal oxygen supply eg. anaerobic respiration, build up of lactate. I would also expect greater detail about the microcysts- eg. what they are caused by, how you could observe and grade them, that you should be looking at the thickest part of the lens for the greatest density of them.

You also seem to have forgotten about vacuoles- they are an epithelial abnormality caused by oedema which is secndary to hypoxia.

With regard to the corneal staining you may see a epithelial plug, again secondary to chronic hypoxia. You are correct in that you might observe some loss or epithelial integrity but you might not necessarily see a smile stain. A smile is caused by drying of the post lens tear film (behind the lens), typically in a thin, high water soft hydrogel- they are much less common in low WC lenses which do not tend to have the dehydration tendencies of higher WC materials. A SEAL stain is more unlikely- this is of mechanical aetiology, rather than hypoxia, and is associated with high modulus (stiffer) silicone hydrogel materials rather than standard hydrogels.

b. List the methods available for improving the oxygen performance of soft contact lenses. (5)

-Using daily disposables instead of monthly disposable lenses or other extended wear lenses
KE- I would organise your answer to this question with methods that are most likely to have more impact towards the top and work down progressively- this demonstrates you understand the relevance of the method, not just that you can recall the information. The first most important thing to improve the oxygen performance is increasing DK or Dk/t or refitting a standard hydrogel with a SiH or RGP. One thing I particularly look for if you suggest increasing WC is that you understand the consequence on the lens parameters, often you will be given bonus marks for displaying understanding beyone simple recall of information you have learned. I know you have said this may be counterproductive but your answer doesn't convey that you fully understand why the lens must be thicker.

A patient has slept for three weeks in standard 38% water hydrogels, and you suspect the cornea to show signs of oedema - describe the signs, symptoms and management of corneal oedema. (15)

Corneal Oedema is a response by the cornea to hypoxia and commonly occurs in contact lens patients that wear their lenses for extended periods or sleep in them. An oedema is an increase in fluid content of a tissue. In the cornea it occurs in hypoxic conditions where there is a lack of oxygen leading to anaerobic respiration and the accumulation of lactate which is very difficult to rid from the body. This causes an osmotic shift bringing fluid into the stroma, which cannot be balanced by the endothelial pump. Stromal swelling of between 3-4% is a normal occurrence while we sleep but this recovers after 4 hours usually. Stromal Oedema can manifest itself in a number of ways and can be diagnosed under three main types. Firstly Striae, these are fine, white vertically orientated lines in the posterior stroma, as the Oedema increases to more than 5%, they become greyer and thicker and increase in number, however they do not affect VA. Stromal oedema can also manifest itself as Folds, these are raised ridges or depressed grooves in the endothelium. If the oedma is greater than 8% the number of folds will increase, these also have no effect on VA. Thirdly Haze, this is when the stroma becomes hazy and has a granular appearance, if the oedema is greater than 15% there will be a loss in corneal transparency and at levels above 20% oedema there will be a reduction in VA. Haze is also known as Sattler’s veil. The prognosis for corneal oedema is excellent, with contact lens induced oedema resolving within 4 hours to 7 days. The recommended management for patients displaying signs of corneal oedema is to improve the oxygen performance of their contact lenses. This can be done by increasing the Dk or Dk/t, or perhaps reducing the thickness of their current lenses. Another option would be to change from standard soft lens to a SiH lens. A reduction in wearing time or increasing the water content of their current contact lenses may also suffice. The patient may also want to consider the prospect of changing over to RGP lenses which would promote tear exchange. In very severe cases a reduced BOZR and total diameter could be used to expose more of the cornea, and the option of fenestrating the lens is also a possibility.

KE- This is a great answer- thanks for posting it. This is only a suggestion but it might be worth considering arranging you answer into subheadings such as signs, symptoms and management. I have a couple of comments that might help with this answer- in particular, try to get as much detail as you can in for each sign.

Striae- these indicate increased separation of the collagen fibrils due to the extra fluid in the stroma. A single striae indicates 4-5% oedema with each extra striae indicating and extra 1%. Observation with direct illumination, high mag (25-40x), grade with CCLRU or Efron grading scale to allow careful monitoring. Differentiate from corneal nerve fibres as these are arrranged radially whereas striae are always verticaly due to the arrangement of the collagen fibrils.

Folds- you definately need more detail here. Folds occur due to physical buckling of the posterior stroma- this is visible only becuase it then causes physical buckling of the endothelium. (So whilst this is a stromal condition- to view it we must look at the endothelium). A single fold indicates 8% oedema with each extra fold indicating a further 1% oedema. Observation with direct/specular illumination, high mag (25-40x), grade with CCLRU or Efron grading scale to allow careful monitoring. Differential diagnosis from other endothelial conditions such as bedewing, blebs, gutatta and polymegethism.

Haze- this occurs because the cornea is so oedematous, there is gross separation of the fibrils so light cannot pass through normally and the cornea has started to lose transparency. View with sclerotic scatter, 10-25x mag.

Symptoms- patients generally asymptomatic below 20% oedema. For oedema above this, the patient is likely to complain of reduced VA. Contrast sensitivity is also likely to be impaired. The patient may have problems with night driving or be photophobic due to the increased light scattering properties of the oedematous cornea.

Management- The most important thing to stress here, that you have missed, is that CL wear needs to be ceased until all signs of hypoxia have gone. Only than can you consider refitting this patient with CLs. Be careful when you suggest increasing the WC as the thickness must be increased also so the increase in Dk/t may be neglibable. You mentioned reducing WT but you could also suggest ceasing overnight wear. Fenestration is limited to RGP lenses only.

For 100%, I would expect you to link this in with Dk/t- this would demonstrate a greater depth of understanding and knowledge. A 38% hydrogel would probably have a Dk/t of less than 20 so it would be worth making comparisons or even stating the levels set by Holden & Mertz and Harvitt & Bonanno for safe overnight wear.

**15. Discuss theoptions for contact lens correction of presbyopia.(15) **

There are different options available for contact lens wearer who is also a presbyope. The options are; single vision contact lenses with readers on top, Monovision and Presbyopic contact lenses.

The first option involves wearing distance vision with correction with single vision contact lenses and then wearing reading spectacles for near vision. It is good because it provides a simple option with optimal vision at distance and near. The problems with this option is that it does not eliminate spectacles, which is usually the reason people opt to wear contact lenses making it inconvenient for the patient. Patients may also require an extra pair of glasses for intermediate work and the need to put/remove spectacles can be inconvenient.

The second option is Monovision; this involves giving the patient single vision distance contact lens in their dominant eye and single vision near prescription in the non-dominant eye. In order to determine their dominant eye; put a +1.25D lens in front of each eye and ask the patient which eye is the most blurred (this is the non-dominant eye)? Another way is to ask a patient to look through a large (hands, or hole in paper) and to see which eye they are looking through the paper with by closing one eye alternatively. Once you have established the dominant eye, show the patient what this option would be like by putting the proposed prescription in the trial frame (over plus the dominant eye and minimum add for non-dominant eye). This option is good for early presbyopes, anything beyond a 2.50 add cannot be done because there is too much disparity between the two eyes as well as blur. The other downside to this option is that during night or prolonged driving a pair of spectacles would be needed to wear on top. There are two types of Monovision:


 * 1) 1. PARTIAL MONOVISION: Low add given to non-dominant eye and that is sufficient for intermittent near vision, e.g. reading menus. If the patient needs to do more prolonged near work then reading glasses can be used on top.
 * 2) 2. ENHANCED MONOVISION: single vision distance prescription to the dominant and a multifocal contact lens in the non-dominant eye to enhance near vision. The other option is single vision near to the non-dominant eye and then a multifocal to the dominant eye to enhance distance vision.

Monovision is a good option because it is convenient, there is not need for spectacle so the patient has a better field of view. It is an easier lens to fit and is cheaper in comparison to a multifocal. This process is uncomplicated, has a good success rate and is good for people with high astigmatism as peripheral fusion is maintained. The patient will be quick to let you know if the option does not work for them. The problems with this option is that the patient has poor depth perception, it can take time to adapt and if the add is over the amount the patient can tolerate then the blur/disparity may cause non-tolerance. This method is not good for patients who have a decompensating phoria, isn’t binocular or is amblyopic. A patient considered this option would need to have good dominance other with it wont work and has poor performance under low luminance so the patient needs to be advised to take care with driving.

The final option is a multifocal lenses; within this bracket there are various types of designs available; Alternating or Simultaneous vision. Within the alternating vision area there are translating design multifocal which rely on the change in eye position to ensure the correct optical portion is required; these can be one piece or fused. These are typically RGP lenses and the lenses must move up on down gaze in order for the near vision segment to align with the visual axis. This method needs some kind of stabilization e.g. prism ballast, peri ballast, etc. RGPs are good for oxygen permeability; this option gives stereopsis, good quality of vision and binocular correction. The limitation to this is that the patient need to learn how to use these lenses, there can be hypoxia due to the ballast and there can be comfort issues due the stabilization. With simultaneous vision there are a few options; concentric (center surround), aspheric (continuous change in power form center to periphery) and diffractive (concentric zones of alternating power, least common). The image below shows concentric lenses. The distance center is fitted to the dominant eye. Light that passes through the near section but from a distance object the light will focus in front of the retina and the brain has to learn to ignored the blurred image and only pay attention the clear one, vice verse for light from the near object falling through the distance portion and falling behind the ret. The visual system chooses the clearer of the two images and ignores the other.



For near C-D lenses: these lenses are pupil size dependent so when the pupil is dilated the patient will see more from the near surround area or during constriction there may not be adequate near vision and vice versa.
 * • Low illumination favours NV, high illumination favours DV
 * • Near pupil reactions mean less light from peripheral near zone
 * • Older px with senile miosis may not get adequate NV

For N-D lenses: light from near object focused by central zone of the retina and competes with out of focus image being formed by lens surround and light from distant objects come into focus from the periphery. Visual system ignores the blurry image.
 * • Low illumination favours DV, high illumination favours NV
 * • Older px with senile miosis may not get adequate DV

Multizone concentric designs minimises the effect that pupil size has on the optical properties of the lens. Zone width and spacing is variated depending on the pupil size and different illuminations. It favours distance portion in high and low light conditions. The aspheric lens design involved continuous change in power from cnetre and peripheral portion of optic zone. There is also some degree of intermediate vision. It comes in C-D and C-N design. It is pupil size dependent. Diffractive lenses are less common; they provide a phase plate on lens surface design causing light to split into two focal points. it is pupil size dependent and reduces contrast sensitivity. This option requires neural adaptation, the brain needs to use correct focus by suppressing the blurred image and with time the halos and image distraction will decrease and disappear. This should take approximately 2 weeks. Good because:
 * • good binocular vision, good contrast sensitivity, stereopsis
 * • Variety of lens designs
 * • Simplified fitting guides, some intermediate vision
 * • Soft and RGPS available

Bad because:
 * • Requires neural adaptation, there can be adaptation problems
 * • Px needs to try lenses for 2 weeks
 * • Very dependent on pupil size and centration
 * • Fit needs to be optimum
 * • More expensive compare to SV contact lenses