CLP Notes Full PDF

CLP - Semester 1 Intro to CLP – Slit Lamp checks - Slit lamp routine: - start with external eye looking at lids and lashes, start with upper lid, checking health of Meibomian glands, scaliness/crustiness, greasiness, lumps/bumps, trauma (lashes missing, pointing in differen...

CLP - Semester 1 Intro to CLP – Slit Lamp checks - Slit lamp routine: - start with external eye looking at lids and lashes, start with upper lid, checking health of Meibomian glands, scaliness/crustiness, greasiness, lumps/bumps, trauma (lashes missing, pointing in different directions), blepharitis (inflammation of edge of eyelids), invert both eyelids and check smoothness. Use a wide beam at low mag (x6 or x10), use direct/diffuse illumination. - check the conjunctiva, look for pigmentation, hyperaemia (check for any sudden increases in hyperaemia as most people have different levels of normal hyperaemia). Use a wide beam at low mag (x6 or x10), using direct illumination. - check limbus, look for limbal hyperaemia, neovascularisation, using indirect illumination, parallelepiped at x16 mag. - check cornea looking to see if it’s clear, arcus ring (older px), check for any opacities, put fluorescein into eyes (cobalt blue filter, low/med mag, high brightness, parallelepiped) and check for corneal staining, use direct/indirect/retro illumination, optic section (45-60 angle beam)/parallelepiped, med mag. Specular reflection for endothelium. Sclerotic scatter is used to detect foreign bodies and oedema (corneal). - check tear film, again with fluorescein check tear break up time, roundness of tear meniscus, greasiness of tears, debris floating in film, check health of tears (tear prism height / quality). Specular reflection, parallelepiped, low/med mag. - record results as seen below in the example: `  Corneal Anatomy and Physiology - Most corneas are described as elliptical (type of aspheric surface), corneas are described by its combination of the steepest radius (apical radius - r0) and the degree of flattening - p value (usually 0 < p < 1) between the steepest and least steep meridian. - With the rule astigmatism – steeper V meridian – most corneas (V meridian has lower apical radius - 7.80 compared to 7.90 and higher p value – 0.82 compared to 0.77 than Hz meridian). - Against the rule astigmatism – steeper Hz meridian. - Asphericity has no link with steep/flat corneas. There is also no association between tilt, asphericity and corneal curvature. - with K readings every 0.05mm between each principal meridian equates to 0.25D of corneal astigmatism. - Males tend to have slight flatter corneas but no difference in asphericity/tilt. -When fitting any contact lens it is often useful and sometimes essential to know what the radius of curvature of the cornea is -The instrument most commonly used to measure corneal radius of curvature is the keratometer. The one position keratometer measures both corneal meridians when in one position, hence the name The two position keratometer only measures one meridian at a time and needs to be rotated for the second measurement  Contact Lens Materials Advantages of CL: Disadvantages of CL: - hyperopes need less convergence at near - hassle of learning to handle CL with proper hygiene - certain lenses can reduce rate of progression of myopia - broken/lost lenses - larger field of view, fewer aberrations/prismatic effects. - cost (solution, check-ups, daily > monthly) - no reflections, normalisation of image sizes, doesn’t obstruct face - can change eye colour and iris size - myopes need more convergence at near - good for sports - practicality - all day wear may not be possible, cause dry eyes - steam / fog won’t affect it like spectacle lenses would be - misuse can cause sight threatening diseases Types: SOFT: flexible lenses that sit over the cornea (~2mm over the limbus), comes in hydrogel or silicone hydrogel material. Can be daily, weekly, fortnightly, monthly or 3-6 months. Adv - Good for comfort, no adaptation needed, large optic zone (red. problems with flare, halos and photophobia), not easily dislodged, hard for foreign bodies to get underneath lens. Disadv – hydrogel lenses provide limited oxygen to cornea, VA not as good as RGP (due corneal irregularities not being corrected), CL with higher water content dry eye more quickly (less wear time). Regular cleaning needed, deposits and contamination common and more expensive (esp. DD). RGP: rigid so provides smooth refracting surface, diameter ~2mm smaller than HVID (corneal lens), different materials varying in permeability and wettability. Replaced once every 6-12 months. Adv – great VA, good stability of vision, spherical lenses correct corneal astigmatism, fit easy to assess with fluorescein, any lens design available. Fewer hypoxia related problems, fewer contamination and solution problems. Disadv – flare/halo problems with large pupils, corneal warpage can occur, dislodged more easily than SCL, can be broken and scratched easily, pain until cornea and lid margin desensitise. 3 and 9 o clock staining. SCLERAL: rest on sclera but vaults over cornea (doesn’t contact cornea), range of materials like RGP and PMMA. Used for ocular conditions such as keratoconus. Custom lens made based on an impression of the eye. Usually fitted in HES or specialist optometry practices. - Important CL properties – good oxygen permeability, good comfort, easy to handle, good reproducibility, easy to handle, compatible with different solutions, cheap to manufacture/afford, possible, how well the lens deposits (replacement schedule), possible UV protection. - O2 getting to cornea depends upon the permeability of the lens, the thickness of the lens, other effects such as tear pump, boundary effect (thin film forms on the front and back surface of CL, at front of lens, PO2 thin film < corneal tissue, at the back PO2 thin film > corneal tissue, reducing oxygen flux, giving lower Dk/t value), edge effect (Dk/t value seems higher due to O2 travelling around lens edge when measurement being taken), hydration (if SCL dehydrates, water content is reduced which affects Dk) and lens deposits. O2 is needed so that aerobic respiration can occur, so that maintenance of the endothelial and epithelial barriers remains, maintain stromal hydration (good corneal clarity) and maintenance of endothelial pump. - Permeability – depends on D (diffusion coefficient) and k (solubility coefficient) of O2 in that material, also inc. with temperature – ISO Dk units (Fatt unit x 0.75) - Transmissibility – ability of lens to transport O2, rate of oxygen flow through a CL of specified thickness (Dk/t), property of CL and material – ISO units/cm - only about 55% of measured value of O2 reaches cornea. Dk/t needed is 18 (daily wear) or 65 for extended wear. - Dk/t is affected by lens power – high positive lens has high Dk/t in periphery compared to centre and high negative lens has highest Dk/t in the centre compared to periphery. - Oxygen flux – volume of oxygen passing through specified area of CL per unit time when on cornea. It takes into account difference in oxygen concentration across the lens as that gradient acts as a driving force for oxygen to move through the lens. Dk/t x ΔPO2. With low Dk/t lenses such as hydrogel, the Dk/t inc in proportion to the oxygen flux. With higher Dk/t lenses such as silicone hydrogel, inc the Dk/t means an inc with oxygen flux but not as high as expected, as you inc Dk/t the PO2 behind the contact lenses also inc, which reduces the gradient of PO2 of front and back surface of contact lens. - SCL water content – (weight of hydrated lens – weight of dehydrated lens) x100 / Weight of hydrated lens), usually lower for silicone hydrogel lens as water content not as important to let oxygen through as it is in hydrogel lenses (as water content inc, Dk inc for hydrogel). Water content decreases as the lens is worn and higher water content lenses evaporate quicker. - High and low water content lenses (hydrogel) are unideal as low WC are thinner lenses that have low Dk/t and are hard to handle due to the thinness. High WC lenses must be made thicker, so it isn’t too fragile to handle, so they dehydrate a lot quicker and the thickness limits the Dk/t. 30 Low water 25 content - With SiH lenses, the lower the water content, the higher the oxygen 20 permeability as oxygen is transported via the silicone not water. Higher 15 modulus lenses tended to have higher Dk/t and less water, however, this 10 caused more problems such as papillary conjunctivitis. Silicone is also 5 not a very wettable material, so wettings agents, surface treatments and Dk/t 0 different designs have been used to inc wettability and comfort. -10 -8 -6 -4 -2 0 2 4 6 8 10 Back vertex power (D) - Silicone attracts lipids which make the lens to become more hydrophobic, red. lubricity (causes CLIPC), also the lipid deposits also attract microbes and leads to infections. However, corneal oedemas have been almost eliminated, longer wearing times, red dryness due to lower water content. - Wettability – ability of a drop of liquid to spread over a surface, very important for RGP lenses so that irritation is reduced, and a smooth refracting surface is produced. Measured by contact angle of a drop of liquid, lower angle = less hydrophobic = good wettability. - ISO classification of CL - Prefix – stem – series suffix – group suffix - (Dk) – (water content %) – modification code - Ionic = more methacrylic acid = more protein deposits, fewer lipid deposits  Contact Lens Pre-fitting Initial Discussion – Need to determine what Px wants from CL, contradications (eg. had eye surgery so they have to wait!), to any type of lens, explain to Px implications and options explain care/hygiene, need for regular aftercare, cost. Also: - CL vs Spectacles, Adv and Disadv of different lenses - determine what they already know about CL - CL history: lens, modality, solution, problems, reason for stopping - social history (occupation and hobbies), allergies, meds, Smoking, general health, quality of vision. Questions in Order – Step by Step! 1. Reason for visit / what they know about contact lenses / why they want them 2. Details of previous CL wear (if for work ask about type of job they do) (close up work like graphic designer etc) and when was your last eye test (up to date prescription) 3. Type of lenses you wore (modality, material, soft, ridgid etc) 4. Solution if used / reaction to solution 5. How long contact lenses worn for / how often 6. Reasons for stopping lens wear if stopped 7. Any issues with previous contact lenses 8. Inform about hygiene, lens care, lens wear, shower, swimming 9. General Health – smoker etc 10. Any medications 11. Allergies 12. Ocular history 13. Current quality of vision? Any issues? Symptoms if any issues 14. Occupation if not already asked and hobbies, social history etc. 15. Any preferences in terms of lenses - companies etc Key contact lens dimensions Dimension Symbol on diagrams Abbreviation Back optic zone radius r0 BOZR Back peripheral radius r1, r2, r3 etc. BOR1, BPR2, BPR3 Front optic zone radius ra0 FOZR Front peripheral radius ra1, ra2, ra3 etc. FPR1, FPR2 etc. Back optic zone diameter 0 BOZD Back peripheral zone diameters 1, 2, etc. BPD1, BPD2 etc. Total diameter (horizontal visible iris T TD diameter) Geometric centre thickness tc tc Front vertex power Fv FVP Back vertex power F’v BVP Ocular Parameters – BOZR, TD and BVP, for single spherical lenses we need sag - We can inc sag to make a contact lens fit tighter by inc diameter or dec radius curvature. - Measure HVID, then add 2mm, choose closest available TD - for BOZR, use keratometer, flattest K reading + 1mm - for BVP use mean sphere, for high Rx, consider effectivity - lens material, lid interactions/pressure, pre and post lens tear film, centre thickness/profile and sag – affect SCL fit Grading scales  Soft Contact Lens Fitting Central corneal radius of curvature 0.05mm difference = 0.25D difference in power 7.40 @ 20; 7.60@ 110 7.60-7.40 = 0.20 0.20/0.05 = 4 The largest number is always the flatter k! 4 x 0.25 = 1D corneal astigmatism 8.00@90; 8.55@180 2.75D corneal astigmatism Choosing the first lens Lens design/material/modality Total Diameter = o HVID + 2mm BOZR = o Manufacturers guidance o Flattest K reading + 0.7-1.00mm BVP = o mean sphere o -3.50/-1.00x90 = -3.75 You can add (-0.25) for the mean sphere power! o -6.00/-1.00x180 = -6.50 o BVD 14mm, at BVD 0mm = -6.00 Trialling the lenses Ideal soft contact lens fit: Crisp/stable vision Good comfort Well centred (sits centrally on the cornea – doesn’t move around) Full corneal coverage in all positions of gaze Adequate movement to allow tear exchange You need to do refraction over the CL/use a trial frame! Easy to over minus Don’t forget +1.00 test and use binocular balancing where appropriate Best time to assess fit after approx 5-20 mins (depending onlens material) Spherical Over–Refraction For BVP and best VA Loose fit/ Tight fit – variable Over Refraction + poor end point If VA is unacceptable, consider cyl/centration of lens Visual stability Loose fitting lens VA more blurred after blink Tight fitting lens VA more blurred before blink Stability of k mires before and after blink (see how the tear film is and its stability) Tear Film Tear film is approx. 3µm When a lens is inserted it’s split into 2 layers: – Pre lens tear film – Post lens tear film Lots of tear in the post lens tear film = lens will move more Pre lens tear film affects comfort and wettability (surface quality) of the CL and a dry pre lens tear film can cause dry patches on the CL, which prevents the fit of the CL and quality of vision. What affects SCL fit? BOZR? Centre thickness/thickness profile Overall Diameter Lens material (firm contact lenses will fit different to soft contact lenses) – Young’s Modulus* – (* Info may not be available) Pre-lens Tear Film Post-lens Tear Film Lid Interactions (lid can cause the lens to move during blinking) (refresh tears across the surface) Slit lamp assessment for fit White light and low/medium magnification Centration (is the CL centred on the cornea – Horizontally and Vertically) /diameter (is the diameter of the CL suitable for the eye it is in) Corneal coverage in all positions of gaze (same diameter all around) Lag on versions (ideal lag is 0.2-0.5mm) (this is the delay in movement when the eye looks to one side in comparison to straight ahead) Edge alignment (no edge stand off or buckling/no conjunctival indentation) (lens may cause blood to be restricted) Post-blink movement (0.2-0.5mm) (if lens moves too much you will get variable vision) Push-up test (see the ease of lens push up) (the ease of the lens going back into position - speed of recovery) Wettability (if the lens is completely covered in tears = good wettability) (if low tbut = poor wettability) (see if any deposits on the CL)  Signs of a loose fit Signs of a tight fit Excessive movement Immobile (very minimal movement) Poor centration Conjunctival indentation/vessel dragging (going white because they are so dung into by CL) Lens awareness (px feels lens more) Conjunctival redness (caused by conjunctival indentation) Fluctuating vision/blurred post blink Improvement in vision post blink Buckling of lens edge (edge of CL fits irregularly) Low grade inflammation Ocular Factors affecting CL fit Ocular sag Corneal apex – decentration Lid pressure – tight lids can cause high riding lens with excessive movement Tear film morphology Lens variables which can affect CL fit Total diameter – Larger TD – less lens movement – Smaller TD – increased lens movement – Larger TD – improved centration BOZR – little predictive value for determining lens movement Centre thickness/thickness profile Lens material Strategies to improve fit Loose fitting soft lens – Increase TD – Thinner lens, – More flexible lens, – Steeper BOZR to aid centration (allow lens to be less loose) Tight fitting soft lens - Decrease TD if possible to do so whilst maintaining complete corneal coverage, - Try thicker or less flexible lens to increase lid interaction Choice may not be available Although changing BOZR may have minimal effect with hydrogel lens, with modern SiH design may help Recording Checking the eye Check the eye with the fluorescein check (using the testing strips and cobalt blue) – taking out CLs and then checking! 4 main factors to check: LOCATION, DEPTH, GRADE, EXTENT Ordering the lens Manufacturer Lens Design (may only be one material) BOZR/TD/BVP Quantity  Contact Lens Contamination and Teaching Contact Lens Deposits This is when something deposits on the surface of the lens and stays there → damaging the CL → leading to people not wearing their CL! ▪ Usually discussed in relation to soft lenses, but also present on RGPs, which are worn for 1-2 years because they are durable and allow that modality → more likely to have deposits o Both come with different common presentations ▪ Deposits best viewed on a black background for contrast → because CL is clear o Consider looking with indirect illumination ▪ Deposits can be either organic or inorganic o consider the differences to differentiate between these ▪ Can lead to contact lens damage, wear intolerance, CL drop out, and infection Patients need to know: ▪ Hygiene o Hand washing of upmost importance o Washing hands both on insertion and removal of lenses before performing anything o Imagine trying to rub and rinse when u have dirty hands ▪ I&R, Lens Handling o Finger nails need to be appropriate for contact lens ▪ Insertion and removal (I&R). o Make-up, to be applied after contact lens insertion o Care Regimen o Hygiene with contact lens case and regular replacement o Regular replacement of contact lens solutions and contact lenses as specified Organic deposits Organic Deposits are split into three main categories: Protein Lipids Calculi / jelly spots Protein Deposits Semi-opaque, grey sheet-like material on surface Initially appears as small blobs or smears, then progresses to a full film Tends to be on high water content & ionic (protein is hydrophilic so binds to high water lens and its is also ionic which means its charged), regular replacement lenses (more likely for protein deposits to build longer you wear the lenses) Patient Symptoms include : – Reduced VA and contrast sensitivity – increased discomfort due to more lens movement, and irritation on lid blinking – Dry eye sensation Ocular Signs include: – See films and bumps on the lens – Superior limbic keratoconjunctivitis – Contact lens induce papillary conjunctivitis (bumps) Causes of Protein Deposits Denatured protein from tear film (due to proteins being in the eye too long or blinking) – In the aqueous layer of tears – Bond to the lens material due to ionic factors Cause can be due to both the patient and the contact lens material/regimen – Material dependent factors High water content lens RGP – fluorosilicone acrylates more resistant that silicone acrylates due to the fluorine Surface charge of lens Contact lens polymer size (larger polymer denature more) Lens age and use – Patient dependent factors Tear film quality and quantity (poor tear film quality = more proteins binding to CL) Hygiene and care regimen (don’t rinse eye properly = protein deposits increase) Reduced replacement frequency (less often = more likely to have protein deposits on CL) Systemic illness  Examples of Protein Deposits Protein bumps Complete surface cover of protein deposits Beginning to form cumulative surface Protein deposits beginning to form Protein film on soft lens viewed in dark field illumination Management of Protein Deposits ▪ Re-examine patient hygiene and care regimen o Ask if the patient has continued to rub and rinse lenses as directed o Has the patient stuck to the recommended replacement schedule o Is the patients case regularly replaced? o Has the patient always changed the solution in their case? Do they just ‘top it up’ or use saline? ▪ Has the patient changed their solution without telling you! Different solutions work better with removing protein and with certain types of lenses ▪ Consider adding protein removal to care regimen o Protein removal tablets containing enzymes to remove the protein or extra surfactants that work specifically with common protein deposits o If osmolality of tears could be a potential issue, add comfort drops (hypoosmolality = lens become dry) (hyperosmolality = lens inc. water content) ▪ Change the patients care regimen completely o Change the patients solution, possibly to a different multipurpose or a 2-step or hydrogen peroxide solution that removes protein better o Increase the patients lens replacement frequency i.e. monthly to fortnightly or daily o Change patients lens to a lens with less water content, or perhaps a silicone hydrogel material Lipid Deposits ▪ A blob like appearance or coating that appears to wet poorly (because lipid is hydrophobic) ▪ Starts as a few small areas that coalesce into a full coat across the lens ▪ Tends to be on high water non-ionic lenses, and now more frequently seen on silicone hydrogel lenses (silicone naturally attracts lipid deposits) ▪ Patient Symptoms include : o Potentially none o Reduced VA and contrast sensitivity o Foreign body irritation (inability to wear CLs for long) ▪ Ocular Signs include: o See films and bumps on the lens o More obvious mucus balls and debris seen in the tears (protein deposits stick on the CL) Causes of Lipid deposits ▪ Due to lipid deposits from tears and cosmetics o From excessive lipids in tears and oil layer o Patients will likely have MGD o Bond to the lens material, can occur in minutes ▪ Cause can be due to both the patient and the contact lens material/regimen o Material dependent factors ▪ High water content lens, non-ionic ▪ Largely silicone hydrogels that get lipid deposits ▪ Lens age and use o Patient dependent factors ▪ Tear film quality and quantity ▪ Hygiene and care regimen ▪ Reduced replacement frequency ▪ Chronic MGD or blepharitis Examples of Lipid deposits Large amount of lipid deposits stuck on the CL This has so many lipid deposits you can actually see droplets of the tear film. Has awful wettability due to too much lipid deposit. Management of Lipid deposits Re-examine patient hygiene and care regimen (same as protein deposits) Investigate the patients tear film quality – Give dry eye advise and MGD treatment to remove excess lipids – Advise dry eye drops – Look at the patients eyelids Change the patients care regimen completely (same as protein deposits) With all deposition types, it’s a lot easier to just replace lenses more frequently if possible rather than try to fix the issue! Lens Calcium Deposits ▪ Plural usually termed calculi o Calcium carbonate and Calcium phosphate ▪ Much less frequently seen in practice ▪ White crystalline or granular film initially o Made from a build up of mucus, lipid and calcium combining in the tear film and sticking on lens surface ▪ Initially appear as ‘jelly bumps’ o Can also appear as a white sheet appearance with small, distinct boundaries (round circle) ▪ May lead to “barnacles” on lens ▪ As with all deposits, leads to patient irritation, reduced wear and contact lens drop out if not addressed o Usually too small to reduce VA, but may reduce contrast sensitivity Examples of Lens Calcium deposits Distinct boundary Deposits appear as 3D / defined Another examples of the calcium deposits Barnacles on the lens (looks like a coral leaf) Jelly spots – look transparent Management of Calcium deposits Difficult or impossible to remove, no treatments have been evidence based – Replacing lens is easiest course of action Other deposits Other material which is in the tear film or around the eye can get onto the surface of the lens and imbed itself if hygiene and care regimen is not kept up – Commonly can see make up debris in tears, and deposited in lens Much worse if patients put on make up before contact lens insertion; trapped underneath lens Eyeliner on the inside of an eyelid margin will near guarantee debris getting into tears and contact lens Appear more frequently at the end of the month in planned replacement lenses Surprising how many patients will leave make up on or not remove it correctly… – May be unpopular, but may need to advise patient on application technique and avoidance of eye make up or getting too close to eye Change to a non-oil based make up and eyeliner Iron or metal work comes into contact with the eye somehow (hasn’t wore goggles) Infection of CL’s This is not the same as an eye infection! This is where microorganisms infiltrate the contact lens material only. However this does increase the risk of developing an ocular infection. – Usually a fungus or bacterium – Extremely uncommon in the UK and western world, more common in hot, humid and developing countries – Viral infections unknown/have not been visible/reported Fungi Examples of common fungi that infect contact lenses are: – Aspergillus niger – Candida albicans – Penicillium White or coloured filamentary pattern Causes irritation and reduced vision Caused by improper adherence to cleaning regime Lenses and case must be replaced as soon as found. – Consider reducing patient lens wear initially and changing patient to a more frequent replacement care regime Here is an example of a fungi on the CL! It has an extremely irregular appearance Another example of Fungus on the CL  This is an example of Aspergillus Niger. Lens Discolouration Usually only seen in older generation lenses with infrequent replacement, less than every three months or so – higher water content lenses – RGP lenses much more common due to length of use Variety of causes – cosmetics – lens cleaners (peroxide) – systemic drugs – Patients who lick their lenses for moisture (1 in 4 patients!) Cannot be removed from lens. Essentially permanent - Replace lenses!! Patients are usually asymptomatic, although they may complain about it during Insertion & Removal - If severely darkened, may cause a reduction in VA and contrast sensitivity. Brown colours may give colour vision changes in blue spectrum Likely that if it is at this stage, an RGP would have also ‘warped’ and misshapen to change the Rx of the lens - Otherwise, unlikely to be symptomatic Some examples of Lens discolouration Causes of Lens Discolouration ▪ Yellow/brown o Cosmetics, hairspray, tear & protein interaction, nicotine, some medications o Patients that lick lenses or leave them in an open and exposed case ▪ Pink o Surfactant cleaners, stabilisers from peroxide ▪ Orange o Systemic drugs eg rifampicin o Extremely rare these days Damage to Lens Although not technically contamination, similar in that they cause lens deformation and require replacement – Can occur in any lens type, soft or RGP – Common, already sure some of you have seen in CLP clinics.. – Can occur anywhere in the lens, edge or centre – Patient can feel discomfort, although this is inconsistent and depends on the damage extent and type As mentioned above, only way to rectify: Replace lens! CL’s Teaches DO’s and DON’T’s MONTHLYS DO’S AND DON’T’S DAILYS  Contact Lens Care & Solutions - Ideal CL solution needs to be cheap to manufacture, non-toxic to the eyes, comfortable for Px, effective as a cleaner/anti-microbial agent, not damaging to CL. - Solution (in contact with eye) must be self-sterilising, non-toxic, compatible with other solutions/treatments used and maintain physical/chemical stability over time. - CL solution must be compatible with CL material, have high antimicrobial properties and resist challenge of contaminated lens. - 5 steps needed for CL hygiene: Cleaning, Rinsing, Disinfection, Wetting, Protein removal - Disinfection – destruction of micro-organisms (failure to do so could lead to microbial keratitis), whilst maintaining lens in microbe free storage. 3% H2O2 is an effective disinfecting solution. - Disinfecting agents contain preservatives to kill invading microbes as they are prone to contamination once opened e.g. polyhexanide used in 0.00005% concentration due to its antimicrobial properties (at this strength has a low patient sensitivity and low molecular weight means it can be absorbed into the lens material) or polyquad (less potent than polyhexanide but claims less allergy/hypersensitivity) (has a higher molecular weight compared to other preservatives so less diffusion into matrix) - Wetting – used in PMMA/RGP lenses and are placed on lens prior to insertion, they act as a buffer between lens and finger on insertion to reduce contamination and it helps minimise initial discomfort. - Protein removal – proteins from tear film enter the matrix of the lens and become attached to the surface which can lead to discomfort, reduced vision and some atopic reactions such as red eye or papillary conjunctivitis. Tablets contain enzyme to break bonds in protein structures. No need for protein removers nowadays due to frequent replacement lenses and new multipurpose solution having protein removal properties. - CL solution should have similar tonicity to tear film (320m mol/kg) to avoid hyperaemia and avoid discomfort/stinging. - pH of solution should be close to average tear which is approx. 7.45, eye contains buffering agents to return eye back to normal pH, so damage is minimal if pH change is small but there still be minor discomfort. - Viscosity is usually inc to inc the contact time of wetting agent to the lens. (Methylcellulose most used to inc. viscosity) - No rub formulations (multi-purpose solution) – slightly inc concentration of the preservatives/involve longer rinse times – for non-compliant Px. Contains wetting agents, protein removers, anti-microbial agents and sequestering agents. - Oxidants such as chlorine and hydrogen peroxide destabilise microbe cell walls by interfering with cell functions. -Hydrogen peroxide solution is very effective BUT toxic to the eye! (3% solution is known to be most effective CL disinfecting agent) - RGP cleaning system – made up of cleaning solution, wetting solution, enzyme cleaner. - soaking/disinfecting solutions are used to store wet RGP lenses and kill pathogenic micro-organisms. They also contain higher amounts of preservatives as they are more robust than SCL and contain wetting agents. - In the clinic, when Px takes their SCL out, if it’s not going to be re-inserted it can be discarded, if Px is going to wear them again, Px needs to clean them with SCL daily cleaner, rinse with saline as well as the CL case and then put CL in to case along with multipurpose CL solution.  SCL Aftercare - First aftercare 2-3 weeks after fit, then 1-6 months depending on outcome of first aftercare, then every year aftercare. - History and symptoms, VA (over-refraction, visual stability), assessment of lenses on eye – fit, lens condition, pre-lens TBUT, then assessment of eye (slit lamp, tear tests, keratometry) once lens has been removed, give advice / recommendations, issue a specification. - History/Symptoms – reason for visit, VA for distance and near, Px comfort rating, LOFTSEA (for Sx), wear time (everyday? Comfort lasting entire day? WT on day of A/C appt), age of lenses, hygiene compliance, CL solution, sleeping/showering/swimming, LEE, previous lens wear, relevant GH/OH. - VA/over-refraction – spherical over-refraction only, if VA has dropped consider and find out the reason why, maybe due to Rx change, ocular pathology, deposits, poor fit etc. - White light assessment – lens centration in primary position, corneal coverage in all positions of gaze, H lag, push up test, lens movement with blinking, lens condition (specular reflection). - ask Px to remove lenses and see how good their hygiene compliance is. - Do full slit lamp examination with lenses taken out. ▪ Tear Film Quantity/Quality o Tear Prism Height/Quality o Post-Wear Tear Film Stability ▪ Check lid margins ▪ Check bulbar conjunctiva for injection/hyperaemia – direct illumination ▪ Check cornea – direct/indirect/retro ▪ Check limbal Loops for dilation/vessel extension ▪ Evert lids and inspect tarsal plates ▪ Corneal staining – the 5 things of staining!! ▪ Examine AC/lens/fundus as required -Keratometry. check K readings for any distortion of k mires. Compare k readings to original, variable k readings suggest poor tear film. - Give advice/reinforce importance of hygiene compliance, discuss any changes you may be making to their lens, Rx, solution etc, make notes of what you have done and what you’re recommending, recommend next A/C appt. - Specification – Px name and address, DOB (if under 16), practitioner name and GOC number, practice name and address, date of appt, details to allow replication of CL given, date when specification expires (next A/C appt recommendation), any other important clinical info e.g. amblyopia or allergy to solution. - Need to also give Px written instructions on handling/care as they’re likely to forget most of verbal instructions given. - Critical factors in reducing risk of MK – hand washing (most Px don’t wash hands before handling lenses), lens cleaning (need to rub and rinse lenses), lens replacement (following scheduled replacement of lens limits risk of infection), case care (rinse case with solution, rub case land lids with lint free tissue and leave to dry upside down on a dry clean tissue away from water/airborne microbes). - reduce contact with water (swimming, showering, rinsing case/lenses with water) – reduce risk of Acanthamoeba Keratitis. - Teaching methods to improve compliance – visual (demonstration with commentary), physical (Px practice cleaning whilst you provide feedback), literature (leaflet/pamphlet with pictures for Px to take away). - For women – use water based make up, avoid putting eye liner on the Meibomian gland orifices, water-based mascara, non-greasy pH neutral make-up remover, avoid lash building mascara. - good compliance – wash hands thoroughly with soap and dry them, don’t use water on your contact lenses. Rinse, rub and store reusable lenses in the recommended solution before and after each use. Don’t sleep, swim, shower in CL. - Acanthamoeba – non-parasitic amoeba in soil, air and water which adheres SCL, especially ionic materials. Can cause acanthamoeba keratitis, causes extreme red eye, with ring infiltrate in advanced cases. Usually severe pain. Aftercare Questions 1) Name, age, occupation 2) RFV → what brings you in today? 3) Wearing lenses → Type of CL?, Modality of CL?, How old are your current CL? 4) Wear time → Days per week ( / 7), Hours per day ( / 24), Hours worn TODAY ( / 24) 5) Px VA → DV Rx C, S NV Rx C, S Does vision change throughout the day? 6) Px Comfort → How is comfort generally with CL?, Initial comfort with CL?, comfort when taking out CLs?, Does comfort change throughout day? 7) Sxs → Redness, Pain, Photophobia (LOFTSEA – Location, Onset, Frequency, Type, Self-treatment, Effect on Px, Associated factors) 8) CL Handling → What CL Solution used?, How old is CL solution?, How often do you replace CL sol? Where CLs stored?, How old is CL case? How often do you replace your CL case? Demonstrate hygiene regiment? (CL SOLUTION should be replaced with modality, CL CASE should be replaced with modality) 9) CL Compliance → Sleeping, swimming, showering in CLs? 10) CL aftercare → When was last CL aftercare? 11) Previous lens wear → Have you ever wore any other CLs prior to todays appt) 12) LEE → when was LEE, is your current spec Rx up to date, anything optom said 13) Px OH, px GH → General EYE health, General Health (allergies, medication)  RGP Contact Lens Fitting The shape of a CL A reminder about the shape of a contact lens. It is not a single curved shape, in both RGP lenses and soft lenses Dimension Symbol on Abbreviation diagrams Back optic zone radius r0 BOZR Back optic zone diameter φ0 BOZD Total diameter φT TD Back vertex power BVP - basic CL design has tricurve back and bicurve front, key measurements from it being the BOZR, BOZD, TD and BVP. Cross section of a tri-curve contact lens. - The following measurements are required to fit an RGP lens, and should be collected at the first instance: History to ensure RGP wear acceptable/tolerable Health check of eye (although this may not be performed in practicals) Keratometry readings → crucial factor for RGP lens wear Pupil measurements HVID VPA → Vertical Pupil Power aperture (the gap between the top and bottom lid) important for idea of diameter of RGP Rx! -When selecting the initial RGP trial lens it is important to consider TD (RGP lenses are smaller than the total HVID), BOZR, BVP, Lens design, Lens material and obviously the cost? Total Diameter (TD) ✓ Largely dependent on HVID (horizontal visible iris diameter), but can specify many different values o Not like soft lenses where only one/two diameters are available o Usually want the HVID - 2mm (almost the inverse of soft contact lenses) ▪ So if HVID average is 11.8mm, TD is 9.8mm in perfect scenario ✓ For spherical corneas, the larger the RGP, the more stable the fit (RGP lens is smaller so more likely to move in spherical cornea) o Essentially less movement seen, and VA stable ✓ For toric corneas, a smaller fit may make the fit/vision more stable (smaller RGP wont “rock” the cornea) o Doesn’t ‘rock’ on cornea or spin with blinking as much Back Optic Zone Radius (BOZR) ✓ The most versatile fitting criteria with RGPs ✓ Worked out using Keratometry values and then used directly ✓ Usually, we start by fitting BOZR that is most similar to largest or flattest K o Example: ✓ K’s of 7.80 @ 180 and 7.85 @ 90 → 7.85 is larger and flatter so use as K ✓ K’s of 8.00 @ 35 and 9.00 @ 90 → 9 is larger and flatter so use as K The TEAR Lens ▪ Water has a weaker refractive index than the lens, but higher than air ▪ From a geometric optics point of view lots of factors to consider Here flatter K is steeper/smaller value around the edges → so you will get more fluid from the tear lens → so more fluid will correct the residual astigmatism. So, you can fit a spherical lens with the flattest K and get astigmatism corrected by the tears from the tear lens. The tear lens is a concept that comes behind the CL and between the CL and the cornea. PLUS TEAR FILM → STEEP LENS → MINUS TEAR FILM → FLAT LENS → BOZR continued when we fit RGP lenses, we always fit on flattest K. The tear lens would make up for the missing cyl However we cannot always fit an RGP on flattest K because at some point, the toricity of the cornea may be too much. (May be an extreme amount of difference between the two meridians) Remember that keratometry only measures central 3mm, and so you may be surprised about the fit of the lens even if you fit the lens perfectly as expected. Cornea flattens out towards the periphery As a rule of thumb 0.10mm difference in keratometry readings equates to ±0.50DC Flattening (increasing)/steepening (decreasing) the BOZR by 0.05mm is equivalent to a change in -/+0.25D, respectively. Flattening(increasing)/steepening (decreasing) the BOZR by 0.05mm requires an increase/decrease of 0.5mm to the BOZD Back Optic Zone Diameter The BOZD is the diameter of the initial central curvature that contains the corrective power. Often you will have no choice in this, and it will not be required to be specified Will be largely dependant on the TD Important that it is larger than max pupil size Usually approx. 0.7mm larger than pupil diameter Peripheral Curves Very often pre-determined by the manufacturer Usually the first peripheral curve is 0.7mm flatter than stated BOZR If the lens is tricurve (as they usually are): The final curvature of the most peripheral curve is approximately 10.50mm Width of final curve is approximately 0.5-1.0mm If you make it flatter, you’ll get less corneal irritation, but it may irritate the lids.. If you make it steeper, you’ll get more corneal irritation, and it won’t irritate the lids. Don’t forget that the cornea needs oxygen! Too little peripheral clearance causes poor tear exchange Too much will make your lens unstable Back Vertex Power Use the spherical power of the spec Rx in negative cylinder form Ignore the cyl power unless needed for calculating the BOZR to start on (look at the table on slide 11 for further details) Examples: If spec Rx is -3.00/-0.75x180 select BVP of -3.00DS. Table indicates flattest K, fluid lens will correct the -0.75DS If spec Rx is -4.00/-1.25x90 select BVP of -4.00DS. Table indicates fitting 0.05mm steeper BOZR than flattest K, fluid lens will correct the -1.25DS Correct back vertex distance… (> ± 4.00D). RGP Lens Material All RGPs have the suffix of –focon when having the material named Made of silicone acrylates and fluorosilicone acrylates Usually limited by availability from manufacturers choice, but will have trendy commercial names such as Boston materials EO or XO All of the same general material, but with different Dk values eg. Very good compromising between wettability, resistance to warpage or deposits, and oxygen permeability Corneal Astigmatism ▪ Usually is in the cornea but there is also lenticular astigmatism (in the crystalline lens) ▪ The following K readings: o 7.80 @ 180 and 7.50 @ 90, Rx -3.00/-1.25x180 (WTR astigm – axis at 180) o What's the amount of astigmatism? ▪ 7.80-7.50 = 0.3 ▪ 0.25D = 0.05mm ▪ 0.3/0.05 = 6 ▪ 6 x 0.25 = 1.50D ▪ So this astigmatism is corneal because the K values and the Rx are very similar Another example: The following K readings: 7.70 @ 180 and 7.00 @ 90, Rx -3.00/-1.00 x 180 What's the amount of astigmatism? 7.70-7.00 = 0.7 0.50D = 0.1mm 0.7/0.1 = 7 7 x 0.50 = 3.50D So was the Rx astigmatism corneal? NOT ALL OF IT.. the difference between the keratometry values is more than 2.50D cyl and the power is less than the corneal estimation Remember with this level of astigmatism, will need a non spherical RGP lens to fit.. A toric lens would need to be fitted if the corneal astigmatism is too high (> 2.50D), or if the majority of the cylindrical correction is not corneal The tear lens ONLY corrects corneal astigmatism, and then leave the lenticular astigmatism, leading to a poor visual outcome Sometimes you’ll find the K readings and the prescription don’t match at all, and the prescription is an amalgamated mess of lens astigmatism and corneal astigmatism Eg. Ks: 7.00@ 90 and 7.20 @180, with an Rx of -1.00/-1.00x35 This isn’t common, but can happen Consider leaving RGPs, and go for a soft toric lens -RGPs are extremely versatile, and if a toric lens is required could order any of the following: Front surface toric, Back surface toric, Bitoric lens. Why would a front surface toric be a bad choice for corneal astigmatism? As the Px blinks the front surface doesn’t have an anchor to sit on because you also have the tear lens behind the front surface toric → so you essentially doubled the correction = too much correction Why would a back surface toric be a bad choice for lenticular astigmatism? Back surface toric has one meridian very curved and the other is really flat, which will cause two sections of the contact lens digging into the cornea. Fitting RGP lenses once you have all prelim measures (Rx, Ks, Pupil size etc.) and you’ve estimated which RGP lens to start with (using info above), we’ll put one in and check the fit for any potential adjustments. Ensure you record all information needed for lens: - Manufacturer: design: BOZR/TD/BVP: material: tint: engraving - B+L: Maxim: 7.80/9.30/-3.00: Boston EO material : blue visibility tint : no engraving RGP Fit Assessment Ensure lens is wet and sterile before insertion In a trial bank, they may be dry so ensure you wet them with the correct wetting/soaking solution (see prev. lecture) RGPs will cause lacrimation and therefore some adaptation time is required for the patient to allow the lens to settle before you can assess the fit meaningfully. Then conduct a white light assessment Then conduct a fluorescein assessment THIS IS DIFFERENT TO A SOFT LENS FIT – NaFL goes in with the lens You should aim to comment on at least 8 features of the fit in order to accurately summarise the fit (i.e. steep or flat or possibly alignment) Note we no longer use the words tight and loose White light assessment As per all of your contact lens fitting assessments, usually stick to the following lighting - Medium magnification - Broad beam (unless using a specific technique) Check how the fit is in relation to: - Centration → Is it central, does it drop down a lot, or is it stuck in place centrally? - Movement on blink → Does it move a lot? What's the average movement on blink for an RGP? Is it more/less than soft? Does the movement just drop down or does it move in an arcuate pattern? Is there a delay in the drop or does it move with blink freely? Coverage ▪ This will be different than soft CLs. Does it cover adequately though? ▪ Pay attention as to whether it covers the entire pupil to ensure good VA Lag/Limbus ▪ You’ll be pleased to know you don’t measure lag and sag with RGPs ▪ Need to comment on whether the lens crossed over the limbus with excursions (when the Px looks in different directions does the lens cover and go across to the conjunctiva) (you need to make sure it stays on the cornea) Push Up Test ▪ YOU DON’T PERFORM PUSH UP TESTS WITH RGP LENSES Lid interaction ▪ Does it move with the lid? Is it attached to the lid? Does it make contact with the lid? ▪ Does it move freely without too much lid involvement (inter-palpebral) → this is between the conjunctival lid areas. Wettability and Deposits ▪ Are there any deposits on the lens (yes you can get these within 5-10 mins..) ▪ Does the lens wet well, or are there patches of dryness occurring? Fluorescein Assessment When you’re ready and you’ve checked all of the fit criteria in white light, you can pop in some fluorescein This is possible because the lens won’t absorb the liquid You can go on to check the following: Edge lift Provides a reservoir of tears that exchange with those underneath lens Usually want a narrow band that glows and isn’t excessive Tends to be a subjective measure, but will involve measuring the flattest curvature on a tricurve lens Excessive edge lift → fluorescein pouring around edges. A really flat fit. The centre doesn’t have any fluorescein because it is making contact with the cornea. Near optimal edge fit → fluorescein is evenly spread A really steep toric CL fit. This is very minimal. It is probably going to stick to the surface. Minimal edge lift. Fluorescein pattern: ▪ Steep lenses will usually have central pooling and extremely steep lenses will have trapped air bubbles inside ▪ Flat lenses will have lots of NaFL spread on the outer areas underneath the lens and extremely flat lenses will have central touch to the cornea and excessive movement ▪ Toric corneas with spherical RGPs will have a strange dumbbell pattern, and will essentially flag up the ever important tear lens ▪ Alignment fit lenses will have great edge lift amounts, along with a darker appearance and evenly distributed fluorescein o It is extremely hard to determine if a lens is only 0.1mm flat/steep because it will look relatively aligned o Experience and matching it with other fitting factors is key Over-Refraction Note that keratometry results will only give an indication of corneal curvature and NOT Rx Change in fit of 0.05mm will give change in over-refraction of 0.25D Remember this is if you want to either adjust the fit pattern, or if you want to keep the pattern, but change the Rx  End Point A full specification requires all of the following (if not using set design): Manufacturer Design Material All back surface radii and diameters BVP May also include tint and engraving if relevant For a tri-curve corneal lens: BOZR:BOZD/BPR1:BPD1/BPR2:TD BVP B&L C3 Boston XO 7.60:7.00/8.30:8.80/12.25:9.00 -6.00 (tint & engraving) BPR1 = First peripheral curvature BPR2: Second peripheral curvature BPD1 = First peripheral diameter When to choose RGP lenses New Wearers: Refits and soft failures: 16/24, 7/7 wear Poor or variable VA in SCLs Corneal cyl over 1.00DC Dry eye symptoms with SCLs Irregular cornea → keratoconus Poor SCL centration Dry eye → RGP don’t suck water from tears Poor handling/repeated lens splitting, etc Dry (but not dusty) environment Corneal vascularisation (again, also consider SiH) High permeability required CLPC History of allergies or CLPC Repeated infections Dilated/injected limbal vessels → lack of O2 SCL deposition Poor compliance with SCL likely Solution or material allergy ‘Financially challenged’ patient Benefits of RGP lenses Crisp vision Stable vision Easy to handle Lower levels of complication Cost effective Good long-term comfort Profitable Example Q Spec Rx -3.00/-1.00x180 → WTR astigmatism K’s 7.80 @ 180, 7.60 @ 90 Trial lens: 7.80/9.80/-2.50DS Fit summary indicates a steep fit Over-refraction -2.00DS Total power found is -4.50DS Fluid lens power is + 1.50DS Lens is 0.3mm steep So the final lens would be 8.10/9.80/-3.00DS  Contact Lens Complications The wearing of contact lenses can lead to undesirable changes to the anatomy and physiology of the anterior eye. Why do we get CL complications Non-compliance → Majority stems from this Mechanical → Not the best fitting/ Material not appropriate Over wear → Hypoxia (Oxygen not available in sufficient amounts), Mechanical, Lens changes, surface etc Solution sensitivity → SICS or toxicity staining Dry eye -CLs complications can arise in the: Eyelids, Conjunctiva/Limbus, Epithelium, Stroma, Endothelium Meibomian Gland Dysfunction normal function is where clear oily secretion produced that forms hydrophobic lining of lid margin and over aqueous to reduce evaporation. MGD causes irritation, inc tear evaporation, inflammation, ocular disease and poor tear film, leading to dry eye problems. Signs – capping of MG, cloudy secretion, greasy tears, froth along lid margin, lid margins become thickened and notched, chronic chalazia and symptoms of dry eyes, red. lens tolerance. Treated with warm compresses, inc. fatty acids in diet, artificial tears (dry eye Sx) and systemic tetracyclines. Management → discuss with px, advice on diet (eat fish), warm compress, eyelid hygiene, artificial tears Blepharitis not caused by CL wear but can affect CL wear due to causing poor tear film. Posterior Bleph is inflammatory conditions at the base of the lid margins, perhaps caused by MGD. Anterior Bleph is an infection at base of eyelashes, it can be staphylococcal (hyperaemia, scaling of anterior lid margins, burning/itching, dry eye Sx), or Seborrheic (affects glands of moll/Zeiss, mild erythema, soft greasy scales along lid margin, telangiectasia of lid margin, Sx similar to staphylococcal but less severe). Treated with ocular lubricants (dry eye Sx), topical steroids, antibiotic ointment (lid margins after removing crusts), lid hygiene very important and DD lenses advisable. Contact lens induced papillary More common on Hydrogel and SiH conjunctivitis (CLPC) (itchy towards end of day, blurred vision, inc. mucous on waking, excessive CL movement, papillae on tarsal conjunctiva, stringy mucous deposits, conjunctival hyperaemia/oedema). Can be caused by mechanical trauma of CL, hypersensitivity to deposits/preservatives, MGD, or allergic reaction e.g. hay fever. Sx treated, lower modulus lens, more protein resistant material, preservative free CL solution or DD. Management → Lid hygiene/MGD treatment if this doesn’t work prescribe mast cell stabilisers preventing inflammatory mediators being released so redness reduced. Change care system? Superior Limbic (lens awareness/intolerance, burning/itching, photophobia, signs of superior limbal Keratoconjunctivitis oedema, hyperaemia, superior bulbar conjunctival staining, thickening of the limbus and chemosis), caused by thimerosal preservative in CL solution as well as hypoxia/lens deposits and mechanical irritation as possible causes (limited evidence). Treated with changing CL solution, ceasing lens wear till Sx go away as well as adapting lens according to Sx. Limbal Hyperaemia engorgement of blood vessels, not vascularisation. Epithelial Staining (fluorescein) Fluorescein fills gaps in the epithelial surface where epithelial cells damaged/misplaced Fluorescein enters damaged cells Fluorescein enters intercellular spaces Can be due to: traumatic (mechanical issue → foreign bodies got into eye → lens damaged) exposure (disruption of tear film), metabolic (hypoxia), toxic/allergic (delayed care), infection Types of Staining Punctuate 1 (small superficial dots aka SPE or SPK) Little dots that are punctured through This is an example of a localised centre punctuate stain → Diffuse (lots of small dots spread all over cornea, caused by solution hypersensitivity and Punctuate hypoxia, dehydration and blepharitis) Mechanical If the lens had something trapped underneath it or lens scratched Coalescent (maybe due to damaged lens or hypoxia) Lots of dots coming into one → all the staining dots coalesced into one Dimple (pooling of fluoresceing on the bubbles trapped underneath a poorly fitting CL, Veiling usually RGP). Central in steep RGP. If over the pupil will get reduction in VA. Symptoms removed rapidly on lens removal. 3 and 9’o caused by RGP, areas of peripheral cornea that dry out due to blinking not Clock wetting these areas. Towards limbus and corneal edges (where is where the RGP would sit) Can be due to lens intolerance and lens wearing time. Smile inferior arcuate stain, area of cornea that dries out the most, give more wettable/thicker lens. Rapid recovery on lens removal. Px will describe dryness. Lens with more movement and tear exchange will help. Can occur in non CL wearers due to dry eyes. SEAL superior epithelial arcuate lesion, mechanical cause of high modulus/thick lens, refit with lower modulus/better wettablility Solution toxic reaction causing disruption of epithelial cells - preservative free Induced solution/DD lens). Tends to be diffuse and tends to be more towards the periphery.  Further CL Complications Epithelial Minute scattered dots, irregular shape (inferior colour to vacuoles) Microcysts important indicator of chronic metabolic stress Up to 10 microcysts can be observed in non-contact lens wearers Seen in low Dk/t lens wear NOT with SiH Usually seen central and paracentral cornea under x15 magnification Generally asymptomatic Increase the Dk/t of the lens Vacuoles Indicate epithelial oedema Found in 10% normal population Similar in size to microcysts/round/mid peripheral cornea Usually due to hypotonoic stress (new RGP wearers) or sometimes to hypoxia (low Dk/t) EW) Asymptomatic Mucin Balls in tear film, seen in hydrogel CL and higher modulus SiH, seen on SL under direct illumination as grey balls, caused my mucous in tear layer rolling up and getting trapped behind CL, refit with lower modulus lens or remove lens more frequently. Stromal oedema >5% may lead to vertical striae (inc separation of collagen fibrils). >12% may lead to folds of posterior stroma. >20% may lead to loss of corneal transparency due lactic acid build up due to anaerobic respiration from hypoxia which also draws in water via osmosis. Stroma absorbs water → Striae – separation of collagen fibrils and Folds – posterior stroma buckles Corneal formation and extension of blood vessels into areas of cornea neovascularisation that weren’t vascularised before. Caused by chronic hypoxia that causes corneal oedema and stromal softening causing an enzyme to release inflammatory cells to site and release vaso-stimulatory agents causing vessels to grow into the cornea. No Sx, signs of superficial (from conjunctiva) and deep (from sclera) vessel growth. Treated with inc. Dk/t lenses or RGP lenses and reduce WT. ‘Sterile’ small opacities in anterior stroma, due to accumulation of inflammatory cells, Infiltrates usually response to hypoxia, debris trapped behind lens, toxicity, allergens (preservative), protein deposits on lens and bacterial exotoxins. Cease lens wear till resolved, usually asymptomatic. Stromal infiltrates Symptoms – may be none. Or acute red eye (EW), irritation, mild pain, lacrimation, photophobia Treatment – remove lenses. Anti-inflammatories? Flatter fit, change sols, Daily Wear (DW). Prognosis – symptoms go in few days, infiltrates in 2-3 months CLARE (CL Acute strong pain, photophobia, inflammatory response due to Red Eye) irritations from toxins, released by specific bacteria getting trapped underneath CL → associated with Px accidentally sleeping in lens/extended wear. Remove lens till eye has healed. CLPU (CL Peripheral Ulcer) inflammatory response, corneal infiltrate, limbal/bulbar hyperaemia, self limiting (end up with bulls eye scar), if epithelial break,treat as MK until proven otherwise (when removing CL, CLPU Sx goes away but MK Sx persist and accelerate). Microbial PEDAL (pain, epithelial defect, discharge, anterior chamber response, Keratitis location – usually larger and more central), used to differentiate between MK and corneal ulcer. Risk factors – poor CL/case hygiene, smoking, internet purchase of CL, higher socio-economic class. Sterile vs Infectious Viral NOT a contact lens complication but looks like infiltrative Keratoconjunctivitis keratitis Acute onset of unilateral, then bilateral papillary and follicular reaction Bilateral tender and enlarged preauricular lymph node Diffuse epithelial punctate keratitis end erosions over the central cornea appear during the first or second week of the disease The epithelial lesions gradually coalesce and form coarse spots of subepithelial infiltrates, may persist for weeks, months or even years… Endothelial Blebs Apparent absence of cells No symptoms Cause – oedema, vacuoles, bulging of posterior surface of cell Due to local pH changes from carbonic and lactic acid No treatment needed Peak 30mins post insertion, falls to steady state after 90mins wear. Disappear 10mins post removal Endothelial lateral cell membranes are no longer parallel, causing variations in endothelial cells size. Corneal Polymegethism oedema – may be due to acidic pH shift/ lactic acid build-up. Endothelial Pleomorphism shape of endothelial cells changes from hexagonal to other shapes. Endothelial seen with marginal retro illumination as deposits/pigment in inferior Bedewing central cornea just below inferior pupil margin, Sx of stinging, red. tolerance of CL and red. vision. Guttae thickening of descemets membrane, associated with corneal oedema, age and Fuchs dystrophy, Sx of BV when waking up. Extra complications - Epithelial Oedema – corneal epithelium has highest oxygen demand of all layers, if sufficient oxygen (9.54µl/hr/cm 2) isn’t given, hypoxia is caused, leading to anaerobic respiration along with lactic acid build up between epithelial cells, water is then drawn out of cells into extra cellular spaced via osmosis resulting in swollen extra cellular space. - Central corneal oedema – oedema caused by anaerobic respiration due to central hypoxia. - CL induced papillary conjunctivitis – deposits on CL, reaction to solution, reaction to material, common in Px wearing reusable lenses complaining of discomfort, itchy towards end of day, BV, mucus, lens awareness/intolerance.  RGP Aftercare - first aftercare 2 weeks after initial fit, second being between 1-3 months, then regularly 3-12 months. - Assess the Px wearing patterns and wearing times, identify Sxs they experience while wearing lenses, record Px current care system, measure refractive status and VA with lens in Px eye, assess lens fit and condition of the lenses themselves, remove lens and look for CL related complications, assess Px compliance with care system, determine best spectacle VA. - what to look out for: upper lid laxity/ptosis (oedema leading to lid swelling or disinsertion/lengthening of the levator palpebrae aponeurosis). Managed by surgery. - for corneal oedema, we want to make the fit looser, we do this by reduce the TD or we can inc/flatten the BOZR. RGP Lens Fits ALIGNMENT FIT FLAT FIT STEEP FIT TORIC PATTERN OF WTR CORNEA ALIGNMENT FIT → although lens is high riding / superiorly displaced Scale of RGP Fits  Contact Lenses for Astigmatism - Astigmatism → difference in refractive power between the two principal meridians of the eye - With the rule: flatter meridian close to 180, steeper meridian closer to 90. Axis of –ve cyl +/-30° of horizontal. - Against the rule: flatter meridian closer to 90, steeper meridian closer to 180. Axis of –ve cyl +/-30° of vertical. - WTR is associated with the younger population that changes to ATR over time as they grow older. Px with oblique astigmatism (20% of population) don’t change with time. - K readings tell us the type of astigmatism, how much is corneal and the degree of astigmatism, e.g. K readings of 8.00 along 180, 7.80 along 90 = 1.00DC (WTR) → calculated using: 0.05mm diff in K = 0.25DC, 0.10mm diff in K = 0.50DC - Spec Rx -2.00/-1.00 x 180 → so in the above example with the Spec Rx: Corneal astigmatism matches spectacle astigmatism, therefore all astigmatism is corneal - Corneal astigmatism increases towards the peripheral cornea. - If K readings are equal but the is astigmatism in the spectacle Rx, the astigmatism is lenticular. - if K readings are unequal but don’t match, there is a mix of corneal and lenticular astigmatism, the residual astigmatism can be calculated using the equation: Residual/lenticular astigmatism = ocular/spectacle astigmatism – corneal astigmatism, e.g. K readings of 7.85 along 180, 7.75 along 90 = 0.50DC corneal astigmatism - Spec Rx -2.00 / -1.50 x 180 Mismatch between spectacle cyl and corneal astigmatism, therefore 1.00D lenticular or residual astigmatism. - Lenticular astigmatism → difference in curvature of the lens - Residual astigmatism → the astigmatic refractive error present when a contact lens is placed on the eye to correct an existing ametropia (a state where refractive error is present) - Irregular astigmatism arises due to: corneal irregularity (signs inc. distorted K mires and K readings not being 90° to each other). - Induced astigmatism → when the liquid lens beneath an RGP lens only neutralises 2/3rds of the corneal astigmatism due to differences in refractive indices between the contact lens and tears. - Corneal astigmatism is corrected by tear lens in an RGP lens as the corneal shape is not transmitted through the lens as the RGP lens doesn’t flex to take up the shape of the front surface of the cornea, however, with spherical soft lenses, they take up the shape of the cornea and transmit it through the lens, so corneal astigmatism isn’t corrected with SCL. - Reasons to correct astigmatism: improve VA, improve contrast sensitivity, red. glare/streaks at night, less variable accommodation so red. headaches/asthenopia, greater Px satisfaction. - Reasons not to correct astigmatism: suitable toric not available in material/modality required (oblique axis, high Rx), cost, chair time (may take more than one appt to achieve optimum VA, comfort and ideal lens), eyes with small degrees of astigmatism may not even the difference and can get away with having uncorrected astigmatism. - Eyes with a small degree of astigmatism (1D or less) → fitting with a toric soft contact lens over spherical contact lenses can improve VA by 3-5 letters. Contact lens options Soft toric (corneal and/or lenticular astigmatism) RGP → Spherical (corneal astig only), Toric back surface (corneal astig), Toric front surface (some lenticular), Bitoric (corneal and corneal/lenticular/induced) All toric lenses must maintain a particular orientation to correct astigmatism Corneal Astigmatism Calculations -0.05 diff = 0.25DC 0.10mm diff = 0.50DC → therefore; 0.30m diff = 1.50DC Methods of stabilising contact lenses 1. Prism ballast → 1-1.5Δ base down, upper lid squeezes thicker lens portion down, it also reduces comfort and Dk/t. Periballast → a technique where there’s a prism free zone (central part where Px looks through), surrounded by a prismatic zone that contains the base prism that does the stabilising. 2. Dynamic stabilisation → both lids take an active role in the stabilisation instead of just the lower lid in prism ballast. There are thin zones superiorly and inferiorly that the lids squeeze against to stabilise the lens, due to these zones, the lens can be made thin (maintains high Dk/t). Modern lenses have optic zone isolated from stabilisation zone. Accelerated stabilisation design → has 4 zones of thickness located within palpebral aperture (minimum lid interaction) so has 4 zones of stabilisation which become active only when the lens becomes misaligned. Fitting for SCL Torics Discussion with patient/decision to fit toric SCLs Choose lens modality/material required Calculate effect of bvd - each meridian separately Choose a prescription as near to that required as possible Select mid-BOZR trial lens for Rx or flatter of two Consider different design for each eye for trial Undercorrect cyls rather than overcorrect Allow to settle for a few minutes Examine fit as for spherical soft lens and If unsure go for more mobile lens fit Examine fit before checking VA Look for the toric lens markers (look below for assessing orientation) and examine orientation of the lens using rotating slit If orientation poor, particularly if unstable, try alternative lens design with different method of stabilisation Orientation success varies with Rx (lens profile) Spherical over refraction only Also → Calculate effect of BVD (for meridians ≥ 4.00D), select mid BOZR or flatter of 2 meridians. Under correct rather than over correct cyl. - When assessing orientation make sure first lens has settles (5 minutes), find axis markings usually in 3 and 9 o clock position or 6 o clock position. LARS – if the axis markings goes left (clockwise) → add supplementary degrees, if axis markings goes right (anti clockwise) – subtract supplementary degrees. - Marking on the lens DOES NOT indicate axis astigmatism → they show orientation of lens to know if lens is astigmatic Examples of SCL Torics Bausch and Lomb - Purevision Toric (Balafilcon A) Johnson and Johnson Acuvue Oasys for Astigmatism 1st generation Silicone Hydrogel (Senofilcon A) Aspheric front surface 3rd generation Silicone Hydrogel Prism ballast, toric back surface (Lo-torque® Toric back surface, ASD design with comfort chamfer) BOZR 8.6mm, TD 14.50mm BOZR 8.7mm, TD 14.00mm Sphere powers available: +6.00D to -9.00D Sphere powers available: +6.00D to -9.00D Cyl powers: -0.75DC, -1.25DC, -1.75DC, - Cyl powers: -0.75DC, -1.25DC, -1.75DC, - 2.25DC in 10° steps 2.25DC in 10° steps 1/52 or 2/52 Monthly replacement inc. CW Dk 77 (ISO) Dk 68 (ISO) tc 0.08mm for -3D tc 0.10mm for -3D Aftercare issues with Soft Torics Discomfort due to thicker lens Handling issues due to larger diameter Hypoxia problems under thicker portions of the lens Less of a problem with new stabilisation techniques Less of a problem now that more SiH torics are available Spherical RGP Cheapest option for corneal astigmatism Sharpest vision No stabilisation issues No hypoxia problems (assuming high Dk material) Astigmatic pooling of tears corrects most of corneal astigmatism Some induced astigmatism due to RI(lens)-RI(tears) Acceptable fit usually possible up to approx 3.00DC of corneal astigmatism Disadvantages → Initial comfort isn’t perfect, difficult in dusty environment, not good for occasional wear due to adaptation and a high cyl with bad fit can cause corneal distortion  CLP - Semester 2 Legal Aspects of Contact Lenses Contact Lens Specification Contact Lens Specification You are required to give patients a written contact lens specification within 3 months of lens fitting Fitting may take > 3 months if complex (Opticians Act 1989, amended 2005) o Note on records Name and address of patient Patient DoB if under 16 years Fitting may involve multiple practitioners Name and address of practice o Last practitioner should issue prescription Name, registration number and signature of practitioner Date fitting was completed Not required but recommended for plano lenses Details for replicating lenses o Medical contact lenses Expiry date (next aftercare 6-12 months) Any additional clinical information deemed necessary o ‘fun’ lenses 6 May, 2019 CONTACT LENS PRACTICE II: LECTURE 1 17 6 May, 2019 CONTACT LENS PRACTICE II: LECTURE 1 17  Dry Eye Disease - A multifactorial disease of the ocular surface, where homeostasis of tear film is lost, causing ocular symptoms and visual disturbance. Multifactorial: having a number of different interacting causes (age, genetics, environment etc) Ocular surface: including the cornea, conjunctiva, eyelids, eyelashes, tear film, main and accessory lacrimal glands, and the meibomian glands Homeostasis: is the state of equilibrium. DED occurs when homeostasis of the tear film is disrupted. Ocular symptoms: may include discomfort and visual disturbance - Risk factors – Age, Sjogren’s syndrome, MGD, connective tissue diseases, Asian, low humidity, CL wear, computer use, androgen deficiency, bone marrow transplant and females. - Possible risk factors with limited scientific evidence – diabetes, rosacea, pterygium, thyroid disease, low fatty acid intake, allergic conjunctivitis, refractive surgery and certain medications. Dysfunctional Sensation → Px doesn’t have fear of sense at front of their eyes (Neuropathic Pain → shooting or burning pain) - Dry Eye Disease may be due to either: (can also be classed and have features of both ADDE and EDE) Reduced tear volume → tear production rate not enough to counteract drainage and evaporation, but evaporation rate is normal – Aqueous Deficient Dry Eye (ADDE) Reduced tear quality → normal aqueous production but quality reduced often due to lipid layer insufficiency and excessive tear evaporation – Evaporative Dry Eye (EDE) - ADDE – Caused by → Sjogren’s syndrome (tear and salivary glands affected), age, hypo secretory states, inflammatory or other lacrimal gland infiltration and lacrimal gland obstruction. - EDE – Caused by → MGD, disorders of lid aperture (abnormal blinking) or ocular surface related (vitamin A deficiency or latroegnic) 5 Questions related to Ocular discomfort and how intense discomfort is towards the end of the day. Hyperosmolarity → condition where blood has a high conc. of salt (sodium) Osmolarity → the measure of solute concentration - Best way to measure severity of DED is by measuring tear film osmolarity as osmolarity inc with severity. - Ocular surface staining (cornea and conjunctiva) using fluorescein/Lissamine green can be used as staining is feature of late stage DED. - Damage to ocular surface also a sign of DED as there will be lid parallel conjunctival folds present in lower quadrant parallel to lower lid margin – classified by number of folds. - Inflammation may also be present but it is not specific to DED (may be caused by conjunctivitis). - Eyelids may be affected too – Lid wiper Epitheliopathy, lid wiper is part of lid that spreads tear film over ocular surface, LWE is when lid wiper stains with dyes such as fluorescein due to inc friction between surfaces throughout blinks. - Interferometry may also be used – allows the surface reflection pattern and dynamics of this lipid layer to be visualised as well as determining its thickness. (looking to see how smooth the ocular surface is and how speedy evaporation is) - MG assessment – meibum quality, quantity and expressibility assessed for signs of MGD, meibum becomes more viscous cloudy and less easily expressed. - Anterior blepharitis are associated with DED but not diagnostic, blink closure analysed – incomplete blink associated with DED and corneal staining. Management of DED – Aim is to restore homeostasis of the ocular surface and break the cycle of DED Stage 1 ▪ education and info regarding condition and prognosis ▪ diet modification ▪ identification and potential modification/elimination of offending medications (liaise with medical practitioner) ▪ ocular lubricants and lid hygiene/warm compress to Tx blepharitis and MGD Stage 2 ▪ non-preserved ocular lubricants (prevent preservative induced toxicity) ▪ tear conservation (such as punctal plugs) ▪ overnight Tx (ointment or moisture chamber devices for incomplete lid closure) ▪ in practice – physical heating and expression of MGD ▪ drugs (topical anti-biotics, topical corticosteroid, topical secretagogues, topical non-glucocorticoid and topical LFA-1 antagonist drugs may be used). Stage 3 ▪ oral secretagogues (encourage mucin secretion) ▪ allogenic eye drops ▪ soft bandage lenses ▪ therapeutic CL or rigid scleral lenses Stage 4 ▪ topical corticosteroid for longer duration ▪ amniotic membrane grafts ▪ surgical punctal occlusion other surgical approaches  Contact Lenses and Presbyopia - Presbyopia → long-sightedness caused by hardening of the lens (lens loses elasticity), occurring typically in old age. Blurred NV is the first sign of ageing over, which we have no control over. Sxs usually noticeable between 40-45. Accommodation also declines with age. - Myopes accommodate more with CLs → The change in lens position from the spectacle plane to the corneal plane is primarily responsible for the change in the stimulus to accommodation. - Why are we not fitting presbyopic Pxs with CLs → Perception that older pxs are not interested in CLs, Increased age reduces suitability (crystalline lens changes, anterior eye changes, Increased prevalence of systemic disease and associated drugs) – so the ability to tolerate CLs changes as you age. - As you age: Pupil changes → get smaller / pupil miosis (minimises aberrations and scatter, reduces retinal illumination) Eyelid changes → have reduced elasticity and muscle tone, as well as inc prevalence of blepharitis, ectropion (eyelid turned outwards), entropion (eyelid turned inwards) and senile ptosis (drooping of the upper eyelid in the elderly) Results of eyelid changes → blink less effective (uneven spread of tears), risk of exposure, modifies lid-CL interaction but less sensitive to RGP lenses Tear film changes → tear stability and quantity reduces with age, along with atrophy/fibrosis of tear secreting glands (atrophy/fibrosis of lacrimal glands, meibomian glands and goblet cells) Ocular surface changes → Inc corneal irregularity (pingueculae – degeneration of the nasal and temporal conj.), conjunctival folds, lid margin irregularity, yellowing of conjunctiva and reduced number of goblet cells. Result of ocular changes → Inc in dry eye, less anti-microbial protection, more CL deposits and variable vision Corneal changes → reduced transparency, sensitivity, fragility, wound healing, staining more common and shape changes Result → Endothelial cell loss, reduction in endothelial pump changes, cornea less resistant to oedema and exacerbated by long term lens wear. - What increases the chances of ocular and systemic disease → Increased fragility and slow healing (diabetes), Dry eye (frequent use of OTC painkillers), Ocular pathology - Overcoming the challenges → Detailed pre-fitting examination (identify possible contradictions, discuss visual needs) Correction for Presbyopia SCL – ideal for current SCL wearers, silicone hydrogel has good oxygen permeability, low water content which will limit dehydration, internal wetting agents give good wettability. RGP – good for current RGP Px and those that want crisp vision, also works well with small pupils. High oxygen permeability and low wetting angle. - Other CLs options → Distance CLs with reading Rx, Monovision, Multi-focal lenses - Ideal CLs for mature px → Correct presbyopia, good quality vision, good oxygen supply, comfortable, cope with poor tear film, easy to handle Monovision – Dominant eye corrected for distance, whilst non-dominant eye corrected which near add, wearer must suppress blurred image (does require some adaptation) Cheapest and simplest solution, single vision lenses, good for Px with astigmatism. Works better for presbyopes where add is relatively small >2.00D, avoid in Px with BV problems, reduces contrast sensitivity and stereopsis – not recommended for driving. Increased add = increased blur. Partial monovision – low add, additional reading spectacles for prolonged reading. Enhanced monovision – single vision for dominant eye at distance, multifocal for non-dominant eye at near. Modified monovision – different multifocal lens designs in each eye, biasing the dominant eye for distance. Multifocals Simultaneous – (distance, near and intermediate images all seen at the same time) (concentrate on the image on interest), multifocals available in RGP or SCL, wont give crisp vision and needs large enough pupil (to be able to see out of different zones) Aspheric – most common design, continuous progression of power from centre to periphery, SCL are usually centre near (front surface aspheric – negative spherical aberration) whilst RGP are usually centre distance (back surface aspheric – positive spherical aberration). Requires good centration for light rays through all powers within lens to pass through pupil Multizone – Centre Near (NV dom) or Centre Distance (DV dom) and used in modified monovision too, example biofinity multifocal , 4% water content, comfilcon A, SiH, Dk 96 and add powers of +1.00, +1.50, +2.00 and +2.50. Pupil independent zone design (zonal aspheric) – CD aspheric zonal, zones sizes change with refractive error/add, example oasys for presbyopia, senofilcon A, 38% water, Dk 77, internal wetting agent, SiH, modulus 0.72 MPa has 3 add options (low, med and high). RGP simultaneous – multifocal or bifocal, aspheric back surface, CD, relies on some degree of translation (when Px looks down to read the lens is pushed up so they see through bottom peripheral part of lens which is more positive). Translating bifocals → has different segments like a bifocal, orientation controlled by Base Down prism, translation requires good lower lid/lens interaction, discomfort can be an issue, no reduction in contrast sensitivity. - 2 types: RGP translating bifocal - true bifocal with segment, lens translates upwards in downgaze Expert progressive – true progressive lens, lens translates upwards in downgaze - Multifocals preferred over monovision by Px for real life tasks inc night time driving. Success will vary depending on the Pxs (Rx, Aberration, pupil size, as well as material and frequency of the replacement on lenses). - For presbyopic drivers → be aware of contrast sensitivity before fitting, be wary fitting vocational night drivers, those with > -0.75 astigmatism, allow adaptation period before driving at night, consider over specs for monovision Px. Px 1 → Multifocal soft lens. Maybe simultaneous? (established presbyope) but has a medium add then normal. Also plays golf – so looking down at ball through near add. Comp -dry eye Px 2 → Monovision with two toric single vision lenses Px has medium add. One eye naturally seems less myopic than the other. Mono more popular due to amount of astigmatism px has. Px 3 → Multifocals No astigm and low add. Drives at night and for living so needs to be cautious. Multifocals easier to adapt for driving then mono. Mulitfocal Lenses (Live Lec) – additional notes Correction options for presbyopes (specs) ▪ Separate pairs of glasses (DV, reading etc) ▪ Bi-focals (DV and reading – not as common for presbyopes / especially you don’t get intermediate) ▪ Varifocals (DV, intermediate and NV) Multifocals vs Monovision Monovision → dominant eye for DV and the non-dominant eye for reading. The brain will automatically supress the blurred image – so if you’re looking in the distance it will ignore the reading eye and vice-versa. However, as reading add increase – the intermediate vision will become a struggle, as well as night-time driving ?