Soft Contact Lens Diagnosis Lecture PDF

-larger the BC – more flat -smaller the BC – more steep 46 47 Know the chart The diameter goes up by 0.5 and the flat K goes up by 0.2 48 49 BC à 7.23 mm 50 • When the lens goes in the eye we want there to be centration, • Limbal to limbal coverage • We are looking at the nasal edge and...

-larger the BC – more flat -smaller the BC – more steep 46 47 Know the chart The diameter goes up by 0.5 and the flat K goes up by 0.2 48 49 BC à 7.23 mm 50 • When the lens goes in the eye we want there to be centration, • Limbal to limbal coverage • We are looking at the nasal edge and ask the pt to blink and we want to quantify the movement à • no movement means stuck on eye, bare movement (0.25 is acceptable) • 0.5 means à with 1mm dot on nasal edge, half of light on lens and half on conj à if the lens moves from center of the beam of light to the edge back to the center then this is 0.5 movement • If it goes half of the dotted line then its quarter movement • If there is no movement then the base curve is too tight for the cornea or there is no traction/friction on the upper lid to create movement • When there is no movement in blink or up gaze, do a push-up test à touch the lower lid and put gentle pressure on the lower lid at the lash line à if the lens to base curve is appropriate then the lens will move up and it will come back to center à + push-up test à we are determining independently determining and recording that there is a or no movement instead of how much movement there is • If the re is neg push-up test à the lens I tight on the eye and has to come 51 off or with wearing time, it will become tighter 51 • Reduce the beam to 1mm circle and focus the 1mm circle on the inferior nasal aspect of the soft lens and half mm should be on the plastic lens and half on bulbar conj • When the patient blinks, If the lens does not move as they blink, the lens is tight • If there is movement of 0.5mm à expect the lens to go to top of the beam and then center back of the beam of light • If the lens move fast such that you cannot quantify and it does not go to the edge of the beamà then the movement is 0.25 or less so it might be too tight and insufficient tear exchange 52 • When the patient looks up, the lens lags down so less lens on up part • We want the lens to lag down 0.5mm to get tear exchange • If there is more than 0.5mm of lag down as the patient look sup or laterally àthen the lens will come more down to bulbar conj and the patient will not have the good correction • Quantify how much movement is up gaze. Take 1mm beam of light and focus at the 6 o clock position and then see if it goes to the edge of the lens as it goes to up and center to quantify the movement of the lens 53 54 • If the lens edge does not move and stays stationary, then think if the BC is too tight or if there is not a lot of interaction between lid margin and the lens or if there is a not lot of friction à so do push up test • Push up test à you can insert a pressure on the lower lid to create a lens floating action à it is a true way to determine if the BC is appropriate or inappropriate. • They look primary gaze and you push vertically to see if you can raise the lens manually • Positive push up test à there will be movement of the lens upward. • If there is positive à then there is not enough interaction between the lid and the lens and the blinking is not enough • Negative push up test à the lens does not move or resist moving then it is tight fit due to the base curve and stuck to the cornea and it will cause red eye • Often time à there is less blinking due to the anterior surface of the lens dry out and the back surface also dries out so the base curve steepens so what was well fitted lens will now be steep so it is stuck to the eye à the eye can feel sore due to the insufficient tear exchange, difficulty in taking off the lens 55 • It is important to get feedback from the patient when they come back because it can become a bad fit 55 • We want there to be tear exchange • There is limited tear exchange in the soft lens compared to gp • The soft lens with 0.5 movement, there is 1% exchange it will take 15-20 mins for the post lens tear film to be entirely exchanged as the pt wears it for time • Gp lens move more in the eye so the amount of exchange is 20% and they have 1mm movement à healthier fit • Lenses that have more than 0.5 mm of movement in primary and up gaze à the pt will feel the edges of the lenses and not comfort. If the pt is not complaining of discomfort or that they can feel the lens and you leave them with the lens à then its good because the greater lens movement means greater tear exchange however generally with movement, there is discomfort • With no movement the lens becomes toxic with waste product and it will irritate the epi surface 56 The lens is decentered temporally so the edge is on the limbus à whenever he blinks, as the lens move the lens edge will irritate the limbal region, there will be hyperemia The nasal quadrant will light up with fluoresceine stain You need to do alternation in lens The diameter is smaller 57 Piggy back lens system The soft lens is on corneal limbal junction The GP lens is worn on top of the soft lens The base curve should be significantly flat and the lens is decentered temporally and there is wrinkling inf nasal region (4 o clocl OD and 8 o clok OS à put the light there to check) à you are most concentered about the nasal quadrant 58 59 The base curve is flat compared to cornea The edge is lifting off so the base curve is too flat 60 Sag depth is only measured for specialty lenses 61 • See if the first lens on the eye is 8.8 BC and the lens is temporally displaces, exposure of the nasal limbus, edge lift at the nasal quadrant (nasal edge lift) and excess movement • à you steepen the BC to 8.4 • Change the base curve and keep the diameter constant for a fitting problem à common method • Many alcon lenses have a single base curve and single diameter à so if you have single diameter and single base curve and doesn’t fit well you cannot steepen anymore to fix so you need to change the brand • If its excessively flat, steepen the base curve when the lens is loose • Another way to resolve a loose lens fit is enlarge the diameter and keep BC stable 62 • 55% water content à hydrogel lenses • 74% water content à 26% plastic à fragile (tyler pg 24). Only silicone hydrogel lens available for custom. Every other material for custom soft lenses are hydrogel lenses. Lathe cutting process à the manufacture has to cut multiple buttons to find the appropaiate one. • If the 8,6 is a loose fit then you can do 8.6 BC with a larger diameter which will create a improvement in lens fit because it will steepen the lens fit since the sag depth will be greater à if that is not an enough improvement then you can keep the 8.6 BC again and go up in diameter again which will tighten he lens fit (pg 24) • Changing diameter is limited • You can improve fit two ways keep diameter same and change BC or vice versa. Most often changing BC is done 63 • The lens goes into the eye and there is central air bubble • The BC is steep compared to corneal curvature à not moving upon blink and – push up test • The central aperture is elevated above the corneal surface à tight fit, no tear exchange, and every time they blink, they will flatten the lens and the vision will be good but the lens will have bubbles again creating bad vision 64 65 • If the starting lens was 8.4 BC and 14.0 diameter à you can change to 8.8 BC in same diameter • there is alternate flatter base curve such as the starting BC is 8.4 and there is no tear exchange and no movement, you can go to the flatter base curve (8.8) to improve the fit • Less common à keep BC same and change diameter à The sag depth will be reduced since the diameter of the lens is smaller. It can be done in made to wear lenses such as kontur precision which goes form 12-16 • Kontur à custom made les (pg 39) à you have the option to do either 66 • In astigmatic lens à you need to put the power in cross and then account for the vertex distance 67 68 Don’t need to know the formula 69 70 71 72 73 • Hydrogel and Silicon Hydrogel • Hydrogen are older à lower oxygen permeability • Sil Hydrogel à newer and higher oxygen permeability • Consider their wearing schedule. If they do DW à hydrogel lenses are fine • For FW or EW or pt needs to sleep in the lens à without cl there is 3.2% swelling that happens every night à with a lens in between closed lid and cornea there is even more reduction in oxygen à then only consider sil hydrogel to deliver higher oxygen • Another consideration à dryness of the eye and how much tear evaporation takes place. Hydorgel materials are group 1-4 on page 1 in tyler, and the percentage shows water percentage. • If someone ahs dryness à if you fit them with 74% water content à the higher the water content, the more water is lost and the tighter the lens is so you should stay under 50% of water content so the water loss is not high so good for someone who has dry eye 74 • DK is the inherit oxygen permeability of the lens • It does no take into account how thick or thin the lens is • -20 lens is thinner in the center than plano lens and also than a +20 lens • The difference in thickness affects how much oxygen is transmitted through the lens • We are taking into account the published permeability which can be diff from DK/t 75 76 Silicone is water repellent Hydorgel lens low water content lens have low DK values As the percentage of water incorporated increases the amount fo oxygen transmission also increases. Hydorgel à the oxygen permeability is dependent by the water content In sil hydrogel due to the addition of silicone, the water content is not driving factor compared to oxygen permeability How much oxygen you deliver to the lens is depended on water content. In hydrogels, more water content means that more oxygen permeability and more fragile so with wear, there will be loss of water meaning dry eye will get worse Low water content à less fragile and with having silicone in the lens à there will now be higher oxygen permeability 77 Any lens with silicone à outer surface has to be in such a way that it has more ability to be wettable and the center has silicone 78 The center of the lens has greatest conc of silicone and the outer surface has hydrogel which is water loving 79 Red eye could happen due to less oxygen transmission and trapped debris We need tera exhcngae under soft lens so the likelihood of the trapping of debris under is less Insufficient tear exchange under the lens can cause red eye and trapped debris 80 The surface, which makes up about 10% of the overall thickness, (5% front and 5% back), is made of an ultrasoft hydrophilic polymer network. These water-loving polymer chains reduce friction to help minimize the interaction with the delicate tissues of the eye. It is important to understand that the water gradient surface of DAILIES TOTAL1® is NOT a surface treatment or coating, but rather a very different structure with a unique and different material composition to the core, containing a network of extremely hydrophilic polymers that are anchored into the silicone hydrogel core. (The surface of DAILIES TOTAL1® is about 300 times thicker than the surface treatment of AIR OPTIX®. ) • Sil hydrogel have more stiffness than hydrogel lenses • With the stiffness, there will be deposition on the lens surface à there is potential for sil hydrogel lenses to have GPC since they have more lipid deposit on the surfaces due to the presence of silicone compared to hydrogel lenses. GPC occurs in pts who are reusing sil hydrogel lenses not the daily disposable • Due to the deposition of lipids on the reused lenses à they will have upper GPC. 82 Stiffness and precision of silicone, there is splitting of the epithelium can be seen à where the upper lid sits on the lens Superior epi lesions Peripheral corneal ulcers à there are deposits/debris trapped. There is sub epi infiltrate presence peripherally in the pt who is wearing reusable sil hydrogel lenses Hydrogel lenses have protein deposition and not lipid deposition and they will be greasier than mucin balls. You don’t have sup epi lesions Peripheral cne central corneal ulcers can happen with sihy and hydrogel lenses 83 84 • You can get ind mucin ball not so much like how the sil hydrogel cover the whole ocular surface 85 86 87 88 89 Consider the replacement lens care appropriate for the pt 90 You don’t use corneal topography to fit soft lens. Keratometry is used where 3mm of the cornea is measured. If there is pinguecula, you can go larger diameter and cover the pinguecula instead of risking the exposure of limbal region 91 • He will give the flat corneal curvature, tera break up time, HVID à analyze HVID, • Four diff lenses that might work • Has appropriate diameter, HVID, power range suits the patient, look at the wearing schedule • He will give the spectacle rx and we get the vertex distance • Pure vision is softer than ultra • He wont give the diameter or the base curve. Not every power is found in daily disposable • He will give the spectacle correction and the name of the lens (use 11 or 12mm vertex distance). Check if the required 92