Lecture 2 SoftCL Diag Len sSelect&Assess PDF

Don’t need to know 1 Don’t need to know 2 Don’t need to know Hybrid lenses – more comfortable than GP lenses and not as comfortable as soft lenses 3 Don’t need to know 4 5 Most successful à Atropine drop by themselves is not as effective 6 7 Good candidates 8 9 First decision...

Don’t need to know 1 Don’t need to know 2 Don’t need to know Hybrid lenses – more comfortable than GP lenses and not as comfortable as soft lenses 3 Don’t need to know 4 5 Most successful à Atropine drop by themselves is not as effective 6 7 Good candidates 8 9 First decision you need to make is what lens material you should fit them with à whether it is soft or GP Soft CL 10 • Soft lenses are more comfortable from the very beginning • Patients buy multi-package lenses à they will have back up lenses. • They do not need to wear soft lenses for occasions that they do • Quality of vision is less distinct compared to with GP lenses and for astigmatic lenses à there is variable quality of vision • The autoimmune reaction causes there to be protein deposit which causes giant papillary conjunctivitis à more of an issue with reusable lenses • The potential to abuse soft cl is done more often à patient sleep with them more often 11 12 • GP lenses will be good option if the quality of the vision matters • ‘variety of diameters, base curve, rx is vast à less expensive • Little adheres to the surface of GP lenses • Patient less likely to abuse GP lense • Initially less comfortable than soft cl however pt can adapt to it \ • It needs ot be worn on a everyday routine. If the nerve ending on the lid margin adapt to the GP lenses, the adaptation allows you to get used to the GP lenses, the adaptation works 10 days so if you wear it only periodically you will not adapt to it à so social wear is not done 13 • Don’t change the physiology of the cornea 14 15 • First parameter à think about the diameter of the lens that you need to fit with • 14mm diameter lens with sph power should be expectable à we want the diameter to cover the entire cornea and go over the limbus (360 degrees) so the limbus is covered because there are stem cells in the limbus and you don’t want to diminish the limbal area ability to produce stem cells. If you cover the limbus and not sitting on it then less likely irritate the stem cells on the limbal region à exposure of the limbus is not good. • You want 0.5mm beyond limbus out to the conj 360 deg à so when lens moves with blink, there is no limbal exposure • 14.00 is the std to fit your avg patient • Lens Edges slips under upper & lower lid à to allow the nerve ending on the limbal region to adapt the prescenc of soft lens. if the soft lenses is displaced superiorly à the bottom edge is bumping on the lower lid the pt will not adapt. • You want the edges under the lid margin 16 • There is a coverage of the limbus 360 • When the patient blinks à does the lens displace upward such that the inferior limbal region is exposed when the patient blinks • In dynamic cond when the pt blinks à will there be exposure of the limbal region 17 18 19 20 The second à lens decenter upwards à would there be risk of exposure of the inf limbal region The third à lens decentered downward à would there be risk of exposure of the sup limbal region 14mm is the std diameter 21 • Take the HVID and add 2mm à you come to close to 14mm for an avg patient • 11.7 + 2 à 13.7 à If you want edges of the lens under the upper and lower lid, increase by little and ends up being 14mm • Patient who have 12.5 HVID à 14mm may not be enough to cover the limbal regions • Patient who have 10.5 HVID à small HVID à you need a starting diameter of 12.5 • So for larger or smaller HVID you will need custom diameter lenses 22 14mm dimeter lens HVID: 11.7 + 2 = 13.7 mm plus you want to take into account the limbal region so approx. 14 mm 23 14mm dimeter lens is too large for them so you need small one HVID: 10.5 mm + 2 = 12.5 mm starting diameter 24 • Soft cl à flat curvature is needed 25 Base curve for soft CL à is always several mm flatter than their flat K Avg 14mm dimaetr lens for the avg cornea has base curve of 8.4mm BC works for patient avg cornea Avg corne is 8.6mm. 26 27 28 29 30 14.2 to will cover the limbal region B&L Specialty Alden Optical à variety of base curves, rx, diameter, water content Made to wear are expensive, takes longer to come à someone who doesn’t have avg HVID, cornea etc 31 32 There is no pre-packaged lens for her so we need to do made to order à start with lens diameter of 12.5mm 33 • If you know the diameter of the lens that you need to fit (HVID +2mm) à there is a flattening factor added to the flat K value • If they have 10.5 HVID +2 à 12.5 dimeter lens then add 0.20mm + the flat K value to get the BC (7.03+0.20 à 7.23mm) • You need made to wear lenses due to powrr, steepness of the cornea, • HVID 11.7 and avg conrea is 42.25 à 13.7 diameter lens. You would take flat K value (7.89) and add 0.8mm à it would give starting base curve of 8.7 • Alcon, johnson&johnson, belshelom, cooper à if they have single BC then they are fitting only the avg patient (the 80%) • If it lists more than one BC à then they want to fit both the avg [ateint and some steep/flat cornea pt (the other 20%) • Kontour CL à they have 3 base curves à 8.3 to fit the steep, 8.6 to fit the avg and 8.9 to fit the flat • Know the chart 34 35 36 OCT à depth of the cornea and anterior chamber Depth of the anterior chamber is sagittal depth Pt with larger HVID and/or steeper corneal curvature à have greater sagittal depth Each lens has unique sag depth and you should match it to their corneal sagittal depth Soft cl à mostly fit based on HVID and cornea curvature and not sag depth so might not always be good fit 37 38 39 40 If soft lens has bc steeper than corneal curvature à there will be gap between back of the contact lens and anterior surface of cornea à there will be air bubbles in areas where base curve is excessively steep As the patient blinks, the lens will be flat against the cornea. Initially vision is good and as the lens goes proapoptotic and there are bubbles the vision will not be good/flucttaue (goes in/out) 41 If the base curve is flat compared to their corneal curvature à there will be gap at the edge of the lens near the limbus but it will be centered. Initially as the patient blink, the lens will wrinkle since its not matching the corneal curvature à when they open their eye first, the vision will be poor but as the wrinkle flattens out the vision gets better Lens sag depth = pt sag depth Base curve should match the corneal curvature if not then you will see these things 42 43 44 • As the patient blinks, how much movement do we want • The ideal is to have 0.5 mm of movement. If you get 1mm of movement then the pt feels the lenses. 0.25 mm of movement is acceptable • We want the lens to move because we want the exchange of tear film under the lens • The tear film under the lens is initially healthy and over the course of wear, there will be waste products on posterior the tear layer so the healthy tear layer is contaminated à you want to exchange the bad tear so that new tear comes into place • With 0.5mm lens movement we are getting 1% tear exchange per blink and takes 17mins to get full exchange. GP lenses have greater tear exchange (20%) and they have less complication because turnover of post exchange of tear compared to soft cl • Gp contact lenses have 1mm movement • If there is no movement of the lens if there is no tear exchange, the post tear film will be toxic, the eye will be red, and ot uncomfortable 45