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What Is an Irregular Cornea?

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What Is an Irregular Cornea? WHAT IS AN IRREGULAR CORNEA? Ed Bennett, OD, MSEd, FAAO Assistant Dean, Student Services and Alumni Relations UMSL College of Optometry AFFILIATIONS Contact Lens Manufacturers Association Bausch & Lomb (Thought Leaders) “To the World You May be One Person, But to One Person You May be the World” Anonymous CORNEAL CONTOUR • Corneal Cap (apical zone, apical cap): the corneal cap is the central region of the cornea. Typically area in which the corneal power does not decrease > 1D • Average area = 4mm • Average curvature = 7.9mm (42.75D) • Cornea is spherical centrally; aspheric peripherally • Gradual flattening from center to periphery which increases as you go further from center KERATOMETRY • Disadvantages include: – Only central 3mm evaluated (2 areas per meridian) – Assumes central 3mm to be spherical; what if cap is small or aspherical – Experimenter error/calibration – Inaccuracy if decentered cap VIDEOKERATOGRAPHY (VKG) • Versus Keratometry: – Many more data points; covers nearly the entire cornea – Easy to operate and interpret – Objective measurement – Can compare change over time Disadvantage: Cost VIDEOKERATOGRAPHY Operation: • Camera captures a frame of live video • Computer digitizes the image and performs ring edge detection • Converts data points to a color map Round Cornea WTR vs. ATR What is an Irregular Cornea? • With keratometry or topography the cornea is not regular or symmetrical in some areas (i.e., corneal distortion is present) • The more images are distorted COMMON CAUSES • Keratoconus (# 1) • Contact lens-induced corneal warpage • Corneal transplants (Post-penetrating keratoplasty) • Post refractive surgery • Pellucid marginal degeneration • Others (dystrophy, trauma) CL - Induced Corneal Warpage Topography PK • Waring’s 5 post PK shapes: Originally Classified on Axial Data – Prolate 31% – Oblate 31% – Mixed (Prolate & Oblate) 17.8% – Asymmetric 8.7% – Steep to Flat 13.5% Post - Refractive Surgery or Orthokeratology POST-LASIK Pellucid Marginal Degeneration KERATOCONUS: DEFINITION • Noninflammatory, self-limiting ectasia of the axial cornea. It is characterized by thinning, steepening and distortion of the apical corneal region INCIDENCE • What do we know about keratoconus??? • Most often begins in adolescents (10 - 20 y/o); 94% between 12 and 39; most severe cases are juvenile onset (i.e., 12 - 16y/o) • Bilateral in 96 - 99.5%; one eye is more progressive • 4 - 7 years progression • 10 - 20% require a penetrating keratoplasty (corneal transplant) Epidemiology • Prevalence = 55/100,000 (about 1/2,000) • Incidence = 2/100,000/year ETIOLOGY • Corneal tissue change • Atopic • Systemic • Contact lens wear • Heredity & Genetic Predisposition IS IT GENETIC?? • Early studies showed 3 - 4% had a family member with reports of 8 twins • CLEK found 13.5% had at least one family member • Rabinowitz - via topography - found 50% of family members showed topo abnormalities suspect of KCN The Cascade Hypothesis of KC Cristina Kenney Ph.D. • Free radicals increase due to exposure to Ultraviolet-B light, mechanical trauma (contact lenses, eye rubbing) and atopic disease. • With these accumulative traumas, there is a deposition of cytotoxic by-products resulting in; – Ruptures Bowmans – Stromal thinning – Corneal scarring ARE KERATOCONICS CRAZY??? • Literature shows KCN patients as paranoid, anxious, compulsive, bizarre, demanding, suspicious & untrusting • Giedd et al (Cornea, April, 2005) • Used popular health survey; 153 responses • 96.1% reported it impacted their life • Concluded that KCN PTs tend to be disrespectful and uncooperative, difficult to satisfy (>52D) • If moderate-severe, they are more passive, withdrawn and pessimistic about life CASE HISTORY • Ghost images, monocular diplopia • Distorted letters & words • Asthenopia CORNEAL TOPOGRAPHY: Keratometry • Progressive steepening • Keratometer is misleading CORNEAL TOPOGRAPHY: Videokeratography • Important in the diagnosis but not the fitting in keratoconus • VKG software often predicts keratoconus with > 48D steep area • According to CLEK, 12.2% have apex above horizontal; average location at 262˚ (inf-temp) Nipple Cone • Small, paracentral cone • Usually < 5 mm diameter • Very steeply curved Oval Cone • Displaced apical center • Inferior quadrant • Cone diameter 5-6 mm Globus Cone • Largest • Involves 75 - 90% of the cornea Marginal Cone • Marginal cone is a non-round or non-oval cone located in the periphery Cone Types • Nipple cones 86/300 = 28.7% • Oval cones 133/300 = 44.3% • Globoid cones 20/300 = 6.7% • Marginal cones 17/300 = 5.6% • Other 33/300 = 11.0% • PK 11/300 = 3.7% + Thinning of the Central Cornea BIOMICROSCOPE • Vogt’s Straie: Thin corneal folds in the posterior stroma (behind apex) due to corneal stretching • Fleischer’s Ring: yellow-brown deposition in the stroma which encircles the base of the cone • Apical scarring CLEK: 38% in K’s > 52D) Keratoconus Signs • Vogt’s Striae (easier to see with CL on) Keratoconus Signs • Fleischer’s ring (cobalt filter helps) Keratoconus Signs • Corneal Scarring CLEK STUDY: BIOMICROSCOPY RESULTS • Vogt’s Straie: 65% ≥ 1 eye; 30% both eyes • Fleischer’s Ring: 86% ≥ 1 eye; 56% both eyes • Scarring: 53% ≥ 1 eye; 22% both eyes MANAGEMENT • Most often with spherical GP lens designs (small diameter, intralimbal diameter, scleral designs) • Soft and GP lenses have been used in combination to form a “piggyback” combination when GPs alone are not successful • Hybrid designs are becoming popular again (SynergEyes & more recently, Duette) • Specialty soft lenses (HydraKone, Kerasoft) CONTACT LENS MANAGEMENT OPTIONS • Small diameter gas permeable (GP) lenses • Intralimbal GP lenses • Scleral GP lenses • Piggybacks • Hybrid designs • Special design soft lenses Small Diameter • Often 8.0 – 10.0mm • Indicated for nipple and small oval cones • Some popular designs include: – Rose K2 (Blanchard & other labs) – Comfort Kone (Metro Optics) – Tru-Kone (Tru-Form) – I Kone (Valley Contax) – McGuire Cone & Soper Cone (many labs) THREE POINT TOUCH FITTING GUIDELINES • Generally the optical zone should be decreased in size as the BCR steepens; a rule of thumb is selecting OZD = BCR in mm; for example: If BCR = 7.00mm; OZD = 7.00mm FITTING GUIDELINES • Multiple peripheral curves are usually necessary to correspond with the rapidly flattening mid-peripheral and peripheral cornea. The peripheral curve should be flatter and wider than conventional designs to provide greater edge clearance GP Materials: Fluoro-Silicone/Acrylate • Combined fluorine with other ingredients (wetting agents, cross-linking agents, methyl methacrylate & “silicone”) to enhance mucin interaction with lens surface = wettability & stability; increase Dk (versus S/A) • Materials can be divided by Dk: • Low Dk = 25 - 50 • High Dk = 51 - 99 • Hyper Dk = ≥ 100 Low Dk GP Materials (www.gpli.info) • Boston ES (B + L): 18 (ISO/Fatt) • Optimum Classic (Contamac): 26 (ISO/Fatt) • AccuCon (Innovision): 25 (revised Fatt) • FLOSI (Lagado): 26 (ISO/Fatt) • Paragon Thin (Paragon Vision Sciences): 29 (revised Fatt) • Fluoroperm 30 (Paragon Vision Sciences): 30 (revised Fatt) • SGP 3 (Lifestyle Co.) 43.5 (CLMA standard) • Boston Equalens (B + L): 47 (ISO/Fatt) • Hydro2 (Innovision): 50 (revised Fatt) High Dk GP Lens Materials (www.gpli.info) • ONSI-56 (Lagado): 56 (ISO/ANSI) • Paragon HDS (Paragon Vision Sciences): 58 (revised Fatt) • Boston EO (B + L): 58 (ISO/Fatt) • Fluoroperm 60 (Paragon Vision Sciences): 60 (revised Fatt) • Optimum Comfort (Contamac): 65 (ISO/Fatt) • Boston Equalens II (B + L): 85 (ISO Fatt) • Fluoroperm 92 (Paragon Vision Sciences): 92 (revised Fatt) • TYRO-97 (Lagado): 97 (ISO/ANSI) Hyper Dk GP Materials (www.gpli.info) • Boston XO (B + L): 100 (ISO/Fatt) • Paragon HDS100 (Paragon Vision Sciences): 100 (ISO/Fatt) • Optimum Extra (Contamac): 100 (ISO/Fatt) • Optimum Extreme (Contamac): 125 (ISO/Fatt) • Boston XO2 (B + L): 141 (ISO/Fatt) • FluoroPerm 151 (Paragon Vision Sciences): 151 (revised Fatt) • Menicon Z (Menicon): 163 (ISO/DIS) 189 (Fatt) VARYING EDGE LIFTS • The leading keratoconus manufacturers have the ability to provide several edge lift designs (i.e., flatter and steeper than standard) • For lenses that exhibit excessive inferior edge lift, “steep-flat” and “asymmetric corneal technology” is available QUADRA-KONE DESIGNS • Several designs being developed with different peripheral curvatures/eccentricities in each quadrant • This is especially important with excessive inferior lift off • For example: e = 0 inf; e = .4 temp.; e = .6 nasal; e = 1.4 sup QUADRA-KONE (Tru-Form Optics) Quad-Sym (Lens Dynamics)_ CONTACT LENS MANAGEMENT OPTIONS • Small diameter gas permeable (GP) lenses • Intralimbal GP lenses • Scleral GP lenses • Piggybacks • Hybrid designs • Special design soft lenses INTRALIMBAL DESIGNS LARGE OAD DESIGNS • 10 - 11.5mm designs used in cases where small designs are unsuccessful (i.e., large oval, marginal & globus cones) • Examples: Dyna Intra-Limbal (Lens Dynamics) & Rose K2-IC (Blanchard); the latter has an aspheric periphery and aberration control optics • These designs are rapidly becoming the most popular with irregular corneas DIL (Inferior Cone) POST-SURGICAL INDICATIONS • Intralimbal designs are often indicated in both post-penetrating keratoplasty and post refractive surgery patients. • Often a reverse geometry(RG) design is indicated (i.e. secondary curve is steeper - not flatter- than the base curve radius as the cornea has flattened centrally) Lens Selection Based on Graft Contour (Szczotka-Flynn) • Oblate Cornea –
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