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 –