LSU Eye Center, New Orleans, LA Robinson v. Grendahl LASIK on keratoconus Stephen D. Klyce, Ph.D. LSU Eye Center, New Orleans, LA

ANATOMY OF THE EYE Corneal Layers Normal cornea: prolate shaped > 20% thinner in the center than the periphery Corneal Layers

OPTICS OF THE EYE Figure 1A. Light rays from a point source an infinite distance away travel as a plane wave. This can be altered by turbulence in the atmosphere. The optics of the eye curve the wavefront to focus images on the retina. A. Diagram of an eye with excellent optics.

Abnormal corneal shape distorts vision OPTICS OF THE EYE Abnormal corneal shape distorts vision

ABERRATIONS REDUCE VISION Normal Mild KC Moderate KC 20/16 20/25 20/32-1

CORNEAL TOPOGRAPHER

Different topographers Large target, coarse mire Cone target, fine mire Large target, coarse mire

Different topographers Large target, coarse mire Cone target, fine mire Large target, coarse mire

Different topographers, similar result

NORMAL CORNEAL TOPOGRAPHY Average corneal power 40.7 – 46.5 diopters. Uniform central corneal powers with regular contours and flattening toward the periphery. Often a symmetrical bow tie pattern is present, an indication of natural astigmatism.

NORMAL

CORNEAL ASTIGMATISM

ABNORMAL CORNEAL TOPOGRAPHY Corneal diseases produce abnormal topography and reduce vision. Examples of pathology: Keratoconus and Keratoconus Suspect Pellucid Marginal Degeneration Basement Membrane Dystrophy

PELLUCID MARGINAL DEGENERATION Typical

KERATOCONUS Keratoconus describes a condition of the cornea that causes thinning and protrusion. Diagnosis is by observation of corneal steepening on corneal topography (usually inferior), corneal thinning, and certain biomicroscope findings. Treatment: when eye glasses or contact lenses no longer provide good vision, a corneal transplant may be recommended.

ADVANCED KERATOCONUS

KERATOCONUS

KERATOCONUS DEVELOPMENT OVER 6 YEARS

KERATOCONUS SUSPECT Keratoconus suspect describes a condition of the cornea that may lead to keratoconus with thinning and protrusion. Identification is by observation of a subtle localized corneal steepening on corneal topography; this may be accompanied by findings on retinoscopy. Management: repeat eye exams every 6 months to a year to watch for progression to keratoconus.

Keratoconus Suspect

Keratoconus Suspect

Keratoconus Suspect

MANUAL PRE-OPERATIVE SCREENING VERTICAL POWER GRADIENT (I-S, RABINOWITZ, 1989) > 1.4 D = KCS OR ABNORMAL > 1.9 D = KC OR ABNORMAL

+ I will show you the specifications for the ARK-10000. The ARK 10000 is unique from other conventional AR and CT’s in that we measure four zones from 2.3mm to 5.5 mm in diameter. We measure 1440 points in less than 0.4 seconds.

Δ = 1.58 D possible KCS + I will show you the specifications for the ARK-10000. The ARK 10000 is unique from other conventional AR and CT’s in that we measure four zones from 2.3mm to 5.5 mm in diameter. We measure 1440 points in less than 0.4 seconds.

REFRACTIVE SURGERY COMPLICATIONS Kerectasia: protrusion of the cornea following refractive surgery. Associated with: Pre-operative signs of keratoconus Too thin a residual stromal bed thickness. Poor vision Irregular astigmatism from LASIK flap complications (for example: button hole, free cap, partial flap). Dry eye.

LASIK ON KCS Pre-op 3 mon 18 mon I will show you the specifications for the ARK-10000. The ARK 10000 is unique from other conventional AR and CT’s in that we measure four zones from 2.3mm to 5.5 mm in diameter. We measure 1440 points in less than 0.4 seconds.

Basement membrane dystrophy

DALE ROBINSON PRE-OPERATIVE SUMMARY Normal corneal findings: Pre-operative average corneal power was within the range for normals (40.7 – 46.5 diopters). Central corneal thicknesses (on calibrated Orbscan II 555, 538 microns) within normal range.

DALE ROBINSON PRE-OPERATIVE SUMMARY Abnormal corneal findings: Topography: Central corneal powers were not uniform, but exhibited a localized, inferior area of corneal steepening, a classic sign of keratoconus. The gradient in corneal power was 8 D in the left eye and 6 D in the right eye, 300-400% greater than the Rabinowitz criterion (>1.9 D). Pachymetry 18 Micron difference in thickness between right and left eyes. Thin inferior corneas. 300-400%

ORIGINAL ORBSCAN PRINTOUT Inferior steepening

ORIGINAL ORBSCAN PRINTOUT Inferior steepening

THICKNESS CORRECTED ORBSCAN The corrected Orbscan is compensated for calibration error in the pachymetry. Our LSU unit has been calibrated properly. Inferior steepening

THICKNESS CORRECTED ORBSCAN Inferior steepening

DALE ROBINSON SUMMARY FINDINGS Dale Robinson was not a good candidate for LASIK surgery. Pre-operative corneal topography revealed the presence of keratoconus in both eyes. When LASIK is performed on eyes with keratoconus, the eyes are at risk for keratectasia which severely impairs vision and often leads to corneal transplantation. The standard LASIK procedure is a contraindicated in patients with keratoconus.