Stephen D. Klyce, Ph.D. LSU Eye Center, New Orleans, LA

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

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

3. OPTICS OF THE EYE

4. OPTICS OF THE EYE Abnormal corneal shape distorts vision

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

6. CORNEAL TOPOGRAPHER

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

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

10. Different topographers, similar result

11. 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.

12. NORMAL

13. CORNEAL ASTIGMATISM

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

15. PELLUCID MARGINAL DEGENERATION Typical

16. 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.

17. ADVANCED KERATOCONUS

18. KERATOCONUS

19. KERATOCONUS DEVELOPMENT OVER 6 YEARS

20. 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.

21. Keratoconus Suspect

22. Keratoconus Suspect

23. Keratoconus Suspect

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

25. +

26. + Δ = 1.58 D possible KCS

27. 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.

28. Pre-op 3 mon 18 mon LASIK ON KCS

29. Basement membrane dystrophy

30. 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.

31. 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%

32. ORIGINAL ORBSCAN PRINTOUT Inferior steepening

33. ORIGINAL ORBSCAN PRINTOUT Inferior steepening

34. THICKNESS CORRECTED ORBSCAN Inferior steepening

35. THICKNESS CORRECTED ORBSCAN Inferior steepening

36. 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.