topography topics

Managing Corneal Warpage

BY KENNETH A. LEBOW, OD

The goal of refitting corneal warpage is to return normal radial symmetry to the cornea by distributing lens mass evenly over the corneal surface. This helps to maintain a uniform corneal geometry and enables the post lens-wearing refraction to correct vision to 20/20. Patients with corneal warpage are rarely aware of their problem, and typically overwear their lenses without the benefit of spectacles to use when lenses are off the eye. Visualizing the changes topographically not only helps to define the problem, but also enables the patient to participate in its resolution.

Patient History

Patient C.W. wore PMMA and RGP lenses for approximately 20 years. She presents with a history of being refit two years ago with RGP lenses that were never comfortable. Wearing time is reduced from all day wear to a maximum of eight to 10 hours. Best-corrected vision with her previous lenses is 20/40, and spectacle correction (-3.50D) upon removal of her lenses is 20/50 with slightly double vision and ghosting of the letters. Post-lens wear keratometry shows a moderate cylinder
(-1.62 x 002, flat K-reading 45.12) and corneal topography demonstrates warpage (high CIM -1.41; low prolate shape factor 0.04; and a high TKM 48.6D).

The current contact lens fit (7.52mm base curve) demonstrated inferior position with moderate apical bearing in spite of the base curve apparently being fit on the flat K reading. There was minimum blink-induced lens movement with a subtle compression ring.

Corneal topography after lens removal clearly demonstrates that this lens fit is too flat, and the acute focalized central bearing pressure has caused a redistribution of corneal mass with marked inferior steepening (Fig. 1 upper left). There is approximately 3.00D difference from the central curvature to the steepest peripheral curvature.

The fitting goals for this patient were to achieve a more centered and aligned fitting relationship that would reverse the warpage and return the post-lens wear refraction to 20/20. The computerized fitting model suggested a smaller, steeper lens (7.35mm base curve) which centered well, showed an alignment fluorescein pattern and moderate blink-induced movement.

Follow-Up

After one month of wear with the new lens, repeat topography revealed marked with-the-rule corneal astigmatism (2.62D) with central steepening and a more normal prolate corneal shape (SF = 0.2) with slightly reduced CIM (1.18) and TKM (46.8). The difference between central and peripheral curvatures reduced to approximately 1.00D. Although there was still some inferior steepening and hence some residual warpage, the patient's contact lens corrected vision returned to 20/20 and the post lens wear refraction (-3.75 -1.00 x 030) returned to 20/20 without doubling and ghosting (Fig. 1 upper right). The steeper base curve-to-cornea fitting relationship had literally "popped" the central curvature back into place. These effects are readily apparent when viewing the difference map (Fig. 1 bottom).

Dr. Lebow is a member of the AOA and a Fellow of the AAO. He is in private practice in Virginia Beach, Virg.