Terrien's marginal degeneration: corneal topography.

Computer-assisted corneal topographic analysis was used to evaluate the corneal contour of four patients with Terrien's marginal degeneration. The corneal topography in these patients was characterized by flattening over the areas of peripheral thinning produced by the disorder. When thinning was restricted to the superior and/or inferior areas of the peripheral cornea, there was a relative steepening of the corneal surface approximately 90 degrees away from the midpoint of the thinned area. This resulted in high against-the-rule or oblique astigmatism characteristic of the disorder. This common pattern is attributable to the frequency with which the superior and/or inferior peripheral cornea is preferentially involved in Terrien's marginal degeneration. In some patients, the central corneal topography may remain relatively spherical if the area of thinning is small or if the disorder extends around the entire circumference of the cornea.