Mean surface area with respect to mean chord radius was plotted for each corneal condition, and curve fitting was used to extend each result to a 5.85-mm limbus. Computer-generated surfaces helped to evaluate the relationship between shape and surface area. An individual with progressive keratoconus exhibited no appreciable trend toward increasing surface area during a 76-month period. The corneas in the other groups resembled normal corneas in their total surface area. Conclusions With the exception of the single case of keratoglobus, corneal surface area tended to be conserved near a value of 120 mm 2 for all groups in the study, including corneas with keratoconus.
Surface area is remarkably insensitive to curvature change near the vertex.
Flattening seen in the periphery of corneas with keratoconus suggests that biomechanical coupling compensates for any increase in curvature occurring in the region of the cone itself. Thus, it seems that keratoconus is not a true ectasia as is keratoglobus, but rather a specialized type of warpage, at least in mild to moderate forms of the disease. Accepted for publication March 21, 2000. Presented in part at the annual meeting of the Association for Research in Vision and Ophthalmology, Fort Lauderdale, Fla, May 14, 1997. All rights reserved.