Round and oval cones in keratoconus.

In advanced keratoconus, there are two cone types. The more common round or nipple shaped cone is limited in diameter but may reach any degree of conicity. The cone center lies mostly in the lower nasal quadrant. The oval or sagging cone, is often larger and lies more commonly in the inferotemporal quadrant close to the periphery. The oval cone is usually associated with more episodes of corneal hydrops, scarring and difficulty in fitting contact lenses. Histopathologic review of 23 cases (10 round, 13 oval), revealed that the oval group had more breaks in Bowman's membrane, 10.1 versus 5.0, (P smaller than 0.01), and a tendency toward greater pannus formation with more ruptures in Descemet's membrane. We hope this clinicopathologic correlation may allow a more logical approach to patient care based on recognizing two different cone types in advanced keratoconus.