Posterior keratoconus.

Posterior keratoconus is a rare corneal disorder characterized by a total or localized noninflammatory thinning of the cornea. In front of a conical protrusion of the posterior corneal curvature, there is a thinned stroma and nonprotruding anterior surface. A corneal button from a patient with bilateral posterior keratoconus was studied by light and electron microscopy. Descemet's membrane, particularly in the area of stromal thinning, demonstrated abnormal anterior banding, a multilaminar configuration, and localized posterior excrescences. These alterations suggest an early pathogenetic mechanism, which probably originated prior to the fifth or sixth month of gestation.