Posterior keratoconus. Case report with scanning electron microscopy.

We report the clinical and scanning electron microscopic findings in an older adult patient with unilateral posterior keratoconus. Clinically, the cornea showed typical posterior concavity with focal underlying anterior ectasia and an epithelial iron ring. Scanning electron microscopy of the cornea removed at penetrating keratoplasty revealed a pericentral posterior concavity. The endothelial layer was intact, with moderate endothelial cell pleomorphism. There were no excrescences of Descemet's membrane or endothelial tags. The lack of discrete irregularities on the posterior corneal surface in this case is different from previous descriptions of the pathological appearance of posterior keratoconus, which have been used to support a relationship of this condition to central corneal mesenchymal dysgenesis. This is the first report of scanning electron microscopic findings in posterior keratoconus.