Pathology of corneal endothelium in keratoconus

Keratoconus is characterized by stromal thinning and conical deformity of the cornea that affects a small but significant portion of the population. Although keratoconus has been well studied, endothelial changes have not been extensively investigated. We studied the endothelium of 14 keratoconus corneal buttons obtained over the past 6 years by penetrating keratoplasty using light microscopy, scanning electron microscopy and transmission electron microscopy. Observations were correlated with patient history. Corneas demonstrated: endothelial cell pleomorphism and polymegathism (6 corneas); endothelial cell degeneration (13), and evidence of anterior chamber inflammation (4). Patterns of endothelial damage were variable ranging from isolated cell membranolysis to denudement of Descemet's membrane. Less damage was present at the apex of the cones than that observed in a circumferential pattern at the bases. In general the damage observed correlated with the severity and duration of the keratoconus with 9 years being the dividing time between mild and severe endothelial cell damage. These observations support other studies that implicate contact lens wear as a cause of pleomorphism and polymegathism in these patients. Endothelial cell alterations are likely a secondary event occurring due to mechanical stresses.