Changes in Corneal Thickness in Patients With Treated and Untreated Ocular Hypertension

Abstract

The elevated intraocular pressure (IOP) in eyes with ocular hypertension is often accompanied by increased corneal thickness. We tested the hypotheses that chronically elevated IOP causes a slow increase in corneal thickness and that lowering the IOP reverses this slow increase. Fifty patients with ocular hypertension were randomized to medication and observation groups in the Mayo Clinic site of the Ocular Hypertension Treatment Study. Central corneal thickness was measured using an optical pachymeter at baseline and annually for 6 years. The rates of change of corneal thickness was compared between the groups. Epithelial thickness was measured by confocal microscopy 8 years after the baseline examination. Corneal thickness increased 1.5 +/- 3.3 microm/yr in the observation group (n = 23) and decreased -1.3 +/- 2.8 microm/yr in the medication group (n = 27, P = 0.002). Both rates were significantly different from zero (P = 0.04 and P = 0.02, respectively). Epithelial thickness was 46.4 +/- 4.9 microm in the observation group and 41.3 +/- 4.4 microm in the medication group (P = 0.008). Results of this single-center series imply that corneal thickness increases slowly in eyes with ocular hypertension and decreases slowly if the IOP is lowered by topical medications. These phenomena could be explained by a causal relationship between elevated IOP and a slow increase in corneal thickness. A decrease in epithelial thickness accounts for a portion of the thinning that occurs with treatment. If confirmed in a larger series, these findings indicate that the effects of previous treatment on thickness should be considered if corneal thickness is to be used as a discriminant factor in the management of patients with ocular hypertension.