Changes in central corneal thickness over time: the ocular hypertension treatment study.

Objective: To describe how much change, if any, occurs between central corneal thickness (CCT) measurements performed an average of 3.8 years apart in participants in the Ocular Hypertension Treatment Study (OHTS) and to identify clinical and demographic factors that are associated with changes in CCT, including baseline intraocular pressure, duration and class of ocular hypotensive medication, medical history, and systemic medication.
Design: Secondary analysis of data from a randomized clinical trial.
Participants: Ocular Hypertension Treatment Study participants. Participants who had undergone incisional intraocular or keratorefractive surgery between CCT measurements were excluded.
Testing: The first CCT measurements were performed starting in 1999, and the second measurements were performed starting in 2002. Measurements were performed by OHTS certified technicians using an ultrasonic pachymeter under a standardized protocol.
Main Outcome Measure: Central corneal thickness measurement (micrometers).
Results: First and second CCT measurements were available from 73% (1191) of the 1636 OHTS participants randomized. Central corneal thickness decreased a mean rate of -0.74+/-3.5 microm/year between the first and second CCT measurements. The mean medication exposure between first and second CCT measurements in participants originally randomized to observation (n = 595) was 1.1+/-1.6 years, versus 5.0+/-2.7 years in participants originally randomized to medication (n = 596). Central corneal thickness decreased by a mean of 1.0+/-3.4 microm/year among participants originally randomized to observation, compared with 0.5+/-3.5 microm/year among participants originally randomized to medication (P<0.0001). Subgroup analyses suggest that participants treated only with topical prostaglandin analogues (PGAs) between the two CCT measurements had a greater rate of decrease per year than participants treated only with topical beta-blockers.
Conclusions: The rate of CCT decrease over 3.8 years is comparable to the cross-sectional age differences reported in the OHTS at the first measurement (0.6 microm/year) and comparable to other cross-sectional studies. Use of topical PGAs may be associated with a slightly higher rate of thinning. The modest age- and drug-related rates of thinning observed are unlikely to influence tonometry or clinical decision-making substantially in most clinical situations.