Central corneal thickness: Will one measurement suffice?

Objective: To evaluate the measurement of central corneal thickness (CCT) in a cohort of glaucoma patients over a 3-month period. Measurements were then applied to the criteria described in the Ocular Hypertension Treatment Study (OHTS). Design: Cohort study. Participants and Methods: Fifty-one patients were recruited from a glaucoma clinic at Moorfields Eye Hospital. Central corneal thickness was measured using an ultrasonic handheld pachymeter by a trained observer. Patients' CCTs were measured at 2 consecutive clinic visits. Main Outcome Measure: Mean central corneal thickness. Results: The readings showed clear fluctuation over the 3-month period, with a mean difference in corneal thickness of 9.6±26.9 μm in the right eye and 19.0±29.2 μm in the left eye. In addition, there was a systematic bias towards increased corneal thickness being recorded at the second reading in both eyes. This reached statistical significance in both the right eye (P = 0.02) and the left eye (P = 0.0003). The criteria used to categorize the risk of patients developing glaucoma in the OHTS were then applied to these results. On the basis of the second reading, 32% of eyes required recategorization in both the right and left eyes. Conclusions: Measurements of CCT taken within a clinical setting by a trained observer may show significant variability. For CCT to become a valuable addition to the assessment of glaucoma suspects, more than one reading may be required. Failure to do so may result in misclassification and, thus, an inaccurate assignment of risk.