Objective: To determine if a single measurement of central corneal thickness (CCT) is an adequate sample to aid in glaucoma risk assessment in clinical practice.
Methods: Central corneal thickness was measured by ultrasound pachymetry (mean of 15 measurements for each eye) on two separate occasions at least one month apart (range, 33 to 610 days). Eyes with a history of prior incisional surgery or corneal pathology were excluded.
Results: Ninety-eight eyes of 98 patients (43 male, 55 female) were enrolled. Mean age was 61.2 +/- 15.5 years. Mean inter-test period was 276 +/- 124 days. No significant difference in mean CCT was observed between the two visits (549 +/- 41 microm versus 548 +/- 42 microm, P = 0.4, two-tailed, paired t test). Measured CCT values differed by more than 20 microm in 20 eyes (20.4%), whereas CCT difference of at least 40 microm was seen in 5 eyes (5.1%). There was no correlation between the measured or absolute difference in CCT and IOP (r = -0.016, P > 0.43), inter-test time period (r = 0.072, P > 0.23), and glaucoma diagnosis.
Conclusion: Central corneal thickness measurements in this study differed by at least 20 microm in 20% of eyes. This has important implications for risk assessment, management, and follow-up of patients with glaucoma and related disorders. Factors affecting CCT measurement, such as examiner error or true alterations in corneal thickness, require continued investigation.