The purpose of this study is to characterize intraday and interday variation in central corneal thickness (CCT) in healthy and glaucomatous subjects.Methods:
In this prospective cohort study, 40 healthy subjects and 42 subjects with primary open-angle glaucoma underwent CCT measurements by ultrasonic pachymetry on 5 days over 1 year: first at baseline, then at 1 week and 1, 6, and 12 months after baseline. On 1visit, CCT was measured every 2 hours from 08:00 to 20:00. Intraday CCT variance was compared with interday CCT variance.Results:
Mean CCT at all visits and time points ranged from 561 to 574 µm in healthy eyes and from 548 to 563 µm in glaucomatous eyes. The mean intraday CCT range (highest minus lowest readings) was 21±10 µm in healthy participants and 21±10 µm in glaucoma patients. The mean interday CCT range was 27±13 µm in healthy participants and 24±14 µm in glaucoma patients. Within-subject variance was significantly larger among the interday CCT measurements than the intraday CCT measurements in both healthy subjects and glaucoma patients (P<0.0001 for both) demonstrating that measurements taken on separate days are more different than measurements taken on the same day. Interday CCT differences of ≥30 µm were seen in 27.7% of normal subjects and 30% of glaucoma patients.Conclusions:
CCT measurements exhibit intraday and interday variation, with the latter being significantly greater than the former. A single CCT assessment inadequately characterizes CCT and may impact risk assessment in patients with suspect and/or diagnosed glaucoma.