Circadian variations of central corneal thickness in glaucomatous patients

Aim: To analyse variations of central corneal thickness (CCT) over 24 hours in a group of glaucomatous patients. Methods: 23 glaucomatous patients were hospitalized and underwent a circadian evaluation of CCT and intraocular pressure (IOP). All patients had abnormal visual fields and abnormal optic nerve heads and were on therapy with timolol 0.5% twice–a–day and latanoprost 0.005% once–a–day. CCT and IOP were measured at 4, 8, 12 a.m. and at 4, 8, 12 p.m. All measurements were performed by a single evaluator with patient on sitting position; CCT was evaluated as the mean value of 3 measurements. At each time–point, slit–lamp examination was performed to ensure absence of corneal epithelial defects that may interfere with CCT assessment; then CCT was performed using DGH 2000 AP ultrasonic pachymeter (DGH Technology Inc., San Diego, USA); finally, IOP was evaluated with Goldmann tonometer. Results: Mean CCT was 540 ± 32 microns (range: 479–599 microns). Mean CCT values were very similar at each time–point during 24 hours (P = 0.1, ANOVA), with a mean standard deviation of 4.3 microns. Mean individual patient CCT variation was 17.2 ± 6.6 microns (range: 6–25 microns, 1.1–5%) during the 24 hours. Mean IOP was 14.5 ± 2.4 mmHg (range: 9–22), with mean individual fluctuactions of 5.0 ± 2.1 mmHg during 24 hours. Conclusions: CCT is an important diagnostic and prognostic parameter for glaucoma. The present study demonstrated that CCT does not significantly fluctuate over 24–hours; besides, significant IOP fluctuactions were found. As a consequence, CCT variations do not significantly interfere with circadian IOP assessment, as IOP adjustment for CCT fluctuations is largely within the limits of inter– and intra– operator variability for Goldmann tonometry.