Does optic disc topography vary during office hours?

Abstract

Purpose: To investigate whether there is variation in optic disc topography as measured by the Heidelberg Retina Tomograph (HRT), in normals during office hours.Methods: Thirty normal subjects (22 females and 8 males, median age 28 years, range 18–58) underwent Goldmann tonometry and optic disc analysis with the HRT. Three HRT readings were taken at each visit and a mean topographic image (MTI) produced. Measurements were performed in the morning (07.00–09.00 hours) and were repeated later the same day (17.00–19.00 hours). We studied the following topographic parameters: cup‐to‐disc area ratio (CDR), rim volume (RV), cup shape measure (CSM), and retinal nerve fibre layer thickness (RNFLT) in relation to time of day and the change in intraocular pressure (IOP).Results: The median changes in the topographic parameters were as follows (a negative value indicates a larger value in the evening): CDR (median 0.001, 95% CI: −0.007 to 0.007), RV (median 0.003, 95% CI: −0.021 to 0.016), CSM (median: −0.003, 95% CI: −0.015 to 0.007) and RNFLT (median 0.006, 95% CI: −0.010 to 0.009). No parameter exhibited statistically significant change. The median morning IOP was 14 mmHg (95% CI: 13–16 mmHg) and was not significantly different (Wilcoxon's W = 234; p = 0.27) to evening IOP when it was 13 mmHg (95% CI: 12–15 mmHg). The median difference in IOP was 1 mmHg higher in the morning than the evening (range 6 mmHg higher in the morning to 4 mmHg higher in the evening). The parameter changes between the morning MTI and the evening MTI were independent of IOP changes using Kendall's tau statistic for each parameter.Conclusions: There was no variation in HRT parameters when measured during office hours. Small intraindividual changes in IOP do not significantly affect optic disc topography.