Purchase this article with an account.
D.C. Pye, K.E. Hamilton, S. Aggarwala, S.–L. Evian, J. Khosla, R. Perera; Diurnal Variation of Corneal Thickness and Its Effects on Intraocular Pressure Estimates by Goldmann Tonometry . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4857.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Corneal properties are believed to affect the accuracy of Goldmann applanation tonometry (GAT). The purpose of this study was to determine if the natural diurnal variation of central corneal thickness (CCT) is sufficient to cause clinically significant errors in Goldmann applanation tonometry (GAT) estimates of intraocular pressure (IOP). Methods: 25 young healthy subjects were recruited. Central corneal curvature (CCC), IOP by GAT (IOPG) and CCT were measured over a 24 hour period in one eye. Data was analysed using SPSS version 12.0.1 with Spearman correlation coefficients(r) set at 0.5% statistical significance. Results: 1. The overnight change in IOPG was +3.08 ± 2.39 mmHg and CCT was +3.85 ± 2.12%. There was no significant change in CCC on waking (p = 0.335, paired t–test). 2. There was a moderate relationship between IOPG and CCT on waking (r = 0.512, p = 0.009). 3. Both IOPG and CCT peaked on awakening at 7 am then dropped rapidly to baseline levels by 9 am at a similar rate (r = 0.964, p < 0.001). This relationship did not hold after 9 am (r = –0.595, p = 0.120). 4. The amount of IOPG increase at 7 am was not related to the amount of corneal oedema (r = –0.099, p = 0.636) or the change of CCT (r = –0.068, p = 0.747). However, when the total range of data is considered, oedema between +1.5 and +6.0% is associated with an increasing IOPG (r = 0.353, p < 0.001). 5. Corneal oedema of greater than +1.5% appears necessary for the IOPG to be elevated. Conclusions: The similar rate of change between IOPG and CCT within the first two hours of waking suggests that corneal oedema may influence the accuracy of GAT. Given that higher IOPGs are likely to be found in corneas undergoing their natural diurnal variation in hydration, clinicians should avoid using GAT to estimate IOP within 2 hours of eye opening.
This PDF is available to Subscribers Only