Abstract
Background: In studies aimed at assessing the accuracy and repeatability of non-contact tonometers, the order in which these tonometers and the Goldmann tonometer are used is usually randomised despite studies in the literature that demonstrate an ocular massage effect that occurs post-applanation but not after non-contact tonometry. The purpose of this study was to investigate the effect of repeated corneal applanation on subsequent assessments of IOP.
Methods: Data were obtained from 65 left eyes of 65 young, oculovisual normals. Three sets of IOP measurements were obtained, one set with the Goldmann applanation tonometer and two with the Topcon CT80 non-contact tonometer (one set each before and after applanation with the Goldmann tonometer), in each one of two separate measurement sessions, one week apart.
Results: The average (and SD) IOP measured with the Goldmann tonometer in the first session (14.8 ± 2.9-mmHg) did not vary significantly from the IOP measured with the non-contact tonometer (pre-applanation) in both sessions or with the average Goldmann IOP in the second session.
The bias (mean difference ± SD) between methods was 0.3 ± 1.4-mmHg and 0.4 ± 1.4-mmHg, respectively, for the first and second sessions, with the CT80 (pre-applanation) recording the higher IOP in both sessions. The within-session repeatability coefficients were ±2.3-mmHg, ±2.6-mmHg, ±2.1-mmHg and ±2.0-mmHg for the CT80 (pre-applanation) in the first and second sessions, and the Goldmann tonometer in the first and second sessions, respectively. Test-retest repeatability coefficients were ±2.8-mmHg and ±2.5-mmHg for the CT80 (pre-applanation) and the Goldmann tonometer respectively.
Post-applanation with the Goldmann tonometer, there was a statistically significant (p < 0.05) reduction (1.5 ± 1.2-mmHg in session 1) in the IOP measured with the non-contact tonometer in both sessions.
Conclusion: These results suggest that repeated corneal applanation leads to a statistically significant reduction in IOP on subsequent measurements.