Repeatability of Goldmann tonometry performed by optometry students on glaucoma patients

Abstract

Background: The purpose of this study was to evaluate the repeatability of masked Goldmann tonometry performed by optometry students on patients with glaucoma. Methods: Subjects were recruited from among patients scheduled to undergo selective laser trabeculoplasty at the Rosenberg School of Optometry clinic. Each subject had masked Goldmann tonometry performed by three examiners at each office visit: two fourth professional-year optometry interns and an attending optometrist. Each examiner performed three sequential masked tonometry measurements on each eye. Results: Twenty-eight interns and two optometrists performed masked Goldmann tonometry on 12 glaucoma patients. The coefficient of variation was 9.1 per cent for the right eye and 12.1 per cent for the left eye for interns compared with 6.4 per cent right eye and 6.6 per cent left eye for optometrists. There was significant interaction between intern and patient on coefficient of variation (two-factor analysis of variance, p = 0.005), indicating coefficient of variation was influenced by both intern and patient factors. No such interaction was found for optometrist-performed measurements (p = 0.96). Mean interobserver difference for interns ranged between 0.9 and 3.1 mmHg, with 95 per cent limits of agreement that were proportional to mean intraocular pressure. Mean interobserver difference for optometrists ranged between 0.6 and 1.8 mmHg without proportionality bias. At higher pressure levels intern measurements became more variable and tended to overestimate optometrist measurements. Conclusions: Both intraobserver and interobserver repeatability of masked tonometry was lower for interns than experienced optometrists. Intern performance differed from optometrists in that intern measurements became more variable at higher intraocular pressure levels and were significantly influenced by patient factors. The present results support the need for trainee exposure to patients with abnormally elevated intraocular pressure. Research into factors that influence trainee Goldmann tonometry repeatability is needed.