Clinical comparison of two intraocular pressure measurement methods: SmartLens dynamic observing tonography versus Goldmann

Abstract.

Purpose: To compare intraocular pressure measurements obtained with SmartLens, a gonioscopic contact lens, to those from Goldmann applanation tonometry. Methods: Eighty volunteers (20 healthy individuals and 60 glaucoma patients from the university eye hospital's outpatient department) were examined using conventional Goldmann tonometry and the new SmartLens tool. For each device three replicate measurements were performed. A paired t-test and the corresponding mean difference confidence interval approach were used to assess deviations in location of the two tonometric methods; the test procedure of Maloney and Rastogi was used for comparison of precision in paired data. Intraindividual differences were evaluated according to the approach of Altman and Bland. Results: There was a mean difference of 5.6 mmHg (95% CI: 4.3 mmHg; 6.8 mmHg; P<0.01) in intraocular pressure between the two methods with a significant overestimation by SmartLens tonometry compared to Goldmann tonometry (P<0.01). The 95%-limits of agreement ranged from –5.4 mmHg to +16.6 mmHg for individual patients. The measurement method variance of SmartLens was higher (Maloney–Rastogi test; P <0.01). The mean coefficients of variation for intraindividual replicates were 10.1% (SmartLens) and 3.8% (Goldmann; P <0.01). Conclusions: Accepting Goldmann tonometry as gold standard for intraocular pressure measurement, the SmartLens method shows considerable variation and therefore is not proven to be an adequate substitute for Goldmann tonometry.