A Comparative Study of the Handheld IC200 and Slit Lamp-mounted ST500 Rebound Tonometers with Goldmann Applanation Tonometry.

Objective: To compare the agreement and repeatability of intraocular pressure (IOP) measured with the slit lamp-mounted ST500 rebound tonometer (iCare Finland Oy), the hand-held IC200 rebound tonometer (iCare Finland Oy), and Goldmann applanation tonometry (GAT).

Design: Cross-sectional study.

Participants: Glaucoma patients and staff of the Eye Care Centre, Nova Scotia Health.

Methods: Intraocular pressure was measured twice each with the IC200, ST500, and GAT. Bland-Altman analysis was used to compare each pair of tonometers and whether the difference between tonometers depended on mean IOP. Intraclass correlation coefficients were also computed. Repeatability of the measurements with each tonometer was assessed by calculating the mean and variance of the difference between the first and second measurements. The relationship between IOP and central corneal thickness was also evaluated.

Main Outcome Measures: Agreement and repeatability of IOP measurements with the IC200, ST500, and GAT.

Results: One eye of 157 participants (64 men and 93 women) with a median (interquartile range) age and central corneal thickness of 62 (45-72) years and 553 (533-572) μm, respectively, were enrolled. Median IOP with the IC200, ST500, and GAT was 17.1 (14.3-21.0), 16.5 (14.0-20.8), and 17.0 (14.0-20.5) mmHg, respectively, while the range of IOP (measured with GAT) was 8.5 to 53.0 mmHg. Measurements with the 3 tonometers were not statistically different from each other, and in neither of the 3 paired comparisons was the difference in IOP between 2 tonometers dependent on mean IOP. The intraclass correlation coefficient values (0.97-0.98) showed excellent agreement between the tonometers. The variance of the difference between the first and second measurements of the ST500 was significantly lower than that of GAT (P = 0.04) and IC200 (P < 0.01). Intraclass correlation coefficients for intratonometer repeatability were also excellent (0.97-0.99).

Conclusions: The ST500 shows good agreement with GAT over a large range of IOP and significantly higher repeatability compared to the IC200 and GAT, suggesting it may be advantageous in clinical settings where topical anesthesia or skilled staff are unavailable.

Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.