Validation of a New Handheld Automated Fixed-Force Applanation Tonometer

Purpose: To validate a novel tonometer on ex vivo human eyes. Methods: A device was constructed to apply a known and constant force using a custom tonometer tip, and the resulting applanation image is recorded with a camera. Software automatically measures the applanation area and converts to an intraocular pressure (IOP). Ex vivo human eyes were cannulated, and the IOP manometrically was set to 5 to 45 mm Hg in 5-mm Hg increments. At each IOP, a 5- to 10-second recording was obtained with the device and converted to an IOP. Measured IOPs were compared to the set IOP value. Results: Eight ex vivo human eyes were included in this study. The mean difference (± SD) and mean absolute difference (± SD) between the stable gravity-induced manometric IOP and the measured IOP were -1.2 ± 4.5 mm Hg and 3.1 ± 3.5 mm Hg, respectively. Within the 10- to 30-mm Hg range, the mean difference and absolute difference were 0.7 ± 1.7 mm Hg and 1.4 ± 1.1 mm Hg, respectively. The prototype IOP and the set IOP showed a significant linear correlation across the full range of set IOPs (R2 = 0.90, P < 0.0001), which improved further for the more clinically relevant range of 10- to 30-mm Hg set IOPs (R2 = 0.95, P < 0.0001). Conclusions: Compared to clamped IOP, measurements using a novel handheld automated fixed-force applanation tonometer demonstrated high accuracy, especially within the 10- to 30-mm Hg range. Translational Relevance: We present a novel tonometer validated on ex vivo human eyes, which demonstrates high accuracy and may have applicability to patient care.