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.