Multi-angle validation of the iFalcon V700 rebound tonometer against implantable pressure sensor in ex-vivo rabbit eyes
Abstract
Rabbits are widely employed as ophthalmic models due to their favorable corneal geometry and biomechanical properties; however, intraocular pressure (IOP) measurements in both clinical and experimental settings are frequently performed under non-ideal body positions that may introduce off-axis spatial orientations relative to gravity. Despite this reality, no rebound tonometer has been validated for multi-angle use in rabbit eyes, leaving the impact of spatial inclination and gravitational deviation on measurement accuracy unknown. To validate the performance of the iFalcon V700 rebound tonometer across a 0–90° spatial inclination range (while maintaining strict perpendicularity between the probe and cornea) using an implanted pressure sensor as the gold standard. Experimental laboratory investigation. Four ex-vivo rabbit eyes. A motorized mechanical assembly facilitated multi-angle positioning of the eyes at seven distinct angles from 0° to 90° using 15° increments. An adjustable lead screw was used to gradually increase pressure to generate a physiologically relevant IOP range (8–50 mmHg). Simultaneous measurements were acquired using the iFalcon V700 tonometer (in rabbit-specific mode) and the implanted sensor, with precise synchronization ensured by a host computer program. Data distribution, linear regression, and Bland-Altman analyses were performed. IOP measurement agreement, correlation, and range-dependent biases between the rebound tonometer and the implanted sensor across various angles. Violin plot distributions of the iFalcon V700 closely mirrored the implanted sensor across all angles, with absolute median differences (|Δ Median|) remaining clinically negligible (range: 0.34–1.35 mmHg) and no significant measurement differences detected ( P = 0.398–0.973). Regression analysis revealed a strong positive correlation (R² = 0.962–0.989). However, range-dependent biases were present; a negative intercept suggested underestimation at lower IOP, whereas a slope > 1 (range: 1.00–1.11) indicated systematic overestimation at higher pressures. Bland-Altman analysis corroborated this slight overestimation bias, demonstrating mean differences ranging from 0.05 mmHg (at 0°) to 1.12 mmHg (at 90°), with 95% limits of agreement tightly confined, reaching a maximum width of -4.46 to 5.89 mmHg at 45°. Validated against an implantable pressure sensor, the iFalcon V700 rebound tonometer demonstrated high agreement across the 8–50 mmHg range and maintained robust mechanical and algorithmic stability throughout 0–90° multi-angle measurements under controlled ex vivo conditions. Despite range-dependent overestimation at higher pressures, this study, heavily constrained by its small sample size ( n = 4 eyes), must be interpreted strictly as a preliminary pilot study and an engineering proof-of-concept for multi-angle tonometry. Therefore, adequately powered, large-scale validation in living animals and clinical populations is definitively required before any translational claims regarding dynamic positional monitoring can be established.
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BibTeX
@article{cui2026multiangle,
title = {{Multi-angle validation of the iFalcon V700 rebound tonometer against implantable pressure sensor in ex-vivo rabbit eyes}},
author = {Xinqi Cui and Yingbo Liu and Lihui Yang and Qianru Chen and Ji Fu},
journal = {Scientific Reports},
year = {2026},
month = oct,
doi = {10.1038/s41598-026-76728-x},
url = {https://www.nature.com/articles/s41598-026-76728-x},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Multi-angle validation of the iFalcon V700 rebound tonometer against implantable pressure sensor in ex-vivo rabbit eyes
AU - Xinqi Cui
AU - Yingbo Liu
AU - Lihui Yang
AU - Qianru Chen
AU - Ji Fu
PY - 2026
DA - 2026/10/21
JO - Scientific Reports
DO - 10.1038/s41598-026-76728-x
UR - https://www.nature.com/articles/s41598-026-76728-x
AB - Rabbits are widely employed as ophthalmic models due to their favorable corneal geometry and biomechanical properties; however, intraocular pressure (IOP) measurements in both clinical and experimental settings are frequently performed under non-ideal body positions that may introduce off-axis spatial orientations relative to gravity. Despite this reality, no rebound tonometer has been validated for multi-angle use in rabbit eyes, leaving the impact of spatial inclination and gravitational deviation on measurement accuracy unknown. To validate the performance of the iFalcon V700 rebound tonometer across a 0–90° spatial inclination range (while maintaining strict perpendicularity between the probe and cornea) using an implanted pressure sensor as the gold standard. Experimental laboratory investigation. Four ex-vivo rabbit eyes. A motorized mechanical assembly facilitated multi-angle positioning of the eyes at seven distinct angles from 0° to 90° using 15° increments. An adjustable lead screw was used to gradually increase pressure to generate a physiologically relevant IOP range (8–50 mmHg). Simultaneous measurements were acquired using the iFalcon V700 tonometer (in rabbit-specific mode) and the implanted sensor, with precise synchronization ensured by a host computer program. Data distribution, linear regression, and Bland-Altman analyses were performed. IOP measurement agreement, correlation, and range-dependent biases between the rebound tonometer and the implanted sensor across various angles. Violin plot distributions of the iFalcon V700 closely mirrored the implanted sensor across all angles, with absolute median differences (|Δ Median|) remaining clinically negligible (range: 0.34–1.35 mmHg) and no significant measurement differences detected ( P = 0.398–0.973). Regression analysis revealed a strong positive correlation (R² = 0.962–0.989). However, range-dependent biases were present; a negative intercept suggested underestimation at lower IOP, whereas a slope > 1 (range: 1.00–1.11) indicated systematic overestimation at higher pressures. Bland-Altman analysis corroborated this slight overestimation bias, demonstrating mean differences ranging from 0.05 mmHg (at 0°) to 1.12 mmHg (at 90°), with 95% limits of agreement tightly confined, reaching a maximum width of -4.46 to 5.89 mmHg at 45°. Validated against an implantable pressure sensor, the iFalcon V700 rebound tonometer demonstrated high agreement across the 8–50 mmHg range and maintained robust mechanical and algorithmic stability throughout 0–90° multi-angle measurements under controlled ex vivo conditions. Despite range-dependent overestimation at higher pressures, this study, heavily constrained by its small sample size ( n = 4 eyes), must be interpreted strictly as a preliminary pilot study and an engineering proof-of-concept for multi-angle tonometry. Therefore, adequately powered, large-scale validation in living animals and clinical populations is definitively required before any translational claims regarding dynamic positional monitoring can be established.
SN - 2045-2322
ER -