Clinical evaluation of corneal elasticity and true IOP using a dual-applanation tonometer.

Abstract

Purpose: To evaluate the clinical feasibility of a modified Goldmann applanation system capable of estimating true intraocular pressure and corneal elasticity in vivo.

Methods: A dual-applanation prism was developed, allowing two sequential IOP readings under identical optical conditions. A mathematical model was applied to compute true intraocular pressure and the corneal Young's modulus measured applanation forces, corneal thickness and curvature. Fifty-three healthy eyes were examined. Model-derived true intraocular pressure values were compared with standard GAT, Pascal dynamic contour tonometry and corneal Young's modulus.

Results: Mean IOPT was 15.72 ± 2.44 mmHg, significantly higher than GAT measurements (14.86 ± 2.71 mmHg; mean difference +0.86 ± 1.82 mmHg, p = 0.0012). IOPT showed strong agreement with Pascal DCT (15.60 ± 2.35 mmHg), with minimal bias (+0.15 ± 1.63 mmHg, p = 0.499) and high correlation (r = 0.93, p < 0.0001). Measurement variance was lower for IOPT than for GAT, indicating improved precision. The mean in vivo corneal Young's modulus was 0.18 ± 0.04 MPa (range 0.057 MPa to 0.296 MPa.), consistent with physiological values. Young's modulus showed significant age-related variation (p < 0.001) and a moderate inverse correlation with IOPT (r = -0.53, p < 0.001), while no significant sex-related differences were observed.

Conclusion: This dual-applanation system enables real-time in vivo estimation of both true intraocular pressure and corneal elasticity. The model provides a physically grounded correction to Goldmann tonometry and introduces a new clinically accessible method to assess corneal biomechanics.