Non-Invasive Ocular Rigidity Measurement: A Differential Tonometry Approach

Purpose: Taking into account the fact that Goldmann applanation tonometry (GAT) geometrically deforms the corneal apex and displaces volume from the anterior segment whereas Dynamic Contour Tonometry (DCT) does not, we aimed at developing an algorithm for the calculation of ocular rigidity (OR) based on the differences in pressure and volume between deformed and non-deformed status according to the general Friedenwald principle of differential tonometry. Methods: To avoid deviations of GAT IOP from true IOP in eyes with corneas different from the “calibration cornea” we applied the previously described Orssengo-Pye algorithm to calculate an error coefficient “C/B”. To test the feasibility of the proposed model, we calculated the OR coefficient (r) in 17 cataract surgery candidates (9 males and 8 females). Results: The calculated r according to our model (mean ± SD, range) was 0.0174 ± 0.010 (0.0123–0.022) mmHg/μL. A negative statistically significant correlation between axial length and r was detected whereas correlations between r and other biometric parameters examined were statistically not significant. Conclusions: The proposed method may prove a valid non-invasive tool for the measurement method of OR, which could help in introducing OR in the decision-making of the routine clinical practice.