Comparison of ocular rigidity between eyes with open-angle glaucoma and eyes with functional trabeculectomy blebs using a novel clinical method based on high-speed OCT choroidal imaging.

Abstract

Purpose : Ocular rigidity (OR) is thought to play a key role in the pathogenesis of open-angle glaucoma (OAG). While there is currently no reliable clinical method to assess OR, our group has recently developed a technique permitting a direct and non-invasive measurement in humans. This will allow us to measure OR on a wide range of patients and further investigate the causes of glaucoma progression. The purpose of this clinical study is to measure and compare OR coefficients between eyes with OAG and eyes with functional trabeculectomy blebs. We expect that the OR will be lower in the bleb group.

Methods : Forty-nine age-matched subjects (36 eyes with OAG and 13 with OAG and functional trabeculectomy blebs) were recruited and OR was measured using our novel method. As described in Beaton et al. (2015), this method, which is based on Friedenwald’s equation, involves high-speed OCT imaging and automated segmentation of the choroid, as well as dynamic contour tonometry, to calculate the OR coefficient. Axial length (AL), central corneal thickness (CCT), corneal hysteresis (CH), corneal resistance factor (CRF) and systemic arterial pressure were obtained from all participants. Univariable and multivariable analyses were conducted to compare OR differences between both groups.

Results : Significant correlations were found between AL and OR (r=-0.265, p=0.001), as well as ocular pulse amplitude (OPA) and OR (r=0.362, p<0.001). After adjusting for the covariates which were shown to have the most influence on the model (Goldman IOP, OPA, CH, age, AL, and systolic blood pressure), the bleb group had significantly lower values of OR (0.0259 ± 0.00527/uL versus 0.0416 ± 0.00285/uL; p= 0.008) compared to the OAG group.

Conclusions : In our study, we found that eyes with OAG and functional trabeculectomy blebs have lower OR than eyes with OAG, even after controlling for IOP which differs between both groups. These findings could lead to a better understanding of the therapeutic effect of filtration surgery which often contributes to the long-term stability of glaucoma patients. Further investigation of a same cohort before and after surgery could also help determine whether the biomechanical properties of the eye are modified following filtration surgery or whether patients with low OR are more likely to require filtration surgery.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.