Ocular rigidity: a novel non-invasive clinical method

Abstract

Purpose : Considerable evidence suggests that ocular rigidity (OR) plays a key role in the pathogenesis of open angle glaucoma (OAG) and other ocular diseases. 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 (Beaton et al., 2015). The purpose of this clinical study is to compare correlations between OR and other factors, such as age, axial length (AL) and ocular pulse amplitude (OPA) to previous studies using invasive techniques or post-mortem eyes.

Methods : Sixty-two subjects (27 normal, 27 with OAG and 8 with functional trabeculectomy blebs) were enrolled and measurement of OR was done using our novel technique. This method is based on Friedenwald’s equation, involving OPA as measured by DCT (Dynamic Contour Tonometry, Ziemer group) and pulsatile ocular volume change (ΔV) as measured with our automated segmentation method. Video-rate Spectral Domain Optical Coherence Tomography (SD OCT, Spectralis OCT Plus, Heidelberg Engineering) time series with Enhanced Depth Imaging was carried out at the macula. Each video was analyzed using our segmentation algorithm to find the mean magnitude of choroidal thickness change (ΔCT) and thus derive ΔV adjusting for AL (IOL Master, Zeiss Meditec). Heart rate was also measured during the video imaging and served as a validation for the pulsatile changes measured by OCT.

Results : The mean OR coefficient calculated with our technique was 0.037 ± 0.022 uL^-1, a similar value to previous invasive methods. As anticipated, a negative correlation was found between OR and AL (r= -0.31, p= 0.01) for all groups combined. A positive correlation between OR and OPA was found in all groups (r= 0.46, p= 0.0002). Although the relationship between OR and age (r= 0.16, p= 0.2) was not significant for all groups, it was positively correlated in the Normal group (r= 0.41, p=0.04), where the age range was much wider. A negative correlation was found between ΔCT and OR (r= -0.58, p= 0.00) and also between ΔV and OR in all groups (r= -0.64, p=0.000).

Conclusions : We found a negative correlation between OR and AL and a positive correlation between OPA and OR, as well as between age and OR, which is the same as expected from older invasive techniques. This confirms the validity of our novel non-invasive technique and will permit us to lead further investigation of OR in ocular disease.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.