Serial changes in optical coherence tomography angiography of glaucoma patients with image asymmetry analysis

Abstract

Purpose : Conventional binarization of optical coherence tomography angiography (OCT-A) images yielding perfusion density (PD) can result in high variability for longitudinal analysis. We tested the hypothesis that image asymmetry analysis would be more resistant to factors influencing global variability and better reflect changes observed with visual field (VF) mean deviation (MD).

Methods : Subjects were selected from an ongoing prospective study of glaucoma patients and healthy controls [followed at 4-month intervals with OCT-A (macula scans, Spectralis OCT2, Heidelberg Engineering) and 24-2 VF exams who had ≥3 exams] for the following groups: i) patients with successive decrease of MD across all visits, ii) patients with variable change in MD not exceeding 3 dB between visits, and iii) controls with variable change in MD not exceeding 3 dB between visits. OCT-A projection images of the superficial vascular plexus were exported. Image asymmetry was calculated by creating an 8×8 grid and for each cell of one hemi-macula, the mean grey value was compared to the mirror-image cell in the opposite hemi-macula. The relationship between changes in MD and PD or image asymmetry was estimated with Pearson’s correlation coefficient.

Results : The median (interquartile range) age was 66 (16) years for progressing glaucoma patients (n=9), 68 (3) years for stable glaucoma patients (n=10), and 66 (12) years for control subjects (n=12). The MD slopes (standard error) were -0.84 (0.99) dB/year for progressing, -0.13 (1.10) dB/year for stable and 0.59 (0.58) dB/year for controls. The average change in PD between visits, by subject, was 1.4 (7.9) for progressing, 0.9 (5.2)% for stable, and 4.6 (4.7)% for controls; whereas for image asymmetry the average change was -0.7 (3.1)% for progressing, -0.1 (5.0)% for stable and 0.7 (3.8)% for controls. In glaucoma patients, the correlation (95% CI) between change in asymmetry and MD was significantly higher than that between PD and MD [0.41 (0.11 – 0.64) and -0.15 (-0.44 – 0.16), respectively; p=0.0046]. In controls, the correlation between change in asymmetry and MD was not significantly different than that between PD and MD [-0.15 (-0.52 – 0.27) and -0.09 (-0.48 – 0.32), respectively; p=0.82].

Conclusions : These findings suggest that asymmetry rather than global indicators, such as perfusion density, better relate to conventional measures of glaucoma progression.

This is a 2020 ARVO Annual Meeting abstract.