Comparing measurements of optic disc ovality index and rotation angle in myopic eyes using manual, clinical disc margin photography-based and automated, Bruch’s membrane opening OCT-based techniques

Abstract

Purpose : To compare manual measurements of optic nerve head ovality index (OI) and rotation angle based on the clinical disc margin identified on optic disc photographs with automated measurements based on Bruch’s membrane opening (BMO) from optical coherence tomography (OCT) scans in healthy, non-myopic and myopic eyes.

Methods : 201 healthy or glaucomatous eyes of 166 study participants enrolled in the Diagnostic Innovations in Glaucoma Study were stratified by level of axial myopia (non-myopic, mild-myopic and high-myopic with axial length > 26 mm). Using ImageJ software, the clinical disc margin of each photograph was manually annotated and the major axis length, minor axis length and angle of major axis from horizontal axis of the annotation were measured and used to derive OI, rotation angle and direction. These derived values were compared to those generated from automated, custom-programmed BMO-based techniques using segmented OCT volumes. R² values from linear mixed effects models were used to describe the associations between manual, photograph-based and automated, OCT-based assessment.

Results : Average (95% CI) axial length was 23.3 mm (23.0 mm, 23.3 mm), 24.8 mm (24.7 mm, 25.o mm) and 26.8 mm (26.6 mm, 27.0 mm) in non-myopic, mild-myopic and high-myopic eyes, respectively (ANOVA, p≤0.001). The R² association (95% CI) between manual photograph-based and automated OCT-based assessment of disc OI for all eyes was 0.26 (0.16, 0.36; p<0.001). This association was weakest in non-myopic eyes (0.09 [0.01, 0.26; p=0.016]), followed by mild-myopic eyes (0.13 [0.02, 0.29; p=0.004]) and strongest in high-myopic eyes (0.40 [0.19, 0.60; p<0.001]). No significant associations were found between photography- and OCT-based assessment of rotation angle with R² values ranging from 0.00 (0.00, 0.08) in non-myopic eyes to 0.03 (0.00, 0.21) in high-myopic eyes (all associations p≥0.33).

Conclusions : Weak associations between manual photograph-based and OCT BMO-based assessment of optic disc ovality and lack of associations between assessment of disc rotation angle indicate that measurements based on these methods cannot be used interchangeably and results should not be directly compared.

This is a 2021 ARVO Annual Meeting abstract.