The Effects of Refractive Error and Related Optic Nerve Head (ONH) Anatomical Parameters on Optical Coherence Tomography (OCT) Retinal Nerve Fiber Layer (RNFL) Deviation Map

Abstract

Purpose : The impact of spherical equivalent (SE) on RNFL thickness (RNFLT) may be modified by anatomical parameters. Here, we evaluate the effects of SE and related retinal parameters on OCT abnormality color marks on RNFL deviation map, independent of glaucoma severity.

Methods : Reliable pairs of Cirrus OCT circumpapillary RNFLT measurements and Humphrey 24-2 visual fields (VF) of 421 eyes of 421 glaucoma patients were included. Retinal parameters related to SE (ONH nasal/temporal curvatures measured by the slope of the best lines fitted to the inner limiting membrane, angle between major superior and inferior temporal retinal arteries [inter-artery angle, IAA], and ONH tilt [TL]) were identified on OCT fundus images and/or B-scans (Figures 1 and 2). RNFL deviation maps were extracted from the OCT fundus image on the area of 5.4×5.4 mm around the ONH center with a resolution of 40,401 pixels. For each pixel, a logistic regression model was calculated with OCT abnormality marks on RNFL deviation map as regressands and each parameter as a regressor independent of glaucoma severity (shown as “parameter|MD”), and independent of SE and MD (shown as “parameter|SE,MD”). The results are presented on spatial maps of the entire scanning area. Each of the 40,401 pixels for which there is a significant effect of the parameter (p < 0.05 after correction for multiple comparisons) on abnormality marks represents a location where the related factor may confound glaucoma diagnosis independent of SE and/or MD and is shown in blue/red colors.

Results : Quantified by the affected scanning area, we observed the following parameter effects: IAA: 38.8%, ONH nasal curvature: 29.8%, SE: 22.5%, TL: 5.8%, temporal curvature: 0%, independent of MD (Figures 1 and 2). After excluding co-variation effects with SE, considerable proportions of the areas for IAA (35.1%), and ONH nasal curvature (23.4%) still remain affected.

Conclusions : Variations in IAA and ONH nasal curvature can affect OCT abnormality ratings independent of glaucoma severity and SE. These parameters should be considered in addition to SE while introducing new RNFLT norms for OCT machines.

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