Purpose: To evaluate the effects of four anatomical parameters (angle between superior and inferior temporal retinal
arteries [inter-artery angle, IAA], optic disc [OD] rotation, retinal curvature, and central retinal vessel trunk entry point
location [CRVTL]) on retinal nerve fiber layer thickness (RNFLT) abnormality marks by OCT machines.
Methods: Cirrus OCT circumpapillary RNFLT measurements and Humphrey visual fields (HVF 24-2) of 421 patients
from a large glaucoma clinic were included. Ellipses were fitted to the OD borders. Ellipse rotation relative to the
vertical axis defined OD rotation. CRVTL was manually marked on the horizontal axis of the ellipse on the OCT fundus
image. IAA was calculated between manually marked retinal artery locations at the 1.73mm radius around OD. Retinal
curvature was determined by the inner limiting membrane on the horizontal B-scan closest to the OD center. For each
location on the circumpapillary scanning area, logistic regression was used to determine if each of the four parameters
had a significant impact on RNFLT abnormality marks independent of disease severity. The results are presented on
spatial maps of the entire scanning area.
Results: Variations in IAA significantly influenced abnormality marks on 38.8% of the total scanning area, followed by
CRVTL (19.2%) and retinal curvature (18.7%). The effect of OD rotation was negligible (<1%).
Conclusions: A natural variation in IAA, retinal curvature, and CRVTL can affect OCT abnormality ratings, which
may bias clinical diagnosis. Our spatial maps may help OCT manufacturers to introduce location specific norms to
ensure that abnormality marks indicate ocular disease instead of variations in eye anatomy.
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