Overlapping of retinal nerve fibers in the horizontal plane.

PURPOSE To describe a previously unreported overlapping trajectory of retinal nerve fibers over other retinal nerve fibers in the horizontal plane, and to report on the incidence of this anatomic variation. METHODS This study included 1410 eyes of 1018 subjects with one or more localized retinal nerve fiber layer (RNFL) defects detected by using red-free fundus photography. All red-free fundus photographs were reviewed, and eyes with overlapping retinal nerve fibers in the horizontal plane were selected. Overlapping nerve fibers were defined as fibers with a trajectory nonparallel to the adjacent fibers, according to the red-free fundus photographs. RESULTS Overlapping of retinal nerve fibers was detected in 33 eyes of 30 subjects. The estimated incidence of overlapping retinal nerve fibers was 2.3% (95% confidence interval [CI], 1.6%-3.1%) per eye and 2.9% (95% CI, 1.9%-4.0%) per subject. For all 33 eyes, a localized arcuate RNFL defect was observed in the inferotemporal quadrant and was partially overlapped by relatively straight nerve fibers. Optical coherence tomography confirmed the overlying retinal nerve fibers and showed a decrease in the RNFL thickness at the corresponding location of the adjacent RNFL defect. CONCLUSIONS Overlapping retinal nerve fibers were identified in the horizontal plane in 33 eyes. In those eyes, the localized RNFL defect was partially obscured by the overlying nerve fibers, leading to an unusual appearance of the RNFL defect. Awareness of this anatomic variation may help clinicians to avoid overlooking RNFL defects that are obscured by overlapping bundles.