Optic disc tilt and rotation effects on positions of superotemporal and inferotemporal retinal nerve fibre layer peaks in myopic Caucasians.

CLINICAL RELEVANCE: In myopic eyes, the optic disc may become tilted and rotated, making glaucoma diagnosis more difficult.

BACKGROUND: To determine the presence of tilted optic disc, the degree of optic disc rotation, and their effects on the angular location of superotemporal and inferotemporal retinal nerve fibre layer (RNFL) peaks in healthy myopic Caucasians.

METHODS: Non-glaucomatous healthy myopic Caucasian eyes with an axial length > 24 mm were evaluated. ImageJ was used to quantify optic disc tilt and torsion on red-free fundus photography. The RNFL was scanned using spectral-domain optical coherence tomography. The angle of the superotemporal and inferotemporal peaks with the vertical-horizontal meridian was measured.

RESULTS: Fifty-four eyes of 54 individuals were evaluated. The axial length was correlated with the angular location for both the superotemporal (r = -0.549, p < 0.001) and inferotemporal (r = -0.415, p = 0.002) RNFL peaks; they were placed more temporally in eyes with higher axial lengths. For each 1 mm increase in axial length, the angle between the superotemporal peak and the temporal horizontal meridian decreased by 3.976°, and the angle between the inferotemporal apex and the temporal horizontal meridian decreased by 3.028°. The angle between the inferotemporal peak and the temporal horizontal meridian decreased by 0.231° for each 1° increase in optical disc torsion (R2  = 0.09 Regression coefficient = -0.231, p = 0.027).

CONCLUSIONS: The temporal shift of superior and inferior peaks, the thickening of temporal and nasal RNFL, the presence of tilted optic disc, and optic disc rotation may cause misinterpretation of the RNFL in myopic Caucasians. When evaluating peripapillary RNFL thickness in myopic individuals, it would be better to consider these to avoid misinterpretation.