Orientation of the Temporal Nerve Fiber Raphe in Healthy and in Glaucomatous Eyes

PURPOSE. To determine the normal variation in orientation of the temporal nerve fiber raphe, and the accuracy with which it may be predicted or approximated in lieu of direct measurement. METHODS. We previously described an algorithm for automatic measurement of raphe orientation from optical coherence tomography, using the intensity of vertically oriented macular cubes. Here this method was applied in 49 healthy participants (age 19-81 years) and 51 participants with primary open angle glaucoma (age 51-80 years). RESULTS. Mean fovea-disc-raphe angle was 173.5 degrees +/- 3.2 degrees (range = 166 degrees-182 degrees) and 174.2 degrees +/- 3.4 degrees (range = 1668-1848) in healthy and glaucoma patients, respectively. Differences between groups were not significant. Fovea-disc-raphe angle was not correlated with age or axial length (P > 0.4), showed some symmetry between eyes in glaucoma (R-2 = 0.31, P < 0.001), and little symmetry in the healthy group (P = 0.06). Fovea-disc angle was correlated with fovea-raphe angle (R-2 = 0.27, P = 0.0001), but was not a good predictor for raphe orientation (average error = 6.8 degrees). The horizontal axis was a better predictor (average error = 3.2 degrees; maximum error = 9.6 degrees), but still gave approximately twice the error previously reported for direct measurement from macular cubes. CONCLUSIONS. There is substantial natural variation in temporal nerve fiber raphe orientation, which cannot be predicted from age, axial length, relative geometry of the disc and fovea, or the contralateral eye. For applications to which the orientation of the raphe is considered important, it should be measured directly.