Influence of the Disc–Fovea Angle on Limits of RNFL Variability and Glaucoma Discrimination

Abstract

Disc-fovea angle measurements demonstrated fair intersession repeatability. While adjusting for DFA improved RNFL prediction limits in some sectors, it did not enhance glaucoma detection.

Automatic identification of the temporal retinal nerve fiber raphe from macular cube data

“…1 are subject to rotations of the head/eyes, but the angle formed by all 3 structures (disc-fovea-raphe) is not. In our 15 subjects this angle was 172.4 ± 2.3° (ranging from 168.5 to 176.2°), which agrees well with prior estimates [9,12,13]. …”

“…Methods based on thickness [2,9] could possibly be improved by manual exclusion or editing of the automated segmentation of retinal layers, however, we advocate an alternate approach based on intensity.…”

“…Further confirmation that our method is as applicable to the patient population as it is to healthy individuals could be achieved by using low density macular cube data to compare the distributions in raphe orientation between the two groups. However, even this may produce unexpected results due to changes in raphe shape that apparently occur as glaucoma progresses [2,[8][9][10]14]. The most instructive approach to improve our understanding in the future will be measurement of the raphe orientation when the retina appears healthy, and tracking the raphe shape and/or orientation in the same patient as the disease progresses.…”

“…Both thickness [2,8,9] and intensity [11][12][13][14] of the RNFL have been used by other groups to estimate the orientation of the temporal raphe, and both are reasonable indicators since the apparent "missing" fibers at the raphe should reduce both thickness and intensity recorded by OCT at the level of the RNFL.…”

“…Hood et al located the axis of minimum RNFL thickness from 128 healthy eyes, reporting approximately horizontal orientation of the raphe despite a large physiological variation in the relative positions of the optic disc and fovea [2]. In glaucomatous eyes, Le et al, Amini et al and Kim et al have exploited characteristic patterns of glaucomatous damage coupled with measured visual field loss to infer the axis between superior and inferior fields, again relying on changes in thickness of particular layers measured with OCT [8][9][10]. Each of the above studies concluded that the temporal raphe is oriented roughly along a horizontal line.…”