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Editors Selection IGR 23-3
Examination methods: Overlapping RNF
Comment by Eytan Blumenthal on:
21005 Overlapping of retinal nerve fibers in the horizontal plane, Jeoung JW; Kim TW; Kang KB et al., Investigative Ophthalmology and Visual Science, 2008; 49: 1753-1757
Diagnosing early glaucoma rests largely on appreciating subtle abnormalities in the optic nerve head and retinal nerve fiber layer (RNFL). Next, one needs to determine whether such 'abnormalities' represent normal physiological variations, or perhaps the earliest manifestation of disease. Towards fi ne-tuning the boundary between normal and abnor-mal RNFL appearance, Jeoung et al. (628) scrutinized numerous red-free fundus photographs and identified a subset of 1,410 eyes of 1,018 subjects presenting one or more localized RNFL defects. On finer appreciation of these photographs, in a small subset of these eyes, they noted a pattern which they called 'overlapping of retinal nerve fibers in the horizontal plane'. Retinal nerve fibers are known to merge towards the optic disc such that axons do not cross each other, but rather merge side-by-side. In their study an aberrant pattern was revealed in a subset of 2.3% of eyes (2.9% of subjects), such that within a wedge-shaped defect, in which the fibers run an arcuate course, a different radially-oriented pattern is seen. Stated otherwise, these observations suggest that axons may cross each other at different levels within the RNFL. In this study, such overlap pattern was detected exclusively at the inferotemporal quadrant. The authors used OCT to corroborate their findings and conclude that appreciation of this variation may assist clinicians in more accurate diagnosis of early glaucomatous optic neuropathy, and that its frequency might be underestimated in this study since the overlap can only be noticed when appearing within a focal wedge-shaped defect. Additional work, preferably also including healthy eyes, is needed to corroborate this unexpected anatomical variant.
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