Earliest location of glaucomatous retinal nerve fibre layer damage is determined by intact baseline RNFL thickness profile.

Background/aims: To identify whether an intact retinal nerve fibre layer (RNFL) thickness profile could determine the location of the earliest RNFL defect in glaucoma.

Methods: Retrospective longitudinal cohort study of patients with initial unilateral glaucoma who eventually developed new glaucoma in the fellow eye. Guided progression analysis (GPA) of serial optical coherence tomography (OCT) examinations was used to identify the angular locations of the earliest RNFL defect, peak and temporal edge of the baseline RNFL profile and major vessels based on the peripapillary OCT scan circle.

Results: We identified 112 new RNFL defects in 109 fellow eyes of 109 consecutive patients. The locations of new defects were superotemporal (22 eyes), inferotemporal (87 eyes) and papillomacular bundle (3 eyes), respectively. Overall, the midpoint location of the earliest RNFL defect strongly coincided with the RNFL peak (p<0.001). Specifically, the location was mildly (4.3±12.0°) temporal to, rather than at the peak thickness, particularly in eyes with a focal thinning pattern of arcuate bundles (7.8±10.8°). The close topographical relationship was consistent regardless of the interindividual variability in the RNFL profile and vessels, as well as hemispheric locations, and after adjusting for potential factors including age, refractive error, baseline intraocular pressure, tilt ratio, tilt axis and glaucoma diagnosis.

Conclusion: The location of the earliest RNFL defect in glaucoma showed a close relationship with the intact RNFL profile within the same eye, regardless of variations in RNFL, hemispheric location and vessel distribution. In addition, the earliest defect was located mildly temporal to, rather than at, the peak RNFL thickness. The baseline RNFL profile may have a significant role in the regional vulnerability of glaucoma.