Asymmetric Retinal Nerve Fiber Layer Defects in Early Glaucoma: A Focus on Superior-Inferior Depth Variability

To investigate difference in the characteristics of retinal nerve fiber layer (RNFL) defects between the inferior and superior retina in early glaucoma.

Cross-sectional study.

A total of 103 eyes with early glaucoma (visual field mean deviation [MD] ≥-6.0 dB), with 131 RNFL defects identified in OCT enface images.

The location of RNFL defect was determined using clock-hour positions around the optic disc. The distribution of RNFL defects was presented as the number of defects in each location. The depth of each defect was assessed as the difference of circumpapillary RNFL (cpRNFL) thickness in the defect from normal values at the same location, using a normal reference database matched for the background characteristics of the glaucoma patients. These features were compared between the inferior and superior retina.

Characteristics of RNFL defects.

The average MD of the included eyes was -2.04 ± 1.64 dB. We found that 51.9% of RNFL defects were located in the inferior retina and 48.1% in the superior retina. The angular location of RNFL defect was significantly closer to the foveola in the inferior retina than in the superior retina (43.5 ± 13.8° vs. 57.8 ± 21.4°, P < 0.0001). The RNFL defects were relatively localized to a narrower region in the inferior retina, whereas they were diffusely distributed over a broader area in the superior retina. The cpRNFL thickness difference in the defect from normal corresponded to 68.4 ± 12.6% of the normal value in the inferior retina and 55.1 ± 16.7% in the superior retina. It was significantly greater in the inferior retina, indicating deeper defects (P < 0.0001). The deep RNFL defects (cpRNFL thickness difference >65%) were significantly more frequent in the inferior retina than in the superior retina (72.1% vs. 28.5%, P < 0.0001).

The RNFL defects exhibited significantly different locations, distributions, and depths between the inferior and superior retina. Notably, considerable thinning of the RNFL was observed particularly in the inferior retina, even in eyes with early glaucoma. Acknowledging these asymmetrical characteristics of RNFL defect provides insights into its nature and may assist initial diagnosis of glaucoma.

The authors have no proprietary or commercial interest in any materials discussed in this article.