Retinal Nerve Fiber Layer Thickness in Nonarteritic Anterior Ischemic Optic Neuropathy in Diabetic Patients: From the Acute to Resolving Phases

Purpose: To describe changes in RNFLp thickness over time in diabetic patients with Nonarteritic anterior ischemic optic neuropathy (NOIA-NA). Materials and methods: This is a prospective observational study, conducted in the ophthalmology department at the University Hospital of Fez, between January 2018 and January 2020. Diabetic patients diagnosed with NOIA-NA underwent, at the time of diagnosis, at three and six months after the initial consultation, a complete ophthalmological examination, including assessment of best corrected visual acuity, a visual field (SITA 24-2 program, Humphrey-Zeiss Instruments), and papillary optical coherence tomography (TOPCON3D-OCT-Maestro). Results: We included 80 eyes of 80 diabetic patients with NOIA-NA. At the baseline evaluation, the average best corrected visual acuity was 0.50 ± 0.28 logMAR, while after six months of follow-up, it improved to 0.401 ± 0.33 logMAR with a significant difference between the two visits. The average peripapillary nerve fibre layer thickness (RNFLp) in the affected eye was 161.91 ± 14.96 μm. This represents an average increase in RNFLp thickness of 70.75% compared to the RNFLp thickness of control eyes. The average percentage loss of RNFLp compared to control eyes was 32.6% (37.5 µm) at three months and 37.7% (42.3 µm) at six months, At the six-month visit, the percentage thinning of RNFLp for the superior, inferior, nasal, and temporal quadrants compared to the control eye was 44% (53.1 µm), 34% (48.4 µm), 21% (17.7 µm), and 31% (21.3 µm), respectively. In the acute phase, there was no correlation between initial average RNFLp thickness and VA or initial mean deviation. However, RNFLp thickness was correlated with mean deviation at 3 months and 6 months (-0.646, p<0.001; 0.610, p<0.001, respectively). Similarly, RNFLp thickness was correlated with average visual acuity at 3 months and 6 months (0.556, p<0.001; -0.395, p<0.001; -0.533, p<0.001, respectively). Using regression analysis, it was found that for each micrometre of mean RNFL thickness lost, there was a 2.1 dB decrease in DM at 3 months and a 1.8 dB decrease at 6 months. Similarly, there was a decrease of one line of VA for every 6.2 µm of mean RNFLp thickness lost at 3 months and for every 2.2 µm at 6 months after onset. Conclusion: The present study confirmed the capability of OCT for the diagnosis and monitoring of RNFLp changes after NOIA-NA in diabetic patients. The characteristics of papilledema as shown by OCT at baseline have limited prognostic value: Initial RNFLp thickness was not correlated with VA and DM. However, the significant correlation between RNFLp changes and visual field deficits and VA in the chronic phase represents an important structure-function relationship and underscores the importance of OCT in assessing the functional and structural course of eyes with NOIA-NA in diabetic patients.