Visual Outcomes and Retinal Nerve Fiber Layer Changes Following Methanol Induced Optic Neuropathy: A Covid-19 Era Experience

Methanol-induced optic neuropathy (MON) is a serious and potentially blinding condition with significant public health concerns. Despite advancements in treatment, predicting long-term visual outcomes of MON remain challenging. The current study aimed to assess the potential association between arterial blood gas parameters and long-term changes of retinal nerve fiber layer (RNFL) in survivors of acute methanol poisoning. This prospective study was conducted on patients hospitalized with diagnosis of acute methanol poisoning at Ali Asghar Hospital, Shiraz, Iran, between 27 June 2020 and 12 August 2021 in COVID-19 era. The treatment included acid-base correction, hemodialysis, ethanol administration, erythropoietin, corticosteroids, and vitamin supplementation. Clinical and laboratory as well as comprehensive ophthalmologic examinations and high-definition optical coherence tomography (OCT) were performed at admission and after a 12-month follow-up to evaluate RNFL thickness and visual acuity (VA) alternations. A total of 61 patients (mean age: 30.08 ± 5.20 years; 91.8% male) with methanol poisoning were included in the study. Optic disc swelling was noted in 29 patients (47.54%), while 32 (52.46%) had normal optic discs. Most patients presented on Day 2 (34.43%) and Day 1 (32.79%) post-poisoning. Arterial blood gas analysis revealed a median pH of 7.0 (IQR: 6.85-7.28), bicarbonate levels of 17.0 mmol/L (IQR: 13.0-23.0), and an anion gap of 12.0 mmol/L (IQR: 9.0-15.0). Initially, 67.2% of patients had a VA ≥ 5/10, increasing to 87.7% after one year, with none of the patients having VA worse than 1/10 at follow-up. The VA improvement was observed during the follow-up in both eyes (<i>p</i> < .001). Also, significant RNFL thinning was observed across superior, nasal, inferior, and temporal quadrants (<i>p</i> < .001). Lower arterial pH, decreased bicarbonate levels, and higher anion gap were significantly associated with RNFL thinning and worse visual outcomes (<i>p</i> < .001). This study revealed the crucial role of arterial pH, bicarbonate levels, and anion gap in predicting long-term visual impairment in patients with MON. Early erythropoietin and corticosteroids therapy showed promising neuroprotective effects, supporting their use in improving visual outcomes. OCT remains an essential tool for monitoring optic nerve damages in patients with MON.