Retinal nerve fiber layer thinning found in amyotrophic lateral sclerosis – Correlation with disease duration and severity

PURPOSE: The retinal involvement of amyotrophic lateral sclerosis (ALS) is a novel idea about a possible correlation between retinal nerve fiber layer (RNFL) thickness in different spectra of ALS patients. Finding the association of RNFL with disease duration and severity will help identify a novel noninvasive biomarker. METHODS: The study was designed as a cross-sectional study and was conducted with a suitable proforma. We included the ALS cases based on the revised El Escorial criteria. Healthy controls were age and gender matched. We used the revised ALS functional rating scale (ALSFRS-R) to assess the operational status of the patients. We measured RNFL thickness in the four quadrants with spectral-domain optical coherence tomography (OCT) and analyzed it. RESULTS: We included 30 cases (60 eyes) and 10 healthy controls (20 eyes) having a mean (standard deviation [SD]) age of 49.5 (11.1) years with a median of 50 years, and a majority of them (65%) were middle aged (between 41 and 60 years). We found statistically significant differences in RNFL thicknesses between ALS patients and healthy controls. On segmental analysis, the right eye superior and nasal quadrants and the left eye superior, inferior, and nasal quadrants were significantly affected, along with a gross asymmetry found between the left and right eyes among ALS patients. There was a significant decrease in average RNFL thickness in definite ALS patients than probable ALS patients, with significantly reduced average RNFL thickness in moderate to severe ALS patients. On correlation analysis, disease duration showed a good negative correlation with bilateral average RNFL thickness, and the ALSFRS-R score demonstrated a good positive correlation with bilateral average RNFL thickness, which was statistically significant. Thus, a reduced bilateral RNFL thickness is associated with a decreased ALSFRS-R score. CONCLUSION: The retinal changes can serve as a marker for diagnosing and monitoring patients with ALS.