OBJECTIVE: In autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) disease, severity and age of onset vary greatly, hindering to objectively measure and predict clinical progression. Thickening of the retinal nerve fiber layer is distinctive of ARSACS patients, as assessed by optical coherence tomography, whereas conventional brain magnetic resonance imaging findings include both supratentorial and infratentorial changes. Because longitudinal imaging studies in ARSACS patients are not available to define these changes as biomarkers of disease progression, we aimed to address this issue in the ARSACS mouse model. METHODS: We performed longitudinal retinal OCT and brain MRI in the Sacs RESULTS: We demonstrated that RNFL thickening by OCT gradually increases in the early stages of pathology in the Sacs INTERPRETATION: We show that both RNFL thickening and MRI changes may represent biomarkers of disease progression in the Sacs