Background: The extent of neurodegeneration in the earliest stages of central nervous system (CNS) demyelination is not known. Optical coherence tomography (OCT) is a powerful tool to study neurodegeneration in demyelinating disorders. Objectives: To study neuroaxonal loss in the retina of individuals with radiologically isolated syndrome (RIS) and investigate whether OCT measurements are associated with brain volumetrics and clinical conversion to multiple sclerosis (MS). Methods: Subjects fulfilling the Okuda criteria for RIS (n = 15 patients, 30 eyes) and age- and sex-matched healthy controls (HC) underwent spectral-domain OCT and magnetic resonance imaging for volumetric measurement of brain structures. Results: Macular ganglion cell-inner plexiform layer (mGCIPL), macular retinal nerve fiber layer (mRNFL), and temporal peripapillary RNFL (pRNFL) thickness; normalized total brain volume (nTBV); and normalized thalamic volume (nTV) were reduced in RIS compared to HC. mGCIPL, mRNFL, and pRNFL measurements were associated with nTBV, nTV, and normalized gray and white matter volumes in the RIS group. pRNFL was thinner in individuals with RIS who converted to MS in 5 years. Conclusions: Retinal neurodegeneration can be detected in the papillomacular region in the earliest stages of CNS demyelination and reflects global disease processes in the brain. OCT can be potentially useful for predicting prognosis in RIS.