Optic neuropathy is a near ubiquitous feature of Friedreich's ataxia (FRDA). Previous studies have examined varying aspects of the anterior and posterior visual pathways but none so far have comprehensively evaluated the heterogeneity of degeneration across different areas of the retina, changes to the macula layers and combined these with volumetric MRI studies of the visual cortex and frataxin level. The authors investigated 62 genetically confirmed FRDA patients using an integrated approach as part of an observational cohort study. They included measurement of frataxin protein levels, clinical evaluation of visual and neurological function, optical coherence tomography to determine retinal nerve fibre layer thickness and macular layer volume and volumetric brain MRI. The study demonstrates that frataxin level correlates with peripapillary retinal nerve fibre layer thickness and that retinal sectors differ in their degree of degeneration. Retinal nerve fibre layer is thinner in FRDA patients than controls and this thinning is influenced by the AAO and GAA1. Furthermore the authors show that the ganglion cell and inner plexiform layers are affected in FRDA. The MRI data indicate that there are borderline correlations between retinal layers and areas of the cortex involved in visual processing. The study demonstrates the uneven distribution of the axonopathy in the retinal nerve fibre layer and highlight the relative sparing of the papillomacular bundle and temporal sectors. Thinning of the retinal nerve fibre layer is associated with frataxin levels, supporting the use the two biomarkers in future clinical trials design.

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