Visual Pathways Involvement in Friedreich’s Ataxia Patients Without Macular Impairment

Abstract

Objectives: Visual Evoked Potential (VEP) abnormalities in Friedreich Ataxia (FA) may result from dysfunction of retinal ganglion cells (RGC), post-retinal visual pathways, or both. Therefore, we aimed to clarify whether in Friedreich Ataxia (FA), abnormal neural conduction is due to dysfunctional RGC, impaired conduction along the post-retinal visual pathways, or both. The secondary aim of the study was to clarify the relationship between a possible RGC and/or post-retinal dysfunction and the patient’s age, age at disease onset, and disease duration. Method: Fourteen FA patients (14 eyes; mean age 38.64 ± 8.21 years) without functional or structural macular abnormalities, confirmed by multifocal electroretinogram (mfERG) and spectral domain–optical coherence tomography (SD-OCT), and 20 age-matched healthy controls were enrolled. Patients were classified as late-onset (FA1, disease onset > 25 years) or early-onset (FA2, disease onset < 25 years). All participants underwent comprehensive ophthalmological and neurological evaluations. RGC function and visual pathway conduction were assessed through simultaneous pattern electroretinogram (PERG) and VEP recordings using 60′ and 15′ checkerboard stimuli. Retino-cortical time (RCT) was calculated as the difference between VEP P100 and PERG P50 implicit times. Statistical analyses included a general linear model. Results: 60′ PERG amplitude (A) was significantly (p < 0.01) reduced in the FA group compared to the Control group. FA patients showed significantly delayed 60′ and 15′ VEP ITs and significantly increased 60′ and 15′ RCT values, particularly in the FA1 group. In late-onset patients, no significant relationships were found between age at onset of disease and all electrophysiological parameters (60′ and 15′ VEP and PERG ITs and As and RCTs). Conclusions: In our selected FA, RCG function and neural conduction along the post-retinal visual pathways are impaired. The abnormal neuronal conduction is greater in late-onset FA patients and is not related to patients’ age and the age at the onset of the disease. The duration of the disease has a slight effect on the post-retinal neural conduction on small optic nerve fibers.