Visual Involvement in Friedreich’s Ataxia: PERG and VEP Study

Abstract

Neuro-ophthalmological assessment, including red-free light retinography, in conjunction with simultaneous visual evoked potential (VEP) and pattern electroretinogram (PERG) recordings were performed in 10 Friedreich’s ataxia patients: 9 patients showed marked VEP abnormalities. Moderate PERG amplitude reduction, with normal latencies, was related to mild and scattered fiber loss revealed by red-free light retinography. The initial part of the visual pathways does not seem to be the main site of electrophysiological abnormalities as demonstrated by the greater extent and relative independence of VEP versus PERG alterations. Primary axonal degeneration of the optic nerve and tracts cannot account for all features of VEP abnormalities, thus implying some dysfunction in succeeding visual structures as well.

Electrophysiological features in patients and presymptomatic relatives with spinocerebellar ataxia type 2

“…Significant abnormalities in visual evoked potential have been observed in Friederich ataxia [28,29], SCA1 [29,30] and SCA7 [31] but have not been observed in SCA2. In 1983 Sridharan and his colleagues [32] reported VEP abnormalities in only one out the five patients with a dominant form of spinocerebellar degeneration that phenotypically resembled SCA2.…”

Ocular Involvement in Friedreich Ataxia Patients and Its Relationship with Neurological Disability, a Follow-Up Study

“…Further possible additional features include diabetes mellitus, pes cavus, hypoacusia or deafness, optic atrophy, and eye movement abnormalities [5,8,13]. These ocular motor anomalies reflect the disruption of the brainstem-cerebellar circuit and include saccadic dysmetria, disrupted pursuit, and vestibular abnormalities, the most common manifestation of which is a fixation instability with frequent square-wave jerks [8,10,[13][14][15][16][17][18][19]. In addition, other visual ophthalmic manifestations have been described in up to 30% of patients, including optic neuropathy, the involvement of the optic radiation, and, less commonly, a retinitis pigmentosa-like syndrome [8,20].…”

Neuro-Ophthalmological Findings in Friedreich’s Ataxia

“…Extrinsic ocular motility disturbances are best characterized as they reflect disruption of the circuit from the brainstem to the cerebellum. Major findings include: (i) saccadic movement dysmetria, (ii) fixation instability with frequent square wave jerks, (iii) disruption of tracking movements, and (iv) vestibular abnormalities [11,13,[43][44][45][46][47][48][49][50] (Table 2, Figure 1). [39,43] Color vision Normal [39] Contrast sensitivity Supplementary role of low-contrast Sloan Chart testing in the assessment of disease status and visual function in FRDA [53,54] Correlation with mean pRNFL thickness and binocular VA with 1.25% and 2.5% contrast [55] Low-contrast visual acuity drop-off linearly with time in FRDA, especially at longer GAA repeat lengths [56] Table 2.…”