Visual dysfunction in patients with mitochondrial myopathies. I. Electrophysiologic impairments.

Seventeen patients with biopsy-confirmed mitochondrial progressive external ophthalmoplegia underwent electroretinography and visual evoked potential testing to checkerboard-reversal stimuli to investigate subclinical visual dysfunction. Seven patients (41%) had impaired Snellen visual acuity that was never less than 0.6. Thirteen patients (76%) showed electroretinographic and/or visual evoked potential alterations, whereas six (35%) showed impairment on both tests. Two patients showed delayed VEP P100 latency without fundus, electroretinographic or visual acuity anomalies. Visual dysfunctions were not related to age at onset and course of the disease.