VISUAL DYSFUNCTION IN PATIENTS WITH MITOCHONDRIAL MYOPATHIES .1. ELECTROPHYSIOLOGIC IMPAIRMENTS

Seventeen patients with biopsy-confirmed mitochondrial progressive ext ernal ophthalmoplegia underwent electroretinography and visual evoked potential testing to checkerboard-reversal stimuli to investigate subc linical visual dysfunction. Seven patients (41%) had impaired Snellen visual acuity that ws never less than 0.6. Thirteen patients (76%) sho wed electroretinographic and/or visual evoked potential alterations, w hereas six (35%) showed impairment on both tests. Two patients showed delayed VEP P100 latency without fundus, electroretinographic or visua l acuity anomalies. Visual dysfunctions were not related to age at ons et and course of the disease.