Aims:To assess the visual function of patients with chronic progressive external ophthalmoplegia(CPEO)using the Visual Function Index(VF-14).To identify discriminatory questions that reflect visual disability in mitochondrial ocular myopathies.To investigate the relationship between visual impairment and the ocular parameters routinely measured in clinical practice.Methods:We studied 40 CPEO patients.Each patient underwent ophthalmological assessment,including best-corrected visual acuity,ptosis measures,and fundus examination for pigmentary retinopathy,and orthoptic assessment including cover test in the primary position,assessment of diplopia,and measurement of uniocular fields of fixation using the Goldmann perimeter.Patients were interviewed by telephone by an independent observer and their visual function was assessed using the VF-14.Results:A total of 38 patients(95%)were visually impaired.The mean VF-14 was 72(95% CI 66-79).Patients reported having the most difficulty with reading small print and driving at night.No significant correlation was found between the VF-14 and ocular motility parameters,ptosis,or pigmentary retinopathy.Conclusions:CPEO is associated with significant visual impairment.Measures of visual disability should be included in studies of natural history and treatment of mitochondrial ocular myopathies. Aims: To assess the visual function of patients with chronic progressive external ophthalmoplegia (CPEO) using the Visual Function Index (VF-14). To identify discriminatory questions that reflect visual disability in mitochondrial ocular myopathies. To investigate the relationship between visual impairment and the ocular parameters routinely measured in clinical practice. Methods: We studied 40 CPEO patients. Each patient underwent ophthalmological assessment, including best-corrected visual acuity, ptosis measures, and fundus examination for pigmentary retinopathy, and orthoptic assessment including cover test in the primary position, assessment of diplopia, and measurement of uniocular fields of fixation using the Goldmann perimeter. Patients were interviewed by telephone by an independent observer and their visual function was assessed using the VF-14.Results: A total of 38 patients (95%) impaired. The mean VF-14 was 72 (95% CI 66-79). Patients reported having the most difficulty with readi ng small print and driving at night. No significant correlation was found between the VF-14 and ocular motility parameters, ptosis, or pigmentary retinopathy. Conclusions: CPEO is associated with significant visual impairment. Measures of visual disability should be included in studies of natural history and treatment of mitochondrial ocular myopathies.