Visual dysfunction in patients with mitochondrial myopathies. II. Contrast sensitivity function.

Contrast sensitivity function with stationary and temporally modulated (8 Hz) black and white vertical sinusoidal gratings was investigated in 11 patients with biopsy-confirmed mitochondrial progressive external ophthalmoplegia. To evaluate contrast sensitivity function results, the contrast sensitivity versus spatial frequency experimental data for each subject were fitted with a second-order polynomial, and the coefficients of the best-fitting function from normal and patient groups were compared. Patients with progressive external ophthalmoplegia, as a group, showed a decreased sensitivity at the intermediate spatial frequencies (i.e., around 1.4 c/deg) with stationary gratings and through a wider range of spatial frequencies with temporally modulated gratings. These findings were confirmed by analyzing contrast sensitivity functions from each individual. The study showed that contrast sensitivity function detects visual function abnormalities noninvasively in a number of patients with mitochondrial progressive external ophthalmoplegia with unaffected Snellen visual acuity.