Ophthalmological signs and sensorimotor evaluation in mitochondrial diseases: a multidisciplinary prospective study

Abstract Background. Primary mitochondrial myopathies (PMM) are disorders that involve defects in oxidative phosphorylation (OXPHOS) and impair mainly, but not exclusively, skeletal muscles. Progressive external ophthalmoplegia (PEO), eyelid ptosis, exercise intolerance and skeletal muscle weakness are the most common symptoms of myopathy in mitochondrial diseases, impairing ocular motility and visual abilities. Methods. Twenty-five patients underwent complete ophthalmological examination, including best corrected visual acuity (BCVA), ptosis evaluation, dilated fundus examination, and orthoptic examinations, including cover and cover-uncover test, ocular motility analysis, fusional amplitude (FA) vergence for near and for distance, Bagolini striated glasses test (BSGs) and Worth four-dot lights test (WFDT). Results. Mean age at evaluation was of 47,2±16.07 years. Twenty-two (88%) out of 25 patients had a PEO disease, while three (12%) of them a Kearn-Sayre syndrome (KSS). Ocular motility impairment was found in 92% of the population. Fifteen patients (60%) didn’t complain of double vision in casual seeing condition despite some of them showed manifest strabismus both at far (53%) and at near (60%). A compensation sensorial mechanism, mainly suppression, was detected through sensory tests. The near and distance fusional capabilities in convergence and in divergence (CFAs and DFAs) were absent in 68 and 72% of the whole sample respectively. PEO manifests at an older age than KSS (p=0.003), diplopia does not correlate with disease duration (p=0.06) and no predictive factors for diplopia can be identified. Conclusions. A significant number of patients not complaining of double vision in casual seeing state showed manifest or latent/manifest strabismus at FAoD and NAoD. Most strabismic patients had a monocular suppression or alternate diplopia and suppression at sensory tests (BSGs and WFDT). The pathophysiology of these sensory adaptations in an adult visual system can only be hypothesized. A multidisciplinary approach is essential for proper clinical management and to analyze an understand clinical features pathogenesis.