Co-occurrence of periodic alternating and pendular seesaw nystagmus in blindness.

Even though pendular seesaw nystagmus (PSN) or periodic alternating nystagmus (PAN) has been reported in blind persons, the co-occurrence of PSN and PAN has not been described. A 69-year-old woman with progressive visual loss to only light perception in both eyes showed PSN with a conjugate torsional component and the vertical components in the opposite directions in both eyes. In complete darkness, she also exhibited PAN in addition to PSN. PSN remained unchanged in darkness. The rest of the neurological examination, testing for mitochondrial mutations of Leber's hereditary optic neuropathy, fluorescent angiography, electroretinogram, and brain MRI were normal except for bilateral optic atrophy. Deprivation of the visual inputs, which are required to calibrate normal eye motion, may produce various ocular motor abnormalities in blindness. Although the co-occurrence of PSN and PAN in our patient with visual loss indicates a common etiology, the different effects of darkness on nystagmus intensity suggest a distinct pathomechanism.