Optic ataxia is impaired voluntary reaching for a visually presented target, with misdirection and dysmetria. It may resemble cerebellar ataxia. Visual fixation is possible but reaching under visual guidance is impaired. Tactile search with the palm and fingers may be undertaken in searching for an object, using somatosensory cues to compensate for impaired access to visual information. Hence this may be characterized as a modality-specific apraxia, wherein visual information cannot be used to guide goal-directed movements. The disorder is both retinotopic and somatotopic.
Optic ataxia occurs with lesions of the intraparietal sulcus and regions medial and superior to it; the primary visual cortex is intact. It is one feature, along with psychic paralysis of gaze ("sticky fixation") and simultanagnosia (visual disorientation), of Balint’s syndrome in which there is some evidence for parieto-occipital (and possibly frontal) lobe dysfunction (disconnection).
Perenin MT, Vighetto A. Optic ataxia: a specific disruption in visuomotor mechanisms. I. Different aspects of the deficit in reaching for objects. Brain 1988; 111: 643-674