Optic Ataxia

History

The term optic ataxia (optische Ataxie in the original German) was coined by the Hungarian physician Rudolf Bálint in his 1909 report of a [Page 707]man with lesions of the posterior parietal lobe on both sides of the brain. Optic ataxia was one of a cluster of symptoms, now known collectively as Bálint's syndrome, which included the restriction of visual attention to single objects and a paucity of spontaneous eye movements. Bálint noted inaccurate reaching of the right hand, and the patient himself commented that this hand was clumsy. For instance, he often found himself lighting a cigarette at its middle instead of at its end. These errors could not be ascribed to any general visual impairment, as his left-hand reaching was accurate. Similarly, he could make coordinated right-hand reaches, with eyes closed, to different parts of his body, ruling out a right-sided movement disorder. Thus, the problem was neither visual nor motor, but visuomotor, emerging only for movements made under visual guidance. This confluence is well captured by Bálint's coinage, which implies a movement disorder (ataxia) that is specifically visual (optic).

Presentation and Diagnosis

When optic ataxia is severe, misreaching will be obvious to the patient and to others. However, specialized testing may be required to confirm the symptom or to diagnose its subtle forms. Typically, the examiner will present an object, such as a pen, to the left or the right side for grasping by each hand. This will be done both when the patient can look at the pen directly and when they must look straight ahead so that it falls outside of central vision. Misreaching most often emerges only in the latter case, with accurate reaching under direct viewing. It may also be specific to certain combinations of the target side and hand. Two main patterns can be expected: a field effect, whereby large errors are made, with either hand, on the side of space opposite the responsible brain damage; and/or a hand effect, whereby the hand anatomically opposite to the brain damage misreaches for targets on either side. To confirm the diagnosis, it should be shown that the errors are not due to other disorders affecting vision or movement.

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