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- optic nerve
- ataxia
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optic ataxia
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What is optic ataxia?
Optic ataxia is a condition caused by damage to specific brain regions, characterized by a loss of visual guidance over reaching with the hand and arm, resulting in inaccurate arm movements.
People with optic ataxia may struggle to reach for objects accurately, even to the point of groping. The key areas of the brain that are involved have been found to be in and around the intraparietal sulcus and at the junction between the occipital and parietal lobes.
Diagnosis may require specialized testing, such as presenting an object to the patient's left or right side for grasping by each hand. The examiner can confirm a diagnosis by showing that the errors are not due to other disorders that affect vision or movement.
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Which part of the brain is affected in optic ataxia?
Optic ataxia typically results from lesions in the posterior parietal lobe, sometimes extending into the occipital lobe. However, optic ataxia can also occur from damage restricted to one side of the brain. Key areas of the brain's involvement include the intraparietal sulcus and the junction between the occipital and parietal lobes, which are critical for visually guided reaching.
Hungarian physician Rezso (Rudolf) Bálint first identified optic ataxia in 1909 in a patient with lesions of the posterior parietal lobe on both sides of the brain.
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How does optic ataxia affect a person's ability to reach for objects?
Optic ataxia is a condition resulting from damage to specific brain regions, impairing visually guided arm movements. A person with optic ataxia may struggle to reach for objects accurately, sometimes groping hesitantly until making contact by chance.
When optic ataxia is severe, the person will be noticeably misreaching. However, in more subtle forms of the condition, misreaching may only occur when the person is not looking directly at the object. Additional impairments that may be present include the failure to rotate or pre-shape the hand appropriately for grasping.
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What are some common causes of optic ataxia?
Optic ataxia results from damage to specific brain regions, particularly the posterior parietal lobe and the junction between the occipital and parietal lobes, which are critical for the visual guidance of reaching in humans. Extensive brain damage may be present, especially when optic ataxia manifests as part of Bálint syndrome. In isolated optic ataxia, lesions restricted to one side of the brain are the more usual cause. Spinocerebellar degenerations, a group of inherited disorders, can also affect the optic nerves.
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How do doctors diagnose optic ataxia?
Optic ataxia is diagnosed through specialized testing that confirms the symptom or identifies its subtle forms. During an examination, an object is presented to the left or right side for grasping by each hand. This is done when the patient can look at the object directly and when they must look straight ahead so that the object falls outside of central vision.
Misreaching often emerges when the object falls outside of central vision, with accurate reaching under direct viewing. The diagnosis is confirmed by showing that the errors are not due to other disorders that affect vision or movement. Additional impairments that may be present include failure to rotate or pre-shape the hand appropriately for grasping.
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How can understanding optic ataxia help us learn about how the brain processes vision and movement?
Optic ataxia results from damage to specific brain regions, especially around the intraparietal sulcus and the junction between the occipital and parietal lobes, which are critical for visually guided reaching. The term optic ataxia was coined in 1909 by physician Rezso (Rudolf) Bálint, who described a patient with lesions of the posterior parietal lobe on both sides of the brain.
Studying optic ataxia can help determine key areas involved in visuomotor control by studying patterns across patients with the condition. This condition implies a movement disorder (ataxia) that is specifically visual (optic).
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optic ataxia, condition in which some or all aspects of visual guidance over reaching with the hand and arm are lost. Optic ataxia is broadly characterized by an inaccuracy of visually guided arm movements. In reaching for an object, a person with severe optic ataxia may seem to grope in the dark, extending a flattened hand hesitantly until chance contact allows the object to be retrieved by touch. Optic ataxia occurs as a result of damage to specific regions of the brain.
History of optic ataxia
The term optic ataxia (optische Ataxie in the original German) was coined by Hungarian physician Rezso (Rudolf) Bálint in his 1909 report of a man with lesions of the posterior parietal lobe on both sides of the brain. Optic ataxia was one of several symptoms of a condition that later became known as Bálint syndrome. Among the symptoms that characterize the syndrome are a restriction of visual attention to single objects and a paucity of spontaneous eye movements. Bálint noted inaccurate reaching of the man’s right hand. The patient commented that his right hand was clumsy; for instance, he often found himself lighting a cigarette at its middle instead of at its end. Those 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 his 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. That confluence is well captured by Bálint’s term, which implies a movement disorder (ataxia) that is specifically visual (optic).
Presentation and diagnosis
When optic ataxia is severe, misreaching is 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 right side for grasping by each hand. That will be done both when the patient can look at the pen directly and when the patient 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 of misreaching are typical: a field effect, whereby large errors are made with either hand on the side of space opposite that of the damaged brain area; and a hand effect, whereby the hand anatomically opposite to the brain damage misreaches for targets on either side. The diagnosis is confirmed by showing that the errors are not due to other disorders that affect vision or movement.
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A range of additional impairments may be present in optic ataxia, including failure to rotate or pre-shape the hand appropriately for grasping, inability to correct ongoing movements for changes in target position, and insensitivity to obstacles in the reach space. Inaccurate visuomotor guidance may also be observed for the foot by asking the patient to touch a target with a toe.
Neuroanatomy
Patients with optic ataxia may have extensive brain damage, especially if symptoms manifest as part of Bálint syndrome. Bálint’s original patient, for instance, had lesions in the posterior parietal lobe and extending into the occipital lobe on both sides of the brain. However, lesions restricted to one side of the brain are the more usual cause of isolated optic ataxia. By studying patterns across patients, it may be possible to discern whether there is any specific subregion that is invariably affected. The key areas of involvement have been found to be in and around the intraparietal sulcus and at the junction between the occipital and parietal lobes. Those brain areas presumably are critical for the visual guidance of reaching in humans.