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Anton syndrome

Picture of a human brain.

Anton syndrome, also known as Anton-Babinski syndrome and visual anosognosia, is a rare neurological disorder that is related to confabulation in situations where there is obvious visual loss. Rather of being caused by abnormalities in the eyes, it is a neurological visual impairment arising from damage or abnormalities in the brain. Those who have it are cortically blind and attempt to fill in gaps of memory with events which never occurred, but strongly affirm that they are capable of seeing, and that their vision is not lost. Failing to accept being blind, people with Anton syndrome dismiss evidence of their condition and employ confabulation to piece together and make sense of their missing sensory input. Anton syndrome is named after the neurologist Gabriel Anton. Only 28 cases have been described from 1965-2016 .

Presentation

Anton syndrome is mostly seen following a stroke, but may also be seen after head injury. Neurologist Macdonald Critchley describes it thusly:

The sudden development of bilateral occipital dysfunction is likely to produce transient physical and psychological effects in which mental confusion may be prominent. It may be some days before the relatives, or the nursing staff, stumble onto the fact that the patient has actually become sightless. This is not only because the patient ordinarily does not volunteer the information that they have become blind, but he furthermore misleads his entourage by behaving and talking as though they were sighted. Attention is aroused however when the patient is found to collide with pieces of furniture, to fall over objects, and to experience difficulty in finding his way around. They may try to walk through a wall or through a closed door on his way from one room to another. Suspicion is still further alerted when they begin to describe people and objects around them which, as a matter of fact, are not there at all. Thus, we have the twin symptoms of anosognosia (or lack of awareness of defect) and confabulation, the latter affecting both speech and behaviour.

Anton syndrome may be thought of ideally as the opposite of blindsight, blindsight occurring when part of the visual field is not consciously experienced, but some reliable perception does in fact occur.

History

Most cases of Anton syndrome are reported from adults. The earliest description of Anton syndrome goes back to the Roman era when a slave named Harpaste became acutely blind. Harpaste used to constantly deny being blind and would dispute unreasonably about the darkness of the room. This case exhibits the main symptoms of Anton symdrome, such as acute acquired blindness and anosognosia.

In 2007, the European Journal of Neurology published an article that examines a case study of a six-year-old child with Anton syndrome and early stages of adrenoleukodystrophy. The child reportedly had abnormal eye movements, would often fall, and would reach for things and often miss his target. When his sight was tested at 20/20 he was still unable to read the large letters on the chart. He denied having headaches, diplopia, or eye pain and seemed unconcerned and unaware of his poor eyesight. Upon examination, his pupils were equal in shape, round, and reactive to light. His mother commented that he developed unusual eye movements and that they had a "roving quality".

Culture and Society

Anton syndrome was featured in a two-part episode of the television series House M.D., titled "Euphoria", although it was ascribed to primary amoebic meningoencephalitis, a disease that usually does not cause the syndrome in real life. The syndrome features prominently in the Rupert Thomson novel The Insult. It is also mentioned in the science fiction novel Blindsight, by Peter Watts.

It is mentioned frequently as "Anton's Blindness" as one of the primary metaphors in Raj Patel's The Value of Nothing. In Lars von Trier's film Dogville, the character Jack McKay acts as if he can see but gives many signs he cannot.

The syndrome is also the main theme of the Malaysian movie Desolasi (Desolation), where the patients live in their own world of imagination, while unable to see the real world. It is also mentioned in Oliver Sacks's An Anthropologist on Mars.

Pathophysiology

Anton syndrome can be caused by lesions along the visual cortices, optic radiations, corpus callosum, posterior limbs of the internal capsules, and the bilateral lateral geniculate bodies. Furthermore, the reliability of the capacity to identify visually presented items depends on visual pathways, the primary visual area of the cerebral cortex (known as Brodmann area 17), the secondary visual cortex (Broddman areas 18 and 19), and the angular gyrus of the dominant hemisphere (Brodmann area 39). Some common patterns of visual deficits in Anton syndrome include:

• Blindness - the anterior visual tracts are unbroken, but the bilateral occipital brain is damaged.
• Gunbarrel vision - small vision islands remain and can fluctuate as images that the person sees.
• Movement perception - the motion of objects can be discerned consciously or unconsciously.
• Motion blindness - people can see the objects, but not necessarily their motion.
• Charles Bonnet syndrome - the person will have vision loss, but will still have an intact insight; they may sometimes encounter visual hallucinations with images of distorted objects or people.

Causes

It is not known why patients with Anton syndrome deny their blindness, although there are many existing theories. One hypothesis is that damage to the visual cortex results in the inability to communicate with the speech-language areas of the brain. Visual imagery is received but cannot be interpreted; the speech centres of the brain confabulate a response.

Patients have also reported visual anosognosia after experiencing ischemic vascular cerebral disease. A 96-year-old man, who was admitted to an emergency department complaining of a severe headache and sudden loss of vision, was discovered to have had a posterior cerebral artery thrombosis with consequent loss of vision. He adamantly claimed he was able to see despite an ophthalmologic exam proving otherwise. An MRI of his brain proved that his right occipital lobe was ischemic. Similarly, a 56-year-old woman was admitted to the emergency department in a confused state and with severely impaired psychomotor skills. Ocular movements and pupil reflexes were still intact, but the patient could not name objects and was not aware of light changes in the room, and seemed unaware of her visual deficit.

Evaluation and Diagnosis

Evaluating someone for Anton syndrome typically involves a neuroophthalmological evaluation testing for field of vision and accuracy, an CT or MRI scan of the brain, or an echocardiogram to ensure that stroke was not the causative factor. In more complex cases or in cases with children, a visual evoked potential may be done, which is a test that identifies the electrical signal produced in response to visual stimulus at the visual cortex.

Treatments and Prognosis

Therapy of the occipital lobe injury is thought to be the primary contributing factor determining how patients with Anton syndrome will be treated. For instance, it was documented that one patient had Anton syndrome as a result of a Multiple sclerosis flare-up. She gradually recovered over two years while receiving IV methylprednisolone and plasmapheresis treatment. Her acuity was restored . Methods of medical therapy used to treat Anton syndrome comprise of statin therapy, taking aspirin daily, and living a better lifestyle to reduce the chance of a recurring stroke (e.g. maintaining normal blood pressure, lipids, and blood glucose levels).

Through correction of the causative factor, occipital lobe damage, some patients had a recovery of visual function . The highest chances of recovery are seen in people who are young, have no prior history of hypertension or diabetes, or do not possess cognitive, language or memory impairment.

See also

• Prosopagnosia – Cognitive disorder of face perception
• Riddoch syndrome – Type of visual impairment
• Visual release hallucinations – visual disturbances and the experience of complex visual hallucinations in a blind person

Further reading

• Prigatano, George P.; Wolf, Thomas R. (2010). "Anton's Syndrome and Unawareness of Partial or Complete Blindness". In Prigatano, George P. (ed.). The Study of Anosognosia. Oxford University Press. pp. 455–469. ISBN 978-0-19-537909-9. LCCN 2009024065