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Anton-Babinski syndrome, also known as ABS or Anton syndrome, is visual anosognosia, or denial of vision loss, associated with confabulation, or making up experiences to compensate for memory loss, in the setting of cortical blindness. This activity reviews the evaluation and treatment of Anton syndrome and highlights the role of the interprofessional team in evaluating and treating patients with this condition. Objectives: Describe the pathophysiology of Anton syndrome. Outline the typical presentation of a patient with Anton syndrome. Review the risk factors for developing Anton syndrome. Describe how an optimally functioning interprofessional team would coordinate care to enhance outcomes for patients with Anton syndrome. Access free multiple choice questions on this topic.

Cortical blindness is among the rare neurological conditions resulting in binocular vision loss due to insult to the occipital cortex. Anton-Babinski syndrome (Anton syndrome or ABS) is visual anosognosia (denial of loss of vision) associated with confabulation (defined as the emergence of memories of events and experiences which never took place) in the setting of obvious visual loss and cortical blindness.[1] It is essentially neurological visual impairment/disturbance resulting from abnormality or damage in the brain rather than due to eye abnormalities. The first description of ABS dates back to the Roman era when Seneca, a Roman philosopher and politician, described the case of Harpaste, a slave who acutely became blind. She used to deny her illness and argue irrationally about room darkness and constantly ask her attendants to change quarters. This case demonstrates the main symptoms of ABS, including acutely acquired blindness and anosognosia in the presence of relatively well-preserved cognition.[2] The next documented description of visual anosognosia was made by the French Renaissance writer Michel de Montaigne (1533 - 1592), who described a nobleman who denied his blindness. In 1895, the Austrian psychiatrist and neurologist Gabriel Anton (1858 - 1933) described the case of Juliane Hochriehser, a 69-year-old dairymaid who had anosognosia with cortical deafness due to a lesion on her both temporal lobes. He also outlined other cases of patients with objective blindness and deafness who denied their deficits. In 1914, the French-Polish neurologist Joseph François Babinski (1857 - 1932) used for the first time the term “anosognosia” to describe the unawareness of the deficit in patients with hemiplegia.[1] In 1920 Meyer first reported occipital lobe infarction and postulated compression of branches of the posterior cerebral artery as the causal factor for ABS.[3]

Causes include: An ischemic stroke involving bilateral occipital lobes due to the involvement of posterior cerebral arteries (most common cause) Cardiac surgery Cerebral angiography MELAS (mitochondrial myopathy, encephalomyopathy, lactic acidosis, and stroke-like episodes) Preeclampsia Obstetric hemorrhage Head trauma Adrenoleukodystrophy Hypertensive encephalopathy Angiitis (autoimmune) of the central nervous system Progressive multifocal leukoencephalopathy, in the setting of human immunodeficiency virus infection Multiple sclerosis Posterior reversible encephalopathy syndrome (PRES) secondary to SARS-CoV-2 (COVID-19) pneumonia Fat embolism syndrome Trousseau syndrome [3][4][5][6][7][8][9][10][11]

Pathophysiology of blindness: The ability to recognize visually presented objects depends on the integrity of the following: Visual pathways The primary visual area of the cerebral cortex (Brodmann area 17) The secondary visual cortex, lying just anterior to area 17 (Brodmann areas 18 and 19) of the occipital lobe The angular gyrus of the dominant hemisphere (Brodmann area 39) - visual association area. Patterns of visual deficits in ABS: Blindness: Although the anterior visual tracts are intact, bilateral occipital brain damage results in blindness. Gunbarrel vision: Tiny islands of vision sometimes persist, and in such cases, the patient may report that vision fluctuates as images are captured in the preserved portions; in rare instances, only peripheral vision is lost, and central vision is spared, resulting in gun-barrel vision Perception of movements alone: Movement of objects may be perceived, either consciously (Riddoch syndrome) or unconsciously (blindsight) Motion blindness: Patients can see objects but cannot perceive their motion. This may be explained by the presence of projections from the lateral geniculate nucleus, to both the primary visual cortex via the optic radiations and the motion-selective middle temporal area (MT or V5) Charles Bonnet syndrome: In this condition, the patient has a loss of vision (due to any reason), but insight is preserved. Such patients may experience visual hallucinations containing images of unfamiliar objects and people. Pathophysiology of anosognosia: Theories to explain the unawareness of the deficit in the Anton-Babinsky syndrome: Disconnection phenomena: Conscious awareness system: The function of this system is to monitor the inputs from all the sensory organs and is located in the bilateral parietal lobes. Another system that integrates the inputs is located within the bilateral frontal lobes and is connected to the former system. This interconnected system helps in performing complex cognitive tasks. In Anton-Babinski syndrome, damage to the association pathways between the visual cortex and the conscious awareness system would be responsible for the lack of awareness of the visual deficit. Disconnection of the visual area from the language area: This makes the patient fabricate answers, as he/she is unable to describe the visual stimulus.

Conscious awareness system: The function of this system is to monitor the inputs from all the sensory organs and is located in the bilateral parietal lobes. Another system that integrates the inputs is located within the bilateral frontal lobes and is connected to the former system. This interconnected system helps in performing complex cognitive tasks. In Anton-Babinski syndrome, damage to the association pathways between the visual cortex and the conscious awareness system would be responsible for the lack of awareness of the visual deficit. Disconnection of the visual area from the language area: This makes the patient fabricate answers, as he/she is unable to describe the visual stimulus. Overaction of the secondary visual pathway: A secondary visual system is located in the superior colliculus, pulvinar, and temporoparietal regions. This system usually sends impulses to the visual association cortex (visual monitor). If there is no transmission of impulse along the geniculo-calcarine pathway, the secondary visual pathway gains predominance, resulting in fabulation in blind patients. Neuropsychological mechanisms: Defective visual monitor: This leads to incorrect interpretation of images. The presence of false-positive feedback from the visual monitor: This leads to a perception of false images, which in turn elicits an abnormal response from the speech areas.[13] Pathophysiology of confabulation: Patients start to confabulate to fill in the missing sensory input. Anton suggested that functioning speech and language areas are disconnected from the damaged visual pathways. If there are no appropriate sensory-visual inputs, the speech areas may confabulate a response. In this, patients adamantly claim that they are capable of seeing and/ or experiencing strange visual hallucinatory episodes, consequently resulting in confabulation.[1] In short, ABS can be caused by lesions along the following structures: Visual cortices Bilateral lateral geniculate bodies Posterior limbs of the internal capsules Optic radiations Corpus callosum

Criteria for diagnosis of cortical blindness: Loss of all visual sensations, including the perception of light and dark Loss of menace reflex Preservation of light and accommodation pupillary reflexes Normal fundoscopic examination, and Preservation of ocular movements The classical description of the clinical features of ABS: Though the patient is blind, they behave and talk as if they have normal vision. 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 a closed door on their way from one room to another. Suspicion is still further alerted when they begin to describe people and objects around them who do not exist. Mental confusion may also be seen. Patients with ABS may give excuses for their blindness. They may explain that their inability to see is due to a lack of proper lighting, and they may try their best to prove that they are not blind, thereby putting themselves in danger.

A proper history and physical examination should be followed by: Detailed neuroophthalmological evaluation, including testing for visual acuity and the field of vision Magnetic resonance imaging of the brain Echocardiogram and carotid Doppler to rule out the cardiovascular cause of stroke Visual evoked potential in confusing cases and pediatric patients

ABS syndrome needs to be differentiated from: Cerebral visual impairment Delayed visual development Homonymous hemianopia Lack of facial recognition Visual agnosia Visual neglect Visual perceptual disorders

Recovery of visual function has occurred in conditions causing ABS, such as hypertensive encephalopathy and cortical hypoperfusion. In these conditions, correction of the causative factor may resolve the symptoms. The outcome of cortical blindness depends on the age of the patient, etiology, severity, duration, initial recovery time, and medical history.

Before diagnosing a patient with ABS, a proper ophthalmological evaluation should be performed. Discussion regarding the etiology of ABS should be done with neuroradiologists, neurologists, and internists. A team of specialty-trained nurses and clinicians is necessary to evaluate and manage this condition for optimal outcomes.