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= Optic Ataxia = Optic Ataxia is a part of Balint Syndrome and is a rare and undiscovered high order deficit that causes problems in achieving visual goals. Since it is related to deficits in visual goals, it is also known as visuomotor ataxia. Ataxia is Greek for "lack of order".

Optic ataxia is usually caused by lesions in the Posterior parietal cortex (PPC), Superior parietal lobule (SPL), and the Intraparital sulcus (IPS). The main characteristics of optic ataxia will be the inability to reach objects in the peripheral vision, having difficulties in preshaping the hands for grasping objects. it also includes attentional and gaze disorders.

The term "optic ataxia" was coined by Balint. Balint believed that the deficit was not an apraxia (difficulty in planning motor movements to perform tasks), rather it was an ataxia (difficulty in coordinating visual inputs with motor outputs). The reason he distinguished between ataxia and apraxia was because optic ataxia has a "hand effect". In the "hand effect", misreaching of objects is mostly confined to the right hand.

Pure Optic Ataxia
Pure optic ataxia means that optic ataxia exists without being a part of Balint's syndrome and without any attentional deficits. It usually is caused by unilateral lesions. The deficit usually has an additional problem of misshaping the hand while in the process of grasping objects. Garcin et al. first described Pure optic ataxia in 1967. Pure optic ataxia is much more of a rare deficit than Balint's syndrome.

History
Optic ataxia was first discovered and explained by Austrian-Hungarian neurologist Rezso (Rudolph) Balint in 1909. he explained optic ataxia as a part of Balint syndrome, along with simultagnosia and oculomotor apraxia.

Balint syndrome
see also: Balint Syndrome

Balint syndrome is known as a rare neurologoical disorder that is related to visual and spatial difficulties. These occur due to lesions in the parietal lobe. Balint syndrome is made up of three deficits, which are also the symptoms of Balint syndrome. These three deficits are simultagnosia, oculomotor apraxia and optic ataxia. The main cause of Balint syndrome is bilateral parietal lesions.

Simultagnosia
see also: simultagnosia

Simultagnosia is another part of Balint syndrome. It is a neurological disorder in which an individual cannot perceive more than a single object. In simultagnosia, a person has difficulty in looking at two objects in the same visual field. They can describe and see the objects in the visual field, individually but they have a hard time describing the overall scene.

Oculomotor apraxia
see also: oculomotor apraxia

Oculomotor is a part of Balint syndrome as well. It is a difficulty in fixating the eyes. People with oculomotor apraxia have a difficulty in moving their eyes horizontally and difficulty in quick eye movements. They have to move their head completely in order to see something. The vertical movements of the eyes are usually not affected. Parts of the brain that are usually affected in oculomotor apraxia are the cerebellum, corpus callousum, and/or the fourht ventricle.

Neuroanatomy
Individuals with optic ataxia show difficulty in reaching visually guided goals, in the peripheral vision. Lesions in the Posterior parietal cortex (PPC), the superior parietal lobule (SPL) and the intraparietal sulcus (IPS) are the cause for optic ataxia.

Posterior parietal cortex (PPC)
see also: posterior parietal cortex The posterior parietal cortex is placed in between the visual cortex and the somatosensory cortex.The posterior parietal cortex has it's own set of functions. In humans, it consists Broadmann's area 5, 7 39 and 40. The function of the PPC is to receive different input from various sensory areas and several regions of the brain. Then, it merges all the inputs received to execute different functions. These functions are usually known to be “high-order functions”.

Superior parietal lobule (SPL)
see also: superior parietal lobule

The superior parietal lobule is a rectangular-shaped area which is involved in functions of mental imagery and recalling personal experiences. The main functions of the SPL involve visuospatial perception, attention and the representation and manipulation of different objects.

Intraparietal sulcus (IPS)
see also: intraparietal sulcus

The intraparietal sulcus (Latin: sulcus intraparietalis) is responsible for visual guidance of hand movements. Its main functions involve visual control of reaching, pointing, grasping and controlling hand movements. The location of the IPS is on the parietal lobe’s lateral surface.

Symptoms
Optic ataxia was first described as a part of the triad in Balint’s syndrome in 1909. There were 3 symptoms that defined Balint’s syndrome, which were as follows: the inability to see the visual field as a whole, the inability to fixate eyes and the inability to grasp objects in the peripheral field.

It is hard to detect proper symptoms for Balint’s syndrome and even more difficult to recognise symptoms for pure optic ataxia, as it usually occurs with Balint’s syndrome in an individual. A lot of research and work is still needed to understand the symptoms of isolated optic ataxia.

Causes
It is very rare that isolated optic ataxia occurs without being accompanied with other deficits. Optic ataxia usually is accompanied with deficits in grasping and shaping of the hand for movements of grasping. As optic ataxia is seen to occur mostly with Balint’s syndrome, some of the causes of Balint’s syndrome can also be causes for occurrence of optic ataxia. Balint’s syndrome is usually caused by neurodegenerative diseases, infectious diseases, traumatic brain injury, inflammatory diseases and iatrogenic causes.

Neurological diseases that occur with the progression of age, can be harmful to several parts of the brain, but they are extremely harmful to the posterior cortex. Some of the neurodegenerative diseases that cause Balint’s syndrome are Alzheimer’s disease, Parkinson’s disease, dementia with Lewy Bodies and Creutzfeldt Jacob’s disease. These are the most common cause of the occurrence of Balint’s syndrome along with optic ataxia in an individual.

Infectious diseases, traumatic brain injury, inflammatory diseases brain tumours and seizures are some of the less common causes of Balint’s syndrome.

X-linked adrenoleukodystropy (X-ALD) is believed to be a cause of Balint's syndrome in children, which becomes a part of Optic ataxia.

Causes of pure optic ataxia are a difficult find. The reason for this is that pure optic ataxia can be caused by lesions in more discrete areas in the unilateral posterior parietal cortex.

Rehabilitation
Prognosis in Balint syndrome is very low. Since, Balint syndrome is so rare, treatment is very low for the syndrome. Pure optic ataxia is even more rare, and treatment for pure optic ataxia is lesser than Balint syndrome. Rehabilitation has a low success rate in Balint syndrome.

= References =