Cortical blindness

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Cortical blindness
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Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex. [1] Cortical blindness can be acquired or congenital, and may also be transient in certain instances. [2] Acquired cortical blindness is most often caused by loss of blood flow to the occipital cortex from either unilateral or bilateral posterior cerebral artery blockage (ischemic stroke) and by cardiac surgery. [2] In most cases, the complete loss of vision is not permanent and the patient may recover some of their vision (cortical visual impairment). [2] Congenital cortical blindness is most often caused by perinatal ischemic stroke, encephalitis, and meningitis. [3] Rarely, a patient with acquired cortical blindness may have little or no insight that they have lost vision, a phenomenon known as Anton–Babinski syndrome.

Contents

Cortical blindness and cortical visual impairment (CVI), which refers to the partial loss of vision caused by cortical damage, are both classified as subsets of neurological visual impairment (NVI). NVI and its three subtypes—cortical blindness, cortical visual impairment, and delayed visual maturation—must be distinguished from ocular visual impairment in terms of their different causes and structural foci, the brain and the eye respectively. One diagnostic marker of this distinction is that the pupils of individuals with cortical blindness will respond to light whereas those of individuals with ocular visual impairment will not.[ citation needed ]

Symptoms

The most common symptoms of acquired and transient cortical blindness include:

Causes

The most common cause of cortical blindness is ischemia (oxygen deprivation) to the occipital lobes caused by blockage to one or both of the posterior cerebral arteries. [2] However, other conditions have also been known to cause acquired and transient cortical blindness, including:

The most common causes of congenital cortical blindness are:

Diagnosis

A patient with cortical blindness has no vision but the response of his/her pupil to light is intact (as the reflex does not involve the cortex). Therefore, one diagnostic test for cortical blindness is to first objectively verify the optic nerves and the non-cortical functions of the eyes are functioning normally. This involves confirming that patient can distinguish light/dark, and that his/her pupils dilate and contract with light exposure. Then, the patient is asked to describe something he/she would be able to recognize with normal vision. For example, the patient would be asked the following:[ citation needed ]

Patients with cortical blindness will not be able to identify the item being questioned about at all or will not be able to provide any details other than color or perhaps general shape. This indicates that the lack of vision is neurological rather than ocular. It specifically indicates that the occipital cortex is unable to correctly process and interpret the intact input coming from the retinas.

Fundoscopy should be normal in cases of cortical blindness. Cortical blindness can be associated with visual hallucinations, denial of visual loss (Anton–Babinski syndrome), and the ability to perceive moving but not static objects (Riddoch syndrome).[ citation needed ]

Outcome

The prognosis of a patient with acquired cortical blindness depends largely on the original cause of the blindness. For instance, patients with bilateral occipital lesions have a much lower chance of recovering vision than patients who suffered a transient ischemic attack or women who experienced complications associated with eclampsia. [2] [3] In patients with acquired cortical blindness, a permanent complete loss of vision is rare. [2] The development of cortical blindness into the milder cortical visual impairment is a more likely outcome. [2] Furthermore, some patients regain vision completely, as is the case with transient cortical blindness associated with eclampsia and the side effects of certain anti-epilepsy drugs.

Recent research by Krystel R. Huxlin and others on the relearning of complex visual motion following V1 damage has offered potentially promising treatments for individuals with acquired cortical blindness. [11] These treatments focus on retraining and retuning certain intact pathways of the visual cortex which are more or less preserved in individuals who sustained damage to V1. [11] Huxlin and others found that specific training focused on utilizing the "blind field" of individuals who had sustained V1 damage improved the patients' ability to perceive simple and complex visual motion. [11] This sort of 'relearning' therapy may provide a good workaround for patients with acquired cortical blindness in order to better make sense of the visual environment.

See also

Related Research Articles

<span class="mw-page-title-main">Optic nerve</span> Second cranial nerve, which connects the eyes to the brain

In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived from optic stalks during the seventh week of development and is composed of retinal ganglion cell axons and glial cells; it extends from the optic disc to the optic chiasma and continues as the optic tract to the lateral geniculate nucleus, pretectal nuclei, and superior colliculus.

Blindsight is the ability of people who are cortically blind to respond to visual stimuli that they do not consciously see due to lesions in the primary visual cortex, also known as the striate cortex or Brodmann Area 17. The term was coined by Lawrence Weiskrantz and his colleagues in a paper published in a 1974 issue of Brain. A previous paper studying the discriminatory capacity of a cortically blind patient was published in Nature in 1973. The assumed existence of blindsight is controversial, with some arguing that it is merely degraded conscious vision.

<span class="mw-page-title-main">Parietal lobe</span> Part of the brain responsible for sensory input and some language processing

The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.

<span class="mw-page-title-main">Temporal lobe</span> One of the four lobes of the mammalian brain

The temporal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.

<span class="mw-page-title-main">Occipital lobe</span> Part of the brain at the back of the head

The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ob, 'behind', and caput, 'head'.

Visual release hallucinations, also known as Charles Bonnet syndrome or CBS, are a type of psychophysical visual disturbance in which a person with partial or severe blindness experiences visual hallucinations.

<span class="mw-page-title-main">Bálint's syndrome</span> Medical condition

Bálint's syndrome is an uncommon and incompletely understood triad of severe neuropsychological impairments: inability to perceive the visual field as a whole (simultanagnosia), difficulty in fixating the eyes, and inability to move the hand to a specific object by using vision. It was named in 1909 for the Austro-Hungarian neurologist and psychiatrist Rezső Bálint who first identified it.

Visual agnosia is an impairment in recognition of visually presented objects. It is not due to a deficit in vision, language, memory, or intellect. While cortical blindness results from lesions to primary visual cortex, visual agnosia is often due to damage to more anterior cortex such as the posterior occipital and/or temporal lobe(s) in the brain.[2] There are two types of visual agnosia: apperceptive agnosia and associative agnosia.

<span class="mw-page-title-main">Inferior temporal gyrus</span> One of three gyri of the temporal lobe of the brain

The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus. This region is one of the higher levels of the ventral stream of visual processing, associated with the representation of objects, places, faces, and colors. It may also be involved in face perception, and in the recognition of numbers and words.

Akinetopsia, also known as cerebral akinetopsia or motion blindness, is a term introduced by Semir Zeki to describe an extremely rare neuropsychological disorder, having only been documented in a handful of medical cases, in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. The syndrome is the result of damage to visual area V5, whose cells are specialized to detect directional visual motion. There are varying degrees of akinetopsia: from seeing motion as frames of a cinema reel to an inability to discriminate any motion. There is currently no effective treatment or cure for akinetopsia.

<span class="mw-page-title-main">Cerebral achromatopsia</span> Medical condition

Cerebral achromatopsia is a type of color blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. It is often confused with congenital achromatopsia but underlying physiological deficits of the disorders are completely distinct. A similar, but distinct, deficit called color agnosia exists in which a person has intact color perception but has deficits in color recognition, such as knowing which color they are looking at.

Cortical visual impairment (CVI) is a form of visual impairment that is caused by a brain problem rather than an eye problem. Some people have both CVI and a form of ocular visual impairment.

<span class="mw-page-title-main">Homonymous hemianopsia</span> Visual field loss on the left or right side of the vertical midline

Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes.

Focal neurologic signs also known as focal neurological deficits or focal CNS signs are impairments of nerve, spinal cord, or brain function that affects a specific region of the body, e.g. weakness in the left arm, the right leg, paresis, or plegia.

The Riddoch syndrome is a term coined by Zeki and Ffytche (1998) in a paper published in Brain. The term acknowledges the work of George Riddoch who was the first to describe a condition in which a form of visual impairment, caused by lesions in the occipital lobe, leaves the sufferer blind but able to distinguish visual stimuli with specific characteristics when these appear in the patient's blind field. The most common stimuli that can be perceived consciously are the presence and direction of fast moving objects ; in his work these moving objects were described as "vague and shadowy". Riddoch concluded from his observations that "movement may be recognized as a special visual perception".

<span class="mw-page-title-main">Posterior cortical atrophy</span> Medical condition

Posterior cortical atrophy (PCA), also called Benson's syndrome, is a rare form of dementia which is considered a visual variant or an atypical variant of Alzheimer's disease (AD). The disease causes atrophy of the posterior part of the cerebral cortex, resulting in the progressive disruption of complex visual processing. PCA was first described by D. Frank Benson in 1988.

Anton syndrome, also known as Anton-Babinski syndrome and visual anosognosia, is a rare symptom of brain damage occurring in the occipital lobe. Those who have it are cortically blind, but affirm, often quite adamantly and in the face of clear evidence of their blindness, that they are capable of seeing. Failing to accept being blind, people with Anton syndrome dismiss evidence of their condition and employ confabulation to fill in the missing sensory input. It is named after the neurologist Gabriel Anton. Only 28 cases have been published.

Cerebral diplopia or polyopia describes seeing two or more images arranged in ordered rows, columns, or diagonals after fixation on a stimulus. The polyopic images occur monocular bilaterally and binocularly, differentiating it from ocular diplopia or polyopia. The number of duplicated images can range from one to hundreds. Some patients report difficulty in distinguishing the replicated images from the real images, while others report that the false images differ in size, intensity, or color. Cerebral polyopia is sometimes confused with palinopsia, in which multiple images appear while watching an object. However, in cerebral polyopia, the duplicated images are of a stationary object which are perceived even after the object is removed from the visual field. Movement of the original object causes all of the duplicated images to move, or the polyopic images disappear during motion. In palinoptic polyopia, movement causes each polyopic image to leave an image in its wake, creating hundreds of persistent images (entomopia).

<span class="mw-page-title-main">Occipital epilepsy</span> Medical condition

Occipital epilepsy is a neurological disorder that arises from excessive neural activity in the occipital lobe of the brain that may or may not be symptomatic. Occipital lobe epilepsy is fairly rare, and may sometimes be misdiagnosed as migraine when symptomatic. Epileptic seizures are the result of synchronized neural activity that is excessive, and may stem from a failure of inhibitory neurons to regulate properly.

<span class="mw-page-title-main">Visual pathway lesions</span> Overview about the lesions of visual pathways

The visual pathway consists of structures that carry visual information from the retina to the brain. Lesions in that pathway cause a variety of visual field defects. In the visual system of human eye, the visual information processed by retinal photoreceptor cells travel in the following way:
Retina→Optic nerve→Optic chiasma →Optic tract→Lateral geniculate body→Optic radiation→Primary visual cortex

References

  1. ↑ "Dictionary of Eye Terminology". Archived from the original on 2017-08-03. Retrieved 2005-10-13.
  2. 1 2 3 4 5 6 7 8 9 Aldrich, Michael S.; Alessi, Anthony G.; Beck, Roy W.; Gilman, Sid (1987). "Cortical Blindness: Etiology, Diagnosis, and Prognosis" (PDF). Annals of Neurology. 21 (2): 149–158. doi:10.1002/ana.410210207. hdl: 2027.42/50318 . PMID   3827223. S2CID   26912063.
  3. 1 2 3 4 5 6 "Archived copy". Archived from the original on 2012-11-10. Retrieved 2012-11-05.{{cite web}}: CS1 maint: archived copy as title (link)[ full citation needed ]
  4. 1 2 3 4 https://www.prcvi.org/cortical-visual-impairment.aspx%5B%5D%5B%5D
  5. 1 2 3 4 "What is CVI?". Archived from the original on 2012-04-15. Retrieved 2012-04-15.
  6. ↑ Waldvogel, B.; Ullrich, A.; Strasburger, H. (2007-11-01). "Blind und sehend in einer Person". Der Nervenarzt (in German). 78 (11): 1303–1309. doi:10.1007/s00115-007-2309-x. ISSN   1433-0407. PMID   17611729. S2CID   31801805.
  7. ↑ Hyperammonemia~followup at eMedicine
  8. ↑ Cipolla MJ (July 2007). "Cerebrovascular function in pregnancy and eclampsia". Hypertension. 50 (1): 14–24. doi: 10.1161/HYPERTENSIONAHA.106.079442 . PMID   17548723.
  9. ↑ Cunningham, F. G.; Fernandez, C. O.; Hernandez, C. (1995). "Blindness associated with preeclampsia and eclampsia". American Journal of Obstetrics and Gynecology. 172 (4 Pt 1): 1291–1298. doi:10.1016/0002-9378(95)91495-1. PMID   7726272.
  10. ↑ Do, D. V.; Rismondo, V.; Nguyen, Q. D. (2002). "Reversible cortical blindness in preeclampsia". American Journal of Ophthalmology. 134 (6): 916–918. doi:10.1016/S0002-9394(02)01753-1. PMID   12470768.
  11. 1 2 3 Huxlin, K. R.; Martin, T; Kelly, K; Riley, M; Friedman, D. I.; Burgin, W. S.; Hayhoe, M (2009). "Perceptual relearning of complex visual motion after V1 damage in humans". Journal of Neuroscience. 29 (13): 3981–91. doi:10.1523/JNEUROSCI.4882-08.2009. PMC   2825043 . PMID   19339594.

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