Cortical blindness is the total or partial loss of

vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain und ...

in a normal-appearing eye caused by damage to the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...

occipital cortex 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". The occipital lobe is the vi ...

. Cortical blindness can be acquired or congenital, and may also be transient in certain instances. 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 A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop funct ...

) and by cardiac surgery. In most cases, the complete loss of vision is not permanent and the patient may recover some of their vision (

cortical visual impairment Cortical visual impairment (CVI) is a form of visual impairment that is caused by a brain problem rather than an eye problem. (The latter is sometimes termed "ocular visual impairment" when discussed in contrast to cortical visual impairment.) Some ...

). Congenital cortical blindness is most often caused by perinatal ischemic stroke, encephalitis, and meningitis. 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. 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 Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

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.

Symptoms

The most common symptoms of acquired and transient cortical blindness include: * A complete loss of visual sensation and of

* Preservation/sparing of the abilities to perceive light and/or moving, but not static objects ( Riddoch syndrome) * A lack of visual fixation and tracking https://www.prcvi.org/cortical-visual-impairment.aspx * Denial of visual loss ( Anton–Babinski syndrome) * Visual hallucinations * Macular sparing, in which vision in the fovea is spared from the blindness.

Causes

The most common cause of cortical blindness is ischemia (

oxygen deprivation Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can ...

) to the occipital lobes caused by blockage to one or both of the posterior cerebral arteries. However, other conditions have also been known to cause acquired and transient cortical blindness, including: * Congenital abnormalities of the occipital lobe * Head trauma to the occipital lobe of the brain * Bilateral lesions of the primary

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...

* Infection *

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD), also known as subacute spongiform encephalopathy or neurocognitive disorder due to prion disease, is an invariably fatal degenerative brain disorder. Early symptoms include memory problems, behavioral changes ...

(CJD), in association with a rapid onset of

dementia Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...

* rarely

Dissociative identity disorder Dissociative identity disorder (DID), better known as multiple personality disorder or multiple personality syndrome, is a mental disorder characterized by the presence of at least two distinct and relatively enduring personality states. The di ...

(DID) * Side effect of some anti-epilepsy drugs ( AEDs) * Hyperammonemia *

Eclampsia Eclampsia is the onset of seizures (convulsions) in a woman with pre-eclampsia. Pre-eclampsia is one of the hypertensive disorders of pregnancy that presents with three main features: new onset of high blood pressure, large amounts of protein in ...

and, rarely, pre-eclampsia The most common causes of congenital cortical blindness are: * Traumatic brain injury (TBI) to the occipital lobe of the brain * Congenital abnormalities of the occipital lobe * Perinatal ischemia * Encephalitis * Meningitis

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: * "How many fingers am I holding up?" * "What does that sign (on a custodian's closet, a restroom door, an exit sign) say?" * "What kind of vending machine (with a vivid picture of a well-known brand name on it) is that?" 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).

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. In patients with acquired cortical blindness, a permanent complete loss of vision is rare. The development of cortical blindness into the milder

is a more likely outcome. Furthermore, some patients regain vision completely, as is the case with transient cortical blindness associated with

eclampsia Eclampsia is the onset of seizures (convulsions) in a woman with pre-eclampsia. Pre-eclampsia is one of the hypertensive disorders of pregnancy that presents with three main features: new onset of high blood pressure, large amounts of protein in ...

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. 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. 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. 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.

References

External links

{{CNS diseases of the nervous system, state=collapsed Blindness Occipital lobe

Symptoms

Causes

Diagnosis

Outcome

See also

References

Further reading

Books

Papers

External links