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 An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

caused by damage to the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

's occipital cortex. 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 The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, as well as the medial and inferior aspects of the temporal lobe of the human brain. The two arteries originate from the d ...

blockage (

ischemic stroke Stroke is a medical condition in which poor blood flow to a part of 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 ...

) 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 Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

). Congenital cortical blindness is most often caused by perinatal ischemic stroke,

encephalitis Encephalitis is inflammation of the Human brain, brain. The severity can be variable with symptoms including reduction or alteration in consciousness, aphasia, headache, fever, confusion, a stiff neck, and vomiting. Complications may include se ...

, and

meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, intense headache, vomiting and neck stiffness and occasion ...

. 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 or vision impairment (VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficul ...

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 trackinghttps://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) 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 thalam ...

* Infection *

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD) is an incurable, always fatal neurodegenerative disease belonging to the transmissible spongiform encephalopathy (TSE) group. Early symptoms include memory problems, behavioral changes, poor coordination, visu ...

(CJD), in association with a rapid onset of

dementia Dementia is a syndrome associated with many neurodegenerative diseases, characterized by a general decline in cognitive abilities that affects a person's ability to perform activities of daily living, everyday activities. This typically invo ...

* Rarely, dissociative identity disorder (DID) * Side effect of some anti-epilepsy drugs ( AEDs) * Hyperammonemia *

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

and, rarely,

pre-eclampsia Pre-eclampsia is a multi-system disorder specific to pregnancy, characterized by the new onset of hypertension, high blood pressure and often a significant amount of proteinuria, protein in the urine or by the new onset of high blood pressure a ...

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 Ophthalmoscopy, also called funduscopy, is a test that allows a health professional to see inside the fundus of the eye and other structures using an ophthalmoscope (or funduscope). It is done as part of an eye examination and may be done as part ...

should be normal in cases of cortical blindness. Cortical blindness can be associated with visual

hallucinations A hallucination is a perception in the absence of an external stimulus that has the compelling sense of reality. They are distinguishable from several related phenomena, such as dreaming ( REM sleep), which does not involve wakefulness; pse ...

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

. 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 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 Neuro-ophthalmology Occipital lobe

Symptoms

Causes

Diagnosis

Outcome

See also

References

Further reading

Books

Papers

External links