Cortical blindness is the total or partial loss of vision in a normal-appearing eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

 caused by damage to the visual area in the brain

Human brain

The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

's occipital cortex. This damage is most often caused by loss of blood flow to the occipital cortex from either unilateral or bilateral posterior cerebral artery

Posterior cerebral artery

-External links: - Posterior Cerebral Artery Stroke* at strokecenter.org* at State University of New York Upstate Medical University* at psyweb.com* at neuropat.dote.hu...

 blockage (ischemic stroke). A patient with cortical blindness often has little or no insight that they have lost vision, a phenomenon known as Anton's Syndrome

Anton-Babinski syndrome

Anton–Babinski syndrome is a rare symptom of brain damage occurring in the occipital lobe. People who suffer from 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...

 or Anton-Babinski syndrome

Anton-Babinski syndrome

Anton–Babinski syndrome is a rare symptom of brain damage occurring in the occipital lobe. People who suffer from 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...

.

Causes

The most common cause of cortical blindness is oxygen starvation to the occipital lobe caused by blockage to one or both of the posterior cerebral arteries. However, other conditions have also been known to cause cortical blindness, including:

• Bilateral lesions of the primary visual cortex
  Visual cortex
  The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
  
  
• Side effect of some anti-epilepsy drugs (AED
  Anticonvulsant
  The anticonvulsants are a diverse group of pharmaceuticals used in the treatment of epileptic seizures. Anticonvulsants are also increasingly being used in the treatment of bipolar disorder, since many seem to act as mood stabilizers, and in the treatment of neuropathic pain. The goal of an...
  
  s)
• Creutzfeldt–Jakob disease, in association with a rapid onset of dementia
  Dementia
  Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
  
  

Presentation

Patients have no vision

Visual perception

Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

 but the response of the pupil

Pupil

The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...

 to light is intact (as the reflex

Reflex

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

 does not involve the cortex

Cerebral cortex

The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

). One relatively easy test for cortical blindness is to first objectively verify the optic nerves and the non-cortical functions of the eyes are functioning normally--patient can distinguish light/dark, and pupils dilate and contract with light exposure, for example. Then, ask the patient to describe something he/she should normally recognize on sight:

• "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?"

Frequently, patients with cortical blindness will either 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 visual center of the brain is unable to interpret input from the eyes.

Fundoscopy is normal. 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 phenomenon

Riddoch phenomenon

The Riddoch phenomenon is an ocular affectation often caused by lesions in the occipital lobe which limit the sufferer's ability to distinguish objects. Only moving objects in a blind field are visible, static ones being invisible to the patient. The moving objects are not perceived to have color...

).