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 visual area in the brain's occipital cortex.»Dictionary of Eye Terminology This damage 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 patient with cortical blindness often has little or no insight that they have lost vision, a phenomenon known as Anton's Syndrome or Anton-Babinski syndrome.
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
- Side effect of some anti-epilepsy drugs (AEDs)
- Creutzfeldt–Jakob disease, in association with a rapid onset of dementia
- Infection »http://www.aph.org/cvi/define.html
- Head trauma to the occipital lobe of the brain »http://www.aph.org/cvi/define.html
- Congenital abnormalities of the occipital lobe »http://www.aph.org/cvi/define.html
Presentation
Patients have no vision but the response of the pupil to light is intact (as the reflex does not involve the cortex). 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).