Cortical blindness is vision loss due to damage to the visual portion of the occipital cortex in the brain. Although the affected eye is physically normal and healthy, damage to the brain results in partial or complete loss of vision. The pupil of a cortical blind eye still dilates and contracts in response to changes in light, because this reaction is a reflex and not dependent on the brain.
There are many possible causes of cortical blindness. It can be the result of physical damage to the occipital cortex, such as injuries. Cortical blindness can also be caused by occlusion of the posterior cerebral artery, which supplies oxygenated blood to the occipital cortex. Cortical blindness is also a side effect of long-term use of some anticonvulsants, prescription drugs used to treat seizures.
Cortical blindness sometimes presents with hallucinations, or denial of blindness. Some patients with cortical blindness can see moving objects, but not stationary objects. In all cases of the disorder, the structures of the eye itself, such as the retina and iris, function normally, unless there are separate eye problems.
In Anton-Babinski syndrome, a rare symptom of brain damage named after neurologists Gabriel Anton and Joseph Babinski, the patient is cortically blind but insists on the ability to see. Anton-Babinski syndrome most often occurs after a stroke, but it can also be the result of a head injury. In Riddoch's phenomenon, a type of cortical blindness, lesions in the occipital cortex cause the patient to lose the ability to see static objects. The patient can see movement, but in some cases cannot perceive the shape or color of moving objects.
When cortical blindness is less than total, it is also called cortical visual impairment (CVI). Symptoms of CVI may include visual ability that varies from day to day, a discrepancy in visual ability between the two eyes, a narrow field of vision, and photophobia or an aversion to light. If the CVI is worse in one eye than the other, impaired depth perception may occur. A CVI patient may also perceive some types of objects better than others; for example, he or she can read texts, but has difficulty perceiving faces. CVI is not usually associated with loss of the ability to see colors, but some colors, especially yellow and red, may be easier to see than others.