Cortical blindness is the loss of vision in a healthy eye that arises from damage to the occipital cortex of the brain. Most often it is caused by vascular events in the brain (cerebrovascular insult) in the elderly population. However, it can also arise due to certain infections (encephalitis or meningitis) in much younger people, also in infants. It can either be transient or permanent, depending on the severity and etiology. Other possible causes also include head trauma, hyperammonemia, a side effect of some anti-epileptic drugs, and eclampsia, although it is worth noting that isolated cortical blindness caused by those conditions is extremely rare. While it is more of a neurological rather than an ophthalmological issue, it is an interesting condition that we feel worth sharing a few words with you.
The symptoms one is experiencing range from a complete loss of all visual sensations on one side of the spectrum, or isolated losses of specific visual sensation aspects (such as visual fixation or the ability for tracking) on the other. Some people can also experience frank visual hallucinations, and in some extremely rare instances, people might have no insight into their visual loss – referred to as visual anosognosia.
Neurological Origin of Blindness
Physicians will suspect cortical blindness in patients who are objectively blind and in whom no abnormalities are found during an extensive ophthalmological examination. One important sign of isolated damage to the visual cortex is an intact pupillary reflex. Since the loss of vision is neurological in origin, the patient will sometimes be able to name the color and shape of an object, but no other details that would help them identify what the object is, or the actual name of the object.
The prognosis depends very much on the cause that leads to the development of cortical blindness. As no specific treatment exists, favorable outcomes can be expected in instances that were caused by somewhat reversible causes (eclampsia, a side effect of some anti-epileptic drugs). In those that suffered extensive damage to the occipital cortex (massive cerebrovascular event or head trauma), the outcome is less favorable. That being said, some promising research published recently shows that more specific treatment options for cortical blindness could be possible in the future.