What is cortical blindness?
This medical condition is experiencing vision loss because the occipital cortex in your brain that controls vision has been damaged in some way. When a person has cortical blindness the eye that is affected is physically healthy and normal but the damage to your brain causes partial or full loss of vision. The pupil will still dilate and constrict in response to any changes in light in the cortically blind eye. The reason the pupil does this is because this particular reaction is considered a reflex and does not depend on your brain to do this. In all cases of this medical condition the structure of their eye itself, such as the iris and the retina, will function normally unless separate ocular problems are present.
When a person has cortical blindness and it is less than total blindness it is called cortical visual impairment (CVI). A person with CVI may also be able to perceive some form of objects better than others such as having difficulty perceiving faces but being able to read text. This type of cortical blindness is not usually associated with the loss of ability to see colors. There are some colors that might be easier for them to see than others especially red and yellow.
Many people experience a period of denial of being blind which is referred to as having Anton-Babinski Syndrome. It is symptom of having brain damage that occurring in your occipital lobe. It is rare that a person would have this disorder. This syndrome is named after neurologist Gabriel Anton and Joseph Babinski.
Cortical Blindness Symptoms
With this medical condition some of the symptoms that might occur are:
- Having hallucinations
- Some are able to see stationary objects but are able to see moving ones
- Complete loss of vision and visual sensation
If a person has CVI some of the symptoms they might experience can include:
- Having visual ability that varies on a daily basis
- Between the two eyes there is a discrepancy in their visual ability
- Having a narrow line of vision
- Having photophobia which an aversion to any light, especially bright light
- Having impaired depth perception if the CVI in one eye is worse than the other eye.
Cortical Blindness Causes
There are several different causes why a person would have cortical blindness that can include:
- Physical damage to your occipital cortex, which is the visual processing center of your cerebral cortex.
- Occlusion of your posterior cerebral artery. This is the artery that supplies your occipital cortex with blood that has been oxygenated.
- Anticonvulsants that have been used for a long period of time can cause cortical blindness as a side effect. These anticonvulsants are prescription medications that are given to patients to treat epileptic seizures.
- Having a traumatic brain injury to the occipital lobe of your brain
- Having congenital abnormalities of the occipital lobe of your brain
Having cortical blindness can be congenital or acquired and in certain instances it could also be transient. In acquired cortical blindness the most often case is from loss of blood flow to the occipital cortex. This can be from having cardiac surgery and ischemic stroke which is cerebral artery blockage that can bilateral or unilateral. If this is the cause most of the time the complete loss of vision is not permanent and some of their vision many be recovered. If the cause is congenial it is most often caused by encephalitis, meningitis, or perinatal ischemic stroke, which is a stroke that happens in near-term and term babies.
Cortical blindness can also occur from Anton-Babinski syndrome which usually results from a stroke or head injury. Another form of cortical blindness is called Riddoch phenomenon which is caused by lesions that form in your occipital cortex and causes the person to lose the ability to see static things. They can see the movement of the things but in some cases they cannot see the color or shape of the moving objects.
One diagnostic test to see if a person is suffering from cortical blindness is to objectively verify the non-cortical functions of the eyes and the optic nerves are functioning. The reason this diagnostic test is done first is that if a person has cortical blindness they have no vision but the response of their pupil to light is intact because the reflex does not involve their cortex. When this test is performed it will help to confirm that they can distinguish light/dark. The tests will also make sure that their pupils dilate and contract with exposure to light. The next test will have them to describe something they would be able to recognize if their vision was normal.
One example would be to answer the question as to how many fingers the person doing the test is holding up. If the person has cortical blindness they would not be able to provide any details other than maybe the general shape or color and not be able to identify the item that is being questioned about at all. This will indicate that the lack is vision is neurological instead of ocular and specifically indicates that their optical cortex is not able to process correctly and interpret the intact input that is coming from the retina
At this time there is no specific treatment available to help reverse cortical blindness but there are rehabilitation exercises that may be able to help stimulate vision. The rehabilitation exercises use objects with contrasting movement, patterns, and colors to promote recognition. It is also recommended by neurologist that a consistent home environment is kept to allow the person with cortical blindness to isolate a specific object and then tract it.