What is Cortical Blindness?
During the past decade, there has been significant increase in vision loss due to substantial damage to the brain rather than diseases or conditions directly related to the eye. One such impairment is the cortical blindness which is the loss of vision because of bilateral lesions of a section of the brain called geniculocalcarine pathways. In simpler terms, Cortical blindness is the complete or partial loss of vision in an eye that has been damaged due to loss or injury to the visual cortex, that part of the cerebral cortex that is responsible for vision, through stroke, traumatic brain damage, cerebral hemorrhaging, and infection such as encephalitis or meningitis.
Such a vision loss in children may either be permanent or transitory depending upon the cause of such damage. In such cases, patients may or may not be aware of the visual deficits. When the patient is unaware of the degree of visual loss they are termed of as “Anton syndrome”.
Types of Cortical Blindness
Cortical Blindness can either be in the form of acquired or congenital or it could be transient. The occurrence of acquired cortical blindness is due to the lack of flow of blood to the occipital cortex, either due to cardiac surgery or ischemic stroke where there is blockage of cerebral artery which can be unilateral or bilateral. In such cases, the vision of the affected person is often recovered and not damaged permanently. The cause of congenital cortical blindness can be because of meningitis, perinatal ischemic stroke or encephalitis.
Another cortical blindness form known as Riddoch phenomenon occurs from lesions formed in the occipital cortex which impairs the ability of the person from seeing static objects. Sometimes they are able to see the movement of the thing but are unable to identify the shape or color of the moving object.
Symptoms of Cortical Blindness
The commonly observed symptoms associated with transient or acquired cortical blindness includes –
- Sudden disappearance of sight in both the eyes.
- Lack of visual tracking and fixation.
- Occasional visual hallucinations.
- A situation called Visual Agnosia in which the patient is completely unaware that he is unable to see anything.
- Preservation or sparing of the abilities to perceive light or moving objects, but not the stationary objects.
- Macular spanning which results in vision in the fovea spared from such blindness.
- The visual appearance of the eyes are completely normal, they are neither painful nor red.
- The reaction of the pupil to outside light is completely normal, expanding and contracting to darkness and light sources.
Causes of Cortical Blindness
The causes of Cortical Blindness can be many driven by several factors out of which the most common cause being ischemia to the occipital lobes in which one or both of the posterior cerebral arteries are blocked. However, the other causes contributing towards transient or acquired cortical blindness include:
- Physical damage to the occipital cortex which the visual processing location of the cerebral cortex.
- Occlusion to the posterior cerebral artery which is the major supplier of oxygenated blood to the occipital cortex.
- Having traumatic brain injury to the occipital lobe of the brain.
- Having congenital abnormalities in the occipital lobe of the brain.
- Anticonvulsants used for a long period of time can lead to the occurrence of cortical blindness as an adverse effect. These are prescription medications that must be taken as advised for the treatment of epileptic seizures.
- Occurrence of eclampsia andpre-eclampsia.
- Conditions of Hyperammonemia.
- Creutzfeldt–Jakob disease associated with the rapid onset of dementia.
- Anton-Babinski syndrome is another major reason which can result from head injury or stroke.
Diagnosis of Cortical Blindness
One of the basic diagnostic tests to check if a person is suffering from cortical blindness is to make an objective verification of the non-cortical functions of the optic nerves and the eyes. This is the first diagnostic test conducted to identify such visionary ailment because although the person affected by such problem has no vision, the response of their pupil to light remains intact as the reflex is not directly related to the cortex. This test will help to check whether they are able to distinguish light and dark as also whether their pupil dilates and contracts to the effects of light.
The next test is to ask the patient to describe a thing that he or she could have been had the vision been normal such the number of fingers held up in front of the person or the identification of a particular sign or identification of any particular object. Patients affected by cortical blindness will not be able to make such distinction with accuracy able to provide any detail other than the shape or color of the object in question. This is a clear indication of the fact that the lack of vision is due to neurological disorder rather than any ocular effects. It points towards the fact that the occipital cortex is unable to process and correctly interpret the input vision coming from the retina. Fundoscopy, commonly known as ophthalmoscopy is a common test conducted in cortical blindness patients.
Treatment of Cortical Blindness
Till date, there has been no specific treatment that can help cure the problem of cortical blindness, but there are rehabilitation exercises that might help to stimulate vision in people suffering from such neurological disorder. These exercises make use of things that have contrasting movement, color and pattern that promote recognition. Tactile and verbal clues might concentrate on a particular stimulus. It is recommended by neurologists conducting such tests to maintain a consistent home environment that will allow the person suffering from such disorder to isolate a particular object and then track it. Some of the patients suffering from such complication might retain a certain degree of vision, especially the peripheral vision.
Prevention of Cortical Blindness
This condition of blindness is not an eye disease and hence the examination of the eye of the patient will show no pathological defects. This is actually a disorder of the brain in the occipital lobe that is in control of the visual stimuli and as such there is no real cure to such visionary problem. The only way out is to keep updated with the checkup of the eye to identify any significant change. The recovery process can be gradual, partial, rapid or even impossible in certain cases.
The outcome of a patient suffering from acquired cortical blindness is generally based on the original cause of the blindness. Such as, patients with bilateral occipital lesions have relatively lower chances of recovery than those suffering from a transient ischemic attack or females experiencing complications arising from eclampsia. Those having acquired cortical blindness have minimal chances of getting a permanent loss of vision. Several efforts are being made to find a proper solution to the problem of cortical blindness and the process of ‘relearning therapy’ might provide a good opportunity for patients to clearly make sense of the visual environment without any major complication.