Cortical blindness is the older term used in neurology to describe acquired blindness that is not due to a diseased eye, but to damage to the primary visual cortex in the brain. Commonly used synonyms are blindsight and blindside. American physicians coined the latter term.
What is cortical blindness?
People who suffer from cortical blindness have completely functional eyes. Only the primary visual cortex in the brain is damaged. The most common cause of this damage is a stroke. However, describing this disease in terms of “blindsight” is not entirely accurate. Cortical blindness prevents optical impressions from reaching the primary visual cortex in the brain via the eye, which enables conscious perception of the environment. The term “blindsight” is a popular euphemism for people who are blind but act as if they can see. In cortical blindness, the various nerve pathways over the eye remain intact. They are responsible for relaying incoming visual stimuli to the brain. However, if the primary visual cortex is damaged, the transmission of these optical stimuli ceases and the person is unable to consciously perceive their environment. The medical specialties are neurology and ophthalmology.
Causes
It is a cortical amaurosis associated with the loss of visual perception with concomitant extensive processes in the visual cortex. However, pupillary responses do not change. There is bilateral loss of function of the primary visual cortex in the posterior lobe. Other causes are tumors, an ischemic cerebral infarction of the arteriae cerebri posteriores (reduced blood flow in the cerebral artery) and all kinds of severe head injuries, for example a skull base fracture after an accident. These patients no longer see their environment consciously, but show visual reflexes. In the back of the head is the visual cortex, the primary visual cortex responsible for assembling incoming visual signals into a consciously perceived image. This visual cortex is, so to speak, the computational center of the human sense of sight. Patients with cortical blindness do in fact see something, they just don’t know it because there is no transmission of visually perceived stimuli via the primary visual cortex to consciousness.
Symptoms, complaints, and signs
Cortical blindness and soul blindness, which is closely related to it, belong to the medical field of agnosia. This term comes from the Greek language and means “not knowing.” Soul blindness differs from cortical blindness in that objects are perceived, but they can no longer be assigned. Sigmund Freud assigned both visual disorders to agnosia. With cortical blindness there are no attention disorders, sensory defects or cognitive disorders. The visual apparatus consists of the eye, visual center, and optic nerves of the cerebral cortex. In cortical blindness, the visual cortex completely fails to function. In a legal sense, a person with this disease is considered blind even though the eyes are not damaged.
Diagnosis and course of the disease
The main symptoms are visual field defects in the temporal area or in the nasal area and subsequent loss of visual perception. Crossed equilateral (homonymous) hemianopsia is typical of this type of disease. If there is a left-sided lesion of the visual cortex, the right halves of the face fail and vice versa. If the end of the tract or corpus geniculatum (medial popliteal tubercle in the largest part of the diencephalon) are affected, the hemianopsia is complete in many cases, otherwise incongruent and incomplete. The corresponding nerve fibers have not yet completely coalesced. In some patients, bilateral optic atrophy (degenerative disease of the optic nerve) is present to a greater or lesser degree. The diagnosis is mainly made in experiments with flashes of light, which cortical blind people do not consciously perceive, but they can intuitively determine from which direction they come. However, they are unable to say why this is so. Neurologists suspect that the affected persons perceive the flashes of light subconsciously. Since medical science has not yet been able to conclusively determine how this process actually occurs, scientists have also conducted experiments with healthy individuals.In these test series, the visual center of the subjects was blocked by means of transcranial magnetic stimulation (TMS). These tested subjects also did not consciously perceive the flashes of light, but were equally able to name the direction. Colors presented to them could be correctly named intuitively. The tests showed that they had not consciously perceived the flashes and the colors, since they denied having seen anything at all. All individuals with cortical blindness can be diagnosed with the same brain injury or disease. Further findings are made on the basis of the neurological and ophthalmological picture and via the evaluation of magnetic resonance imaging or computed tomography.
Complications
Cortical blindness may develop as a complication after surviving a stroke, bleeding in the visual cortex, brain tumors, or traumatic brain injury. In the course of these diseases, sometimes the visual cortex is destroyed, which can lead to blindness. Through the normally functioning eyes, the images are indeed recorded. However, they can no longer be processed and made conscious due to the cortical damage. Serious complications leading to life-threatening courses are not caused by cortical blindness. They are then complications of the underlying disease. Since the damaged cortex cannot be regenerated, curative treatment of bark blindness is not possible. As a direct consequence of cortical blindness, the risk of suffering an accident may increase for those affected. This risk is particularly pronounced in a special form of cortical blindness in which the patient has no insight into the disease. This is the very rarely occurring Anton syndrome. Patients affected by Anton’s syndrome cannot recognize that they do not see anything. The challenge of the treating physician is first to convince the affected person of their blindness in order to prevent them from exposing themselves to the risk of suffering an accident. Convincing them is often very difficult and can only be achieved with the help of a combination of physiotherapy, psychotherapy and occupational therapy.
When should you see a doctor?
Cortical blindness is a serious condition that requires medical attention. If vision is impaired after a stroke or other medical emergency, the doctor must be informed. Further visits to the doctor are indicated if vision continues to decline even though treatment measures have already been taken. In this case, there may be other underlying disorders that are best clarified promptly. If treatment is given early, the chances of recovery are relatively good. In the absence of treatment, the visual disturbances may worsen. In the worst case, complete blindness in one or both eyes may result. Therefore, early diagnosis is important in any case. Cortical blindness is treated by a neurologist or ophthalmologist. The actual therapy takes place in a specialized center for visual disorders, where NEC, VRT and other visual therapies are offered. Close medical monitoring is needed during treatment. The physician should be informed of any unusual symptoms as well as any side effects of treatment so that therapy can be adjusted accordingly.
Treatment and therapy
The results of the studies show that consciousness is generated within the visual cortex and that information processing occurs even without conscious awareness. For this reason, the patients studied are able to intuitively tell which direction the flashes of light are coming from or correctly name presented colors. Further studies show that people with a lesion of the visual cortex that has led to hemianoposia (hemifacial loss) perceive emotional contents of faces. These are presented in the visual field that is no longer consciously perceived. This process occurs through the activation of visual centers in the superior colliculus (four-mound plate of the midbrain). The unconscious perception is projected to the limbic system, specifically to the amygdala (paired core area of the brain of the medial part of the respective temporal lobe), which is important for the perception and processing of emotions. Since the prognosis is usually that visual field loss will not regress, therapy is causally oriented.Stroke patients receive extensive physiotherapy and speech therapy, while tumor patients primarily receive radiation therapy. For craniocerebral injuries, various rehabilitation measures take place in addition to surgery.
Aftercare
Cortical blindness does not meet the usual criteria for blindness. It is not congenital, but is caused by damage to the area of the brain responsible. The eyes themselves remain functional. Affected persons of cortical blindness are furthermore not (always) completely unable to see, they can only recognize outlines or shades. The blindness occurs with certain sensory impressions that are not processed correctly by the brain. For patients, this new situation is unfamiliar and stressful. Follow-up care is necessary to learn the appropriate way to deal with cortical blindness. Follow-up care is provided in both a neurological and ophthalmologic setting. The extent to which cortical blindness is treatable depends on the causative disease. In some patients, vision is fully restored after treatment is complete; in others, visual impairment persists. Follow-up care includes exercises for the eyes and for sensory processing. In parallel, the affected person learns to cope with cortical blindness in everyday life. Depending on the severity of the blindness, aids such as canes for the blind may be useful. If the disease causes additional mental stress, psychotherapy should be considered. Attending self-help groups for support can also have a positive effect on the affected person’s quality of life.
What you can do yourself
Cortical blindness must be treated depending on the cause. A congenital condition significantly limits affected children, who require ongoing support in the early years of life. The guardians should seek early placement in a special kindergarten and later in a special school. Depending on the severity of the cortical blindness, the lack of vision can be compensated by glasses or other visual aids. Which measures are useful must be decided by a doctor depending on the severity of the condition. Acquired cortical blindness, for example after a stroke, requires regular training. Physical and speech therapy are important components of the therapy. Tumor patients who have developed cortical blindness should initially take it easy. The symptoms usually disappear during radiation therapy. If this is not the case, a visual aid must be worn. In individual cases, surgery of the eyes is possible. If the cortical blindness is due to an injury to the skull or brain, physiotherapeutic measures are indicated. The patient should consult a specialist and also perform exercises independently to restore neurological abilities.
