Empower Yourself With The Truth About Cortical Blindness

There may be moments when you believe you've discovered all there is to know about a topic, only to have it debunked by something new. In the world of vision and the eye, researchers are constantly learning new things about how we see, what can go wrong with our vision, and ways to improve it. Recently, a new form of blindness was discovered that challenges everything we thought we knew about vision and the eye.

This new form of blindness, called cortical blindness, is caused by damage to the brain's occipital cortex. This article will explore what cortical blindness is, how it differs from other forms of blindness, and the prospects for those with it.

What is cortical blindness?

Cortical blindness is a form of blindness caused by damage to the brain's occipital cortex. The visual cortex is the part of the brain responsible for processing visual information. When it is damaged, the brain cannot process visual information correctly, which leads to blindness.

Everyday vision works by sending the eye's pictures to the brain through optic nerves. The brain then processes these pictures, and we see them. With cortical blindness, the damage to the visual cortex means that the brain cannot process pictures correctly, so the person becomes blind.

There are two types of cortical blindness: complete and incomplete. Incomplete cortical blindness means that the person can still see some light and shadows, but they cannot see any details. Complete cortical blindness means the person cannot see anything, not even light or shadows. Incomplete cortical blindness is more common than complete blindness.

The same book states that cortical blindness can affect children and adults, though it is most common in children.

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Cortical blindness vs. cortical visual impairment (CVI)

Cortical blindness is a subset of neurological visual impairment (NVI) caused by damage to the cortex. This type of visual impairment can result in a complete loss of vision or a partial loss that may be accompanied by some other symptoms, such as seizures. On the other hand, cortical visual impairment (CVI) is a subset of NVI caused by damage to the visual cortex that results in a partial loss of vision. This type of visual impairment may not be accompanied by other symptoms.

It is important to distinguish between cortical blindness and CVI because they have different causes and structural foci. The pupil response is also an important diagnostic marker for distinguishing between these two types of visual impairment. Individuals with cortical blindness will respond to light stimuli, whereas those with CVI will not.

However, some experts, such as the American Association for Pediatric Ophthalmology & Strabismus, refer to cortical blindness as CVI and vice versa.

Delayed visual maturation vs. cortical visual impairment

People often use the terms "cortical visual impairment" (CVI) and "delayed visual maturation" (DVM) interchangeably, even though they are two different things. CVI is a neurological disorder that results in a lack of vision, while DVM is a condition in which a child's vision does not develop normally but improves over time.

CVI and DVM can cause a child to have problems seeing objects clearly, tracking moving objects, and understanding what they see. However, CVI is a permanent condition, while DVM usually resolves by one year of age.

There is no cure for CVI, but treatments available can help improve a child's vision. DVM does not require treatment, but if your child's doctor thinks they may benefit from some help improving their vision, they will recommend an appropriate course of action.

Blindsight

Blindsight is a phenomenon where individuals with damage to the visual cortex can still partially perceive their surroundings even though they are considered blind. This is because the visual pathway is not entirely destroyed, and some visual processing still occurs unconsciously. As a result, these individuals may be able to detect coarse flickering movement in their blind field. They may also experience other features of visual cortex lesions such as Anton syndrome, the Riddoch phenomenon, and formed visual hallucinations.

Blindsight is typically tested by having individuals walk along a blind field of stimuli while avoiding obstacles in their environment. Individuals with Blindsight can walk along the path and avoid obstacles without being able to see them consciously.

Blindsight has been found to occur in various types of visual cortex lesions and is a relatively common phenomenon. However, the extent to which it occurs and the mechanisms by which it occurs are still not fully understood.

Cortical blindness causes

The causes of cortical blindness can vary, but it is most often caused by damage to the visual cortex. This damage can be caused by many things, including:

• Cardiac embolism
• Stroke
• Head trauma
• Occipital lobe epilepsy
• Infection, e.g., HIV
• Hyponatremia
• Severe hypoglycemia
• Eclampsia
• Creutzfeldt-Jacob disease
• MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes)

According to the same source, there are a few rare conditions that can cause transient cortical blindness, such as:

• Hypertensive encephalopathy
• Infective endocarditis
• Posterior reversible encephalopathy syndrome (PRES)

The most frequent factors leading to cortical blindness in children, as stated in the same book, are:

• traumatic brain injury to the occipital lobe,
• congenital abnormalities of the same lobe, and
• perinatal ischemia.

What are the symptoms of cortical blindness?

The symptoms of cortical blindness are determined by the degree of damage to the occipital cortex. Incomplete cortical blindness may cause someone to see only light and shadow, while complete cortical blindness will cause a person to see nothing. Cortical blindness may also be accompanied by other symptoms such as;

• The complete loss of the ability to see and identify colors.
• Preservation of the ability to see moving objects, but not static ones. (Riddoch syndrome)
• Denial of visual loss (Anton–Babinski syndrome)
• An inability to fixate or track visually
• Visual hallucinations 
• Vision in the fovea is spared from blindness (Macular sparing)

How is cortical blindness diagnosed?

Cortical blindness is diagnosed through various evaluations, including complete blood count with ESR, metabolic profile, electrocardiogram, neuroimaging, automated perimetry, and visually evoked potential. The most important diagnostic tool for cortical blindness is neuroimaging, including a simple CT scan of the brain or an MRI brain. These scans help to identify any lesions or abnormalities in the brain that may be causing the blindness. Other evaluations may help diagnose cortical blindness, such as visual function testing and visual stimuli assessment.

Can cortical blindness be corrected?

If the cause of cortical blindness is treatable, then it is possible that the blindness may be reversed. However, if the damage to the brain is permanent, then cortical blindness will also be permanent.

In several cases, blindness was caused by a treatable condition, such as eclampsia or hyponatremia, and the patient obtained complete visual recovery after the underlying condition was treated. However, in other cases where the damage to the brain was permanent, such as stroke or cerebral palsy, the patient continued to suffer from chronic cortical visual impairment.

There is no cure for cortical blindness, but there are therapies that can help patients live a more comfortable life with it.

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Cortical blindness treatment

There is no one-size-fits-all approach to cortical blindness treatment. The most appropriate treatment for a particular patient will depend on the underlying cause of the blindness and the extent of the damage. However, most treatments involve some form of visual training and rehabilitation. This may include restitution therapy, compensation therapy, or substitution therapy.

Restitution therapy is used to recover any visual field deficits. Compensation therapy involves using saccadic eye movements to capture visual stimuli that would otherwise fall onto the blind part of the visual field. Substitution therapy uses a prism or other devices to project visual stimuli from the blind side of the visual field to the normal one.

Conclusion

Cortical blindness is a condition that results from damage to the occipital lobe of the brain. It can be caused by various conditions, including stroke, traumatic brain injury, cerebral palsy, or hyponatremia. The symptoms of cortical blindness vary depending on the severity of the damage to the primary visual cortex. In some cases, the blindness may be temporary, while in others, it may be permanent. There is no cure for cortical blindness, but there are treatments that can help improve the quality of life for those affected by this condition.

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