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What is visual agnosia? -

Visual agnosia is a condition in which the brain doesn’t process the information the eyes are receiving. This disruption manifests in different ways and has different effects (more on that later).

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Who’s at risk? -

Visual agnosia affects people of every age, but it seems to be more common among those who suffer from certain health conditions. These include stroke and brain injury.

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How common is it? -

There is not a lot of data available that can give us a clear picture of how recurrent visual agnosia is, but, overall, it’s a pretty rare condition.

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How does it manifest? -

Our eyes receive information and send nerve signals to the brain so that we can process that information and make sense of it. In those with visual agnosia, the parts of the brain responsible for processing that information don't work as they should, and this manifests in a discrepancy between what they see and what the brain “sees.”

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Causes -

As mentioned previously, visual agnosia occurs when a condition affects the brain or there is brain damage. Damage to the brain leads to injuries known as lesions. Here are a few examples of conditions or problems that cause them.

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Brain damage -

Brain tumors can cause lesions (these include both cancerous and non-cancerous growths). Traumatic brain injuries, as well as cerebral hypoxia (when there’s damage caused by lack of oxygen to the brain), can trigger visual agnosia.

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Brain damage -

Strokes are also a common culprit, as are brain infections (e.g. encephalitis). Those who suffer from epilepsy and seizures are also at higher risk.

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Brain diseases -

In addition to brain damage, some degenerative and progressive brain diseases can be the root cause of visual agnosia. These include Alzheimer’s disease, dementia, Lewy body dementia, and posterior cortical atrophy.

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Symptoms -

Symptoms vary, depending on the type of visual agnosia. Let’s take a look at some of the most common forms of visual agnosia.

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Akinetopsia -

People who suffer from this form of visual agnosia are able to recognize objects, but are unable to recognize that they’re moving.

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Alexia -

Those with alexia can’t recognize words when they look at them. They see the words but can’t understand or read them. People who suffer from this form of visual agnosia can, however, still write without any issues.

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Amusia -

Amusia is a form of visual agnosia in which the person loses the ability to read music.

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Autotopagnosia -

Those with this type of visual agnosia are unable to recognize body parts. This applies to both their own body parts and those of others. People with autotopagnosia might also struggle to recognize body parts from an image.

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Achromatopsia -

People with this type of visual agnosia can see different colors and tell them apart, but are unable to identify which color is which. Achromatopsia is also known as color agnosia.

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Balint syndrome -

People with Balint syndrome don’t see the world around them as a big picture with several objects and how these are connected. Instead, they see scattered objects and are unable to understand how they relate to one another.

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Cortical blindness -

Cortical blindness occurs when the parts of the brain that receive visual input get damaged. The eyes still work, but the signals they send are not processed by the brain.

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Environmental agnosia -

People with this type of visual agnosia are unable to recognize where they are, describe a location, or give directions.

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Form agnosia -

Those with form agnosia are able to see the parts of an object but have trouble recognizing the object itself. For instance, one could see the wheels and steering wheel of a car individually, but wouldn’t be able to recognize them as part of the whole car.

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Simultanagnosia -

There are different forms of simultanagnosia. Dorsal simultanagnosia is where a person is only able to see one object at a time. This means that they need to be focused on a specific object in order to see it, otherwise they won’t.

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Simultanagnosia -

Central simultanagnosia is another common one. This is where a person can see various objects at a time but is only able to identify them individually. E.g. being in a garden but only recognizing one flower at a time and never recognizing the garden as a whole.

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Prosopagnosia -

There are several forms of prosopagnosia, but all relate to the inability to recognize familiar faces, or facial expressions in general. This form of visual agnosia is also known as “face blindness.”

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Social-emotional agnosia -

This is where people are unable to recognize nonverbal cues such as facial expressions, body language, and tone of voice.

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Diagnosis -

Diagnosis of visual agnosia usually involves looking at the person’s health history, as well as a number of physical and neurological exams. Here are a few of the tests and exams that may be prescribed.

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Diagnosis: exams -

Sensory tests may be done to rule out any sensory issues. Imaging tests may also be performed to look for structural abnormalities and damage in the brain.

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Diagnosis: exams -

Cognitive, memory, and familiarity tests may also be performed. These are used to assess any issues with the person’s thinking process and to rule out any other condition that may affect memory.

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Treatment -

There is no cure for visual agnosia, but some of the underlying causes may be treatable. Nonetheless, brain lesions are often permanent, and in these cases the condition will not improve.

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Treatment -

Treatment will depend on the underlying cause, but may include medications (e.g. antibiotics for infections or antidementia drugs). For people whose underlying cause of visual agnosia is a growth pressing on the brain, surgery is often recommended.

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Treatment -

There are also a number of rehabilitation programs that help people live with the condition. These include learning how to use the other senses for the effects of recognition, as well as techniques such as the labeling of objects.

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Prevention -

The condition is not quite preventable as such. Preventing visual agnosia boils down to reducing risks that may lead to conditions and problems that cause it. This may include a healthy lifestyle, including a healthy diet and exercise for the prevention of strokes.

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Prevention -

Infections should never be ignored. If these spread to the brain, they can have serious consequences. And if you work in a place where a head injury is a risk, wear protective gear at all times.

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Prevention -

Managing other conditions is equally important. Things such as epilepsy or sleep apnea can affect your brain and cause visual agnosia.

Sources: (Cleveland Clinic) (ScienceDirect) (Healthline)

See also: How this rare syndrome can change your accent

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