Visual Agnosia: Symptoms, types and causes

What is visual agnosia?

Visual agnosia is a neurological disorder. A person won’t be able to recognize a familiar object using only sight even when they have otherwise normal vision. A person with visual agnosia may need to rely on other senses to recognize everyday items.

For example, a person who can’t identify a banana by looking at it will likely be able to name the familiar fruit by touch, smell or taste. Or, they would look at a toothbrush and not know it’s used to clean teeth without using the other senses to recognize it. 

Visual agnosia is a type of agnosia. Agnosia is a neurological disorder. It interferes with the ability to recognize familiar objects using one of the five senses. The word agnosia comes from a Greek word meaning “lack of knowledge.” 

With visual agnosia, a patient has difficulty recognizing objects or aspects of objects by sight. This happens because there is damage along one of two main visual pathways in the brain. The “what” pathway relates to what you are seeing. The “where” pathway relates to the location of an object in space.

People with visual agnosia may have no other problems with their eyesight or with their memory. But they likely have damage in certain parts of the cerebral cortex. These areas are responsible for processing specific aspects of vision. 

Types of visual agnosia

General visual agnosia involves inability to recognize known objects by sight. There are two main types of general visual agnosia: apperceptive visual agnosia and associative visual agnosia.

With apperceptive visual agnosia, a person has trouble recognizing images their eyes see. Depending on the type and severity of apperceptive visual agnosia, a person with this type of visual agnosia may not be able to:

• Perceive the form or size of an object
• Distinguish between objects in a group
• Copy a drawing of a common object like a tree or a shoe

With associative visual agnosia, a person has difficulty linking an object with memories of similar objects. However, they can typically draw or verbally describe objects. For example, they may be able to look at an object and tell you it’s small, gray and smooth but not that it is a stone.  

Other types of visual agnosia

There are also some very specific types of visual agnosia. These affect the ability to recognize certain types of things, people, places or scenes by sight. People who have one of these types of visual agnosia may also have general visual agnosia. 

These other types of visual agnosia include:

Hollywood celebrity, Brad Pitt, struggles with “face blindness,” also known as prosopagnosia.

• Autotopagnosia – Inability to recognize or name parts of their own body, such as fingers or toes
• Prosopagnosia – Inability to put a name to a familiar face, such as a relative, a neighbor or a celebrity
• Simultanagnosia – Inability to recognize a collection of objects, such as a set of tools, or a scene, such as a landscape
• Topographagnosia – Inability to recognize familiar or famous places, such as the Grand Canyon or a friend’s living room

In many cases, people with visual agnosia have good visual acuity, which is the sharpness of eyesight your eye doctor checks with an eye chart.

What causes visual agnosia?

Visual agnosia may happen suddenly as a result of a brain injury from a car crash or a stroke. It may also happen gradually over time as the result of a condition such as dementia.

Different types of visual agnosia are caused by damage to specific areas in the brain. For example, associative visual agnosia may be caused by damage to the bilateral inferior occipitotemporal cortex. The occipital and temporal lobes are parts of the brain that play a role in vision. 

The brain damage that leads to visual agnosia may be caused by a number of issues, such as:

• Brain tumors
• Dementia, such as from Alzheimer’s disease or Posterior Cortical Atrophy
• Developmental disorders
• Head injuries
• Infections
• Lack of oxygen (hypoxia)
• Stroke
• Exposure to toxins such as carbon monoxide or mercury 

Not everyone who has one of these conditions or injuries will get visual agnosia, but some patients may develop the disorder.

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Visual agnosia diagnosis and treatment

A diagnosis of visual agnosia may require multiple consultations. These may be with an eye doctor, a neurologist and/or other healthcare professionals.

Th following steps may be a part of the process of diagnosing visual agnosia:

• Interviewing the patient about their history and challenges in daily life
• Showing the patient simple items like an apple, a cup or a phone and asking them to identify the objects by sight
• Doing thorough physical, eye and neurological exams and looking for problems with vision (such as visual acuity)
• Giving standardized tests to rule out problems with memory and cognition
• Ruling out other reasons for inability to identify objects (such as general dementia or anomia)
• Ordering brain imaging tests such as a CT (computed tomography) scan or MRI (magnetic resonance imaging)

Treatment for visual agnosia typically consists of using exercises and rehabilitation therapy. This will help a person learn or re-learn everyday tasks. The patient may also need treatment for any underlying condition, such as a brain tumor, that is causing visual agnosia.

Get regular eye exams

To protect your eye health, get regular eye exams, and see your eye doctor if you have any vision symptoms. If your eye doctor suspects visual agnosia, they may refer you to a neurologist for further testing and a diagnosis.

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