Achromatopsia- Loss of Color Vision

What if you couldn't see color anymore? That is exactly what happens to people who experience a rare syndrome called achromatopsia, which is the inability to distinguish colors from each other. People who have achromatopsia literally can only see black, white and shades of grey.

How does achromatopsia occur?

There are a few different causes of achromatopsia, including alcohol toxicity, genetic birth defects, nutritional deficiency and brain damage from trauma or stroke.

It is not uncommon for a stroke to cause vision changes such as loss of peripheral vision or complete loss of vision in one eye. However, it is unusual for a stroke to cause achromatopsia because several regions of the brain on both the right and left side control color vision. So, it isn’t really only one single stroke that causes achromatopsia, but a combination of several strokes in very specific locations of the brain.

Several reports describe stroke survivors who have experienced stroke-induced achromatopsia. In these instances, sophisticated imaging methods detected the presence of bilateral strokes, which means that there were strokes on both the right and the left sides of the brain.

The specific locations of the strokes were in the ventral occipitotemporal regions on both sides of the brain. The ventral occipitotemporal regions are located towards the back of the brain, near the top of the head, above the ears.

It is only recently that neuroscientists have identified that the ventral occipitotemporal regions play a central role in controlling our perception and recognition of different colors.

The amazing thing about some of the people who experienced achromatopsia after a stroke is that they remained healthy, and did not experience the more typical effects of a stroke, such as weakness, balance problems or slurred speech.

What do people see if they can't see color?

Color blindness is a well known hereditary condition that affects individuals from a young age. Most people who are colorblind can identify some colors, but have problems differentiating red and green from each other.

But achromatopsia after a stroke is different from typical color blindness because it causes people who already had the ability to see color for their whole lives to suddenly lose the ability to see any color at all after the stroke. It is a huge and sudden change in how people see the world around them.

Complete achromatopsia means that a person cannot distinguish colors at all, while dyschromatopsia means that a person can see some color, but has lost some or most of his or her ability to recognize the difference between colors.

A person who has achromatopsia can see shapes, objects, and textures because the inherent variation in pigment between dark and light colors provides enough of a contrast to see the outlines and the defined edges of objects.

A person with achromatopsia literally sees black and white and shades of gray.

How does achromatopsia affect a person’s life?

Achromatopsia can have a profound impact on daily life. It can, most obviously, make it difficult to match clothes or decorate one’s house. That would certainly be one of the effects of achromatopsia. But we use color perception for a lot more than design.

There are many practical problems that a person with achromatopsia has to live with. Driving is an important safety issue, because the lack of color vision makes it difficult to see which traffic lights are activated. Other driving problems include trouble recognizing cars, bicycles or pedestrians when it is dark outside.

Other safety issues can arise when cooking, using tools and caring for children. A person living with achromatopsia has to learn to function without the extensive built in color coding that helps us get through life safely and easily. Achromatopsia makes it necessary to learn to distinguish and recognize objects based on characteristic surface features such as form and texture, rather than color.

Interestingly, one of the stroke survivors who vividly described his symptoms of achromatopsia was, in fact, an art professor. The experience and enjoyment of many of life’s scenes is based on color perception. Individuals who have achromatopsia also have to learn to appreciate their surroundings through other qualities besides color.

Sources:

A functional MRI case study of acquired cerebral dyschromatopsia, Beauchamp MS, Haxby JV, Rosen AC, DeYoe EA, Neuropsychologia, July 2000

Colour Vision Impairment in Young Alcohol Consumers, Brasil A, Castro AJ, Martins IC, Lacerda EM, Souza GS, Herculano AM, Rosa AA, Rodrigues AR , Silveira LC, PLoS One, October 2015 ;10(10):e0140169. doi: 10.1371/journal.pone.0140169. eCollection 2015.

The locus of color sensation: Cortical color loss and the chromatic visual evoked potential, Michael A. Crognale, Chad S. Duncan, Hannah Shoenhard, Dwight J. Peterson, and Marian E. Berryhill, Journal of Vision, August 2013

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