Oliver Sacks, in the Case of the Colorblind Painter, describes how an artist, who was famous for his brilliantly-colored abstract canvasses, suddenly and irreversibly loses all color perception as the result of a car accident. This tragic case depicted by Sacks is one example of an acquired color vision deficiency. What were once vibrant works of art now appeared to him grayish or black and white. It was a devastating blow for a lifelong painter whose art and life were now without meaning. Not all cases of this affliction, however, are as sudden, complete or permanent: onset can be slow and appreciation of colors can change gradually over time depending on the particular eye disease. However, whereas inherited alterations to color vision tend to remain stable through life, late onset color vision changes can be an early sign of disease or a side effect of prescribed medication. It is important, therefore, that you consult your doctor should you become aware of any changes in your perception of color. To clarify matters, let's look at the differences between acquired color vision deficiency and inherited or congenital deficiencies: Typically congenital deficiencies involve confusion over red and green. Acquired deficiencies more often than not are a blue-yellow problem.There is a gender imbalance in congenital defects as they are linked to the X female chromosome. This means mothers (whose vision will be apparently normal) carry the defect to their sons. Inherited color vision deficiency is, therefore, more prevalent in males than females.By contrast, acquired defects are not gender-related except by gender differences in the experience of brain trauma injuries, for example. As touched on above acquired defects are less likely to be stable over time. With congenital defects both eyes tend to be affected equally whereas acquired color deficiencies are more likely to affect one eye more than the other. Stroke victims typically experience a more pronounced color deficiency in one eye.Acquired defects are not as easily diagnosed or detected with standard color vision tests. The changes can be very subtle which is why early reporting is essential.If you acquire color deficiencies you are more likely to encounter difficulties in correctly naming colors. This is because life-long experience with defective color perception enables those with the inherited form to use compensatory techniques to overcome their handicap. Because acquired color vision deficiencies are the result of life events, they can arise from a variety of different causes affecting the retina, visual pathways or areas of the brain which process color information. A wide range of prescription drugs, conditions such as multiple sclerosis, diabetes and cardiovascular diseases, some liver diseases and many eye diseases can affect the cone nerve cells which enable us to discriminate fine detail and colors by day. As a result, and often in only one eye at a time, color vision is temporarily or permanently changed. Both men and women are affected equally. Sufferers from arthritis, heart disease and depression sometimes find their color vision impaired as a side effect of their long-term use of prescription drugs. Even stroke patients who take aspirin over many years to thin the blood can encounter altered color perception. Cataracts, glaucoma and the majority of eye problems affecting the retina or nerve pathways to the brain are associated with a reduced ability to differentiate colors, including blues and greens. But the most widespread form of acquired color vision deficiency in the developed world, affecting some 23 per cent of people over the age of 65, is age-related macular degeneration (AMD). Involving a loss of the cone-rich area of central vision (the macula) where color vision is sharpest it often leads to blindness. Finally, the condition known as optic neuritis, which can result in a distortion or lack of color vision, illustrates well how one example of acquired color vision deficiency can be an indicator of two very different prognoses. This inflammation of the optic nerve is sometimes diagnosed in young children following an illness such as measles or mumps. The symptoms - blurred vision accompanied by distortion of color vision - are generally transient. However, it can also be an early indicator of neurological impairment. Optic neuritis affects mainly adults in their thirties, one-third of whom go on to develop multiple sclerosis later in life. So, the best advice to give an individual is to have an eye examination, which includes a test for color vision, if there is the slightest reason for concern. |
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