COLOR VISION DEFICIENCY

What is color vision deficiency?

The nerve cells which receive and process light at the back of the eye – the retina – are of two main types: the rod-like cells, which operate at night and the cone-like, which allow us to see fine detail and colors by day. Three different chemicals can be found within the cone nerve cells, so that each cone responds best to red, green or blue light in a similar manner to color television.  The fault of defective color vision lies in one set of chemicals, usually those controlling principally either red or green colors.

It is not generally realized that defective color vision can range from near-normal appreciation of hues, where the chemical within the red or green cones is only slightly altered, to a medium degree of confusion where the chemical is altered considerably.  For the first group, pale colors will be confused if the lighting is poor, or the person is tired or under pressure to make a quick decision on the name of a color.

Only a third of those with color vision problems have the more severe form, where one sort of chemical is completely lacking and very strong colors are frequently confused, though still within a limited range of up to ten main colors. Complete color deficiency, where all colors are seen as varying shades of black and white is extremely rare.

Why are more men than women color deficient?

Like many other medical conditions, defective color vision may be inherited and carried through the mother (whose vision will be apparently normal) to the son. Frequently, brothers within the same family are affected, but this is not always the case as there is only a 50/50 chance that sons of ‘carriers’ will have altered color vision. 

A female can only inherit defective color vision if her father has the problem and her mother is a carrier or is color deficient herself. The pattern of inheritance is simple, so future generations of color blind individuals can be easily predicted.

Will inherited color deficiency change with age?

No. The inherited alterations to color vision involve both eyes and remain stable throughout life.  

Can one develop color deficiency?

Yes, but not in the inherited form. A whole range of prescribed drugs, systemic conditions such as diabetes, multiple sclerosis and cardiovascular disease (including high blood pressure), some liver diseases and many eye diseases, can affect the cone receptor, color vision may be temporarily or permanently altered, often in one eye at a time. Difficulty in color discrimination may be noticed with other visual problems, such as overall blurring of near or distance vision, or gaps in the field of vision. Women and men are equally at risk.

Drugs prescribed for arthritis, depression and heart disease can, on occasion, significantly impair color vision. Even long-term use of aspirin can change color perception. Tobacco and alcohol taken in excess can have similar effects. Many industrial chemicals can permanently alter our appreciation of colors.

Glaucoma, cataract and most eye problems affecting the retina or nerve pathways to the brain can give gradually worsening problems with many different colors, including blues and greens. 

Since color vision changes can be an early indication of disease or a side effect of prescribed medication, it is important that you consult your doctor if you are aware that your appreciation of colors is changing.

Can color deficiency be a handicap?

Color is relevant to many aspects of everyday life and some jobs and careers do involve some degree of color identification. 

Many large companies involved with printing inks, textiles, paints and electronic components screen prospective employees and may refuse entry for certain jobs if color perception is inadequate.

Despite the introduction of instruments for color matching, the human eye is still the most sensitive instrument of all.

Although some people with abnormal color vision are not denied a driving license, there have been a few cases of death caused by people with faulty color perception driving through a red traffic light. In some countries, law prohibits color defective people from driving commercial vehicles.

Color also has a special place in the child’s world, being used as an aid to learning. Studies have failed to show any educational handicap resulting from faulty color vision, but parents, GPs and teachers may not necessarily be well informed on this subject. It is always sensible to inform teachers if a child is known to have difficulty in identifying colors.

Can anything be done to correct color deficiency?

Although nothing can replace a faulty mechanism in the retina of the eye – which is essentially a part of the brain – many color defective people do learn ways of compensating for their difficulty with experience and help from relatives and colleagues. It is important that good lighting is always available.

Many people find help, albeit limited, identifying certain colors that they would otherwise misname, with the aid of a small red or red-mauve filter of transparent plastic or glass held in front of the eye. Often red cellophane can help. This can be tried at home with a selection of transparent colored materials. There is no way of restoring the lost sensation or appreciation.

How can I have my color vision tested?

Straightforward clinical tests have been devised to screen for defective color vision, most taking only a matter of minutes. These involve reading colored numbers from a book or arranging colored papers in order, or naming colored lights. 

Optometrists can give such a test as part of an eye examination. Some school medical examinations may include color vision tests. If a detailed evaluation of color vision is required, a professional opinion should be sought.

- Information provided by the American Optometric Association -

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