Poor colour vision, which is usually an inherited condition, is a reduced ability to distinguish between certain colours. On contrary to the so called colourblind-condition, where the patient lacks colour vision, in the state of poor colour vision, the patient’s ability to discriminate between colours is reduced. Most people with poor colour vision can't distinguish between certain shades of red and green. Less commonly, people with poor colour vision can't distinguish between shades of blue and yellow.
A person may have poor colour vision and not know it. Some people figure out that they have the condition when it causes confusion when they have problems differentiating the colours in a traffic light or interpreting colour-coded learning materials. People affected by poor colour vision may not be able to distinguish:
- Different shades of red and green
- Different shades of blue and yellow
- Any colours
The most common colour deficiency is an inability to see some shades of red and green. Often, a person who is red-green or blue-yellow deficient isn't completely insensitive to both colours. Defects can be mild, moderate or severe.
Poor colour vision can be caused by certain eye diseases and some medications.
Seeing colours across the light spectrum begins with the eyes' ability to distinguish the primary colours red, blue and green. Namely, light enters the eye through the cornea and passes through the lens and the tissue in the eye to colour-sensitive cells at the back of the eye in the retina. Chemicals in the cones distinguish colours and send that information through the optic nerve to the brain. If the eyes are normal, a person can distinguish different colours, but if the cones lack one or more light-sensitive chemicals, then they may see only two of the primary colours.
Poor colour vision has several causes:
- Inherited disorder. Inherited poor colour vision is much more common in males than in females. One person can inherit a mild, moderate or severe degree of the disorder that usually affects both eyes and the severity doesn't change over the lifetime.
- Diseases, such as diabetes, glaucoma, macular degeneration, Alzheimer's disease, Parkinson's disease, chronic alcoholism, leukemia and sickle cell anemia. One eye may be more affected than the other, and the colour deficit may get better if the underlying disease can be treated.
- Certain medications, as some drugs that treat heart problems, high blood pressure, erectile dysfunction, infections, nervous disorders and psychological problems.
- Exposure to some chemicals in the workplace, such as carbon disulfide and fertilizers, may cause loss of colour vision.
Men are more likely to be born with poor colour vision than women.