The exact cause of color vision deficiency is unknown. In most individuals, the condition is an inherited disorder and around 5% of the general population are color vision deficient.
Inheritance patterns of color blindness
Studies have shown that at least 19 different chromosomes and many different gene alterations are involved in color vision deficiencies. However, the condition is mostly inherited on the X chromosome. Males are at a greater risk of color vision deficiency than women, with 5% to 8% of the male population suffering from the condition compared with less than 1% of females. This is because males are more likely to inherit an X- linked disorder, owing to the fact that they only inherit one X chromosome. Women inherit two copies of the X chromosome and the mutation for color deficiency would need to be present on both of these chromosomes for a woman to develop the condition.
In inherited color vision deficiencies, symptoms may appear at any time through childhood or later on in adulthood. If a person has a progressive form of deficiency, the retina and other parts of the eye degenerate over time, eventually leading to vision that is poor enough to classify as blindness (6/60 vision).
Diseases that may cause color vision deficiency
Some inherited diseases can also cause color blindness. These include:
- Cone dystrophy
- Cone-rod dystrophy
- Retinitis pigmentosa
- Age-related macular degeneration
- Diabetes mellitus
- Leber’s congenital amaurosis
- Shaken Baby Syndrome
- Optic neuritis or inflammation of the optic nerve
- Sickle cell anemia
Other causes of color vision deficiency
Certain medications can cause color vision deficiency as a side effect. Some examples include digoxin (used in heart failure), ethambutol (used in tuberculosis), chloroquine (used in malaria treatment), hydroxychloroquine and phenytoin (used in treatment of epilepsy) and sildenafil or viagra (used in erectile dysfunction). Certain chemicals and pollutants such as carbon disulfide and styrene may also affect color vision. In addition, aging also causes deterioration of color vision.