By Linda Conlin, Pro to Pro Managing Editor

Researchers used to think that eye color was determined by a single gene and followed a simple inheritance pattern in which brown eyes were dominant to blue eyes. However, later studies showed that this model was too simplistic. The inheritance of eye color is more complex than originally suspected because multiple genes are involved. Most of the genes associated with eye color are involved in the production, transport, or storage of the pigment melanin. Eye color is directly related to the amount and quality of melanin in the front layers of the iris. People with brown eyes have a large amount of melanin in the iris, while people with blue eyes have much less.

While previous studies identified 10 to 12 genes associated with eye color, according to a recent article in ScienceDaily, researchers led by King's College London and Erasmus University Medical Center Rotterdam have identified 50 new genes for eye color in the largest genetic study of its kind to date. The study involved the genetic analysis of nearly 195,000 people across Europe and Asia. One finding of the study was that while many genes affect eye, hair, and skin color together, 34 genes associated with eye color had no affect on hair or skin color. The team also found that eye color in Asians with different shades of brown is genetically similar to eye color in Europeans ranging from dark brown to light blue.

There are several disorders that affect eye color. Ocular albinism is characterized by severely reduced pigmentation of the iris, which causes very light-colored eyes and significant problems with vision, such as diminished acuity, depth perception, nystagmus, strabismus, and photophobia. Another condition called oculocutaneous albinism affects the pigmentation of the skin and hair in addition to the eyes. Affected individuals tend to have very light-colored irises, fair skin, and white or light-colored hair. Both ocular albinism and oculocutaneous albinism result from mutations in genes involved in the production and storage of melanin. Another condition called heterochromia is characterized by different-colored eyes in the same individual. Heterochromia can be caused by genetic changes, a problem during eye development, or as a result of a disease or injury to the eye. Pigmentary glaucoma, in which pigment from the back of the iris is released and becomes trapped in the trabecular meshwork blocking it and leading to an increase in eye pressure, is presumed to be an inherited trait.

While the research continues, the findings from this study will aid in the understanding of eye diseases in which pigment plays a role. Learn how contact lenses can help patients with genetic eye conditions with our CE, Therapeutic Contact Lenses and Beyond, at