Genetic Eye Problems

Genes are the portion of DNA that determine traits such as eye color or height. Genetic disorders may run in families. A child may inherit a specific eye disease such as Stargardt’s disease or a complex developmental disorder such as Turner’s syndrome that involves visual abnormalities. Eye problems may also be caused by a random mutation–or alteration to a gene that causes an abnormality.

Men and women have a pair of “sex chromosomes” in each cell. The woman’s pair is made up of what is called XX chromosomes and the man’s pair is made up of the XY chromosomes. The embryo will receive an X chromosome from each parent and either a second X chromosome from the mother (to produce a girl) or a Y chromosome from the father (to produce a boy). Inherited eye abnormalities may be carried on either the X or Y chromosome and they are classified as either “dominant”, “recessive” or “sex-linked.” Dominant genetic disorders occur when the trait is linked to either the X or Y chromosome received from one parent. A recessive disorder requires the abnormal trait to be carried by a cell from both parents. A parent may actually be a carrier for a genetic disorder such as color blindness without actually manifesting symptoms. Sex-linked genetic disorders are those that affect only children of one sex. For example the gene for ocular albinism is on the X chromosome and is carried by women, but transmitted to sons.

Stargardt’s Disease

Stargardt’s disease is transmitted when both parents carry the recessive gene. It typically develops during childhood as the macula gradually degenerates causing destruction to the child’s central vision. The “macula” is an area of the retin–the light sensitive part of the eye that functions much like a camera. The macula has the largest concentration of cells responsible for sharp, central vision. Stargardt’s disease is usually active for about 10 years and then stabilizes.

Retinitis Pigmentosa

Retinitis pigmentosa (RP) has several different forms and may be passed along as a dominant, recessive or X chromosome-linked gene. RP involves progressive damage to the retina–first impacting night vision and then causing gradual loss of peripheral vision (vision from the sides). Symptoms often begin in early adulthood with gradual vision loss causing “legal blindness” when patients reach their forties or fifties. Legal blindness is defined as visual acuity of less than 20/200 in the best corrected eye or a visual field of less than twenty degrees.

Color Blindness

The gene for color blindness is on the woman’s X chromosome, and women often pass the disorder on to their sons without experiencing it themselves. Individuals with color blindness may have difficulties discriminating shades of colors or have total absence of color perception so that the world looks gray. The most common form of the disorder involves inability to differentiate red and green.

Eye Problems in Cri-du-chat Syndrome

Children with cri-du-chat have part of chromosome 5 missing, resulting in severe mental and motor delays, including what is called “strabismus.” In persons with strabismus, one or both eyes turn inward or outward and the eyes do not work together to enable depth perception. The name of the disorder reflects the high- pitched sound these babies make, which sounds like a cat.

Eye Problems in Turner’s Syndrome

Children with Turner’s syndrome have part of or all of an X chromosome missing. Persons with this syndrome have many physical symptoms and health problems, including drooping eyelids, strabismus, glaucoma (decreased visual field) and damage to the cornea (the transparent front of the eye that refracts light).

Eye Problems in Down’s Syndrome

Down ‘s syndrome involves an extra chromosome that causes developmental delays. These children experience far higher rates of poor focusing (acuity), strabismus and astigmatism. About 30% of school age children with Down’s syndrome have an astigmatism that causes the two eyes to have different acuity levels.

Ocular Albinism

Individuals with ocular albinism lack eye pigment even though their skin and hair are of almost normal color. Other symptoms include reduced acuity, strabismus, light sensitivity and nystagmus. Nystagmus is a condition of involuntary eye movements, making it difficult to focus. In most cases, ocular albinism is passed from mother to son because the gene is on the X chromosome. A less common form involves both parents carrying the recessive gene, and in such cases boys or girls can inherit the disorder.

About this Author

Barbara Smith, M.S., OTR/L, is a graduate of Tufts University with more than 30 years of experience working with children and adults with disabilities. She is the author of “The Recycling Occupational Therapist” — a guide to designing and fabricating therapeutic activities and “Still giving Kisses: A Guide to Helping and Enjoying the Alzheimer’s Victim You Love.”