Genetics is a complex field with genes passed down from parents, grandparents, even great-grandparents, and having an influence on areas ranging from hair or eye colour to medical conditions. Heredity can increase our risk of developing a number of chronic health conditions including some that impact eye health and vision. Many eye diseases develop gradually with no symptoms in the early stages. Although their occurrence does not depend exclusively on genetic factors, lifestyle and environmental factors have a contribution to make, understanding our family history can play a vital role in being aware of potential problems and managing them before they become serious.
Recent research has revealed that a significant number of ocular conditions are genetically linked and passed down through generations. Some conditions do not pass directly from parents to offspring but may miss a generation and manifest in later generations, while others may be influenced by multiple genes. Even then, their cause may be an interplay of genetic, environmental and lifestyle factors. It is important to be proactive by learning your family history and sharing it with your optometrist.
Genetics is believed to play a major role in many forms of glaucoma, a condition that irreversibly damages the optic nerve due to pressure build-up within the eye. If left untreated it leads to vision loss and is one of the leading causes of blindness worldwide. Having a family member with glaucoma significantly increases the risk of developing it.
Another cause of blindness, age-related macular degeneration (AMD) seems to be inherited in a large proportion of cases, although not all types of AMD are hereditary. If age-related macular degeneration (AMD) runs in your family, you have 50 percent chance of developing it, which is four times the risk compared to people who do not have relatives with the condition.
If you have close relatives who have had cataracts, you have a greater chance of developing them than those without a family history. The success rate for patients who undergo cataract surgery is high, but it is important to detect the condition early before it impacts vision and quality of life.
Inherited retinal diseases are a group of eye diseases that include retinitis pigmentosa, a progressive degenerative disease that eventually causes night blindness and affects peripheral and central vision, which are essential for reading, driving and recognising faces. While rare, inherited retinal disease can affect individuals at any age and progress at different rates. Significant progress is being made in identifying the genes that play a role in causing these conditions.
The most common visual disorders are refractive errors. These occur when the shape of the eye prevents light from being focused correctly on the retina, and include myopia (shortsightedness), hyperopia (farsightedness) and astigmatism. There is growing evidence that the risk of refractive errors in otherwise healthy eyes is significantly increased for individuals whose parents have a refractive error. Included in this list is amblyopia ('lazy eye') and strabismus (misalignment of the eyes or 'cross-eyes'). Up to 40% of patients with certain types of strabismus have a family history of the condition.
Among infants, more than 60% of cases where blindness has occurred are caused by inherited eye diseases such as congenital cataracts, congenital glaucoma, retinal degeneration, optic atrophy and eye malformations.
Less common eye disorders that are inherited include albinism, choroideremia (which affects the blood supply to the retina), corneal dystrophies (in which the cornea loses clarity and becomes cloudy), keratoconus (thinning and eventual bulging of the cornea), retinoblastoma (a rare cancer of the eye) and colour vision deficiencies.
Over and above these vision conditions it is estimated that eye abnormalities accompany approximately one third of inherited systemic diseases, such as diabetes and cardiovascular disease. In fact, the presence of the eye condition is often the most important factor in confirming a diagnosis. It is frequently detected by an optometrist during a routine eye examination before symptoms of the systemic disease have appeared.
Early detection is the key to the treatment and management of health conditions. Regular eye examinations coupled with sharing your knowledge of your family's health history with your optometrist so that he is aware of what to look out for is the key to early detection of visual problems.