SAN FRANCISCO, CA—The June 2008 issue of Ophthalmology, the journal of the American Academy of Ophthalmology, includes a groundbreaking study on genetic factors and nearsightedness, a cautionary tale on age-related macular degeneration (AMD) patients’ vitamin use, and good news for people who have had an acute attack of optic neuritis.
Strong Evidence for a Genetic Marker for Nearsightedness
Research by Gu Zhu, M.D., and colleagues supports the theory that the refractive errors known as nearsightedness and farsightedness are primarily inherited. The group also identified the probable location---on the long arm of chromosome 5---of genes that help determine axial length, a key factor in these refractive errors. Axial length is a specific measurement from the front to back of the eye; this distance is longer than normal when a person is nearsighted and shorter than normal in a farsighted person. Dr. Zhu’s study focused on nearsightedness, or myopia, building on previous research on genetic aspects and environmental factors. Myopia compromises the eye’s ability to focus on and see objects clearly at a distance. Especially when myopia is severe, it is expensive to treat and costly to patients’ quality of life. The disorder is on the rise in the United States and globally and research efforts have intensified accordingly.
Dr. Zhu’s team recruited 893 individuals from the Tasmania Twin Eye Study and Brisbane Adolescent Twin Study (BATS), Australia, and obtained axial length measurements. They analyzed the proportional impacts of genetic and environmental factors on axial length in this sample of identical and fraternal twins, and found that genetic factors explained approximately 80 percent of the axial length values, after adjusting for age and sex. This study breaks new ground in linking axial length to the heritability of refractive error. Research team member David Mackey, M.D., said that new measurement techniques will likely make collection of axial length data routine in future research on myopia and other refractive error.
By performing a genome scan on a subset of 318 individuals, the researchers found “strong evidence” for the role of chromosome 5 (specifically the 5q region) in the inheritance of axial length. Dr. Zhu’s team has launched a genomic analysis of a larger study group to confirm and refine this finding. Other studies have suggested that environmental factors such as regular periods of outdoor play during childhood---rather than having children concentrate only on reading and other “near work”---might help reduce the development of nearsightedness, at least in those who are genetically susceptible. Identifying strong genetic markers could further this and other preventive efforts.
Vitamins Help Prevent Vision Loss from AMD---If Used Correctly
A study of individuals with age-related macular degeneration (AMD), based at the Wilmer Eye Institute, Johns Hopkins University School of Medicine, found that nearly 40 percent of those likely to benefit from specific vitamin/mineral supplements were either not taking the supplements or not using the recommended dosage. The study also showed that some patients used high-dose supplements even in the absence of evidence that these would be effective for their levels of AMD or other eye conditions. The ophthalmic researchers, led by Susan B. Bressler, M.D., concluded that AMD patients appear to lack a clear understanding of supplement use in AMD treatment, and that “improved patient education may be vital to maximize the potential” of this therapy.
The public health impact could be substantial: in the United States if the appropriate patients used the correct supplements, about 300,000 people could potentially avoid advanced AMD within a five year period. At least eight million Americans are at risk for advanced AMD which can destroy the central vision needed to recognize faces, read, drive and enjoy daily life. In 2001 the Age-Related Eye Disease Study (AREDS) reported findings on its clinical trial that identified a specific formula of antioxidants (vitamin C, vitamin E and beta-carotene) and zinc that reduced the probability of progression to advanced AMD by 25 percent— either the “wet” or central geographic atrophy forms---among individuals at risk. Those who have AMD and smoke may need to use a formula that omits beta-carotene since high doses of this micronutrient have been associated with increased rates of lung cancer and mortality. Though effective treatment for advanced AMD is available, it can be expensive and is limited to the “wet” form. Also, since such treatment may not restore vision already lost to the illness, it remains important to use all effective approaches to preventing AMD progression.
The Wilmer Institute-based study surveyed 332 individuals who identified themselves as having AMD; the median participant age was 79 years. Of these, 228 were considered candidates for benefit from the AREDS formula, but only 140 patients (61 percent) in this group were using the correct formula as recommended. Nearly 50 percent of the candidates-for-benefit did not correctly answer questions on the relevance of vitamin/mineral supplements to their eye condition and how their vision might benefit. But patients who indicated that they partially or fully understood the rationale for supplements were about twice as likely to be using the AREDS formula correctly.
Optic Neuritis Patients Recover Good Vision
What are the long term vision consequences when a person has an acute attack of optic neuritis, a sudden-onset eye disease of the nerves that carry visual signals to the brain" Are the consequences different if the person is treated with corticosteroids, or if the patient’s attack is complicated by having multiple sclerosis (MS)" The Optic Neuritis Study Group recently conducted a 15-year follow-up study of 454 patients who had acute optic neuritis--a disorder that is often the first sign of MS---in one eye and who participated in the Optic Neuritis Treatment Trial (ONTT), a 1988 – 1991 randomized clinical trial. Optic neuritis causes symptoms such as blurred vision, blind spots, dimmed colors and sometimes eye pain.
The researchers concluded that ophthalmologists (Eye MDs) can advise acute optic neuritis patients that the “long-term outlook for their vision is favorable,” even if they currently have or develop MS. Of the original ONTT study cohort, 294 patients completed the follow-up exam in 2006. Seventy-two percent of patients had 20/20 vision or better in the affected eye and 66 percent had 20/20 or better vision in both eyes. Mild decreases in vision (20/25 to 20/40) were attributed to lens changes in nine patients, which would be expected in an age group with an average age of 48, the life-stage when the eye’s lens becomes less flexible and many people need reading glasses. Long-term vision quality was similar among patients who were treated with high-dose intravenous corticosteroids and patients who were not, although the initial recovery period was shorter for treated patients.
Even though their vision was found to be normal about 60 percent of the time, the patients with MS were more likely to report somewhat reduced quality-of-life, including: difficulty with daily tasks like parking a car and using a computer, and problems such as double vision and trouble focusing on moving objects.
The study was funded by the National Eye Institute of the National Institutes of Health.
Eds: Full texts of the studies are available from the Academy’s media relations department.
About the American Academy of Ophthalmology
The American Academy of Ophthalmology is the world's largest association of eye physicians and surgeons—Eye M.D.s—with more than 27,000 members worldwide. Eye health care is provided by the three “O’s” – opticians, optometrists and ophthalmologists. It is the ophthalmologist, or Eye M.D., who can treat it all: eye diseases and injuries, and perform eye surgery. To find an Eye M.D. in your area, visit the Academy's Web site at www.aao.org.
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Ophthalmology