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Clinical studies establish role of nutrition in treating eye disease
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Clinical studies have shown a correlation between nutrition and some ocular diseases, but these data do not apply uniformly to all ocular maladies. While nutrition has been definitively linked to age-related macular degeneration, clinical findings on diseases such as glaucoma are comparatively sparse.
“There is a definite connection between nutrition and eye disease,” said Robert Abel Jr., MD, author of The Eye Care Revolution and The One Earth Herbal Sourcebook. “This also goes along with choosing healthy options, such as not smoking, maintaining your weight and carefully managing other diseases you might have.”
AMD: highly responsive to nutrition
One recognized source of data regarding nutrition and eye disease is the Age-Related Eye Disease Study (AREDS), a major clinical trial sponsored by the National Eye Institute. The AREDS study found that high levels of antioxidants and zinc significantly reduce the risk of advanced age-related macular degeneration (AMD) by about 25%. These same nutrients also reduce the risk of vision loss caused by advanced AMD by about 19%.
Dr. Abel discussed the results of the AREDS study and its bearing on AMD treatment. “The study stated that a combination of beta carotene (15 mg), vitamin C (500 mg), vitamin E (400 IU) and zinc (80 mg) significantly retards vision loss of moderate and advanced macular degeneration,” Dr. Abel said. “In fact, they had to end the study early, because the results were becoming so obvious, and the researchers felt compelled to offer the placebo group the same benefits.”
Dr. Abel also discussed with Primary Care Optometry News the role of lutein, which was not included in the AREDS study. “The primary carotenoid in the eye was not included in the AREDS study because it was not yet commercially available at the time the study was organized,” Dr. Abel said. “However, a great deal of scientific studies demonstrate a clear association between a diet rich in lutein and a decreased risk of AMD.”
Dr. Abel cited studies conducted on lutein by Dr. Paul Bernstein at the University of Utah. The researchers looked at autopsy eyes and found that those eyes with the least macular degeneration were those with the highest levels of lutein in the retina and pigment epithelium.
“It is a definite correlation,” Dr. Abel said. “Multiple studies show that if you take it by mouth, it is reflected within a week in your blood and within a month in the pigment density of your eye.”
Dr. Abel said there are other important nutrients that are helpful in combating AMD. One such nutrient is dicosahexanoic acid, which is the end product of the omega 3 essential fatty acids.
“DHA is part of every cell membrane in the body,” Dr. Abel said. “Because the retinal receptors are constantly breaking down and building up, you need the essential fats, especially DHA, vitamin E and lutein, which are fat-soluble vitamins.”
Antioxidants, cataracts: negligible effect
Studies have been more ambiguous regarding the relevance of nutrition in slowing the progress of cataracts. According to Leo P. Semes, OD, FAAO, a practitioner from the UAB School of Optometry, the AREDS study concluded that antioxidants had a negligible effect on cataract formation.
“The study demonstrated that there was no effect from antioxidant supplementation on the risk of cataract formation,” Dr. Semes said. “That was the bottom line.”
Dr. Semes said the AREDS study looked at 4,600 patients who were followed for 7 years. Over the course of the study, the antioxidants reportedly failed to reduce the risk or confer protection of lens opacities.
However, Dr. Semes cited two studies done in China in 1993 that showed some correlation between nutritional supplements and cataracts. “One study involved more than 2,000 patients, and the other involved more than 3,000 patients,” he said. “They showed that there might be some reduced risk of nuclear opacities in folks who took vitamin and mineral supplements.”
The patient population who seemed to show the most benefit in both studies was the 65- to 75-year-old age group, Dr. Semes said. “What that suggests is that patients in the older age groups may be at greater risk and therefore show the greatest benefit,” he said. “So, in terms of overall nutritional health, these folks may be at risk because of a nutritional deficit in their everyday eating habits. For that reason, supplements may do more good for them.”
Dr. Semes said those studies were followed up by a “snapshot study” in 1995. In this study, researchers analyzed patients’ blood samples for carotenoids. “They found no association with either nuclear or cortical cataract protection,” he said. “But there may have been some subgroups who showed some protective effect.”
Among those who benefited from this “slightly protective effect” were male smokers, Dr. Semes said. “This could be because smokers have poorer nutritional habits,” he said, “and so the antioxidant supplementation in this case may have exerted some protective effect, such as lowering cholesterol.”
Despite the questionable data regarding cataracts and nutrition, Dr. Semes said he would still recommend supplements in certain situations. “The water-soluble vitamins will probably not be harmful,” Dr. Semes said. “But it is probably good for us to at least encourage nutrient-rich and nutrient-dense diets for our patients.”
Dr. Semes said the natural absorption of nutrients through diet is almost always the safest approach. “We don’t want to rely on vitamins as a ‘magic bullet’ or a magic substitute,” he said. “Vitamin and mineral supplements are not scrutinized by the Food and Drug Administration, and based on the scientific evidence, their effectiveness is limited.”
Dry eye: encouraging possibilities
Practitioners are finding that certain nutritional supplements are helpful in negating dry eye. Charles G. Connor, Jr., OD, PhD, FAAO, a professor at the Southern College of Optometry, has found borage oil to be useful for this purpose.
“I actually use borage oil (1,500 mg/day) most often, because it has a product called gamma-linoleic acid (GLA) in high concentration,” Dr. Connor said. “This is an essential fatty acid that comes primarily from plant-based oils. It fits into the arachidonic acid cascade, which produces prostaglandins. This gives patients a way of feeding precursors into the prostaglandin pathway to generate an anti-inflammatory response.”
Dr. Connor said the use of gamma-linoleic acid can be a safer alternative to oral or topical steroids. “It is becoming pretty apparent that dry eye has an inflammatory component. Anti-inflammatories can definitely calm down the eye, especially the inflammations in the lacrimal glands and eyelids,” he said. “So by taking gamma-linoleic acid, you get a similar anti-inflammatory effect without the toxic effects of a steroid.”
One impediment to gamma-linoleic acid as opposed to steroids is the amount of time it takes to work, Dr. Connor said. “With a steroid, you get a quick response, because it acts directly on the inflammatory pathway,” he said. “With something like gamma-linoleic acid, you are probably looking at a 6-week delay until the body builds a large enough reservoir to give a beneficial response.”
Dr. Connor said he has not had much success with flaxseed oil, which is touted by some practitioners as being effective for dry eye. “There are some doctors who have had success with flaxseed oil, but I don’t know how they measured benefit,” he said. “I assess the effectiveness of a dry eye treatment by improvement in Schirmer’s test and tear breakup time.”
Dr. Connor said he has had patients who have reported feeling better after using flaxseed oil. “Sometimes that happens – with a dry eye treatment, you get subjective improvement but no objective results. You have to factor that into your treatment decision,” he said. “To be fair to doctors who really like flaxseed oil, I haven’t had a large enough patient base using it to be 100% sure that it doesn’t work.”
Glaucoma and nutrition: studies ongoing
Although nutrition’s effect on glaucoma has not been studied as extensively as with the other ocular diseases, it is an area where the focus is increasing.
“There have been studies on the correlation between glaucoma and nutrition,” said Steven G. Pratt, MD, a practitioner located in La Jolla, Calif. “There are data linking certain nutrients to glaucoma.”
Dr. Pratt explained that there are high levels of carotenoids, especially lutein and zeaxanthin, in the ciliary body. “This suggests that carotenoids might function as antioxidants in the tissue,” he said. “Their usefulness in treating glaucoma remains to be explored.”
Dr. Pratt cited several studies regarding glaucoma and nutrition. The first of these involved the potential role of ginkgo biloba extract in treating the disease.
The study was performed at the Glaucoma Research and Diagnostic Center, Department of Ophthalmology, Indiana University Medical Center by Chung and colleagues. A phase I crossover trial of ginkgo biloba extract with placebo control in 11 healthy volunteers (eight women, three men) was performed. Patients were treated with either ginkgo biloba extract 40 mg or placebo three times daily orally for 2 days.
It was found that gingko biloba extract significantly increased end diastolic velocity (EDV) in the ophthalmic artery (baseline vs. gingko biloba extract treatment; 6.5 ± 0.5 vs. 7.7 ± 0.5 cm/sec, 23% change), with no change seen in the placebo (baseline vs. ginkgo biloba extract treatment; 7.2 ± 0.6 vs. 7.1 ± 0.5 cm/sec, 3% change). No side effects related to ginkgo biloba were found. Ginkgo biloba extract did not lower arterial blood pressure, heart rate or IOP.
Dr. Pratt also referred to an article by Robert Ritch, MD, which found that ginkgo biloba has “several biological actions, which combine to make it a potentially important agent in the treatment of glaucoma.”
These actions include the improvement of central and peripheral blood flow, reduction of vasospasm, reduction of serum viscosity, antioxidant activity, platelet activating factor inhibitory activity, inhibition of apoptosis and inhibition of excitotoxicity.
Studies have also been performed on the role of fatty acids in treating glaucomatous optic neuropathy.
One such study, conducted at the University of Bologna, evaluated 30 chronic open-angle glaucoma patients in good tensional compensation with local therapy. These patients were given a combination drug comprised of docosahexaenoic acid (DHA), vitamin E and vitamin B complex.
The results show significant differences after 90 days of treatment both in perimetric indices and in the Retinal Contrast Sensitivity (RCS) frequency values. It was concluded that this combination of nutrients is a useful support for preventing or delaying the process of damage. Other nutrients which show promise in glaucoma treatment, according to Dr. Pratt, include lipoic acid, vitamin C, magnesium, and melatonin.
Clinical studies continue to examine the link between nutrition and glaucoma, Dr. Pratt said.
“In the meantime, don’t forget to exercise, as numerous studies demonstrate a pressure-lowering effect of this health-promoting activity,” he said.
For Your Information:
- Robert Abel Jr., MD, is a practitioner based in Delaware and is the author of The Eyecare Revolution and The One Earth Herbal Sourcebook. He can be reached at Concord Plaza Naamans Building, 3501 Silverside Road, Wilmington, DE 19810; (302) 479-3937; fax: (302) 477-2650.
- Leo P. Semes, OD, FAAO, is an associate professor at the UAB School of Optometry in Birmingham, Ala., and a Primary Care Optometry News Editorial Board member. He can be reached at UAB School of Optometry, 1716 University Blvd., Birmingham, AL 35294-0010; (205) 934-6773, ext. 5161; fax: (205) 934-6758.
- Charles G. Connor Jr., OD, PhD, FAAO, is a professor at the Southern College of Optometry. He can be reached at 1245 Madison Ave., Memphis, TN 38104; (901) 722-3346; fax: (901) 722-3275.
- Stephen G. Pratt, MD, is a practitioner based in La Jolla, Calif. He can be reached at 9850 Genesee Ave., La Jolla, CA 92037-1205; (858) 457-3010; fax: (858) 457-0028.