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Eyes, in this day and age, are under great duress. From unrelenting computer screens to incessant cigarette smoke and pollution, the conditions under which modern eyes function are less than supportive of good general eye health. Vision is one of the most prized of the senses, and even a slight loss of vision is cause for concern.

Humans enjoy the advantage of stereoscopic vision thanks to a pair of highly evolved, complex organs. At about one inch cubed, the eye is a small, multi-layered orb cushioned by fat in the orbital cavity of the skull. The eye consists of a number of delicate parts, each with a distinct role in collecting and processing light, transmitting vision signals to the brain, nourishing the eye with nutrient-rich blood or protecting the eye from harmful elements and activities.

Light enters through the cornea, is regulated by the iris aperture and passes through the lens, which focuses the light onto the retina. This light-sensing interior eye layer is comprised of rods, which handle low light vision, and cones, which handle color vision and detailed sight. In the back, center portion of the retina is a small, pigmented area called the macula, which is home to the cones. A fluid called rhodopsan converts light into electric pulses, which are channeled through nerve fibers extending from each cone. These fibers join shared fibers from the rod area of the retina and form the optic nerve behind the retina at the optic disk. This feeds the visual signals to the brain.

Other parts of the eye perform important supporting roles. The choroid layer (also called the uvea tract) contains blood vessels that feed the eye and houses the ciliary body, a muscular area that controls the shape of the lens. The shape of the eye is due largely to the sclera and two fluid/gel bodies: the aqueous humor enveloping the iris and the vitreous humor filling the larger interior part of the eyeball. The Canal of Schlemm is the draining point for the aqueous humor.

If any of these eye parts malfunctions or functions poorly, the health of the eye is jeopardized, increasing the risk of eye diseases and conditions. This sensory organ is very dependent on good nutrition for optimal health, making eye health a prime category for dietary supplement products. Research on the many natural substances indicated for use in eye health has been limited, but increased attention to these supplements is driving an upsurge in clinical trials in the area of nutrition and eye diseases. Of the more researched diseases and conditions, macular degeneration, cataracts, glaucoma, diabetic retinopathy and dry eye are among those that may benefit the most from nutritional support.

Age-Related Macular Degeneration (AMD)

Reading, driving and recognizing faces. These are a few common tasks that rely heavily on the eyes. Unfortunately, as many people age, both the rods and cones can deteriorate, damaging finely detailed vision. Some peripheral vision may remain, but central vision is progressively compromised, leading to the loss of vision-reliant functions.

Ninety percent of AMD patients suffer from "dry" AMD, which develops slowly and is characterized by dry, white macular deposits called drusen. One theory is that drusen results from a lack of antioxidants to clear eye waste. Robert Abel Jr., M.D., author of The Eye Care Revolution (Kensington Health, 1999), reported that the retinal pigment epithelium (RPE), a pigment layer under the retina, nourishes the macula and clears metabolic waste from the photoreceptor cells. He explained that aging sometimes leaves the RPE with insufficient antioxidant levels to perform waste removal. The waste then accumulates on the macula.

The other 10 percent of AMD patients suffer "wet" AMD, a severe and rapid condition caused by unhealthy blood vessels leaking into the retina. Symptoms of either form of AMD include blurry vision, loss of detail (especially in the center field of vision), straight lines appearing crooked and reduced color perception.

Dry Eye Dehydration, eye diseases and systemic diseases such as arthritis, lupus and Sjogren's disease cause dry eyes. The most common form is the lack of sufficient tear production. Eyes can feel gritty, have dry deposits or experience burning, itching and inflammation. EFAs (namely flaxseed oil), glucosamine sulfate (NSAID substitute), antioxidants, vitamin A (deficiency common in dry eyes), B vitamins, zinc, magnesium and water are all recommended non-drug remedies.

Conventional therapy for AMD is virtually non-existent compared to the nutritional supplement developments. Laser surgery for wet AMD is used to stop retinal bleeding, but Abel reported that its effectiveness is confined to early stages of the disease. Jay Lavine, M.D., author of The Eye Care Sourcebook (McGraw-Hill, 2001), noted that the laser surgery for wet AMD has not been very successful to date. "Since the laser treatment destroys the retina as well as the blood vessels [originating behind the center of the retina]...such treatment would be impossible...since it would wipe out the very vision it is intended to preserve," he explained. The condition can also return after an apparently successful surgery.

Hope for AMD prevention and treatment is coming from the natural products arena. Zinc and numerous antioxidants, foremost among them the carotenoids, form the base of the nutritional treatment of AMD. This is because antioxidants fight the oxidative damage that can contribute to AMD progression. Abel added, "Quite simply, the macula is very responsive to free-radical-fighting antioxidant nutrients."

Atop the list are lutein and zeaxanthin, two carotenoid antioxidants found in leafy green vegetables such as spinach and kale. Scientists have found that these two carotenoids are responsible for the yellow pigment of the macula. Lavine noted that lutein predominates in infant maculas, while zeaxanthin predominates in adult maculas.

Carotenoids such as lutein and zeaxanthin are vitamin A-related pigments that absorb light, which protects eye cells from light damage. They also help the retinal blood vessel-to-cone pathway, clearing debris and delivering nutrients. This family of nutrients has shown positive results on AMD prevalence.^{1, 2}

Vitamin A and its food source precursor beta-carotene have long been heralded as good for eye health. In fact, vitamin A deficiency has been linked to an increased prevalence of AMD.³ A study involving vitamin A concluded that carotenoid consumption decreased risk of wet AMD.⁴ However, there are hundreds of carotenoids, a few of which have provided researchers some positive results.

Clinical evidence on lutein and zeaxanthin in relation to AMD continues to mount. First, scientists discovered lutein and zeaxanthin as the two components of macular pigment.⁵ Then the research on AMD began to develop.

Scientists from Sweden reported significantly reduced formation of lipofuscin (which accumulates in aging retinal pigment epithelium) when the antioxidant substances lutein, zeaxanthin, lycopene or alpha-tocopherol were added to rabbit and bovine (calf) retinal pigment epithelial (RPE) cells.⁶ Other researchers have found that supplemental lutein and zeaxanthin may delay, avert or modify the course of AMD.⁷

Specifically, sufficient levels of these two carotenoids in the retina have been linked to a lowered risk of AMD.^8,9 They also combated ultraviolet oxidation in the eye.¹⁰ Lutein supplementation by itself led to a reduction in blue light reaching the photoreceptors, Bruch's membrane, and the retinal pigment epithelium, the vulnerable tissues affected by AMD.¹¹ Then, combined with vitamin A, lutein supplementation improved short-term vision in cases of retinal degeneration.¹²

Another antioxidant indicated as useful against AMD is vitamin C, which is present in high levels in the eye and is thought to protect against UV light. Also highly present in the retina is vitamin E, another protector from UV light. Flavonoids are strong antioxidants that mitigate the effects of AMD. Among the well-studied sources of flavonoids that lower the risk of AMD are those found in blueberries, grape seed extract and bilberries. Bilberry is known as a diuretic, refrigerant and astringent. It has been found to strengthen visual performance, reduce eyestrain and aid in the ability to focus and adapt to the dark, thus enhancing night vision. Bilberry extract, which contains the class of flavonoids known as anthocyanidins, may strengthen and reinforce the collagen structure of the retina, as well as decrease capillary fragility and permeability.

The supplemental mineral selenium is found in high amounts in the eye and is lauded for its antioxidant action against UV light. In the Eye Disease Case Control Study, a combination of carotenoid, selenium and vitamins C and E, when found in high levels, were associated with a lower risk of neovascular MD.¹³ Another antioxidant, the enzyme superoxide dismutase (SOD), has been found in low amounts in those suffering AMD. Low levels of lycopene, the red pigment antioxidant found in tomatoes and other red fruits, have also been linked to increased risk of AMD.

Beyond free radical hunters, zinc has generated some interest from AMD experts. The mineral is abundant in the retina and choroid areas of the eye, thus researchers have speculated on a connection between zinc supplementation improvements to AMD symptoms. Zinc has led to less vision loss,¹⁴ but has produced mixed results when administered in both low and high levels.¹⁵ Low levels had a protective effect, while high supplemental levels had a damaging effect on AMD. However, antioxidants and zinc reduced the visual acuity loss in AMD patients¹⁶ and stalled the progression of AMD.¹⁷

There are still more natural products for treatment and prevention of AMD. Similar to the action of many antioxidants, the amino acid taurine is plentiful in the retina and is thought to shield the eye from UV damage. Fellow amino acid and antioxidant glutathione is found in low levels in people suffering from AMD.

Cataracts

When the lens loses some of its transparency, cloudiness on the lens can be the result. This is known as a cataract, which inflicts more than half of all Americans over the age of 65, according to the National Eye Institute. Cataracts are categorized by the location of the opacity on the lens (center, peripheral, etc.). The lens contains a wealth of its own special proteins that can lose shape under attack from free radicals. Abel explained that these proteins then clump together, causing the lens to become opaque. Age, sunlight, diabetes, smoking and poor nutrition are all cause of cataracts.

Styes This infection of the eyelid is caused by staph bacteria and causes lid swelling  and eye inflammation. Chamomile-soaked compresses and natural bacteria fighting herbs such as echinacea, garlic and goldenseal are natural remedies for styes.

Conventional therapy for cataracts consists mostly of surgery, which is largely successful. Complications of cataract surgery include a migration of the cloudiness to the back of the eye, irregular pupil, retinal tear and detachment, corneal swelling, chronic eye inflammation and corneal infection.

Natural therapy for cataract treatment and prevention is primarily focused on antioxidant levels. Vitamins C, E and A, along with lutein and zeaxanthin, are the frontrunners in the category. Studies have shown an inverse relationship between levels of vitamin C and carotenoids and risk of developing cataracts.^{18, 19} Vitamin A and carotenoids also led to a reduced risk of cataracts (requiring extraction).²⁰ Vitamin C supplementation taken for at least 10 years was responsible for a reduced risk of cataract development in women in one Tufts University clinical trial. The results mirrored two previous studies, the Second National Health and Nutrition Examination Study (NHANES II) and the Beaver Dam Eye Study, the latter of which found that lutein intake was inversely associated to incidence of nuclear (central on the lens) cataracts²¹ and the former of which discovered that higher blood levels of vitamin C lowered risk of cataracts.²² The U.S Department of Agriculture (USDA) found that vitamin A precursors and vitamin E in the lens reduce oxidative damage.²³ For its part, vitamin E by itself reduced cataract risk by 50 percent.²⁴

Ocular Herpes Marked by eye, oral and genital lesions, this herpes simplex type I causes red eye, tears, irritation and some vision loss. Lysine balances herpes stimulants, while Juglans rogia (which contains quercitin) treats herpes infections. Olive leaf is another herb suggested to contribute antiviral and antibacterial actions.

Vitamins B2 (riboflavin) and B5 (pantothenic acid), as well as selenium and glutathione are other antioxidants considered effective in reducing free radical damage related to cataract formation. Abel reported that glutathione is vital to curbing free radicals and diligent at preventing cataract formation. Lenses with a cataract have shown decreased glutathione levels, as much as one-fifth the normal count. Lavine noted that riboflavin is a precursor to FAD (flavin adenine dinucleotide), an active antioxidant in the eye. In support of the connection, researchers found that people with cataracts had a riboflavin deficiency.²⁵ Where the benefit of extra dietary B2 would be increased FAD levels, the fear of supplementation with B2 is that it would increase the eye levels of riboflavin, which would lead to the production of more harmful oxidation. Niacin (vitamin B3) is another precursor to an antioxidant found in the eye. Coupled with riboflavin, niacin protected against cataracts in one study.²⁶

Polyunsaturated fats are also present in the lens, leading some scientists to investigate their possible role in affecting the incidence or progression of cataracts. One study concluded that essential fatty acids may play a sizeable role in preventing or treating cataracts.²⁷

Glaucoma

Irreversible damage to the optic nerve is the handiwork of glaucoma. The optic nerve is a virtual entanglement of millions of fibers, which die off under the activity of glaucoma. Though the damage must be severe to create vision loss, the lost fibers can result in blind spots. Researchers have not yet pinpointed the exact cause of the dying fibers, but a common thread in glaucoma is lack of blood flow to the retina and optic nerve. Without the necessary nourishment from blood, these eye elements tend to function improperly or not at all.

Retinitis Pigmentosa Often hereditary, pigmentosa is a slow deterioration of the retina that affects vision. Vitamin A is the main alternative remedy, as a deficiency of the nutrient is linked to pigmentosa. Fish oil or microalgae DHA, digestive enzymes and B vitamins are also indicated.

It was once thought that intraocular pressure (IOP), maintained by an exact amount of inner eye fluid, was the entire indicator of glaucoma. This proved to be not entirely true.²⁸ In fact, 40 percent of glaucoma patients have normal eye pressure. This is called chronic, open-angle glaucoma, which involves a sufficiently opened drain that may not filter the fluid very well.

However, a malfunction in eye fluid drainage can have dire effects. This is called closed angle glaucoma, which is responsible for 50 percent of glaucoma incidence worldwide. The increased pressure can burst capillaries and keep blood flow from the retina and optic nerve. This is often the case in people who are under a great deal of stress. Abel noted that the fluid does not drain as easily in stressed people.

In addition to these two primary types, circulation problems, as well as congestive heart failure and chronic obstructive lung disease can also block drainage.

Abel reported that people are more likely to suffer blindness from glaucoma than from cataracts, because cataracts are gradually degenerative and usually only limit vision. Glaucoma is dangerous, producing relatively no symptoms early in its development and affecting less noticeable peripheral vision first. About three million Americans experience some vision loss from glaucoma, while another two to three million are at risk of glaucoma.

Many conventional therapies exist, and the focus is on improved blood circulation and maintenance of proper eye pressure. Medications for controlling eye fluid include beta blockers, alpha agonists and carbonic anhydrase inhibitors. Beta blockers disrupt the nervous system pathway, thus exacting a possibly negative effect on heart rate, breathing, asthma, blood pressure and heart rhythm. They are often used in tandem with the carbonic anhydrase inhibitors. These enzyme inhibitors decrease eye fluid secretion but have been associated with negative side effects such as lethargy, fatigue, depression, impotence, nausea and poor appetite, according to Lavine. Alpha agonists limit eye fluid production but produce severe allergic reaction in as much as 30 percent of patients. Drugs such as Pilocarpine help fluid drainage by affecting pupil size. Common side effects include blurred vision, eye aches and poor night vision. A powerful hormone-like drug called latanoprost is very effective at lowering eye pressure but can be very expensive. Abel confessed that the other oft-cited drawback of this drug is that it can turn blue eyes brown. However, his patients have reported eye irritation and pain after long-term use. While these drugs are used for open angle glaucoma, surgery is the primary treatment for closed angle glaucoma.

Thankfully, there are many natural therapies for glaucoma. Exercise can reduce stress, as can many relaxation or meditation techniques. Digestion, especially of nerve nourishing vitamin B12, is important to glaucoma prevention and general eye health. Also, blood flow to the eye is impaired in smokers, thanks to nicotine, so foregoing cigarettes is a must for lowering risk of glaucoma.

People interested in supplements for prevention of glaucoma have a number of options. Increased EFAs in the diet can replace trans fats in the bloodstream; high levels of trans fatty acids have been found in glaucoma patients and those with elevated eye pressure. EFAs also improve circulation, which is crucial for retinal and optic nerve health. They further protect the retina's photoreceptor rods and cones and can even lessen stress. A deficiency of EFAs has been linked to decreased visual acuity.

Vitamin C again weighs in with eye health benefits, this time showing an ability to lower IOP drastically. This requires high dosages, however, so its use and effectiveness should be properly monitored. As is the case in other areas of eye health, vitamin A is indicated for its protection of photoreceptors, vitamin E taken with selenium supports retinal health, and the lutein-zeaxanthin duo are found in the aqueous humor, the eye fluid involved in glaucoma. B vitamins are also helpful. As previously noted, B12 protects the optic nerve and nerve fibers, especially in those who smoke or use alcohol. Folic acid can help control arterial blocking, including the retinal arteries, while B6 helps fatty acids attach to nerves.

Herbs can also be beneficial for people interested in preventing or treating glaucoma. Anthocyanins in bilberry inhibit vitamin C breakdown and strengthen capillary walls. It helps night vision in glaucoma patients. Ginkgo biloba is indicated for its vasodilation, opening of the blood vessels leading to improved blood flow. This herb has been found to increase blood flow to the ophthalmic artery, which supplies blood flow to the eye.²⁹

The Ayurvedic herb Coleus forskohlii reportedly lowers eye pressure. Abel cautioned that the herb has shown only temporary benefit, lowering blood pressure for just six months in most patients. Another Asian herb, the three-herb combination Trifola, decreases IOP by as much as 20 percent. Additionally, cnidium, citrus, capillaries and corydalis have improved retinal blood flow.

Exacting a less direct effect on glaucoma, flavonoids such as rutin can help glaucoma patients who are taking pilocarpine. Rutin was credited with lowering pressure in one clinical study.³⁰

Diabetic Retinopathy

Many diabetics develop blindness, though it is not a given development associated with the disease. It occurs in about six percent of diabetics with eye disease. The inability of diabetics to control blood sugar and energy levels can have devastating effects on the eye. "Diabetes can affect the entire eye," Lavine explained. High blood sugar (hyperglycemia) can contribute to eye disease by changing the amount of sugar in the lens, and high blood pressure can affect blood flow to the eye. The disease can also hinder the connection of cornea cells to deeper layers, rendering the cornea easily damaged, and can be detrimental to the health of cornea cells that keep fluid in the eye from clouding the cornea. Nerve damage in diabetics can cause double vision, and low blood sugar can contribute to double vision and light flashes. Research has even found that a too rapid fall in blood sugar in diabetics can cause some permanent clouding of the lens.³¹ Both cataracts and glaucoma are a bit more frequent in diabetics.

One of the biggest threats of diabetes to eye health is diabetic retinopathy. This condition develops when blood vessels feeding the retina become damaged and leak, causing a fluid build-up (edema) or even retinal detachment. The major vision problems begin when the build-up affects the macula. Lack of oxygen due to poor circulation to the retina can also cause retinopathy.

The primary conventional treatment for diabetic retinopathy is laser surgery, which involves burning parts of the retina to increase blood shares to the remaining retinal areas or eliminating small leakages. Laser treatment is often performed unnecessarily, and the burned retina can cause small blind spots. A vitrectomy can remove damaged eye fluid, which treats the symptom, but not the cause. Beyond procedures, a host of drugs are used to treat diabetes and insulin, but they come with a host of side effects.

Consequently, many natural remedies are indicated for use in general diabetes, but a great number of these substances are also specific to avoiding and relieving diabetic retinopathy.

The soy isoflavone genistein can help inhibit the growth of new blood vessels that occurs when oxygen is lacking. Squalene from shark liver oil has a similar effect. Soy and other cholesterol-lowering natural products also help, because higher cholesterol levels are associated with more hard exudates, the fat-rich deposits on the macula. EFAs can also contribute to decreased retinopathy by protecting photoreceptors from oxidative light damage.

The real focus of natural therapy on diabetic retinopathy is on the blood. Substances that strengthen blood vessels, improve blood flow, control blood sugar levels and arrest bleeding are vital to retinopathy patients.

For all its functions and benefits, vitamin C's primary action is in producing collagen and strengthening capillaries. The nutrient works even better when taken with the bioflavonoid quercitin, as they are both potent antioxidants that address capillary leakage. Bioflavonoids from bilberry also keep capillaries strong and even improve night vision. Research has indicated that bilberry results in less bleeding in the eye in diabetic retinopathy patients.³²

Other antioxidants including vitamins A and E are important for retinopathy diabetics. Many such patients have tested low in vitamin E, a nutrient that reduces platelet stickiness, which is more prevalent in diabetics. Magnesium also addresses blood stickiness, as a deficiency in this mineral has been linked to increased blood flow.

Ginkgo biloba is an important retinopathy herb due to its ability to inhibit platelet-activating factor (PAF), a substance that causes inflammation and blood clumping. It is also praised for reducing high blood viscosity, a problem in diabetics, increasing blood flow and relaxing the blood vessels (less likely to be damaged).

Natural substances are taking on a greater part of eye health, especially in prevention stages. The presence of many nutrients in the eye is a good indication of the potential for nutritional alternatives in relieving and evading the visual damage associated with AMD, cataracts, glaucoma, diabetic retinopathy and many other eye diseases and conditions. Knowledge of the nutritional anatomy and functions in the eye have helped researchers home in on these treatments and preventive substances and can help retailers offer their customers the best in natural eye health care.

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Article References

1. Handelman, G. The evolving role of carotenoids in human biochemistry. Nutr. 17, 10:818-22, 2001.

2. Goldberg, J. et al. Factors associated with age-related macular degeneration. An analysis of data from the first National Health and Nutrition Examination Survey. Am J Epidemiol. 128, 4:700-10, 1988.

3. Seddon, J. et al. Dietary carotenoids, vitamins A, C, and E, and advanced age-related macular degeneration. Eye Disease Case-Control Study Group. <I>JAMA. 272, 18:1413-20, 1994.

4. Sundelin, S and Nilsson, S. Lipofuscin-formation in retinal pigment epithelial cells is reduced by antioxidants.Free Radic Biol Med 31, 2:217-25, 2001.

5. Bone, R. et al. Preliminary identification of the human macular pigment. Vision Res. 25, 11:1531-5, 1985.

6. Beatty, S. et al. Macular pigment and risk for age-related macular degeneration in subjects from a Northern European population. Invest OphthalmolVis Sci. 42, 2:439-46, 2001.

7. Snodderly, d. Evidence for protection against age-related macular degeneration by carotenoids and antioxidant vitamins. Am J Clin Nutr. 62:1448S-1461S, 1995.

8. Bone, R. et al. Preliminary identification of the human macular pigment. Vision Res. 25, 11:1531-5, 1985.

9. Bone, R. et al. Lutein and zeaxanthin in the eyes, serum and diet of human subjects.Exp Eye Res. 71, 3:239-45, 2000.

10. Sujak, A et al. Lutein and zeaxanthin as protectors of lipid membranes against oxidative damage: the structural aspects.Arch Biochem Biophys. 371, 2:301-7, 1999.

11. Landrum, J. et al. A one year study of the macular pigment: the effect of 140 days of a lutein supplement.Exp Eye Res. 65, 1:57-62, 1997.

12. Dagnelie, G. et al. Lutein improves visual function in some patients with retinal degeneration: a pilot study via the Internet.Optometry. 71, 3:147-64, 2000.

13. Christen, W. et al. Design of Physicians' Health Study II--a randomized trial of beta-carotene, vitamins E and C, and multivitamins, in prevention of cancer, cardiovascular disease, and eye disease, and review of results of completed trials.Ann Epidemiol. 10, 2:125-34, 2000.

14. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 119, 10:1417-36, 2001.

15. Ugarte, M. and Osborne, N. Zinc in the Retina. Prog Neurobiol. 64, 3:219-49, 2001.

16. Larkin, M. Vitamins reduce risk of vision loss from macular degeneration.Lancet. 358, 9290:1347, 2001.

17. Jampol, L. and Ferris, F. Antioxidants and zinc to prevent progression of age-related macular degeneration.JAMA. 286, 19:2466-8, 2001.

18. Taylor, A. et al. Long-term nutrient intake and early age-related nuclear lens opacities.Arch Ophthalmol. 119, 7:1009-19, 2001.

19. Gale, C. et al. Plasma antioxidant vitamins and carotenoids and age-related cataract. Ophthalmol. 108:1992-98, 2001.

20. Chasan-Taber, L. et al. A prospective study of carotenoid and vitamin A intakes and risk of cataract extraction in US women. Amer J Clin Nutr. 70:509-16, 1999.

21. Simon et al. Serum ascorbic acid and other correlates of self-reported cataract among older Americans. J Clin Epidemiol. 52, 12:207-11, 1999.

22. Mares-Perlman, J. et al. Association of zinc and antioxidant nutrients with age-related maculopathy. Arch Ophthalmol. 114, 8:991-7, 1996.

23. Taylor, a. et al. Effect of photooxidation on the eye lens and role of nutrients in delaying cataract.EXS. 62:266-79, 1992.

24. Lyle, B. et al. Serum carotenoids and tocopherols and incidence of age-related nuclear cataract. Am J Clin Nutr. 69, 2:272-7, 1999.

25. Skalka, H and Prchal, J. Cataracts and riboflavin deficiency. Amer Clin J Nutr. 34, 5:861-3, 1981.

26. Cumming, R. et al. Diet and cataract: the Blue Mountain Eye Study. Ophthalmol. 107, 3:450-6, 2000.

27. Borchman, D. et al. Regional and age-dependent differences in the phospholipid composition of human lens membranes. Invest Ophthalmol Vis Sci . 35, 11:3938-42, 1994.

28. Klein, B. et al. Prevalence of glaucoma. The Beaver Dam Eye Study. Ophthalmol. 99, 10:1499-504., 1992.

29. Chung, h. et al. Ginkgo biloba extract increases ocular blood flow velocity. J Ocul Pharmacol Ther. 15, 3:233-40, 1999.

30. Stocker, F. et al. Clinical experiments with new ways of influencing intraocular tension. Effect of Rice diet. Arch Ophthalmol. 40:46-55, 1948.

31. Kato, s. et al. Influence of rapid glycemic control on lens opacity in patients with diabetes mellitus. Am J Ophthalmol. 130, 3:354-5, 2000.

32. Perossini, M. et al. Clinical study of bilberry anthocyanosides in the treatment of diabetic and hypertensive microangiopathy of the retina. Ann Ottalm E Clin Ocul. 12:1173, 1987.