Lipoic Acid
Lipoic acid may support health in people with cataracts and diabetic neuropathy by reducing the glycosylation of proteins, preventing oxidative stress, improving blood flow to nerves, and improving glucose utilization. It is a fat- and water-soluble antioxidant with the ability to cross the blood-brain barrier and powerfully deactivate a broad range of free radicals. Lipoic acid mimics less powerful antioxidants like vitamins C and E, recycles dietary antioxidants like vitamin E, and raises glutathione levels (1).

Ginkgo Biloba Extract
Ginkgo biloba may protect macular health in multiple ways. It is an effective free radical quencher and membrane stabilizer, and it increases ocular blood flow through vasodilation and inhibition of platelet aggregation. Ginkgo acts synergistically with bilberry and grape seed in stabilizing the collagen matrix and the glycosaminoglycan matrix that help make up the lining of the arteries and micro vessels that feed the retina. In a double-blind study, Ginkgo biloba intake increased visual acuity in individuals suffering from ARMD (2-4).

Bilberry
Bilberry contains flavonoid compounds known as anthocyanosides. Anthocyanosides are potent antioxidants and vascular stabilizers. Anthocyanosides improve ocular microcirculation and protect the vascular endothelium. Bilberry is used extensively in Europe and has demonstrated efficacy in reducing myopia and improving night vision.

N-Acetyl Cysteine
N-acetyl cysteine is a derivative of the sulfhydryl amino acid, cysteine, which is converted into glutathione by endothelial cells. Cysteine is often called the rate-limiting factor in the production of glutathione, a key component in the free radical protection system of the eye. N-acetyl cysteine has cytoprotective, antioxidant effects on the human endothelium by directly scavenging reactive intermediates rather than by stimulating glutathione synthesis. N-acetyl cysteine protects against nitric oxide, ameliorates oxidant injury and helps prevent the development of a hyperdynamic circulation (5,6).

Vitamins C and E
Studies indicate that impaired endothelial vasodilation can be improved by raising antioxidant defenses. A prospective analysis of participants in a large study found that vitamin E intake was inversely associated with development of early cortical opacities (7).

Increasing concentrations of ascorbate in the aqueous humor through vitamin C supplementation can reduce intraocular pressure (IOP) (8). The IOP-lowering action of vitamin C is due to its ability to improve collagen formation, increase blood osmolarity, improve aqueous outflow, inhibit lipid peroxidation, and raise glutathione levels. A study at Tufts University found that supplementation with vitamin C over a 10-year period has been associated with a 77% lower prevalence of early lenticular opacities in a group of women (9).

Carotenoids
Studies have shown that elevated serum carotenoid levels may support eye health(10). A well-balanced mixture of carotenoids is important because different structures of the eye concentrate and use different carotenoids. For example, in contrast to beta-carotene, lutein and zeaxanthin are found in the lens where they protect against free radical damage (11,12). These carotenoids are also found in the retina, where they serve as integral components of the macular pigment. As such, they protect photoreceptors from light-generated oxygen free radicals and thus support macular health. Supplementation with lutein and zeaxanthin may be beneficial to the macula by increasing protective macular pigmentation (13).

Selenium
The mineral selenium is necessary for the integrity of the microvasculature of the retina and the antioxidant defense system in the eye. It is a cofactor for the enzyme glutathione peroxidase, which defends against damaging free radicals. Low Selenium levels, which reflect decreased antioxidant defenses, have been detected in the lens of patients with senile cataracts (14). Increased intake of selenium, in conjunction with other antioxidants including the carotenoids and vitamins C and E, is associated with a protective effect on macular health (15).

Lutein
Lutein is a xanthophyll that protects photoreceptors from light-generated oxygen free radicals and thus promotes macular health. It is also an important macular pigment. Lutein promotes gap junction communication between cells and inhibits lipid peroxidation.

Taurine
The sulfur-containing amino acid, taurine, is concentrated in the eye where it is essential for retinal function. Taurine protects photoreceptors from free radical damage, controls ion flux, and regulates signal transduction. Taurine deficiency has been associated with significant negative impact on the macula (16). Taurine also may assist retinal macrophages in the elimination of debris from photoreceptor cells that are continually dying and being replaced. It may also help promote healthy ganglion cells and optic nerve function (17).

Zinc
Zinc plays a role in the metabolic function of several important enzymes in the chorioretinal complex, and is an essential constituent of the major form of the antioxidant enzyme, superoxide dismutase (SOD), which is present in all cell types. Studies suggest that zinc is important for the protection of retinal pigment epithelium and photoreceptor cells. Zinc deficiency has been shown to impact the health of the macula (18). In a recent double-blind study, less visual acuity loss was observed in ARMD patients who received zinc supplementation (19).