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Antioxidants May be Beneficial in Glaucoma

Glaucoma

Glaucoma affects 3-4 million Americans according to the National Eye Institute. Worldwide, it affects about 90 million people and is the leading cause of irreversible blindness. The most common form, open-angle glaucoma, is often referred to as the "silent thief" because most people with undetected glaucoma don't suffer from symptoms until they begin to lose their peripheral vision. The term glaucoma really refers to a group of diseases that share a common problem: a gradual degeneration of the cells that make up the optic nerve.

The optic nerve is a bundle of over one million nerve fibers that conduct electrical signals from the light-sensing retina at the back of the eye to the brain. Also called the "nerve of sight", the optic nerve is an essential link between the eye and the brain that makes vision possible.

Damage to the Optic Nerve

In many cases of glaucoma, damage to the optic nerve is caused largely by increased pressure in the eye that results from fluid build-up. However damage can also occur even when eye pressure is normal. Many clinicians now view glaucoma as a neurodegenerative disease - one caused by damage to, and loss of nerve cells - rather than a disease of elevated eye pressure alone (1). Although it's not known exactly how the optic nerve is damaged in glaucoma, poor or disordered blood flow to the retina and optic nerve appears to play a role. When blood supply to the nerve is interrupted, it slows the delivery of vital oxygen and nutrients, leading to cell damage or death.

Ginkgo Biloba Improves Vision

The botanical Ginkgo biloba is popularly known for its beneficial effects on brain function and memory in older people (2). This herbal can enhance cerebral blood flow and provide antioxidant activity. Because ginkgo has also been shown to increase ocular blood flow (3), its effect on visual field damage in glaucoma patients with normal eye pressure was recently evaluated in a double-blind trial (visual field is the amount of space you can see without moving the eyes) (4).

In this study, twenty seven patients with visual field damage received 120 mg of supplemental ginkgo extract for 4 weeks, followed by 8 weeks of no supplementation, then 4 weeks of placebo treatment. Other patients underwent the same regimen, but took the placebo first and ginkgo last. Visual field tests, were performed at the beginning and at the end of each phase of the study. Significant improvement in visual field measurements was found only after the period when ginkgo was taken, and did not continue after supplementation was stopped.

A Clue to Glaucoma Cause: Antioxidants May Help

Oxidative damage to the eye's fluid drainage system has recently been shown to match up, or correlate, with higher eye pressure and visual field loss (5,6). This finding is important because in some cases of glaucoma, fluid drains too slowly from the eye resulting in elevated pressure. The researchers measured a biomarker for oxidative DNA damage in the fluid drainage region of the eye (known as the trabecular meshwork) from 42 glaucoma patients and 45 patients of similar age and sex without the disease. Oxidative damage to the genetic material in trabecular meshwork cells was found to be significantly higher in those with glaucoma.

The optic nerve is a bundle of over one million nerve fibers that conduct electrical signals from the light-sensing retina at the back of the eye to the brain. Also called the "nerve of sight", the optic nerve is an essential link between the eye and the brain that makes vision possible.

Not only do these findings shed light on one possible cause of this disease, they also raise the possibility that antioxidants could help reduce damage to the trabecular meshwork in addition to protecting nerve cells. A host of experimental studies suggest that antioxidants such as alpha lipoic acid, vitamins C and E and bioflavonoids are useful in quelling such oxidative damage. According to these authors, antioxidants are well worth more clinical study to evaluate their potential in preventing or treating open-angle glaucoma.

References

1. Ercoli L et al. Society for Neuroscience Meeting, New Orleans, November, 2003
2. Chung HS et al. Ginkgo biloba extract increases ocular blood flow velocity. J Ocul Pharmacol Ther 15:233-40, 1999.
3. Quaranta L et al. Effect of Ginkgo biloba extract on pre-existing visual field damage in normal tension glaucoma. Opthalmol 110:359-62 (discussion 362-4), 2003.
4. Schwartz M. Neuroprotection as a treatment for glaucoma. Eur J Ophthalmol Suppl 3:S27-41, 2003. .
5. Izzotti A et al. Oxidative deoxyribonucleic acid damage in the eyes of glaucoma patients. Am J Med 114:638-46, 2003.
6. Chen JZ et al. A new clue to glaucoma pathogenesis. Am J Med 114:697-8, 2003.