Vitamin C levels in the eye decrease with age. Supplementing with vitamin C prevents this decrease and has been linked to reduced risks of developing cataracts and reductions in eye pressure associated with glaucoma.

Because people who supplement with vitamin C have developed far fewer cataracts in some research, nutritionally oriented doctors often recommend 500-1,000 mg of vitamin C supplementation as part of a cataract prevention program. The difference between successful and unsuccessful trials may be tied to the length of time people actually supplement vitamin C. In one trial, people taking vitamin C for at least ten years showed a dramatic reduction in cataract risk, but those taking vitamin C for less than ten years showed no evidence of protection at all.

Several studies have shown that supplementing with vitamin C significantly reduces elevated eye pressure in individuals with glaucoma. These studies used at least 2 grams per day of vitamin C, but sometimes much larger amounts were given. Higher quantities of vitamin C appeared to be more effective than smaller amounts. Vitamin C does not cure glaucoma and must be used continually to maintain a reduction in eye pressure.

Lutein and zeaxanthin are antioxidants in the carotenoid family. From the many carotenoids in the diet, the human retina selectively accumulates only two: zeaxanthin and lutein. Their concentration is so high in the macula, (the retinal region responsible for fine visual activities) that the carotenoids are visible as a dark yellow spot called the macular pigment.  Because these carotenoids absorb blue light, and because they are powerful antioxidants, scientists have hypothesized that they protect the retina. Working with quail as an animal model, the Schepens project provided the first direct experimental evidence that carotenoids do protect the retina.

Clinical Relevance of the New Findings Macular pigment has been implicated as a risk factor in age-related macular degeneration (AMD), the most prevalent cause of vision loss in the elderly. Vision loss in AMD is due to the irreversible death of photoreceptors and/or the invasion of leaky, unwanted blood vessels into the retina. At advanced stages of this progressive disease, everyday activities such as reading, driving, or even seeing the face of a loved one become impossible.

In the short-term study, reported in the November 2002 issue of Investigative Ophthalmology and Visual Science (IOVS), the team divided the carotenoid-deficient quail into two groups, and for one week preceding light damage, they fed one group zeaxanthin-supplemented diet. The study established that photoprotection was strongly correlated with the concentration of zeaxanthin in the retinas of the quail. Retinas with low concentrations of zeaxanthin had suffered severe light damage, as evidenced by a very high number of apoptotic photoreceptor cells, while the group with high zeaxanthin concentrations had minimal damage.  Apoptosis is programmed cell death, the final common pathway for photoreceptor death in retinal degeneration.

In the long-term study, reported in the November 2002 issue of Experimental Eye Research, groups of quail were raised for six months on carotenoid-deficient, normal or zeaxanthin-supplemented diets before exposure to brighter light.  The results showed extensive damage to the retina in the carotenoid-deficient animals, as evidenced by large numbers of both dying photoreceptors and gaps or "ghosts" marking sites where photoreceptors had died.  The group of quail with normal dietary levels of zeaxanthin showed significantly less retinal damage than did the zeaxanthin-deprived group, while the quail group receiving high levels of zeaxanthin had few ghosts in their retinas.

These experiments by Dr. Dorey's team showed protection of both rod and cone photoreceptors.  The research further demonstrated that retinas were protected by both zeaxanthin and another antioxidant, vitamin E.  Damage in these experiments was clearly reduced by zeaxanthin and tocopherol, but not lutein.  Further experiments would be needed to determine whether elevated lutein would offer protection.

These carotenoids, found in high concentrations in spinach, collard greens, and kale.  People who eat a lot of spinach and kale have also been reported to be at low risk for cataracts. In one preliminary study, lutein and zeaxanthin were the only carotenoids that were associated with protection from cataracts. People with the highest intake of lutein-zeaxanthin were half as likely to develop cataracts as those with the lowest intake.

Vitamin B2 and vitamin B3 protect glutathione, an important antioxidant in the eye. Vitamin B2 deficiency has been linked to cataracts. Older people taking 3 mg of vitamin B2 and 40 mg of vitamin B3 per day were partly protected against cataracts in a Chinese trial. Most researchers in the field do not believe that higher amounts would be helpful, and it remains unclear whether these vitamins would help protect people in societies that eat higher levels of B vitamins than the Chinese, whose intake appears to be low.

Vitamin E supplements have been reported to protect against cataracts although the evidence remains inconsistent. In one trial, people who took vitamin E supplements had less than half the risk of developing cataracts compared with others in the five-year study. Nutritionally oriented doctors typically recommend 400 IU of vitamin E per day as prevention.

Some studies report that eating more foods rich in beta-carotene or vitamin A reduces cataract risk, while synthetic beta-carotene supplementation has not been found to reduce the risk of cataract formation. Whether natural beta-carotene from food or supplements protects the eye or is a marker for other protective factors in fruits and vegetables high in beta-carotene remains unclear.