One of the number one causes of adult blindness is diabetes — especially in people with the insulin-dependent (Type 1) form. Studies have shown that this form of diabetes causes a disruption of the neurons and glia of the retina, leading to an accumulation of excitotoxic glutamate, and eventually resulting in the destruction of these cells.

One study found that an extract called resveratrol, which is found in grapes among other foods, can significantly lower glutamate levels in the retina, thus protecting against blindness. The resveratrol acted by increasing several of the mechanisms that prevent accumulation of glutamate. Resveratrol is generally safe, but very high levels can cause a drop in blood sugar.

A better alternative is pterostilbene, which is converted to resveratrol once it is absorbed in the blood. The advantage is that pterostilbene is far better absorbed than resveratrol and distributed all over the body, including the nervous system. It has been shown to be safe as well. The usual dose is 100 mg taken twice to three times a day with meals.