One of the most common causes of adult blindness is diabetes, especially insulin-dependent (type 1) diabetes. A number of recent studies have shown that the reason for this blindness is the destruction of nerve cells within the retina at the back of the eyeball by the amino acid glutamate.
Several studies have shown that glutamate, a destructive excitotoxin, builds up in the vitreous humor in the back of the eyeball in diabetics as well as in those with macular degeneration and glaucoma. While the source of the glutamate is from the injured nerve cells and supportive cells (glia) themselves, there is growing concern over the consumption of extreme amounts of excitotoxins in the diet in the form of MSG and aspartame. Aspartame contains the excitotoxin aspartate as well as the neural eye toxin methanol (which breaks down into formaldehyde and formic acid).
Since the eyeball has no protective system, such as the brain’s blood-brain barrier, anything in the bloodstream, including these excitotoxins, can enter the interior of the eye quickly. Careful studies have shown that when people eat and drink foods containing excitotoxins, their blood levels can increase as much as 20 times higher than normal.
Even if the excitotoxins do not cause these diseases, they certainly make them much worse and cause them to advance more rapidly.
Let’s say an elderly person eats a bowl of soup and drinks a diet soda. He will be consuming excitotoxins in concentrations that can damage brain cells as well as the retina.
In the case of diabetics, studies in patients have shown eyeball (vitreous) glutamate levels to be greatly elevated, especially in the case of proliferative diabetic retinopathy, the type most likely to lead to blindness. A recent study of animals with diabetes demonstrated a 40 percent increase in eye glutamate levels and a 100 percent increase in lipid peroxidation, a measure of free radical damage associated with excitotoxicity.
Similar findings have been demonstrated in the eyeballs of those with glaucoma. Excitotoxicity is considered the major reason for blindness in this condition and not the high intraocular pressure, as once thought. The high pressure reduces the blood flow in the retina and this triggers the release of the destructive glutamate.