Introduction
The body utilizes glucose abnormally in diabetes mellitus. The persistently high levels of blood glucose and high levels of fatty acids and other free radicals in diabetes leads to the development of abnormalities in structure and function of major organ systems in the body--chiefly the heart and blood vessels, nerves, kidneys and the eye. According to the National Eye Institute within the National Institutes of Health, 40 percent to 45 percent of diabetics have some form of eye complication.
Vision in Diabetes
Vision is coordinated between the eyes, optic nerves and the visual cortex in the brain. Light entering the eye through the pupils is focused by the lens on the retina at the back of the eye. The retina transforms the light into nerve signals that are transmitted to the visual cortex of the brain for interpretation. The eye is held in a compartmentalized global form by a system of fluids under closely controlled pressure--namely, the aqueous and vitreous humors. Diabetes affects vision by affecting several structures and altering some functions in the pathway from the eye to the brain.
Diabetic eye disease affects several parts of the eye. The high blood sugar can lead to increased density in the lens with the development of opacities called cataracts. This decreases the amount of light allowed through the lens to the retina. Thus, objects appear blurred at first and as the cataract matures, vision is lost completely in the affected eye.
Diabetics also develop glaucoma more frequently than the rest of the population. Here, the pressure in the eye (intraocular pressure) increases above normal. The raised eye pressure damages the optic nerve at its origin in the optic disc. This gradually narrows the field of vision and leads to total loss of vision.
By far the most common of the diabetic eye diseases is diabetic retinopathy, characterized by damage to the small blood vessels supplying the retina. Some small vessels on the retina are blocked and swollen with the development of new, weaker vessels. These vessels easily develop leakages of blood or burst altogether. Bleeding into the vitreous humor appears as "floaters" in a person's field of vision. These developments impair the ability of the retina to function smoothly, leading to gradual vision loss. Scarring caused by attempts to heal the ruptured vessels can lead to retinal detachment, which shows as flashes of light. A detached retina is an emergency. The retina quickly sustains permanent damage if not repaired immediately.
Diabetes can also affect vision by the development of plaques in the arteries supplying the visual cortex of the brain. A stroke involving that part of the brain can also affect vision, leading to defective vision or blindness.
Recommendations
The National Eye Institute recommends well-controlled blood sugar levels to reduce the risk of development of eye disease in diabetics or the progression of the disease where it has occurred. Close monitoring with regular eye checks can also detect early treatable defects before irreparable damage has occurred.
