Introduction
Diabetes mellitus is a condition of defective blood sugar utilization and control with persistently high levels of blood sugar leading to the malfunctioning of other organs. Major organs affected by diabetes are the heart, the brain, the kidneys, the eyes and the peripheral nerves and arteries. One complication of diabetes is blindness.
Vision
Vision is governed from a functioning eye and interpretation of visual stimuli to the visual cortex. Diabetes causes blindness by affecting any part of this mechanism. The eye is made up of the cornea, the iris, which operates the pupil like a camera shutter, the lens and the retina. The whole apparatus is housed in the eyeball which is filled by two fluid systems, the aqueous humor and the vitreous humor. It is the retina that changes the light signals to nerve impulses to be carried by the optic nerve to the visual cortex of the brain for interpretation.
Diabetes and Blindness
Persistently high levels of blood sugar and the resulting high levels of free radicals predispose the small arteries everywhere in the body, including the retina, to damage. These arteries may become blocked and swollen as a result of increased stickiness of their linings and deposits from the high blood sugar and fats. New weaker vessels are formed when the old ones are blocked. These new vessels burst or leak fluids that bleed into the vitreous making it opaque and unable to transmit light to the retina. The resulting scars from burst arteries can contract and detach the retina from the wall of the eyeball, further compromising vision and endangering any chance of recovery. This whole process is called diabetic retinopathy.
The high levels of blood sugar also lead to altered chemical state of the molecules that make up the lens, causing this normally clear structure to develop a whitish cloudy look. These are called cataracts, which causes loss of vision in the affected eye. According to the American Diabetic Association, there is also a finding of early development of glaucoma in diabetics. In glaucoma there is an increase in the pressure of fluids within the eyeball. This adversely affects the optic disc, the origins of the optic nerve in the eye. The damaged disc also leads to blindness.
Finally, in an indirect manner, the increased incidence of stroke in diabetics is another link to blindness. The loss of blood supply to areas of the brain in stroke, leads to loss of function. This can cause blindness, particularly if the loss of function in the brain affects the visual cortex.
Precautions
The NIH recommends regular eye exams for all diabetics to monitor changes in the eye in response to diabetes. This would require a standard referral to an eye specialist who would examine the eye thoroughly and monitor any developments for prompt intervention to prevent irreversible damage to the eyes.
