“…the eyes are the windows of the soul.”
— Max Beerbohm
Much of the effort you put into your daily diabetes care is aimed at preventing the chronic or long-term complications that can occur with diabetes. Over time, less than optimally controlled blood glucose and blood pressure levels can cause damage to blood vessels, nerves, and organs in the body, including the eyes.
There are several diabetes-related complications that affect the eyes; the most common is retinopathy. Every year, retinopathy results in blindness for over 10,000 people with diabetes, and many more experience partial vision loss. In addition to retinopathy, cataracts may occur at a younger age in people with diabetes, and a person with diabetes is twice as likely as the general population to develop glaucoma.
The positive message regarding eye diseases that are related to diabetes is that many are preventable by keeping blood glucose levels and blood pressure levels well controlled. Regular visits with an eye specialist are also key to keeping your eyes healthy and catching problems early, when they’re most treatable.
How the eye works
For such a small organ, the eye is both fascinating and complex. Your eyes make constant adjustments to allow you to see objects that are nearby as well as those that are far away at all different levels of light. And they do it instantaneously.
The outermost layer of the eyeball is a tough, white layer called the sclera, which has a transparent window in front called the cornea, through which light enters the eye. Just behind the cornea are the iris, the colored part of the eye, and the pupil, the black opening in the center of the iris. The iris controls the amount of light that enters the eye. When it is dark, the muscles in the iris contract, allowing the pupil to dilate and let in more light, and when it is bright, the muscles of the iris cause the pupil to constrict, letting in less light.
Behind the iris is the lens, a flexible structure that focuses light on the retina, the innermost layer of the eyeball. The retina contains millions of cells called rods and cones, which respond to light. A small area in the retina called the macula contains only cones and is the area of sharpest vision. Signals from the rods and cones travel via the optic nerve to the brain, and the result is vision.
The lens divides the eyeball into two fluid-filled chambers, the anterior (front) chamber, and the posterior (back) chamber. The anterior chamber contains a watery fluid called aqueous humor, and the posterior chamber contains a gel-like substance called vitreous humor. Both substances help the eyeball maintain its shape, and the aqueous humor additionally provides nutrients for the lens and cornea, which do not have a blood supply.
The eye is connected to a number of muscles, nerves, and blood vessels that work together to maintain its function. The structures around the eye, such as the eyelids, eyelashes, and tear ducts, help protect the eyes from wind, dust, germs, and other substances. A delicate membrane called the conjunctiva lines the eyelids and covers part of the outer surface of the eyeball. The conjunctiva secretes mucus, which helps to keep the eyeball moist. (See “Anatomy of the Eye” for an image of the various structures of the eye.)