by John Walsh, P.A., C.D.E., Ruth Roberts, M.A.
Changes in vision may happen at the time that diabetes is first diagnosed or at any time that blood sugar control is poor. Fluctuating blood sugars cause the lens to swell and shrink, and result in fluctuating vision. Many times, people who have "borderline" diabetes finally decide to take their diabetes seriously when their vision becomes blurred.
Sometimes, people coming down with diabetes marvel that they no longer need their glasses to see in the distance. But as insulin or other therapy is begun and the blood sugar drops, the abnormal swelling diminishes. In the short-term vision becomes blurred and is not corrected by their prescription lenses. Either of these scenarios can be frightening to people who have heard of the severe eye damage that goes along with diabetes.
Blurred vision in both eyes when insulin or other treatment begins is almost never caused by damage to the eye. Rather, it results from the speed at which the swelling, due to high blood sugars in the previous weeks and months, dissipates from the lens. Vision is usually out of sync for 3 to 4 weeks, sometimes with an accompanying headache.
After a visit to the physician to confirm that the abnormal vision is actually a temporary problem caused by lowering the blood sugars, a common treatment is to visit the reading glasses section in a large pharmacy. There, the person tries on different strengths of "reading glasses" until he finds one that allows him to see clearly at distances. As the days pass, a weaker version may be needed until eventually his own prescription lenses again work. Never buy prescription lenses during any period of uncontrolled blood sugars. These lenses are unlikely to work once the blood sugar is normalized.
These vision changes at the time diabetes is diagnosed rarely indicate real damage unless uncontrolled high blood sugars have been present for 5 years or more. It takes about 5 years of elevated blood sugars before damage to the eyes can be seen with an ophthalmoscope. However, the "It ain't gonna happen to me crowd" should remember that whenever blood sugars are high, damage may be underway and once it starts, it becomes much harder to stop!