High blood sugar
causes the lens of the eye to swell, which changes your ability to see. To correct this kind of blurred vision, you need to get your blood sugar back into the target range. For many people this is from 70 mg/dl to 130 mg/dl before meals and less than 180 mg/dl one to two hours after the start of a meal. Ask your doctor what your personal target range should be. Blurred vision can also be a symptom of more serious eye problems. If your vision is blurred, contact your doctor.