Don't run out and buy a new pair of glasses as soon as you notice you have blurred vision. It could just be a temporary problem that develops rapidly and is caused by high blood sugar levels.
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 from70 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.