Based on your description, it might be hyperglycemia and diabetes triggered your difficulty in focusing your vision. It is not weird but common for diabetes patients. Diabetes is a condition people can't produce enough insulin or cells of body don't respond to insulin properly. Hyperglycemia is a very serious problem for people have diabetes. There is one hyperglycemia called postprandial or after-meal hyperglycemia, which is defined as a blood sugar usually greater than 180 mg/dL. For people who has no diabetes or hyperglycemia, it is possible that after a large meal, their blood sugar lever, which are usually below 140mg/dL, will rocket to above 180mg/dL. It will cause fatigue, weight loss, difficulty in concentration, blurry vision, headaches and increased thirsty. This is a signal sent by the body. It means these people are at a very high risk to develop type 2 diabetes. My suggestion is that you should visit your doctor and take an physical examination.
