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.
Yes, eating can cause it and it is just one of the symptoms of postprandial or after-meal hyperglycemia, which means that a blood sugar can usually greater than that before your eating. So the changes make you can not focus easily. What's more, increased thirst, difficulty concentrating of mind are also the symptoms. So it is just normal and temporary, you do not have to worry about it. Just take your eyes for some rest and they can focus later. What's more, eye focusing problem can also happen when someone's continued viewing of near objects for a long time.Pay attention to this and deal with it correctly, good luck!
You may eat something wrong or something that be sensitive to your skin. That is why your eyes get affection and can't focus on something. You'd better stop eating and check your eyes under the bright light and see whether there is the change in the color. You need to have the rest and use the warm compress to make the eyes have the good rest. Then you will see the effect.