The problem you experience , most likely does not arise primarily from your eyes but is vascular in nature. You need to have your blood pressure checked and a cardiac evaluation. Post a heavy meal there is increased blood supply to the gastrointestinal system and a postural hypotension
which means a lower blood pressure following lying down or sitting can cause giddiness for a few minutes as well. A blood evaluation can rule out any lipid abnormalities also. The temporary reduced blood supply to the retina
can cause vision problems.