Why does my one eye gets small n one eye gets big?

See MD: If you mean your pupils are of different sizes, you need to see your physician. It can be a sign of an abnormality in your brain.

Drooping eyelids: I you have one eyelid that droops, known as ptosis the other eye may appear paradoxically large since the innervation needs to open the droopy lid also goes to the normal lid, thus the droopy lid eye may look smaller while the other eye opens wider and thus looks bigger. This is known as the law of equal and opposite innervation.