The average person with two eyes that are equal in size will not have one eye large and one eye small. There are several reasons why one eye is large and one eye is small: one eye has a double lid and the other eye is not, the lid fissure is not the same size and the appearance looks like one eye is large and one eye is small, no special treatment is needed for this condition, just do a double lid. Second, congenital developmental abnormalities, where one eye is normal and the other eye is underdeveloped or more delayed, are caused by disease and there is no treatment for this condition. Third, acquired diseases can also cause eyeball atrophy, where the eyelid cannot be fully lifted and the appearance of one eye is large and one eye is small.