What do i do if my kitten has one small eye and one normal eye.?

My cat had kittens about 2 weeks ago and on day 8 all 3 opened their eyes. two have two normally opened eyes and normal size. one kitten has one normal sized eye open and the other eye only opens about 1/3rd of the amount of the other eye. like the outer lid seems underdeveloped. other than that they all see healthy and are growing normally. there is no color discharge or eye goop or anything, the eyelid is just too small. What is this and what do i to?