It may be either a birth defect, or the kitten's eye was injured early on. Was the baby born outside, or in? http://www.messybeast.com/disabled.htm#blind
The above link is a great resource to bookmark.
Here's an excerpt....
BLIND CATS

Cats that keep bumping into things either can't co-ordinate their limbs or can't see. A blind eye is often cloudy or the pupil remains dilated even in bright light. Some cats are born without eyes (anopthalmia) or with very small eyes (micropthalmia) which may not function. Others lose their sight either permanently or temporarily as a result of illness, physical injury, brain damage or poisoning (including extreme reaction to anaesthesia) and conditions such as glaucoma, cataracts or scarring caused by untreated entropion (inturned eyelashes).