this is due to the eye disease that they have. for example, blind people who have congenital cataracts can have eyes that look very opaque. i happen to have juvenile cataracts that i was born with and i've been told by all of my opthalmologists that they make my eyes look as if they have a cloudy film over them although for the most part they are clear.
You also have ROP. Does ROP and cateracts often exist together?
I've heard their was a link between glycoma and cateracts.