I can't say for sure what that is, but I read something about cats' third eye lid earlier. It says that sometimes their third eyelid could get infected and would cover their eyes. Maybe you should take your cat to a vet to examine. If that is the case, your vet might give you some eyedrops to put on the eyes.
Samantha/BB (11-month-old ~~ Born on Oct 9, 2007)
Mama (17-year-old) - passed away
Sabrina (11 year-old) - passed away on Feb 7, 2006
Meow Meow (8 year-old) - passed away on May 15
Bor Bor (6 year-old puppy)