Third eyelid does not open
Please advise! My cat (3 month old) was normal until today. Today his third eyelids do not get opened :0( They get opened half way only when he is active. Is this something serious and I need to go to a vet ASAP? Or, maybe it will go away, maybe it is some kind of allergy? I have 4 cats, and all of them are OK but that one.
Did anyone had something similar happened to their cats?
Thank you for your help!