Cat Third Eyelid Stress. Redness and swelling around the outer lids, conjunctiva, and the third eyelid; As long as the third eyelid is covering less than 50% of the cornea, your cat will still be able to see fairly well.
The third eyelid in cats functions the same as the dogs, keeping the “windshield clean. Therefore, anything that affects the eyes, even if it seems minor, should not be ignored. The nictitating membrane may also appear as a symptom of feline upper respiratory virus or conjunctivitis (pink eye).
You may be seeing the third eyelid which appears in times of pain, stress or illness.
If it is protruding, it will come out and at least partially cover the cornea (clear covering of the eye). If your cat gets a clean bill of health, then you can begin to take steps to reduce or manage your cat's stress. He could have something in his eye. Tory johnson, gma workplace contributor, discusses.