Occasionally you'll glimpse a milky-white membrane in the corner of your cat's eye, near his nose. This is his third eyelid, which helps protect his peepers from damage as he goes about his day. If this lid is constantly visible, it typically indicates an underlying problem that requires veterinary care.
Cats spend a good amount of their day sleeping, dozing or napping, which can cause their third eyelid to creep across their eye under the outer lid, and sometimes cats don't close their eyes entirely when they snooze. Depending on your schedule, it's entirely possible to mostly see your cat when he's catching some z's, so his third eyelids look like they're always extended. Check him when he's wide awake to verify that the third lids are retracting correctly to put your mind at ease.
If your cat's third eyelid isn't retracting properly when he's awake and making him look as though he's wearing a milky eye patch or two, this generally indicates a deeper medical issue. Various eye-related conditions trigger the extension of the third eyelid, such as Horner's syndrome, Haw syndrome and cherry eye. Injury to the eye or lids can cause the third eyelid to appear, often changing from its typical white shade to a brighter red.
The appearance of your cat's third eyelids by themselves don't always mean there's some sinister underlying medical issue. Cats can get something caught in their eye just as you can, and the third eyelid offers an additional bit of assistance to get it out. Keep watch over your kitty to see if the eye clears up within a day or two, or if he offers any other symptoms that may point to a bigger problem. Check for any discharge from his eyes, and note if either eye seems to bulge or look sunken within the socket. Compare pupil sizes and positions, and watch your cat's behavior to pick up any oddities.
The Doctor Is In
If your cat's been rocking the squinty pirate look for a few days and shows no signs of improvement, or if the third eyelid has crossed over to cover more than half of his eye, contact your veterinarian. Eye-related problems rarely heal on their own and may result in vision damage if left too long. Your veterinarian can run various tests to narrow down the cause and provide the proper treatment plan. Quick diagnosis and treatment can have your cat back to binocular vision in no time.
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