A pale membrane appears at the inner corner of your cat’s eye and remains visible while the cat is awake. That structure may be the third eyelid. A new or persistent change deserves veterinary advice rather than an internet diagnosis based on one photograph.
PDSA’s guide to eye problems in cats includes a visible third eyelid among possible signs of an eye problem. It advises contacting a vet when eye changes appear and seeking immediate help if the cat is in pain.
Describe what you see without forcing the eye open
Note whether one or both eyes are affected, when you first noticed it and whether it stays visible after the cat is fully awake. Mention discharge, redness, cloudiness, squinting, rubbing or changes in behaviour if present.
A clear photograph taken without distressing the cat may help show the change to the clinic, but it cannot replace an examination. Do not hold the eyelids apart, press on the eye or repeatedly use a bright light to test the reaction.
Let the clinic decide how urgently to examine it
Call promptly and describe the observations. Pain, a closed eye, an injury or a sudden apparent change in vision needs urgent attention. If you are unsure whether the cat is uncomfortable, say what the cat is doing rather than waiting until you can name the symptom confidently.
Do not use human eye drops, leftover pet medication or a home remedy. Different causes need different treatment, and an unsuitable product can make the situation worse. Follow the veterinarian’s instructions for any immediate care and transport.
Keep the cat in a calm, safe place while arranging help, especially if vision may be affected. Bring details of recent illness, medicines or possible injury. Those details give the veterinarian context beyond the visible membrane.
The third eyelid is a useful observation, not a diagnosis. The responsible next step is to communicate the change clearly and obtain an assessment, rather than deciding that it must be one particular condition because another cat’s photograph looked similar.