What does it mean when a cats 3rd eyelid is showing?

Hi there!  Thanks for your question about your cat’s elevated third eyelids.  For starters, this can be a complicated issue to sort out as the list of possibilities for potential causes can be quite long.  But the good news is that most causes, if not all, can be screened or narrowed down based on a thorough history of the cat’s life-style, risk factors, and complete physical examination including comprehensive eye examination.  From there, a veterinarian could then determine what the next course of action, or testing, would be advised based on the most likely rule out.  The most common cause in cats with both eyelids elevated seems to be gastrointestinal in nature, such as gastrointestinal parasites (especially Tapeworms as being the most likely causing agent).  So sometimes a veterinarian will recommend a fecal floatation to check for gastrointestinal parasites (or eggs) in the stool that you cannot see with the naked eye, maybe even deworm the cat with a medication, and ensure that the cat is on monthly systemic flea control (such as Revolution).  But there are several other causes, such as dental disease or an infection/abscess in the back of the mouth that you cannot see (called a retrobulbar abscess) that can both affect the nerve that supplies the eye that could explain this clinical signs, so a comprehensive examination is really key to treatment and diagnosis.  It is also really important for a veterinarian to distinguish two possible syndromes for the condition as well.  One is called Haw’s Syndrome, which is the term used for an idiopathic (which means no known cause) for the protrusion of both third eyelids.  The other is called Horner’s Syndrome, which is the result from an interruption of the sympathetic nerve supply to the eye.  A veterinarian could perform a simple test on the eye using an eye drop containing the drug called Phenylephrine to determine if the pupil dilates or not after application.  Another quick and easy test at home on your cat is to determine if the pupils are equal in size and that the pupils DO dilate (or enlarge) in the dark.  Regardless of the outcome of this test, a veterinarian could not recommend, treat, or give you anything that could possibly help your cat without their own comprehensive and neurologic examination first.  We would be more than happy to take a look at your cat at any of our four practices.  There would be many options that could be further discussed with you in regards to working up or treating your cat after we had additional information after an exam was performed.  I hope this helps you on your quest!  Thanks for your interest in our website!  Good luck!  Call us with any other questions at 813 973 8566.