Dear Christopher Cat
Tigger Tom, my 8-year-old cat, has an eye problem. His third eyelid protrudes across part of his eye. Everything else is normal. What’s happening?
Unlike humans, cats and dogs have three eyelids.
The third eyelid, called the nictitans or nictitating membrane, lies against the eyeball, providing an additional layer of protection.
Occasionally my nictitans is more prominent than usual, like Tigger Tom’s. Mom calls the condition “haws,” but while veterinarians have named it, they don’t understand it well.
Sometimes it occurs in association with mild diarrhea or gastrointestinal viruses or parasites.
Experts think gastrointestinal disease causes the neurologic problem that gives rise to haws.
Other times, it’s associated with pain, dehydration or decreased size of the eyeball or its muscles.
Less often, a mass in front of the eye pushes the eyeball back, allowing the nictitans to protrude.
Usually the cause is innocuous, and the nictitans returns to its normal, nearly hidden position without treatment in a few weeks, but occasionally it takes a few months.
However, it’s still best to have your veterinarian check Tigger Tom’s eyes to rule out an underlying problem.