An extra layer of protecton

Sharks are among the creatures with a third eyelid, a special membrane that protects their eyes.
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Sharks are among the creatures with a third eyelid, a special membrane that protects their eyes.

There is an element of morbid fascination when it comes to crocodiles and sharks and they unfortunately bring the human race down a peg or two in the food chain.

But, if you ever watch those documentaries, check out their eyes. Apart from being beady, cold and very, very scary, they have a special protective covering called a "third" eyelid.

Humans seem to have lost this little feature along the way, along with tails.

There is an endless procession of cardboard boxes every day at the hospital, but when Leticia stepped back with a look of horror while pointing at a box, I was a bit apprehensive. Crouched down in among the towels was Fred, who isn't scary at all. He is a 2-year-old ginger tabby cat.

He did, however, look a bit strange because both his eyes where half covered by a pale membrane extending from the inner corner of his eyes.

This membrane is their "third eyelid". It has two primary functions;

  • To protect the eye
  • To contribute to the production of tear film that lubricates the surface of the eye.

When an object approaches the eye, the reflex is to blink. When this happens, the cat's third eyelid also flicks across the surface of the eye to protect it even before the main eyelids close.

There are lots of cats with large nicks out of the edge of this eyelid from another cat's claw. And we have had to trim a few of the loose flaps of this eyelid as a result of cat fights lately.

Dogs seem to have slower reflexes and can suffer nasty injuries to their cornea because their third eyelid and main blink reflex hasn't had time to cover the eye. Hence why the cat can do some damage with a quick swipe.

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Also, behind the third eyelid is a gland which produces about one third of the tears that lubricate the eye.

This gland can be a problem, especially in young dogs of certain breeds, because it enlarges for some unknown reason and can then no longer fit between the eyelid and the surface of the eye.

The little enlarged red gland then pops out from behind the third eyelid, giving rise to the term "cherry eye". The gland can either be surgically removed or replaced and stitched back in the right place. These cherry eyes are common in short-faced dog breeds like bulldogs.

But back to Fred. There are numerous possible causes for both third eyelids to be across in a cat and it certainly can be a good indicator that your friend is not well.

Some of the common causes include:

  • Dehydration and/or weight loss with retraction of the eyeball in to the socket
  • Something lodged behind the eyelid like a grass seed
  • The use of sedatives and therefore can sometimes be seen when patients go home after surgery
  • Haws Syndrome 

This last one is by far the most common cause in young cats, but can only be diagnosed once all the other causes are eliminated.

Fred's examination showed no other detectable problems. He was eating fine, active, purring, teasing the dog and ducking in and out of the cat flap as usual.

Haws syndrome was very likely. The cause of this disease is not known, but is commonly thought to be related to mild gut upsets and diarrhoea, possibly associated with a viral infection (those mystical viruses get blamed for any unexplained diseases). The condition usually disappears within 3-4 weeks.

In the meantime, we gave Fred a short course of antibiotics, to be on the safe side and have arranged to see him again in one week for a check up.

But please remember that if your furry feline or licking, nuzzling canine has those funny eyelids showing in the inside corners of one or both eyes, it can be a sign they are unwell.

 - Stuff

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