Ailments of the eye
The third eyelid
You may recall that we had mentioned that dogs and cats and other species had a third eyelid (nictitating membrane) – in addition to the upper and lower lids, which cover the eyeball during sleep and blinking. From time to time, this ‘third eyelid’ slides across the eyeball from the nasal corner of the eye to the other side.
When the cat (or dog) wakes up from a deep sleep you can see the third eyelid retracting to its original position. In some cases, however, this membrane remains visible, partially or wholly covering the visible surface of the eyeball. One speaks then of a ‘protrusion’ or a ‘prolapse’ – according to the degree of surface coverage.
There are several reasons attributed to the protrusion/prolapse of the nictitating membrane. Among those are:
(i) General Ailment
Often, as a result of a debilitating ailment, the animal loses weight dramatically. As a part of this sickness-induced emaciation, the quantity of peri and retro-orbital fat (fat around and behind the eyeball) decreases. The eye then sinks into the socket and allows the third eyelid to prolapse across the eyeball. Also, a serious bout of malnutrition can reduce the size of the pad of fat which is around, and especially behind, the eyeball. The same prolapse effect is thereby produced.
This nictitating membrane has a lymph plate (made up of several tiny lymph buds) on the side that rubs against the eyeball. This lymph plate (like the tonsils) can become infected, sometimes secondarily as a result of an original eye infection. Like the tonsils, the lymph buds swell and keep rubbing on the eyeball. The whole tissue becomes inflamed (red).
(iii) Involvement of foregin bodies
On other occasions, a foreign body (grass seeds, dust particles, etc) can lodge itself between the membrane and the surface of the eyeball. This is painful and elicits an inflammatory response. The end result is a prolapse of the third eyelid.
I should mention that there are many who argue convincingly that the nictitating membrane is a defence mechanism which is actively protruded in order to protect an infected eye.
Just as it happens in humans who have experienced continuous fluid loss (the gaunt appearance), so too, a dehydrated condition caused by haemorrhage, diarrhoea, constant vomiting, etc) can make the eyeballs sink into the sockets. The third eyelid will then protrude.
(v) Congenital defect
The animal could be born with the prolapse. This is then a genetic defect; it will not get better. You will have to discuss next step/options with your vet.
The animal with a protruding nictitating membrane looks ill and haggard. Whatever the initial cause is, it must be removed. If it is a general/specific ailment, then this condition must first be addressed. If a foreign body is the culprit, then it must be removed.
In any case, the cure for the prolapsing/protruding third eyelid is a job for your veterinarian who may prescribe antibiotics and anti-inflammatory medication. From experience I can tell you that this antibiotic/corticosteroid regime seldom works if there is a long-standing infection present. I advise placing the dog/cat under full anaesthesia and scraping the lymph plate (quite similar to the removal of tonsils, when there is a chronic infectious condition of the throat).
Some veterinarians champion the surgical removal of the third eyelid in its entirety. Sometimes this radical action is the only solution for an obstinate infection of the nictitating membrane, but negative developments may follow.
Lastly, in passing, allow me to advise that not all protrusions of the third eyelid indicate a defect or are precipitated by a sickness. For certain breeds (eg the Bloodhound) the visible nictitating membrane is part of the breed standard (characteristic for that particular breed).
Enjoy the week ahead.
Please implement disease preventative measures (vaccinations, routine dewormings, monthly anti-heartworm medication, etc) and adopt-a-pet from the GSPCA’s Animal Clinic and Shelter at Robb Street and Orange Walk, if you have the wherewithal to care well for the animals. Do not stray your unwanted pets, take them to the GSPCA’s Clinic and Shelter instead. If you see anyone being cruel to an animal, or if you need any technical information, please get in touch with the Clinic and Shelter by calling 226-4237.