What is the third eyelid?
Dogs and cats have an extra eyelid called the ‘third eyelid’ or the nictitans or nictitating membrane, at the inside corner of their eyes.
The third eyelid is a triangular membrane of conjunctival tissue that sweeps across the surface of the eye to provide protection and to distribute the tear film; it also has one of the most important tear glands attached at its base.
Young dogs, usually less than 12 to 18 months old, may suffer from two common conditions of the third eyelid. These are described below and may require treatment by a veterinary eye specialist.
Cherry eye is a colloquial term to describe prolapse of the third eyelid gland from its normal position so that it appears as a pink or reddish smooth mass above the edge of the third eyelid. The gland does not function normally when it is in the wrong position, and may also cause minor discomfort, conjunctivitis and ocular discharge. In some cases, the gland becomes very inflamed, red and enlarged. Although there are several glands responsible for the total tear production for the eye, the third eyelid gland is thought to be the most important for tear production to keep the surface of the eye wet. Historically, the prolapsed gland was removed, but the current recommendation is to replace the gland instead. If the gland is removed, the eye has an increased risk of developing ‘dry eye’ due to low tear production, which requires medical treatment for the rest of the animal’s life.
Scrolled cartilage, or cartilage eversion
This condition is less common than ‘cherry eye’ and affects young giant breed dogs, usually during the rapid growth phase. The third eyelid has a T-shaped cartilage within it, to provide some rigidity. One small area of the T grows abnormally fast, so that the cartilage becomes bent, everted or ‘scrolled’. This results in the whole third eyelid becoming scrolled so that it appears as a pink to reddish mass in the corner of the eye. A scrolled cartilage can appear very similar to a ‘cherry eye’ and examination under general anaesthesia may be necessary to distinguish the different conditions.
As with ‘cherry eye’, there is no medical treatment to correct the abnormal cartilage and an operation is required. The operation is straightforward as the abnormal part of the cartilage is identified, dissected free and completely removed. Recurrence is highly unlikely in the same eye.
What does the operation involve?
Your pet will need a general anaesthetic for the operation and will usually stay in overnight. All sutures placed will be dissolvable, so suture removal will not be necessary. A Buster collar or light foot bandage may be required to prevent self-trauma to the eye region for the first few days after surgery.
Antibiotic and/or anti-inflammatory eye drops or ointment will be prescribed for 7-10 days. Oral medication will also usually be prescribed for 5-10 days.
Rest is advised for the first 5-7 days. Swimming or bathing of the head area should be avoided for the first 14 days. The third eyelid may appear more prominent for several days but this resolves in most cases.
Some breeds are predisposed to developing both conditions, either at the same time, or within several months of the first symptoms being noticed. Both conditions can affect one or both eyes, although usually there is a delay between the first and second eye being affected.
If you are concerned about the health of your pet you should contact your veterinary surgeon.