Entropion is the inversion of part or all of an eyelid, and can involve upper or lower lids, or both. It is common in dogs, but only seen occasionally in cats.

There are two forms of entropion, primary and secondary (spastic).

1. Primary entropion is usually seen in cats with short noses and extra folds of skin around the nose and face such as Persians & Himalayans. Primary entropion is usually identified in cats less than 1 year old, and can be seen in kittens 6-8 weeks of age. Primary entropian usually affects the medial portion (close to the nose) of the lower eyelid.

2. Secondary entropion is seen as the result of excessive blinking associated with irritation of the eye (e.g. extra hairs on the inside of the lid, foreign body or conjunctivitis), and is seen at any age. Secondary entropion usually affects the centre or outside of the lower eyelid.

Eyelashes and hair of the eyelid irritate the cornea (front clear part of the eye), causing the signs of entropion. These vary with the duration and severity of the condition, ranging from excessive tear production, to a mucoid discharge with pigmentation or ulceration of the cornea. Secondary infection of the eye is common. Severe cases may involve rupture of the eye.

Treatment of primary entropion is surgical

Primary entropions are corrected by the surgical removal of skin to permanently evert the eyelid edge to the point where it sits normally on the eye. It can be very difficult to judge how much skin needs to be removed. Surgeons will err on the side of caution to prevent removal of too much skin, which results in the opposite problem of the eyelid being everted and not resting on the cornea. Occasionally this procedure may need to be performed more than once to achieve a good result.

Treatment of secondary entropion involves correction of the underlying problem if possible and will usually correct the entropion. Occasionally surgical correction is required after the underlying problem is solved. Any cat with entropion (especially if young) is examined carefully for underlying causes of spastic entropion, and often treated to rule these out prior to a diagnosis of primary entropion being given and treated.