Entropion is when the eyelid margin rolls in towards the eye, which causes the eyelid fur to rub on the cornea. Hair rubbing on the cornea is very irritating, and causes squinting, tearing, redness and ulceration. Most cases of entropion are related to eyelid and head conformation. This can occur in animals with long eyelids and blocky head shapes, such as Mastiffs, Pit bulls, Labradors, Rottweilers and tomcats, or in dogs with heavy facial folds like Shar peis and chows. Animals can also develop entropion because of age-related loss of fat in the eye socket, which causes sinking of the eye and rolling in of the eyelid. Less common causes of entropion include inappropriate healing of eyelid lacerations and congenital entropion (usually in foals or lambs). Entropion can affect one or both eyes.
Treatment for entropion involves rolling the eyelid margin back out so that the hairs no longer rub on the cornea. This can be done with permanent surgical correction or with temporary tacking. Clinical signs and corneal ulcers usually resolve quickly once the underlying problem of hairs rubbing is solved. Most cases of entropion usually need permanent surgical correction with congenital entropion being the exception. Permanent surgical correction is relatively minor outpatient procedure, though it still requires general anesthesia. A small strip of skin below or above the eyelid is excised, and the eyelid may be shortened. Usually only one surgery is required to permanently resolve entropion, but some cases may require additional surgery as their conformation changes with age.