Eversion of the Third Eyelid Cartilage in a Cat
Authors: Momesso Eric Orlando Barbosa , Brunato Carinne Liessi , Teixeira Adriana Lima 
Published: June 2021

Background: Eversion of the cartilage of the third eyelid is a rare congenital disease in cats. It is caused by the anterior eversion of the cartilage edge of the third eyelid. Clinical signs may be associated with secondary keratoconjunctivitis, third eyelid gland protrusion, and ocular surface irritation. The diagnosis is made by ophthalmic examination, and treatment consists of surgical resection of the everted cartilage portion. The goal of the present study was to report a case of eversion of third eyelid cartilage in a cat, given that it is an unusual abnormality in this animal species, and an important differential diagnosis to be considered in the disorders of the third eyelid.Case: A 6-year-old neutered female Persian cat was presented with a presumptive diagnosis of protrusion of the third eyelid gland, history of ocular irritation, and epiphora in the left eye. The disorder had been intermittently present since the animal was 1-year-old, with spontaneous disappearance after approximately 15 days. The owner related the reappearance of the disorder to stressful situations, with no previous history of trauma or other ocular alteration. During the ophthalmic examination, suspended solute was observed through biomiscroscopic examination in both eyes, as well as an increase in volume of the third eyelid in the left eye, without other changes. A thorough examination, under general anesthesia, indicated the protruding volume of the cartilage of the everted third eyelid. The third eyelid was pleated in its upper portion, demonstrating that the cartilage of the third eyelid was folded instead of following the curvature of the ocular surface. Under general anesthesia, the cartilage was partially removed through two parallel incisions on the bulbar conjunctival surface, divulsioning 5 mm in length in the vertical portion of the cartilage in a ‘T’ shape, and separating the conjunctiva from the underlying cartilage. The everted portion of cartilage, once removed, was in fact considered curved in its most dorsal portion, in a manner similar to what was reported in dogs. The third eyelid returned to its anatomically correct position after removing the deformed portion of the cartilage. The patient was treated postoperatively with topical drops of tobramycin and dexamethasone 3 mg/mL + 1 mg/mL (Tobradex®), and lubricant based on sodium hyaluronate 2 mg/mL (Hylo®-Gel). No complications were observed in the postoperative consultations during a 8 month follow-up.Discussion: It is suspected that the eversion of the third eyelid cartilage occurs due to a differential growth rate between the posterior and anterior portions of the cartilage; even though other theories have been proposed. The cartilage of the third eyelid can commonly be everted in large dog breeds, being classified as a disease of hereditary character. However, it has rarely been reported in cats, which can be explained by the more elastic histological constitution when compared to that of dogs. The surgical procedure performed in the present case of eversion of the third eyelid cartilage in a cat was in accordance with that described in the literature. Complete recovery of the third eyelid function was achieved, and the patient's ocular health was preserved. The reported case showed a favorable prognosis after diagnosis, associated with correct treatment and postoperative management. Although there was an effective recovery of the third eyelid, the issues related to the pathophysiology of cartilage eversion are unknown. This way, further studies are necessary to elucidate its etiology.