Features: Diagnostic Ophthalmology

History and clinical signs

An 11-month-old crossbred Bernese mountain dog was examined by the ophthalmology service at the Western College of Veterinary Medicine. This dog presented for evaluation of an abnormal appearing third eyelid of the right eye. The menace responses, and palpebral, oculocephalic, direct and consensual pupillary light reflexes were normal bilaterally. Schirmer tear test (Schirmer Tear Test Strips; Alcon Canada, Mississauga, Ontario) values were 20 and 22 mm/min in the right and left eyes, respectively. Intraocular pressures were estimated with a rebound tonometer (Tonovet; Tiolat, Helsinki, Finland) and were 12 and 13 mmHg in the right and left eyes, respectively. Fluorescein staining (Fluorets; Bausch & Lomb Canada, Markham, Ontario) of the cornea was negative in both eyes. Retropulsion of both globes was unremarkable. On direct examination, including palpation and exteriorization of the third eyelid, the leading edge of the third eyelid in the right eye was folded anteriorly due to an outward curvature in the third eyelid cartilage. Following application of 0.5% tropicamide (Mydriacyl; Alcon Canada, Mississauga, Ontario), examination of both eyes using a transilluminator (Welch Allyn Finoff Transilluminator; Welch Allyn, Mississauga, Ontario) and handheld biomicroscope (Kowa SL-17 Portable Slit Lamp; Kowa Co Tokyo, Japan) revealed no abnormalities. Indirect ophthalmoscopic (Heine Omega 500; Heine Instruments Canada, Kitchener, Ontario) examination was completed and did not reveal abnormalities in either eye. A photograph of the right eye at presentation is provided for your assessment (Figure 1).

Figure 1.

Photograph of the right eye of an 11-month-old crossbred Bernese mountain dog.

What are your clinical diagnoses, differential etiologic diagnoses, therapeutic plan, and prognosis?

Discussion

The ophthalmic diagnosis was everted third eyelid cartilage in the right eye. This is a congenital or developmental disorder in which the shaft of the third eyelid cartilage is abnormally bent such that it causes folding of the third eyelid. The condition is also known as scrolled third eyelid cartilage. This may be unilateral or bilateral, is most often seen in large-breed dogs and may be inherited in German shorthaired pointers (1). Third eyelid cartilage eversion has also been reported in cats and an Anglo-Nubian goat but is rare in other species (2,3).

The third eyelid is situated in the anterior ventromedial orbit and is completely covered by conjunctiva that is divided into bulbar (adjacent to the globe) and palpebral (adjacent to the eyelid) surfaces. A T-shaped hyaline cartilage supports the structure of the third eyelid and a lacrimal gland is situated superficially to the base of the cartilage on the bulbar surface (4). The function of the third eyelid is to protect the globe, distribute tears, and aid in removal of debris. Everted third eyelid cartilage is postulated to be the result of more rapid growth of the posterior portion of the T-shaped cartilage compared to that of the anterior portion (1).

The primary differential diagnosis for everted third eyelid cartilage is a prolapsed third eyelid gland, as both occur in young dogs. These conditions may be differentiated with careful examination of the third eyelid. Prolapse of the gland of the third eyelid is characterized by a reddish round to oval, smooth mass protruding from the bulbar surface of the third eyelid with a normal anatomical appearance of the third eyelid margin. In contrast, everted third eyelid cartilage most often appears as eversion of the leading edge of the third eyelid with exposure of the posterior aspect of the third eyelid (5). The folded cartilage may be visible as a white structure below the bulbar conjunctiva of the third eyelid and can often be palpated as a firm structure. Less commonly, the fold in cartilage may be inward or S-shaped (6). The location of the bend along the cartilage shaft can vary and will affect the extent of the abnormality and amount of exposure of the bulbar surface of the third eyelid. Third eyelid cartilage deformities may occasionally present concurrently with prolapsed gland of the third eyelid (2,7).

Corrective treatment of everted third eyelid cartilage is indicated in cases in which exposure of the bulbar surface of third eyelid and reduced third eyelid function result in chronic conjunctivitis and ocular discharge. Surgical excision of the bent portion of cartilage is a common and effective treatment option. A vertical incision is made in the conjunctiva of the bulbar surface of the third eyelid over the folded portion of cartilage which is then isolated from the surrounding conjunctiva via blunt dissection using tenotomy scissors and subsequently excised with a scissor cut on either side of the cartilage bend. The conjunctival incision is not closed but left to heal by second intention (5). This is a relatively simple procedure; however, if large portions of cartilage are removed, the stability of the third eyelid can be reduced and this may contribute to third eyelid gland prolapse (6). Allbaugh et al (6) describe a novel technique that utilizes low-energy thermal cautery to remodel the bent cartilage. This is a simple, quick, and less invasive procedure that preserves the structural support of the third eyelid. The tip of an electrocautery handpiece or a handheld cautery unit is applied to the bulbar conjunctival surface of the third eyelid at the central location of the curve in the cartilage. When monopolar cautery is being used, the power is set to the lowest coagulation energy setting and cut is set to zero. The power is gradually increased until the desired effect of conjunctival contraction and cartilage softening is seen such that the third eyelid is remodeled into a more normal physiologic position (6). Complications with this procedure are minimal but can include heat-associated disturbance to the conjunctiva causing local irritation. In addition, care must be taken to not overtreat the area as this can cause a reversal of the curvature (6).

This dog was treated with thermal cautery. Postoperative treatment included topical antibiotic prophylaxis (Polysporin Eye and Ear Drops; Johnson & Johnson, Markham, Ontario) in the right eye, q8h, for 7 d, topical anti-inflammatory treatment with diclofenac sodium 0.1% (Voltaren Ophtha; Novartis, Mississauga, Ontario), in the right eye, q8h for 7 d, and topical ocular lubrication (Optixcare Eye Lube; Aventix Animal Health, Burlington, Ontario), in the right eye, q8h for 7 d. The dog healed well following surgery and no further follow-up was required.

Everted third eyelid cartilage is a congenital or developmental condition most common in large-breed dogs and may have a genetic basis. The main differential diagnosis is a prolapsed gland of the third eyelid; however, sometimes these conditions present concurrently. Careful clinical examination will differentiate the 2 conditions. The prognosis for everted third eyelid cartilage is excellent. Treatment is not always necessary but recommended when there is chronic conjunctivitis and ocular discharge. Surgical correction, by cartilage resection or thermal cautery are both straightforward techniques that have good success in restoring normal third eyelid positioning and function.