Common Ocular Problems of Shih Tzu Dogs Richard E
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Common ocular problems of Shih Tzu dogs Richard E. Christmas Abstract In recent years the Shih Tzu has become a popular breed of dog. It has a number of serious diseases of the eye which are not being recognized by breeders, owners, and sometimes veterinarians. The purpose of this communication is to assist veterinarians in recog- nizing and treating, where possible, some of the com- mon ocular problems of this breed, including medial canthal entropion, various trichiasis problems, dermoids, third eyelid gland prolapse, chronic keratitis and corneal ulcers, progressive retinal atrophy, vitreal syneresis, and retinal detachment. Because most of the problems are inherited or of suspected genetic origin, breeders should receive genetic counselling from their veterinarian. Resume Los problemes oculaires frequents du ShIh Tzu Le Shih Tzu, au cours des dernieres annees, a connu une popularite croissante. Cette race de chien peu cependant developper certaines maladies oculaires serieuses souvent non reconnues par les eleveurs, les propriitaires et meme occasionnellement, par les Figure 1. Medial canthus. Note the infolding of the skin veterinaires. Cet article a pour but de familiariser le bringing facial hair in contact with the cornea and veterinaire aux problemes oculaires frequemment ren- conjunctiva. contres chez cette race et de l'aider a reconnaitre et a traiter ces pathologies lorsque c'est possible. Parmi of the cornea by eyelashes or facial hair. The conjunc- celles-ci, nous rencontrons l'entropion du canthus tiva and cornea are sensitive to trauma from hair, and medial, les problemes de trichiose, les dermoides, le the ocular response is increased (reflex) tearing which prolapsus de la glande nictitante, Ia keratite chronique causes epiphora. For added lubrication and corneal et l'ulcere corneen, I'atrophie progressive de la retine, protection, mucus production by goblet cells in the la degenerescence du vitre et le detachement de la conjunctiva is also increased, which causes a mucoid retine. ocular discharge which the dog owner will notice. The Etant donne que plusieurs de ces maladies sont chronic accumulation of moisture and the persistent hereitaires ou possiblement d'origine genetique, il est wetting of facal hair may cause dermatitis or objec- recommande aux veterinaires de renseigner les eleveurs tionable odor. Persistent irritation of the corneal a ce sujet. (Traduit par Dr Thirkse Lanthier) epithelium stimulates vascularization of the normally avascular cornea. Chronic neovascularity increases the Can Vet J 1992; 33: 390-393. probability of pigmentary keratitis. Any decrease in quality or quantity of the tear film will increase the possibility of a corneal ulcer because of deficiency in Introduction the lubrication required to protect the cornea from the The Shih Tzu has become a very popular breed of continual irritation caused by abnormally directed dog in Canada within the last decade. There is a hair. The nature of the hair also influences the degree high frequency of a variety of ocular problems within of corneal damage. For example, long soft hairs the breed. Because many of these problems are not appear to be less damaging than short coarse ones. The being recognized, the dogs are receiving inadequate presence of hair rubbing on the cornea may prevent treatment, and breeders are not getting advice needed or delay healing after simple superficial corneal to reduce the occurrence of these problems. injuries. If an ulcer develops, ocular pain evidenced by blepharospasm, epiphora, or photophobia may Diseases of the eyelid occur. When these signs are present, the veterinarian The most common ocular problems affecting the Shih should examine the dog carefully for medial entropion, Tzu originate with abnormalities in the conformation caruncular trichiasis, or eyelash anomalies. of the eyelids. I will describe each abnormality Medial entropion is the rolling inward of the skin separately, but the clinical signs for each are similar of the medial canthus (Figure 1). This allows facial and the lesion in each is caused by persistent irritation hair to contact the cornea or conjunctiva or both. Medial entropion tends to be more common in 17th Avenue Animal Hospital, 233 17th Avenue SW, brachycephalic breeds with prominent nasal folds such Calgary, Alberta T2S OA4. as the Shih Tzu, Pekingese, Lhasa Apso, English 390 Can Vet J Volume 33, June 1992 Figure 2. Medial canthus of a five-month-old Shih Tzu. The long hairs (marked by thick arrows) that lie across the cornea originate from the caruncle (thin arrow). Unless this problem is corrected surgically, pigmentary keratitis will likely develop. Figure 4. Upper eyelid of a Shih Tzu with recurring corneal ulcer. The cause of the ulcer was the ectopic cilium (arrows). The conjunctival surface of the upper eyelid is indicated by the "e", and the "s" is the scleral surface of the globe. Figure 3. Cornea of a Shih Tzu with keratitis (white arrow) due to distichiasis (black arrow) and medial entropion. Bulldog, and Pug. Correction of the problem requires surgery, and three techniques and subtle variations of each of them are described in surgical texts and papers. The first technique involves resection of the skin or skin plus orbicularis oculi muscle in a triangular pat- tern under the medial canthus in an attempt to evert the entropic lid(l). In my experience, this technique Figure 5. Shih Tzu puppy with a dermoid on the cornea is of value only when the inferior lid is involved but near the lateral canthus. Note the trichomegaly (excessive in most cases in the Shih Tzu both the superior and length) of the hairs growing from the dermoid. inferior parts of the medial canthus are entropic. I have found too, that in some patients the skin may later resume the entropic conformation. ence of a caruncle from which grow long hairs, Medial canthoplasty, while technically more dif- referred to as caruncular trichiasis (Figure 2). These ficult, has several advantages. First, both superior and hairs not only irritate the cornea, but also act as a wick inferior aspects of the medial canthus are remodelled. that transports moisture from the ventral cul de sac Second, because many Shih Tzus with medial entropion and into the medial canthus and then onto the face. also exhibit euryblepharon (primary symmetric enlarge- Treatment involves surgical excision of the caruncle ment of the horizontal palpebral fissures), and ensuring that the excision is deep enough to be under therefore are predisposed to exposure keratitis and the hair follicles. Without treatment the dog will likely traumatic proptosis, the permanent lid-shortening develop keratitis and subsequent deposition of pigment aspect of the medial canthoplasty enhances the benefit on the cornea (Figure 3). from this procedure. Third, the medial canthoplasty Medial canthoplasty is best performed with the assis- allows the surgeon to excise the caruncle if caruncular tance of an operating microscope or at least a head trichiasis exists. Commonly associated with medial loupe magnifier. It is important to identify and leave entropion in the Shih Tzu is the propensity for the pres- intact the inferior and superior lacrimal puncta. Two Can Vet J Volume 33, June 1992 391 districhiasis has been suggested (11). Clinical observa- tion that ocular conformation tends to be familial sug- gests that improvement by careful selection may be possible. Dermoids In my experience, in the geographic location in which I practice, dermoids are seen more frequently in the Shih Tzu than in any other breed. It is not unusual to see more than one affected puppy in a litter. Dermoids are unsightly and can cause corneal irrita- tion if there is hair growing from them that contacts the cornea; they should be surgically excised (Figure 5). Typical locations for dermoids in the Shih Tzu are on the cornea and at the lateral canthus either on the Figure 6. Three-year-old Shih Tzu blind in this eye as a bulbar or palpebral conjunctiva or both. Removal by result of retinal detachment. The other eye is normal. "T" is the tapetal part of the retina which in this animal is heavily surgical excision can usually be achieved without com- pigmented. "DR" is on the retina which is detached at the promising vision. Caution must be exercised in surgical optic disc and is billowing ventrally over the nontapetal removal because the depth of the lesion will vary. In retina. cases where the dermoid involves deep stromal layers, an attempt to remove all "stained" tissue could result techniques for medial canthoplasty have been in perforation. If the lateral canthus is involved, a described. One involves surgical excision of the offend- lateral canthoplasty to remove the offending dermoid ing skin and closure in two layers (2,3). One variation and to reform the lateral canthus is required. of this technique is closure of skin only. There is a tendency for wound separation if closure involves skin Prolapse of the gland of the third eyelid only rather than skin and conjunctiva. Another excel- This condition, also called "cherry eye", occurs more lent technique is the pocket flap canthoplasty that commonly in puppies than in adults. It is thought to is illustrated and described in several ophthalmic be a genetic problem but the mode of inheritance has texts and papers (3-7). The pocket flap canthoplasty not been determined (12). The prolapsed gland should offers superior wound strength and is preferred in not be excised but rather rtpositioned surgically by one those patients with exophthalmic conformation or of the techniques described in the literature (6,8,9). euryblepharon. Once the gland is repositioned, there is no visible Distichiasis (the presence of an extra row of eye- evidence of the prolapse. As a result, the animal will lashes) and districhiasis (the presence of more than one not be recognized as having had the problem and eyelash from the same opening) are also common buyers may unwittingly use the animal for breeding.