Ocular Disorders Proven or Suspected To Be Hereditary in the Shih Tzu

By Denise M. Lindley, D.V.M



The Shih Tzu has several genetic eye diseases. One of the most important diseases in this breed is due to the brachiocephalic skull. Brachiocephalic dogs are those dogs that have shortened noses and very prominent eyes due to shallow orbits. The orbit is the bony socket that surrounds the eye. The shallow bony orbit in the short-nosed dog causes the eyeball itself to be in a more prominent position, giving the appearance of being larger than dogs of similar sizes with longer noses. Along with this skull conformation, there is the problem of lagophthalmos. Lagophthalmos is an inability to properly close the eyelid over the cornea. Lagophthalmic dogs are generally those dogs that have an enlarged palpebral fissure. The palpebral fissure is the space between the upper and lower eyelids. Brachiocephalic dogs classically have all their cornea exposed when the eyes are open and generally they have sclera (the white of the eyeball) exposed also. This conformation causes two clinically serious consequences to the Shih Tzu. The first is they are more prone to exposure keratitus. Keratitus is inflammation of the cornea. In its most severe form, it is ulcerative. A deep ulcer can cause the cornea to rupture. Chronic low grade exposure keratitus leads to central scarring of the cornea and pigmentary changes on the surface of the cornea which can decrease vision. The second big problem related to brachiocephalic skull conformation that the Shih Tzu has, is proptosis. The brachiocephalic breeds of dogs are more pre-disposed to traumatic proptosis of the globe than dogs that have longer noses. When a globe moves forward out of the orbit, as happens with proptosis, the eyelids clamp behind the eyeball itself and cause the venous blood from the eye not to be able to return. This causes a lack of oxygen to the retina and can lead to blindness within minutes. If a Shih Tzu has a proptosed globe it is an emergency! Veterinary care has to be sought immediately (within 20 minutes) in order to attempt to save vision and save the eye.

Other problems found in the Shih Tzu include eyelash disease, which consists basically of two conditions. The first condition is distichiases. These are the eyelashes abnormally located at the eyelid margin which may cause ocular irritation. Distichiasis may occur at any time in the dog's life. The hereditary basis of the condition is not established. Distichiasis can cause severe scarring of the cornea and/or ulcers that could lead to blindness. Second condition is ectopia cilia. Ectopic cilia is like distichiasis in the fact that ectopic cilia are eyelashes that instead of emerging from the eyelid margin, the hairs emerge through the eyelid conjunctiva. They most commonly occur in the upper central eyelid. These are found in younger dogs and can cause significant pain as exhibited by squinting and facial wetness. Like distichiasis, corneal ulcers can occur.

Two conditions that involve the inside of the eye in the Shih Tzu include hereditary cataracts or juvenile cataracts and progressive renal atrophy (PRA). The breeding recommendation for either one of these conditions is NO. This is unlike the breeding recommendation in the previous conditions that were described, where the breeding advice is breeder option. A cataract is a lens opacity which can affect one or both eyes and may involve the lens partially or completely. In cases where cataracts are complete and affect both eyes, blindness results. Progressive retinal atrophy is a degenerative disease of the retinal visual cells which progresses to blindness. Usually seen in the young adult anima, it starts out as night blindness, which progresses slowly to complete blindness. PRA is recessively inherited in most breeds.

Other problems that the Shih Tzu has include dry eye, which is technically called keratoconjunctivitis sicca. Dry eye is dryness of the cornea and the conjunctiva. It is an abnormality of the tear film that most commonly is a deficiency of the water part of the tear film. The mucous and fat layers of the tear film are also affected, but when the water layer is not present the mucous in the fat layer makes very hard, dry, ropy debris which is found on the eyelids. Dry eye leads to chronic corneal irritation and this leads to ulcers or scarring which can cause visual impairment. A less common defect found in the Shih Tzu is retinal detachment. This is due to a vitreoretinal dysplasia. The vitreous is the gel found in the back of the eye, and it is very closely adhered to the retinas. Dysplastic means that it has not developed normally which means that the abnormal interface between the vitreous and the retina can cause the retina to come loose. This causes blindness.

FOR MORE INFORMATION about inherited eye diseases in the Shih Tzu, I recommend Ocular Disorders Proven Or Suspected To Be Hereditary In Dogs, by the American College of Veterinary Opthalmologists. In this book, the conditions for each breed are described in layman's terms and advice for breeding is given. The Canine Eye Registration Foundation (CERF) is most helpful in gathering information about inherited eye disease in the Shih Tzu and other breeds. CERF and the ACVO recommend annual eye exams on all animals. There is no minimum age. So first eye exams can be done as early as five to six weeks of age as these dogs are large enough that the opthalmologist can perform a complete eye examination.

Only by examining animals and identifying problems can breeders be responsible and make informed decisions about breeding animals with eye disease. CERF membership entitles the national Shih Tzu club to bi-annual data on inherited eye disease in its breed. Animals that are found to be free of major inheritable eye disease on CERF examination have their CERF numbers given to AKC. AKC in turn publishes them quarterly in the AKC Awards. CERF numbers are then placed on the AKC certificates along with OFA numbers.



Reprinted from the ASTC Bulletin