Heredity Ocular Disorders 

by Denise M. Lindley, DVM, MS, Diplomate, ACVO, Staff Opthamologist, President, Animal Eye Consultants.
 Reprinted from the ASTC Bulletin


Shih Tzu have several genetic eye diseases. One of the most important diseases in this breed is due to the brachiocephalic skull. Brachiocephalic dogs have shortened noses and very prominent eyes due to shallow orbits-- the bony socket that surrounds the eye. The shallow bony orbit in the short-nosed dog causes the eyeball 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-- an inability to properly close the eyelid over the cornea. Lagophthalmic dogs generally have an enlarged palpebral fissure-- 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 the white of the eyeball exposed also. This conformation causes two clinically serious consequences to the Shih Tzu.

First they are more prone to exposure keratitus-- 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 that can decrease vision. 

The second big problem related to brachiocephalic skull conformation in Shih Tzu is proptosis. 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-- 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. The second condition is ectopia cilia. Ectopic cilia is like distichiasis in that ectopic cilia are eyelashes that 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 (see the separate article on dry eye that appears elsewhere on the ASTC web site). 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. 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 American 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. 

by Tracey King, DVM, ACVO
Dr. King specializes in veterinary opthamology in Marietta, Georgia.
Her article is reprinted from the ASTC Bulletin.

Distichiasis describes a condition in which eyelashes are abnormally located in the eyelid margin. This condition may occur at any time in the life of a dog and is probably inherited in many breeds.
Clinical signs of distichiasis include tearing (in varying amounts), redness of the conjuctiva, and inflammation and possible ulceration of the cornea. Diagnosis can be made by your veterinarian.

Treatment of distichiasis includes epilation, electro-epilation, cyrotherapy, or surgical excision. Each procedure can offer an effective treatment regimen for canine distichiasis.

In Shih Tzu, distichiasis occurs with reasonable frequency and, in some dogs with shallow orbits, produces chronic inflammation of the cornea. Most dogs are only mildly affected. The hereditary basis has not been established, although it seems probable due to the high incidence in some breeds. Breeding discretion is advised; reducing the incidence of distichiasis is a logical goal.