Shih Tzu Are Among the Breeds Considered At Risk for Distichiasis
When "Harvey," a young male Shih Tzu, awoke from sleeping, he often had gummy eyes. His owners, Jonathan Fowler and Louise Sherratt of Northwich, England, diligently wiped the corners of the eyes clean.
Though Harvey showed minimal signs of irritation, his owners realized something wasn't quite right about the dog's eyes. Fowler had researched the Shih Tzu breed before they acquired Harvey, so they were aware of the importance of eye care. Like other breeds with big eyes and long hair, Shih Tzu are prone to eye problems.
A visit to the veterinarian provided the answer: Harvey had distichiasis, a condition in which extra eyelashes, or cilia, grow in an abnormal direction or location along the eyelid. Harvey's condition was mild and probably would have gone unnoticed if Fowler hadn't been so attentive.
"The lashes most likely accounted for the secretions that made Harvey's eyes so gummy and required daily care," Fowler says. "Fortunately, I don't think the condition caused discomfort."
An Underreported Eye Disease
Other Shih Tzu dogs are not so lucky. With continued irritation, the normally clear cornea can become vascularized, with small blood vessels running through it, or the cornea may appear darkened, with a dull or bluish area. When scarring occurs, the cornea looks dull, cloudy or white. Left untreated, corneal scarring can lead to loss of vision or the eye. Dogs that experience corneal ulceration may squint or rub their eyes due to increased tearing, redness and discomfort.
Among the 1,038 Shih Tzu examined by veterinary ophthalmologists from 1991 to 1999 for Canine Eye Registration Foundation (CERF) certification, 21 percent had distichia, and 1 percent had ectopic cilia, a condition in which the lashes grow from the inside of the lid, nearly always irritating the eye. Similarly, from 2000 to 2008, of the 824 Shih Tzu examined for CERF certification, 19 percent had distichia, and 3 percent had ectopic cilia.
Heather Kaese, D.V.M., DACVIM, DACVO, a veterinary ophthalmologist at Eye Care for Animals in Pewaukee, Wis., says the CERF data underreports the prevalence of distichiasis. "You have to consider that the CERF statistics represent dogs that are presented for evaluation in hopes of using them in a breeding program. The statistics do not account for the large number of dogs that do not have an ocular evaluation prior to being bred.
"I would estimate that the majority of Shih Tzu dogs that I examine have distichia," Kaese continues. "Not all these dogs have clinical signs of irritation. Ectopic cilia are far less common than distichia, but both are more commonly seen in Shih Tzu than many other breeds."
Due to the prevalence of distichiasis in some breeds, the eye disorder is believed to be hereditary. Other commonly affected breeds are: Cocker Spaniel, Bulldog, Boxer, Miniature Longhaired Dachshund, Flat-Coated Retriever, Golden Retriever, Pekingese, Cavalier King Charles Spaniel, Pug, Chesapeake Bay Retriever, Samoyed, Staffordshire Terrier, American Pit Bull Terrier, Toy and Miniature Poodle, Boston Terrier, Lhasa Apso, and Shetland Sheepdog.
Distichiasis usually occurs in young dogs, some as young as 6 weeks old. Most affected dogs are diagnosed by 3 years of age. Whether the eye is irritated depends on the number of affected lashes, their size, orientation and stiffness. In most dogs, the distichia, or abnormal eyelashes, grow from the duct openings of the meibomian oil gland along the smooth surface of the lid margin next to the eye. Because the oil gland normally lubricates the eye, the openings are oriented toward the eye. The distichia exit from the gland openings, pointing toward the eyeball and often rubbing against the cornea.
A veterinary ophthalmologist can detect distichiasis during a routine eye examination. If the abnormal lashes are irritating the cornea, the dog's eye may by watery and inflamed. The surrounding lid area and "whites" of the eyes also may be red, and the dog may blink repeatedly, squint or rub his face and eyes. On close examination using a slit-lamp biomicroscope to illuminate and magnify the eye area, the veterinarian will see one or more small lashes growing from the normally smooth lid margin. To get a good look at the distichia, the veterinarian may anesthetize the eye.
Additional testing to rule out other eye disorders may include a Schirmer tear test to assess tear production and keratoconjunctivitis or dry eye, another common problem in the Shih Tzu dog. Fluorescein staining may be used to detect corneal abrasions, and the lids are closely examined to rule out entropion, or rubbing of eyelid hairs against the eye surface. Progressive retinal atrophy and cataracts are other possible eye disorders.
Harvey's veterinarian promptly plucked some of the hairs that caused his distichiasis, while cautioning Fowler and Sherratt that the hairs would regrow. Due to the mildness of Harvey's condition, they opted not to repeat the process. Instead, they continued to closely monitor and wipe away the hairs and gumminess from the dog's eyes.
"I routinely see older Shih Tzu dogs with multiple distichia that have never shown irritation," Kaese says. "The decision not to remove distichia may be fine for dogs with mild cases. I caution owners of dogs that are minimally affected to look for signs of irritation, particularly tearing and redness. They should be aware that some dogs do not act as though they are in pain, even if the damage is ongoing."
Dogs with mild cases and minimal tearing may benefit from ointments applied two to four times daily to lubricate and protect the cornea. In dogs that suffer from irritation, treatment usually consists of removing the lashes and treating the hair follicles to prevent the lashes from growing back. While there is no ideal treatment for all dogs, choices include cauterization, cryoepilation and carbon dioxide laser therapy.
Cauterization of the affected Meibomian gland using heat or an electrical current can be used with a moderate number of distichia. This method isn't considered the best choice for a large number of distichia because destroying too many glands will remove necessary lipid components of the tear film.
Cryoepilation, the most popular treatment, destroys hair follicles using a super-cooled probe. The procedure freezes the lid margin, often causing pigmentation of the eyelashes to be lost temporarily or permanently. The eyelids will be swollen following the procedure. Specialized equipment, general anesthesia and the expertise of a veterinary ophthalmologist are required, with treatment ranging from $1,500 to $2,000, depending on the geographical area where the procedure is performed.
Since the regrowth of lashes can occur, particularly in young dogs, cryoepilation sometimes needs to be repeated, usually performed at a lower cost. Several follow-up visits are needed to ensure the lashes are not regrowing.
"The procedure is not 100 percent on the first treatment," explains Alan Brightman, D.V.M., DACVO, of Houston. "This is because you cannot destroy a hair if it is not there, and hairs fall out over time. Even under an operating microscope, some hair follicles are not always destroyed."
Another possible treatment is carbon dioxide laser therapy. This procedure, which costs from $1,500 to $2,000, uses a laser to vaporize the hair and its follicle. Even the smallest power laser beam can cause scarring in the very thin eyelids, thus the procedure may not be appropriate for all Shih Tzu.
"Unless you only treat a few eyelashes, I feel that this method causes too much damage or scarring of the eyelids," Kaese cautions. "In most Shih Tzu, the hairs are present in large numbers and can run from one edge of the lid margin to the other."
Effective treatments can help Shih Tzu suffering from distichiasis irritation to live more comfortably. Though the genetics behind the disease is not known, researchers at Clarion University in Pennsylvania have begun collecting pedigree information and blood samples from affected dogs of all breeds to determine the mode of inheritance. In humans, distichiasis associated with lymphedema has been mapped to a mutation in a single gene, but there is no evidence that the same gene is the culprit in dogs.
Aside from avoiding breeding dogs from at-risk bloodlines, there is no way breeders can guarantee a litter won't produce affected dogs. The high incidence of the disease in Shih Tzu means that breeders can't simply remove all affected dogs from the gene pool. The best advice is to refrain from breeding affected dogs to each other. Hopefully one day researchers will pinpoint the gene or genes that cause distichiasis.
Purina appreciates the support of the American Shih Tzu Club and particularly Carlene Synder, chair of the Health, Education and Research Committee, in helping to identify topics for the Purina Pro Club Shih Tzu Update newsletter.