Dogs do not get "lazy eye" or amblyopia in the way children do. But dogs, particularly brachycephalic or flat-faced breeds with bulging eyes like a Shih Tzu can have vision problems in an otherwise normal looking eye. "Lazy eye" is also a common term applied to cross eyes or strabismus, which can also appear in brachycephalic breeds.
Shih tzus are prone to having birth defects of their eyelids or eyelashes. These will be apparent when the shish tzu is still a puppy. This may cause blindness in the eye. Because the eyes are so large, they are more prone to getting injuries, even if those injuries are not at first visible. Shih tzus, like other brachycephalic breeds like the Boston terrier can be born with crossed eyes. But Shih Tzu puppies can get crossed eyes due to head injuries, a sudden drop in blood sugar or infections like encephalitis.
Strabismus in puppies tends to only affect one eye and not both. But lazy eye can appear differently for each Shih Tzu puppy. Seizures can makes one or both eyes cross or move in a strange repetitive pattern, as if the puppy was watching an invisible fly. Shih Tzu puppies are not as prone to getting epilepsy as other breeds like the American water spaniel but they are prone to other seizure disorders such as hypoglycaemia, encephalitis or a head injury.
All toy sized dog breeds, including shih tzus, are prone to low blood sugar or hypoglycaemia, according to "The Veterinarians' Guide to Your Dog's Symptoms." This is often apparent in dogs under a year old. One sign of collapse or a seizure from hypoglycaemia is lazy eye.
Since Shih Tzu puppies are so small, just falling out of the arms of someone standing up may cause a head injury. Kneel before picking up a puppy. Restrict Shih Tzu puppies to playing with other puppies or dogs similar in size. Small, frequent meals three to six times a day can help prevent seizures from hypoglycaemia. Getting the puppy regularly wormed and keeping it in a temperature controlled environment can eliminate stress which may cause juvenile hypoglycaemia.
Shih Tzu puppies born with lazy eyes generally adjust to their eye position and do not need surgery or medication. If the lazy eye is due to a birth defect of the eyelid, it will need corrective surgery. Shih Tzu puppies with lazy eye due to hypoglycaemia can often live long lives with management and check ups. But Shih Tzu puppies aren't given a good chance to have a normal lifespan if they suddenly develop a lazy eye due to encephalitis, head injury or a seizure disorder.