Usually, a puppy who's born with an eye birth defect is experiencing an inherited condition. Defects can happen in utero, too, developing spontaneously or due to environmental influences. A mother's poor nutrition, infections and exposure to toxins are among the potential causes of eye defects for a puppy in the womb.
Rare for One, Not Another
Each breed of dog carries its own unique strengths and vulnerabilities. Eye defects are included in the genetic lottery, and a condition that's not too unusual for a dog of one breed can be rare for a dog of a different breed. However, eye problems can strike any dog. Progressive retinal atrophy, a slow deterioration of the retina, is one of the more common congenital eye disorders in dogs, along with congenital cataracts and glaucoma.
Dogs usually have brown or blue irises. Sometimes a hole or a thin spot exists in a dog's eye, known as a coloboma. If your pup has an iris coloboma, it means his iris didn't form correctly. This condition can be mild or severe; if the holes in your pup's iris are large, more light can enter his eye, causing the dog to squint more than normal. According to the book "Essentials of Veterinary Ophthalmology," dogs rarely have iris coloboma; however, the defect is a common element in ocular merling in Australian shepherds. Nothing can correct this condition. But it's not a big problem for most dogs. A dog with an iris coloboma will benefit from avoiding bright light or wearing doggy goggles.
Lenticonus and Lentiglobus
The dog with lenticonus has a conical protrusion of his eye's lens; if he has lentiglobus, the bump is spherical. The condition often occurs with other conditions, such as congenital cataracts and retinal dysplasia. This condition can affect a dog's visual acuity, but treatment is not usually necessary.
It's extremely rare, but, once in a while, a dog is born without a lens in his eye. Known as primary aphakia, this condition is rooted in the pup's embryonic development and comes with malformation of the other parts of his eye. Since the lens influences how other parts of the eye develops, it's normal for other eye problems, such as a missing pupil, to accompany aphakia. As well, his eye will look underdeveloped. A dog with aphakia may be totally blind or may experience a bit of squinting.
Other potential congenital eye defects in dogs include missing pupils, tear duct openings and irises. The optic nerve can be underdeveloped, a condition that's common for miniature and toy poodles, often resulting in blindness. More rarely, a dog can be born without eyes or with a hidden eyeball. Some defects can be corrected with surgery or medication; others cannot. However, blindness in and of itself isn't lethal for a dog. Most blind dogs are able to live well despite lacking vision.