Collies are highly intelligent, trainable, and loyal dogs, suitable for a wide range of lifestyles. Originally bred for herding, the collie now occupies homes as an ideal family dog, competes in dog sports, and steals hearts on the silver screen. Collies are generally regarded as healthy, but their eye health is a major concern. Most collies are born with some form of eye abnormality, and the abnormality severity determines the potential impact on vision.
Most of the collie’s eye problems have a known genetic basis, which means diligent puppy screening examinations with Veterinary Vision Center, combined with genetic testing for breeding dogs, can gradually help reduce the incidence. Although fewer collies are now born with eye disorders, the process will take time. For now, here are the most common genetic eye diseases in collies.
#1: Collie eye anomaly
Collie eye anomaly (CEA), which is an inherited syndrome, is a collection of several different eye changes that can occur alone or in combination. Because the CEA inheritance pattern is recessive, dogs must have two copies of the faulty gene—one from each parent—to develop the disorder. Dogs who inherit only one copy do not develop the syndrome, but they become carriers who can pass on the gene to some of their offspring. Genetic testing can identify affected and carrier dogs to guide breeder decision-making and produce dogs with healthier eyes.
CEA causes varying degrees of vision impairment through alterations in retinal development, and the following changes may occur:
- Choroidal hypoplasia — Areas of underdeveloped retina (i.e., the tissue that detects light) and choroid (i.e., the tissue that nourishes the retina) lead to blind spots or diminished ability to process visual information.
- Optic disc coloboma — The optic disc (i.e., the visible portion of the optic nerve in the back of the eye) transmits messages from the retina to the brain. Congenital malformation or incomplete development in this area may result in partial to complete blindness.
- Retinal folds or detachments — Poor retinal development causes the tissue to fold in on itself during development and may separate from the back of the eye, resulting in partial to complete blindness.
#2: Persistent pupillary membranes in collies
Persistent pupillary membranes (PPMs) are residual blood vessel fragments that fail to regress after birth. They form tissue strands that can connect or obstruct different eye structures, leading to functional alterations. Most collies with PPMs have the iris-to-iris form, which may partially or completely cover the pupil opening and obstruct vision.
#3: Microphthalmia in collies
Microphthalmia is an eye that is smaller than normal, often underdeveloped, with structures inside the small eye possibly located abnormally and obscuring vision. Microphthalmia in collies is usually associated with the Merle color gene and is most severe in dogs born with a predominantly white coat. White dogs with microphthalmia also may be deaf.
#4: Distichiasis in collies
Distichiae are extra eyelashes that may grow toward the eye and rub on the cornea. Dogs with distichiasis often have many of these extra hairs, with multiple hairs growing out of each follicle. This disorder is not exclusive to collies—many other breeds develop this problem—but because collies have a rough, stiff haircoat, the eyelashes tend to cause serious corneal damage and must be removed surgically to prevent scarring.
#5: Cataracts in collies
Cataracts also occur across many different dog breeds. The incidence is low in collies compared with their other issues, but significant enough to warrant a mention in the Orthopedic Foundation for Animals (OFA) database of breed-related eye diseases. Cataracts are presumed to have a genetic basis, but the specific genes have not been identified. The OFA recommends that dogs with evidence of early cataract formation not participate in breeding programs, since the genetic basis is uncertain.
Only 16% of collies examined for an OFA certification have completely normal eyes. The rest have at least one congenital abnormality, and many have multiple issues. Eliminating genetic eye disorders has been challenging because of the breed’s small gene pool, but responsible breeders who commit to juvenile eye screening examinations with our Veterinary Vision Center ophthalmologist and who seek appropriate genetic testing for parents can help reduce this problem. Contact us to schedule your collie or collie puppy’s next screening, pre-breeding, or routine eye examination.