A dog's eyes are vulnerable to literally dozens of diseases. One of the more unusual of these is known as Persistent Pupillary Membrane, or PPM.
With this condition, strands of membrane are present in the eye, often crisscrossing it and connecting to various structures within the eye. These strands are leftover remnants of blood vessels that supplied nutrients to the developing eye before the puppy was born. In most cases these vessels deteriorate and disappear before or shortly after birth. When they do not, PPM is the result.
PPM may or may not impair your dog's vision, depending upon the location of the membrane strands. Often these cross from the iris to the cornea, where they can cause cloudiness (opacity) in the cornea. In other cases, the strands cross from the iris to the lens of the eye, potentially leading to early-onset cataracts. Or, they can clump together as sheets of fibrous tissue within the anterior chamber of the eyeball. For many dogs, PPM causes no problems. Even when cataracts result from PPM, they usually will not worsen, as do normal cataracts.
Researchers do not yet know exactly how PPM is caused. It is believed to be and/or suspected to be inherited in the Basenji, Corgi, Chow Chow, and Mastiff breeds. It's most notable in the Basenji. These dogs are prone to having PPM with strands that attach to the dog's cornea, often impairing their vision. In Basenjis the problem also often appears in conjunction with another eye condition, optic nerve coloboma, which is a cavity inside the optic nerve that can cause blindness. Dogs of these breeds with PPM should not be bred, in order to help eliminate the defective gene within the breed.
PPM, meanwhile, also is found in the following breeds: Akita, Alaskan Malamute, Australian Shepherd, Basset Griffin Vendeen (petite), Beagle, Belgian Sheepdog, Belgian Tervuren, Bichon Frise, Bouviers des Flandres, Cocker Spaniel, Doberman Pinscher, Havanese, Lowchen, Norwegian Elkhound, Old English Sheepdog, Papillon, Portuguese Water Dog, Samoyed, Shetland Sheepdog and Springer Spaniel, plus all types of Collies, Poodles, Retrievers, Setters, and Terriers. If affected dogs of these breeds have parents or siblings with the disorder, then they also should not be bred.
In some cases, the owner will notice the membrane in their dog's eye in the form of small white spots. Or, your veterinarian may diagnose the condition using an ophthalmoscope. The problem itself is untreatable, but in most cases PPM does not affect the dog's vision. If there is swelling or "bluing" of the cornea, however, anti-inflammatory eye drops may be prescribed to reduce the swelling. If there are extensive cataracts, surgery may be performed as well.