Hyaloid arteries are fetal structures that nourish the area of the developing lens, extending from the optic disc to center of the posterior part of the lens. Sometimes part or all of this vessel will persist (persistent hyaloid artery if entire or hyaloid remnant if partial), occasionally it will still transport blood (patent hyaloid artery). Some persistent hyaloid arteries will go away in the first few weeks of life. Usually they are benign defects and do not impact vision, but sometimes a cataract will be associated with the lens attachment. These cataracts may progress until the dog is blind in the affected eye.
Hyaloid arteries are not considered a hereditary problem, however their association with cataracts and the frequency with which they occurred among dogs which were part of the CEA study in the early 1990s is reason for concern. Until such time as the heritability, or lack thereof, is clearly established, breeding a dog with a hyaloid-associated cataract should be discouraged. If a dog has a hyaloid, select mates for it that were not born with them and are not CEA carriers.