PHPV/PTVL stands for Persistent Hyperplastic Primary Vitreous/Persistent Tunica Vasculosa Lentis. PHPV is a congenital defect, meaning it is present at birth. It is due to abnormalities in the development and regression of the hyaloid artery. The hyaloid is a fetal structure that is necessary before birth for proper development of the lens. It is supposed to go away around the time the pup is born. Occasionally it fails to do so, at least in part, and is then called a hyaloid remnant.
PHPV abnormalities involve the back of the lens and sometimes include Persistent Tunica Vasculosa Lentis (PTVL), the failure of vascular tissue on the back of the lens (originally connected to the hyaloid) to go away. The correlation between PHPV/PTVL and hyaloid remnants is not known. PHPV/PTVL can cause visual impairment and is sometimes associated with other eye defects. It will not pass an eye exam.
PHPV/PTVL is recognized as inherited in some breeds but no mode of inheritance has been identified in breeds thus far studied. The extremely low incidence in Aussies may indicate it is not inherited in this breed. To be safe, consider it a major fault, Breeding an affected dog, especially if it has vision loss, is probably ill advised. If the dog or its close kin are bred, avoid mates who have PHPV/PTVL or have a family history of it. Also avoid dogs that had persistent hyaloids, since PHPV/PTVL is associated with the hyaloid artery.