PRA is a family of hereditary progressive degenerative eye diseases that affect the retina and most branches lead to total blindness. The typical symptoms of a dog having PRA are night blindness or a green sheen on the eye in dim lighting. After having lost the ability to see at night time, the dog will also lose the ability to see in fully lighted rooms. The reason for night blindness coming first is that the cells that allow vision in reduced lighting (rods) degenerate before those cells that allow vision in fully lighted rooms (cones).

Veterinarians who examine dogs with PRA will discover that the size and number of blood vessels in the retina have reduced, and an alteration in the reflectivity in the shinny membrane behind the retina (tapetum). An important test made by the ophthalmologist is an electroretinogram (ERG). This test discovers small electrical signals given by the retina when it reacts to light. ERG works in the following way; a lense is placed on the dog’s eye, while to electrodes are placed on his head. Then a bright light is shone on the eye. If the retina is normal, there comes a signal from the retina which is measured in a computer. A normal retina and the signal will be amplified in strength. If there is an irregularity in the retina, the signal diminishes in strength.

It is difficult to make this disease extinct from a breed since to recessive genes are needed, one from the mother and one from the father, for the pup to receive PRA. The PRA gene can be hidden in the gene pool and not show itself for several generations of puppies. Then, when two dogs who are carriers are mated, the disease is there again.

There is more than one known form of PRA. For some you can do a gene test or a marker test. The foremost will prove the gene directly, whilst the other proves a marker connected to the gene. Mastiffs may now have a DNA test executed. You can send in a blood sample and get back whether the mastiff is a carrier, has PRA or is PRA free (none of the PRA genes proven), before the mastiff has become old enough to show any symptoms.

This also makes it possibles for breeders to plan their litters so that PRA free are possible. There is more than one wat leading to PRA mastiffs:

• Both parents DNA tested as free

• Both of the fathers parents DNA tested free, and the mother DNA tested as free.

• Both of the mothers parents DNA tested free, and the mother DNA tested as free.

• All four granparents have been DNA tested as free.

• …

Diagnoses made by other laboratories other than those approved by the kennel club, will not be registered.