Progressive Retinal Atrophy

TL;DR. Progressive Retinal Atrophy (PRA) is an inherited, painless eye disease that causes gradual, permanent blindness in dogs and cats, though affected pets maintain an otherwise normal lifespan and excellent quality of life.

Progressive Retinal Atrophy is an inherited condition that affects both dogs and cats.

What is it?

Progressive Retinal Atrophy (PRA) is a group of inherited, degenerative diseases that affect the photoreceptor cells in the retina of dogs and cats. The retina is the specialized, light-sensitive tissue lining the back of the eye. It acts much like the film in a camera, capturing light and converting it into electrical signals that the brain interprets as images.

Within the retina, two primary types of photoreceptor cells exist: rods and cones. Rods are responsible for detecting motion and facilitating vision in low-light or dark conditions. Cones are responsible for high-acuity vision and color perception in bright-light conditions. In pets affected by PRA, these cells develop abnormally or begin to degenerate prematurely.

In the vast majority of cases, the rod cells degenerate first, leading to a gradual loss of night vision. Over time, the cone cells also deteriorate, culminating in complete, bilateral (both eyes) blindness. Because the degenerative process is slow and entirely painless, pets typically adapt remarkably well to their fading vision, often hiding the early signs of the disease from their owners.

Causes & risk factors

Progressive Retinal Atrophy is an inherited genetic disorder. It is not caused by trauma, dietary deficiencies, or infections. In most affected breeds, the disease is transmitted via an autosomal recessive inheritance pattern. This means an animal must inherit two copies of the mutated gene—one from each parent—to develop the clinical disease.

Animals that inherit only one copy of the mutated gene are classified as "carriers." Carriers will never develop symptoms of PRA and will maintain normal vision throughout their lives, but they can pass the mutated gene to their offspring. If two carriers are bred together, there is a 25% chance that each puppy or kitten in the litter will inherit both mutated genes and eventually go blind.

While PRA can affect any mixed-breed or purebred dog or cat, certain breeds carry a significantly higher genetic risk.

Signs to watch for

Because PRA progresses slowly over months or years, the clinical signs can be subtle in the early stages. Owners often do not notice a problem until the disease has advanced significantly.

• Nyctalopia (night blindness) [Cardinal]: This is almost always the earliest clinical sign. Affected pets may hesitate to go outside into a dark yard, bump into furniture in dimly lit rooms, or refuse to walk down dark hallways.
• Complete blindness [Cardinal]: As both rod and cone cells completely degenerate, the pet will lose all functional vision in both bright and dim light.
• Mydriasis (dilated pupils) [Common]: Because the retina is receiving less light stimulation, the pupils will remain widely dilated even in bright environments to let in as much light as possible.
• Decreased pupillary light reflex (PLR) [Common]: When a veterinarian shines a bright light into the pet's eyes, the pupils will constrict much slower than normal, or they may not constrict at all.
• Tapetal hyperreflectivity [Common]: The tapetum lucidum is the reflective layer at the back of the animal's eye. As the overlying retina thins due to degeneration, more light reflects off this layer, making the eyes appear unusually shiny or "glow" more intensely in the dark.
• Secondary cataracts [Common]: As the retinal tissue degenerates, it releases toxic byproducts into the vitreous humor (the gel inside the eye). These byproducts can cause the lens of the eye to become cloudy, forming cataracts that further block light from reaching the retina.
• Retinal vascular attenuation [Common]: This is a clinical sign observed by your veterinarian during an ophthalmic exam. The blood vessels that supply the retina shrink and thin as the tissue degenerates.

Dilated pupils and increased reflectivity (tapetal hyperreflectivity) are common signs of PRA.

How vets diagnose it

Diagnosing Progressive Retinal Atrophy requires a thorough ophthalmic examination. Your veterinarian will begin by evaluating your pet's basic visual reflexes, such as their ability to follow a falling cotton ball or navigate an obstacle course in both bright and dim light.

To confirm a diagnosis, your veterinarian will perform or refer you to a veterinary ophthalmologist for the following tests:

• Indirect Ophthalmoscopy: After dilating your pet's pupils with specialized eye drops, the veterinarian will use an indirect ophthalmoscope and a hand-held lens to examine the fundus (the back of the eye). They will look for classic signs of retinal degeneration, including retinal vascular attenuation (thinning blood vessels) and tapetal hyperreflectivity (increased shininess of the reflective layer).
• Electroretinography (ERG) [Gold Standard]: An ERG is the definitive diagnostic test for PRA. It measures the electrical activity of the photoreceptor cells in response to light flashes. This test is highly sensitive and can detect abnormal retinal function long before any visible changes can be seen during an ophthalmic exam. Because it requires precise electrode placement on the eye, it is typically performed under light sedation or general anesthesia by a board-certified veterinary ophthalmologist.
• Genetic Testing (DNA): For many breeds, specific DNA tests are available to identify the genetic mutations responsible for PRA. This test is non-invasive, usually requiring only a simple cheek swab or blood sample, and can identify clear, carrier, or affected animals long before clinical signs develop.

Treatment options

Currently, there is no proven medical or surgical treatment that can reverse, halt, or slow the progression of Progressive Retinal Atrophy. Once the photoreceptor cells begin to degenerate, the process inevitably leads to complete blindness.

Management of PRA focuses entirely on supportive care and environmental adaptation:

• Antioxidant Support: Some veterinary ophthalmologists recommend specific oral antioxidant supplements formulated for canine or feline eyes. While these supplements cannot cure PRA or stop its progression, they may help support overall ocular health and delay the onset of secondary cataracts.
• Managing Secondary Cataracts: If your pet develops secondary cataracts, they must be monitored closely. While cataract surgery is highly successful at restoring vision in pets with healthy retinas, it will not restore vision in a pet with PRA because the underlying retina is dead. However, cataracts can sometimes cause painful internal inflammation (lens-induced uveitis). If this occurs, your veterinarian will prescribe anti-inflammatory eye drops to keep your pet comfortable.
• Environmental Modifications: Blind pets adapt incredibly well by relying on their highly developed senses of hearing and smell. You can help your pet navigate their environment safely by keeping furniture in consistent locations, using textured mats near food bowls and doorways, utilizing scent markers (such as a drop of lavender oil) to identify boundaries, and keeping them on a secure leash during walks.

Prognosis

While the prognosis for preserving your pet's vision is poor, the prognosis for their overall systemic health, comfort, and lifespan is excellent. PRA is a completely painless condition. It does not cause physical discomfort, and it does not affect any other organ systems in the body.

With patience, consistency, and a safe home environment, blind dogs and cats continue to play, navigate their homes, and enjoy an exceptionally high quality of life.

Prevention

Because Progressive Retinal Atrophy is an inherited genetic disease, it cannot be prevented through lifestyle changes, diet, or vaccines. Prevention relies entirely on responsible breeding practices.

Before breeding any high-risk dog or cat, genetic screening should be performed. Animals that test positive for the PRA mutation (either as carriers or affected individuals) should be removed from breeding programs, or bred only to confirmed "clear" partners under strict genetic guidance to ensure no affected offspring are produced.

When to call your vet

Schedule a non-emergency appointment with your veterinarian if you notice early signs of vision loss, such as hesitancy in the dark, bumping into objects, or if your pet's eyes appear unusually shiny or cloudy.

You should seek immediate veterinary attention if your pet experiences sudden blindness, signs of eye pain (such as squinting, tearing, or pawing at the eye), or if the eyes become red and inflamed. These signs are not typical of PRA and may indicate a painful, acute condition such as glaucoma, uveitis, or sudden acquired retinal degeneration syndrome (SARDS).

For specific breeds

Several breeds are highly predisposed to specific genetic forms of PRA:

• Toy Poodles: Highly susceptible to the progressive rod-cone degeneration (prcd-PRA) form of the disease, which is inherited as an autosomal recessive trait. Clinical signs typically emerge in young adulthood.
• Labrador Retrievers: Also frequently affected by the autosomal recessive prcd-PRA mutation. Genetic screening is highly recommended for all breeding stock.
• Abyssinian Cats: Predisposed to an autosomal recessive form of PRA (known as rdAc), which causes progressive retinal degeneration leading to blindness, typically by 3 to 5 years of age.

Sources

• Standard veterinary ophthalmic consensus and genetic screening guidelines.
• Long-term clinical observation data regarding inherited retinal degenerations in companion animals.