Progressive retinal atrophy

Symptoms an owner can spot at home

• Hesitation in dim light: refusing unlit stairs, the garden at night, or dark hallways
• Bumping into furniture after dusk while navigating normally in daylight
• Unusually bright, greenish eyeshine in photographs or torchlight
• Pupils that stay dilated in bright conditions
• Startling more easily, or becoming reluctant in unfamiliar places
• Cloudiness developing later, as cataracts can accompany advanced disease

When to see a vet

• Any suspected vision change, since sudden blindness has causes that are urgent and treatable and needs distinguishing from PRA
• Vision loss appearing over days rather than months, which points away from PRA toward something requiring immediate attention
• A red, painful or cloudy eye, or one the animal is holding shut, all of which are separate problems
• A dilated pupil that does not respond to light
• Before breeding any animal of an affected breed, so the correct DNA test and an eye examination can be arranged

What it is

The retina lines the back of the eye and converts light into nerve signals using two cell types: rods for low light and cones for daylight and detail. In progressive retinal atrophy these photoreceptors degenerate. Rods usually fail first, which is why night blindness precedes day blindness, and complete loss of vision typically follows over one to two years.

There are many genetically distinct forms, documented across more than a hundred dog breeds, and they differ in age of onset and speed of progression. Some appear in puppyhood as the photoreceptors fail to develop properly; the more common late-onset forms develop normally and then deteriorate in adulthood. Most forms are autosomal recessive, so an animal needs two copies to be affected and single-copy carriers are entirely normal.

How vets diagnose it

• Retinal examination, usually by a veterinary ophthalmologist, which shows characteristic thinning and increased reflectivity at the back of the eye.
• Electroretinography, which measures the retina's electrical response to light and can detect disease before an owner notices anything.
• Breed-specific DNA testing, which identifies a known mutation. A test validated in one breed says nothing about a different breed's form.
• Ruling out the urgent alternatives, including sudden acquired retinal degeneration, hypertension, and inflammatory disease inside the eye.

Living with a blind animal

Owners consistently dread this more than the animal experiences it. Vision is not the primary sense for either dogs or cats, the loss is gradual enough to permit adaptation, and most affected animals go on living ordinary lives. The practical work is mostly arranging a predictable environment rather than buying equipment.

• Keep furniture, food, water and beds exactly where they are. Consistency is the entire strategy.
• Speak before touching, so the animal is never approached silently or startled awake.
• Block stairs, ponds, pools and drops during the adjustment period.
• Textured mats at doorways and stair heads give underfoot landmarks.
• Scent-based and sound-based toys keep enrichment working once visual play stops.
• Keep the animal on lead in unfenced areas, and consider a tag noting reduced vision.

Be sceptical of products sold to halt or reverse it. No supplement or diet has been shown to slow progressive retinal atrophy, and the marketing around antioxidant preparations outruns the evidence considerably.