Pannus is an immune-related eye disease in dogs where the body’s own immune system attacks the cornea, causing a progressive pinkish film of blood vessels and pigment to spread across the eye’s surface. Left untreated, pannus can eventually cover the entire cornea with dark, opaque tissue and lead to significant vision loss. The good news: with consistent treatment, most dogs retain functional vision for life.
How Pannus Develops
The medical name for pannus is chronic superficial keratitis (CSK). It starts when the immune system mistakenly targets the clear outer layer of the eye, the cornea, triggering inflammation. The earliest visible change is typically a pinkish, fleshy lesion at the outer edge of the cornea where it meets the white of the eye. Tiny new blood vessels grow inward from this edge toward the center of the cornea, a process called neovascularization.
As the disease continues, dark pigment cells from the edge of the cornea follow those blood vessels inward. Over time, fleshy granulation tissue infiltrates the surface layers of the cornea, and small fatty deposits may appear just ahead of the advancing lesion. In advanced cases, the entire cornea can become vascularized, pigmented, and opaque, seriously impairing the dog’s ability to see. The condition affects both eyes, though one may look worse than the other at any given time.
Breeds and Age of Onset
German Shepherds and Belgian Shepherds have especially high rates of pannus, and researchers at Cornell University have been investigating specific immune system genes (within the major histocompatibility complex) that appear to confer risk in these breeds. Border Collies and Greyhounds are also commonly affected. That said, pannus can occur in dogs of any size or breed.
Age of onset matters for prognosis. Dogs diagnosed young, between one and five years old, tend to experience faster progression and more aggressive disease. Dogs that develop pannus later in life, after age four or five, often have milder lesions that are easier to control.
Why Altitude and UV Light Matter
Ultraviolet radiation is a major environmental driver of pannus. A study of dogs across Colorado found that altitude of residence was strongly correlated with disease prevalence. Dogs living above 7,000 feet were 7.75 times more likely to develop corneal lesions than dogs living between 3,000 and 5,000 feet. At higher elevations, the thinner atmosphere filters out less UV light, so a greater proportion of solar energy reaches the eye at the short wavelengths (around 290 nanometers) thought to be most damaging.
Interestingly, total sunlight intensity alone didn’t predict pannus rates. What mattered was the UV composition of that sunlight, explaining why a dog in a sunny but low-altitude city might fare better than one in a moderately sunny mountain town. Dogs living in any high-UV environment, whether at altitude or in states like Texas, face increased risk and faster progression.
This UV connection also explains the typical pattern of the disease on the cornea. The outer and lower portions of the eye receive the most direct sunlight exposure, and that’s exactly where pannus lesions usually appear first.
How Pannus Is Diagnosed
In most cases, a veterinarian or veterinary ophthalmologist can diagnose pannus based on the dog’s breed, age, and the characteristic appearance of the corneal lesions. The combination of blood vessel growth and pigment creeping inward from the edge of the cornea, particularly starting on the outer (temporal) side, is distinctive enough to identify without invasive testing.
A few other conditions can look similar. Pigmentary keratitis, dry eye (keratoconjunctivitis sicca), chronic irritation from eyelid problems, and scar tissue from old corneal wounds can all cause corneal cloudiness or discoloration. Your vet may perform a tear production test or examine the eyelids to rule these out, since each has a different treatment approach.
Treatment: What to Expect
Pannus cannot be cured, but it can be controlled. Treatment is lifelong, and the goal is to halt the advance of blood vessels and pigment across the cornea, preserving the dog’s remaining clear vision.
The cornerstone of treatment is topical eye drops that suppress the local immune response. Cyclosporine, typically in a 1% to 2% concentration, is the most commonly prescribed option, sometimes combined with a mild steroid. For dogs that don’t respond well to cyclosporine, tacrolimus is an alternative that works through a similar mechanism. These medications are applied directly to the eye, usually once or twice daily depending on disease severity. Most dogs need more frequent application during flare-ups and can taper to a maintenance schedule once the disease stabilizes.
You’ll likely notice improvement within the first few weeks of treatment: the pink, fleshy tissue becomes less inflamed, and the cornea may partially clear. Complete reversal of pigmentation is rare, which is why early detection matters so much. The pigment that’s already deposited tends to be permanent, while new pigment can be prevented from advancing.
UV Protection
Because ultraviolet light accelerates the disease, many veterinary ophthalmologists recommend UV-blocking dog goggles (commonly sold under the brand name Doggles) for outdoor time. These come in multiple sizes to fit different breeds. Not every dog tolerates wearing them, and they’re not strictly required, but they can meaningfully reduce UV exposure during walks, hikes, or extended time outside. Keeping outdoor activity to early morning or late afternoon hours, when UV intensity is lower, is another practical step.
When Standard Treatment Isn’t Enough
For dogs with advanced disease that hasn’t responded adequately to eye drops, more aggressive options exist. Superficial keratectomy, a surgical procedure that removes the affected tissue from the cornea’s surface, can restore clarity in severely pigmented eyes. This is sometimes combined with a form of radiation therapy using a strontium-90 applicator placed directly on the cornea. In one study, dogs that received both keratectomy and radiation regained and preserved adequate vision. Among dogs treated with radiation alongside standard medications, 69% to 77% of eyes were prevented from worsening further, even when some progression eventually occurred. Side effects were minimal, limited to brief squinting in the days after treatment.
Living With Pannus Long-Term
The most important thing to understand about pannus is that it never goes away. Stopping treatment, even when the eyes look good, allows the disease to resume its march across the cornea. Many owners find that once they establish a routine with eye drops, it becomes a simple part of daily care, no different from feeding or walking.
Regular veterinary check-ups, typically every six to twelve months depending on severity, help catch any progression early so treatment can be adjusted. Dogs diagnosed later in life or those living at lower elevations often do well on minimal maintenance therapy. Dogs diagnosed young, living at high altitude, or belonging to highly predisposed breeds like German Shepherds may need more intensive and consistent management throughout their lives.
With diligent treatment, most dogs with pannus maintain comfortable, functional vision. The disease is far more manageable than it looks, and the prognosis is generally good for owners willing to commit to the daily routine.