Pannus is a chronic eye condition in dogs where the immune system attacks the clear surface of the eye (the cornea), causing it to become clouded with blood vessels, scar tissue, and dark pigment. Left untreated, it can lead to blindness. The good news is that with lifelong treatment, most dogs maintain functional vision.
The medical name is chronic superficial keratitis, and it’s one of the more common corneal diseases veterinarians see, particularly in certain breeds. It typically appears between ages 3 and 6, though some breeds develop it even younger.
What Happens Inside the Eye
In a healthy eye, the cornea is completely transparent. With pannus, the dog’s own immune cells, primarily a type of white blood cell called lymphocytes and plasma cells, migrate into the cornea and trigger inflammation. This causes three visible changes: new blood vessels grow across the corneal surface, the tissue becomes cloudy or opaque, and dark pigment gradually deposits over the cornea.
The process usually starts at the outer edge of the cornea and the membrane lining the inner eyelids. A pinkish film appears first, then slowly creeps toward the center of the eye. Over time, the cornea can become so darkly pigmented and opaque that the dog loses vision entirely. UV light appears to play a key role in triggering this immune response. Researchers believe UV wavelengths around 290 nanometers chemically alter proteins in the cornea, making them look foreign to the immune system and provoking the attack.
Breeds Most at Risk
German Shepherds are by far the most commonly affected breed. In one large study of 463 cases in the Rocky Mountain region, more than 80% occurred in German Shepherds. The condition also appears in German Shepherd crossbreeds, suggesting a dominant pattern of inheritance.
Greyhounds are the other notably affected breed. About 4% of retired racing Greyhounds in the U.S. develop pannus, and they tend to show symptoms earlier, sometimes as young as 1 to 2 years old. Other breeds reported to develop the condition include Belgian Malinois, Border Collies, Australian Shepherds, and Siberian Huskies, though at lower rates.
How Altitude Changes the Risk
Where your dog lives matters significantly. A large epidemiological study found that the prevalence of pannus correlated strongly with altitude of residence, with a correlation coefficient of 0.90, which is remarkably tight. Dogs living between 5,001 and 7,000 feet above sea level were nearly 3 times more likely to develop the condition than dogs living between 3,001 and 5,000 feet. Dogs above 7,000 feet were 7.75 times more likely.
It’s not the altitude itself but the UV exposure that comes with it. At higher elevations, the thinner atmosphere filters out less UV radiation, so a greater proportion of sunlight reaching the ground consists of shorter, more damaging wavelengths. Interestingly, total solar radiation didn’t correlate with pannus rates. What mattered was the wavelength composition, specifically the UV-heavy mix that comes with thinner air. Low humidity also played a role, potentially because drier eyes are more vulnerable to UV-induced damage.
What Pannus Looks Like
The earliest sign is a pinkish or reddish film that appears on the outer portion of one or both eyes. This film is made of tiny new blood vessels growing across the cornea’s surface. At this stage, many owners mistake it for mild eye irritation or conjunctivitis.
As the condition progresses, the cornea turns white or grayish and increasingly opaque. The most distinctive feature of advanced pannus is dark brown or black pigment spreading across the cornea. Both eyes are almost always affected, though one may look worse than the other. The pigmentation and blood vessel growth tend to be most prominent on the side of the cornea closest to the outer corner of the eye and along the lower portion, which makes sense given that these areas receive the most direct sunlight exposure.
How Vets Diagnose It
Veterinarians diagnose pannus primarily based on the characteristic appearance of the cornea combined with breed. The combination of bilateral corneal vascularization, pigmentation, and the right breed background is often enough. When confirmation is needed, a vet may take a small sample of cells from the cornea or conjunctiva for cytology. Under a microscope, the sample typically shows an abundance of lymphocytes and plasma cells, the immune cells driving the condition.
This helps distinguish pannus from other causes of corneal cloudiness, such as infections, injuries, or other forms of keratitis that require different treatment.
Treatment With Eye Drops
The cornerstone of treatment is topical immunosuppressive medication applied directly to the eyes. These drugs calm the overactive immune response that’s damaging the cornea. The most commonly used options are cyclosporine (often in a 1% or 2% concentration in an oil base) and tacrolimus (at a much lower 0.02% to 0.03% concentration). Both work by suppressing the local immune cells in the cornea.
Corticosteroid eye drops, such as dexamethasone or prednisolone, are also used, sometimes in combination with the immunosuppressive drops. Steroids are particularly useful during flare-ups when inflammation spikes. Depending on the severity, your vet may prescribe drops anywhere from twice daily to four times daily. Most dogs start on a more aggressive schedule, then taper to a maintenance dose once the cornea improves.
Some dogs that don’t respond well to cyclosporine do respond to tacrolimus, so switching medications is a reasonable option if the first choice isn’t working. The key thing to understand is that these medications control the disease but do not cure it. Stopping treatment allows the condition to come back, often worse than before. One study found that in untreated eyes, 85% showed worsening blood vessel growth and spreading pigmentation, with 62% showing increasingly dense pigment deposits.
UV Protection for Your Dog
Because UV exposure drives the disease, reducing your dog’s sun exposure is an important part of management. Dog-specific UV-blocking goggles, commonly called “Doggles,” are recommended by veterinary ophthalmologists at institutions like Texas A&M. These wrap-around goggles block UV light from reaching the cornea during outdoor time.
Not every dog will tolerate wearing them, and they’re not strictly required, but they can make a meaningful difference for dogs that spend a lot of time outdoors, especially in high-altitude or sunny environments. Limiting outdoor activity during peak UV hours (roughly 10 a.m. to 4 p.m.) also helps. For dogs living at high elevations, UV protection becomes even more important given the dramatically higher risk at altitude.
When the Disease Is Advanced
For dogs whose vision has already been significantly impaired by dense pigment and scarring, more aggressive interventions exist. Keratectomy, a surgical procedure that removes the superficial layers of damaged cornea, can be combined with a form of radiation therapy using strontium-90. In one study, all dogs that received keratectomy followed by radiation regained and preserved adequate vision.
Radiation therapy alone also showed benefits. Nearly all treated eyes improved initially, and even when some progression occurred later, the treatment prevented the severe worsening seen in untreated eyes in 69% to 77% of cases. These interventions are typically performed by veterinary ophthalmologists and reserved for cases where medications alone aren’t enough.
What to Expect Long Term
Pannus is a lifelong condition. There is no cure, and treatment cannot be discontinued. The Cornell Canine Genetics Research Laboratory describes it plainly: management requires lifelong topical medication to prevent vision impairment or blindness. The good news is that most dogs respond well to treatment, especially when caught early. With consistent daily medication and reasonable UV protection, the majority of dogs keep functional vision for the rest of their lives.
Flare-ups can happen seasonally, particularly during summer months when UV exposure peaks. Your vet may adjust the medication schedule during these periods. Regular eye checkups, typically every 6 to 12 months once the condition is stable, help catch any progression before it threatens vision. Dogs diagnosed earlier and treated consistently tend to have the best outcomes, which is why recognizing those first signs of pinkish film or cloudiness matters.