What exactly is pannus and why does it attack the cornea?

Pannus, formally called chronic superficial keratitis, is an immune-mediated disease in which a dog's own inflammatory cells infiltrate the cornea, the clear dome covering the front of the eye. The Merck Veterinary Manual describes it as pink or gray fibrovascular tissue that grows across the cornea's surface, usually starting at the outer edge nearest the ear and creeping toward the center (Merck Veterinary Manual, 2022). Because the reaction is thought to be triggered or worsened by ultraviolet light exposure, it behaves less like an infection and more like a sunlight-aggravated autoimmune response confined to the eye.

Almost all dogs develop the condition in both eyes, though one side is often noticeably worse than the other at first. The cornea itself has no blood vessels normally, so the arrival of blood vessels and pigment during a pannus flare is a visible marker of how far the disease has progressed. Cornell University's ophthalmology researchers note that untreated cases can eventually cover enough of the corneal surface with scar tissue and pigment to significantly impair vision (Cornell University College of Veterinary Medicine, n.d.).

What do the first signs of pannus actually look like in a dog's eye?

Owners typically notice a pink or reddish-brown film creeping in from the outer edge of one or both eyes, sometimes alongside a grayish haze that dulls the normal glossy black of the cornea. Merck Veterinary Manual describes an early, raised, pinkish-gray area at the lateral (outer) limbus, the junction where the white of the eye meets the cornea, that gradually extends inward over weeks to months (Merck Veterinary Manual, 2022). Many dogs also develop a dark line or patch of pigment along the lower eyelid margin, sometimes called plasmoma, which can occur alongside or even before corneal changes appear.

Because pannus is not painful in the way a corneal ulcer or glaucoma flare would be, dogs rarely squint excessively, paw at their face, or show obvious discomfort in the earliest stages. That absence of pain is actually one of the trickier parts of catching it early, since many owners assume a non-bothersome cosmetic change can wait for the next routine visit. A board-certified veterinary ophthalmologist can usually identify early pannus with a slit-lamp biomicroscope exam well before the change is visible to the naked eye across a room (American College of Veterinary Ophthalmologists, n.d.).

Which dogs are genetically predisposed to developing pannus?

German Shepherds are by far the most commonly affected breed, and the condition is strongly enough linked to the breed that it is sometimes still called German Shepherd pannus in older veterinary literature. Border Collies, Siberian Huskies, Australian Shepherds, and various sighthound breeds such as Greyhounds also show increased risk, which points to a heritable, likely polygenic, immune-mediated trait rather than a random environmental illness (Merck Veterinary Manual, 2022).

Altitude and UV exposure clearly interact with that genetic risk. Veterinary ophthalmologists have long observed that predisposed dogs living at higher elevations in the western United States and similar regions, where UV intensity is markedly higher, tend to develop more severe and more rapidly progressive disease than genetically similar dogs at sea level. Middle-aged dogs, roughly four to seven years old, are most commonly diagnosed, though the disease can appear earlier and tends to run a more aggressive course in younger dogs (Merck Veterinary Manual, 2022).

How do veterinarians diagnose pannus versus other eye diseases?

Diagnosis is largely made through a thorough ophthalmic exam rather than bloodwork, since pannus has a very characteristic appearance: symmetrical, vascularized, pigmented tissue creeping in from the outer cornea in a predisposed breed. Veterinarians typically perform a Schirmer tear test to rule out concurrent dry eye and fluorescein staining to check for corneal ulcers, since ulcerated corneas require a different, more cautious treatment approach before anti-inflammatory drops can be started (American College of Veterinary Ophthalmologists, n.d.).

A slit-lamp biomicroscope exam, usually performed by a general practice veterinarian or a referral to a board-certified veterinary ophthalmologist, allows for close magnification of the corneal layers to confirm the depth and pattern of the infiltrate. Because pannus looks similar to some corneal tumors and certain infectious keratitis presentations in rare cases, ophthalmologists rely on the classic bilateral, breed-associated, non-ulcerative pattern to confirm the diagnosis clinically rather than through biopsy, which is rarely necessary (Merck Veterinary Manual, 2022).

What treatments actually control pannus long-term?

Topical corticosteroids, most commonly formulations containing dexamethasone or prednisolone acetate, are the first-line treatment and are applied directly to the eye multiple times daily during an active flare. Topical calcineurin inhibitors such as cyclosporine or tacrolimus ophthalmic drops or ointment are frequently used either alongside steroids or as a long-term maintenance therapy, since they suppress the local immune response without some of the risks associated with chronic steroid use (Merck Veterinary Manual, 2022).

In more severe or advanced cases where topical therapy alone isn't controlling the corneal changes, veterinarians may recommend subconjunctival injections of corticosteroids directly under the surface tissue of the eye, or in select cases, adjunctive treatments such as beta radiation therapy at specialty ophthalmology practices. Because pannus is a lifelong condition, treatment is almost never a finite course; instead, most dogs move to a lower daily maintenance dose of drops indefinitely once the initial flare is under control (American College of Veterinary Ophthalmologists, n.d.).

What can owners do day to day to keep a dog's pannus from worsening?

Consistency with prescribed eye drops matters more for this disease than almost any other chronic condition, since gaps in treatment reliably allow the corneal infiltrate to progress again. Beyond medication, limiting UV exposure is one of the few controllable environmental factors: dog-specific UV-blocking goggles, often referred to by the brand name Rex Specs, are widely used by owners of predisposed breeds living at higher altitudes or in sunny climates to reduce flare severity (Merck Veterinary Manual, 2022).

Regular rechecks, typically every few weeks during the initial treatment period and then every three to six months once stable, let veterinarians adjust drop frequency and catch early regression before it becomes visually significant. Owners should also avoid abruptly stopping medication even when the eye looks completely normal, since pannus is controlled rather than cured and will often rebound within weeks of discontinuing therapy without a supervised taper (American College of Veterinary Ophthalmologists, n.d.).

What is the long-term outlook for a dog diagnosed with pannus?

With consistent lifelong treatment, most dogs maintain functional vision and a good quality of life, and many owners find that once the drop routine becomes habit, the disease has minimal day-to-day impact on their dog's activities. The prognosis is generally good for vision preservation as long as therapy starts before significant corneal scarring and pigmentation have accumulated over the central visual axis (Merck Veterinary Manual, 2022).

Dogs diagnosed late, or those whose treatment lapses repeatedly over years, are at real risk of progressive central corneal pigmentation dense enough to cause partial or complete blindness, even though the disease itself is never painful. Because pannus tends to worsen seasonally with increased sun exposure, many veterinary ophthalmologists recommend slightly increasing drop frequency during summer months as a proactive measure rather than waiting for a visible flare to reappear (American College of Veterinary Ophthalmologists, n.d.).