CONDITION
Pannus (Chronic Superficial Keratitis)
Pannus is a condition in which the immune system begins to treat part of the eye's surface as something foreign, leading to inflammation and the gradual appearance of a pigmented, fleshy tissue that can grow across the cornea. It tends to start at the outer edge of the eye and move inward over time, and both eyes are often affected, though not always at the same rate. Certain breeds, particularly German Shepherd Dogs and their relatives, develop this condition more often than others, and it is sometimes referred to as chronic superficial keratitis. Owners often notice a dark or reddish discolouration beginning at the corner of the eye, or a hazy, thickened appearance to the clear part of the eye. In some animals, there may be slight discharge or mild squinting, though many dogs show little obvious discomfort in the early stages. The changes can be subtle at first and may be mistaken for a simple irritation or ageing. This page explores what an owner may observe, what is happening beneath the surface, how the condition is investigated, and the range of approaches used to manage it over time.
Why this matters now
Pannus tends to appear in young to middle-aged dogs, often becoming noticeable between two and five years of age, though the timing can vary. German Shepherd Dogs, Belgian Shepherds, Border Collies, and Greyhounds develop the condition more frequently than other breeds, suggesting an inherited component to susceptibility. Environmental factors, particularly exposure to ultraviolet light and living at higher altitudes, appear to influence both the likelihood of developing pannus and the speed at which it progresses in affected animals.
The condition typically begins as subtle discolouration or haziness at the outer corner of one or both eyes, then extends slowly across the corneal surface over months to years. The rate of progression varies considerably between individuals; some dogs experience gradual change with long periods of stability, whilst others may see more rapid thickening and pigmentation if the underlying inflammation is not addressed. Left unmanaged, the tissue can eventually cover large portions of the cornea, reducing the amount of light that reaches the retina and affecting vision in the longer term.
Signals & patterns
Early signals
Pink or reddish film at eye corner
A faint pinkish or reddish tissue may appear at the outer edge of the eye, where the white meets the clear cornea. This represents inflammation and new blood vessel growth beginning to extend onto the corneal surface.
Slight haziness over the cornea
The normally transparent cornea may develop a faint cloudy or milky appearance, often most noticeable in bright light. This early change reflects fluid accumulation and cellular activity beneath the surface.
Dark pigment creeping inward
A brownish or greyish discolouration may begin at the edge of the cornea and gradually move toward the centre over time. This pigmentation develops as the body deposits melanin in response to chronic inflammation.
Minimal or absent discomfort
Many dogs in the early stages show little sign of pain or irritation, and may not squint or rub at the eye. The absence of obvious distress can make the condition easy to overlook during routine observation.
Later signals
Thickened, fleshy tissue over cornea
As the condition advances, the corneal surface may appear noticeably thickened, with a raised, fleshy texture where clear tissue once was. This represents ongoing immune activity and tissue remodelling that has accumulated over months or years.
Widespread pigmentation obscuring vision
In later stages, dense brown or black pigment can cover substantial portions of the cornea, reducing the clarity of the eye and potentially affecting the animal's ability to see clearly, particularly in affected areas.
Occasional mucoid discharge
Some dogs develop a sticky, mucus-like discharge at the corners of the eyes as the condition progresses, reflecting ongoing surface irritation and tear film disruption, though this is not present in all cases.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
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