CONDITION
Corneal Sequestrum in Cats
A corneal sequestrum is a discrete area of dead tissue that forms on the surface of a cat's eye, most often appearing as a dark brown or black patch on the cornea. The tissue becomes isolated from the healthy cornea around it, and over time the body treats it as foreign material. This condition is almost exclusive to cats and tends to occur following injury, chronic irritation, or certain viral infections affecting the eye. Owners often first notice a dark spot on the eye itself, sometimes accompanied by squinting, tearing, or a change in how the eye looks. The appearance can be striking—a small brown or black island on the clear part of the eye—and it may prompt worry about whether the eye is damaged or infected. In some cases the area causes discomfort, while in others the cat shows few outward signs. This page explores what signals may accompany a corneal sequestrum, what is happening in the tissue of the cornea, how the condition is investigated and confirmed, and what approaches exist for managing it. The course and outlook vary depending on the underlying cause, the size and location of the affected area, and how the eye responds over time.
Why this matters now
Corneal sequestra tend to develop in young to middle-aged cats, though they can appear at any life stage. Certain breeds—particularly Persians, Himalayans, and other brachycephalic cats with prominent eyes—appear more prone, likely because their eye shape makes the cornea more vulnerable to drying and minor trauma. The condition often follows a period of irritation: a scratch from another cat, persistent dust or pollen exposure, or a flare of feline herpesvirus affecting the eye. In some cases no clear trigger is identified, and the sequestrum forms gradually over weeks or months.
Once the patch of dead tissue appears, it typically remains stable in size or expands slowly over weeks to months. The sequestrum may loosen at the edges as the surrounding cornea begins to wall it off, and in some cases the body gradually extrudes the fragment, leaving an ulcer beneath. In other cats the sequestrum remains adherent for months or years, and the degree of discomfort can vary—some cats show persistent squinting and tearing, while others tolerate the lesion with minimal outward signs. The course is difficult to predict for any individual animal.
Signals & patterns
Early signals
Dark spot on the eye
Owners often notice a small brown or amber-coloured patch on the clear surface of the eye, usually near the centre or slightly to one side. The colour can deepen over days to weeks, becoming darker brown or black as the tissue dies and oxidises.
Squinting or holding the eye partly closed
The affected eye may be held narrower than the other, or the cat may blink more frequently. This can signal discomfort from the rough surface of the sequestrum or from inflammation in the tissues around it.
Clear or slightly cloudy discharge
A small amount of watery tearing is common, and the fur below the eye may become damp or stained. The discharge tends to be clear or faintly cloudy rather than thick or coloured, unless a secondary infection has developed.
Redness around the edge of the eye
The conjunctiva—the pink tissue lining the eyelids—may appear pinker or more prominent than usual. This reflects mild inflammation in response to the irritation on the cornea.
Later signals
Deepening or enlargement of the dark area
Over weeks to months, the sequestrum may expand in diameter or develop a more irregular shape. The tissue can become jet black and raised slightly above the surrounding cornea.
Cloudiness around the dark patch
The cornea surrounding the sequestrum may lose some of its clarity, appearing hazy or milky. This represents swelling or scarring in the tissue as the eye attempts to isolate the dead area.
Persistent pawing at the face
Some cats begin to rub or paw at the affected side of the face, particularly if the sequestrum has loosened or if an ulcer has formed beneath it. This can increase the risk of further injury to the eye.
Click to read about the biological mechanisms
How this is usually investigated
The diagnosis of a corneal sequestrum typically begins with a careful history of any recent eye problems, trauma, or viral illness, followed by close examination of the eye under magnification. The appearance of the dark brown or black plaque on the cornea is often distinctive enough to identify the condition on visual inspection alone. Additional tests may be used to assess the depth of the lesion, check for underlying causes such as herpesvirus, and evaluate the health of the surrounding cornea and deeper structures of the eye.
Ophthalmic examination under magnification
Fluorescein staining
Viral testing for feline herpesvirus
Assessment of tear production and eyelid conformation
Options & trade-offs
Management of a corneal sequestrum depends on the size and depth of the lesion, the degree of discomfort, and the underlying cause. Some cats are managed with medical support to reduce inflammation and encourage the sequestrum to loosen naturally, while others undergo surgery to remove the affected tissue. The choice often involves balancing the invasiveness of surgery against the timeframe and uncertainty of waiting, and different owners and animals find different combinations workable.
Medical management
Topical medications such as lubricating drops, anti-inflammatory agents, or antiviral drugs may be used to reduce irritation, support the tear film, and address any underlying herpesvirus activity. The aim is to make the eye more comfortable and create conditions that may allow the sequestrum to loosen and extrude on its own over weeks to months. This approach is often combined with observation to monitor for signs of progression or spontaneous sloughing.
Trade-offs: The sequestrum may remain in place for an extended period, and there is no guarantee it will detach. Some cats continue to show discomfort despite treatment, and the lesion may expand slowly over time. This approach avoids surgery but requires patience and regular monitoring.
Superficial keratectomy
A surgical procedure in which the sequestrum and a thin layer of surrounding corneal tissue are carefully removed under general anaesthesia. The goal is to excise the dead tissue and allow healthy epithelium to regenerate over the defect. The procedure is typically performed by a veterinary ophthalmologist and may be followed by medical treatment to support healing.
Trade-offs: Surgery carries the usual risks of anaesthesia and requires postoperative care, including topical medications and sometimes an Elizabethan collar. The cornea may take weeks to heal, and in some cases a scar remains. If the underlying cause is not addressed, sequestra can recur.
Corneal grafting
In cases where the sequestrum extends deep into the cornea or where removal leaves a significant defect, a graft of tissue—often from the conjunctiva or, less commonly, donor corneal tissue—may be placed to support healing and maintain the structural integrity of the eye. This is a more involved procedure, usually reserved for larger or deeper lesions.
Trade-offs: Grafting adds complexity and cost, and the grafted tissue may remain partially visible as a pale patch on the cornea. Healing can be slow, and there is a risk of graft failure or infection. This approach is typically considered when simpler surgery is unlikely to be sufficient.
Monitoring without intervention
In cats with small, stable sequestra and minimal signs of discomfort, some owners and vets choose to observe the lesion over time without active medical or surgical treatment. The sequestrum may remain unchanged for months or years, or it may eventually loosen and shed on its own.
Trade-offs: This approach avoids the risks and costs of treatment but means living with the uncertainty of how the lesion will behave. Some cats develop increasing discomfort or secondary complications such as ulceration, which may then require intervention at a later stage.
Common misconceptions
"The dark spot on the eye is dirt or debris that can be wiped away."
A corneal sequestrum is dead tissue embedded in the cornea, not a foreign object sitting on the surface. It cannot be removed by flushing or wiping, and attempts to do so may cause further irritation or injury to the eye.
"Once the sequestrum is removed surgically, the problem is permanently solved."
Surgery removes the existing sequestrum, but if the underlying cause—such as herpesvirus or abnormal eyelid conformation—is not addressed, new sequestra can form. Recurrence is possible, particularly in cats with chronic or recurrent eye irritation.
"A corneal sequestrum will always cause severe pain and blindness if left untreated."
The degree of discomfort and impact on vision varies widely between individuals. Some cats tolerate small sequestra with minimal signs, while others show persistent squinting and tearing. Vision loss is uncommon unless the sequestrum is large and centrally located, or unless secondary complications develop.
Related conditions
Corneal Ulcers
Corneal ulcers can precede the formation of a sequestrum, particularly when an ulcer fails to heal or becomes chronically irritated. In some cases, persistent ulceration provides the initial injury that allows dead tissue to accumulate and become isolated on the corneal surface.
Chronic Upper Respiratory Disease in Cats
Chronic upper respiratory disease in cats, often linked to herpesvirus infection, can lead to recurrent or persistent eye irritation that may contribute to sequestrum formation. Viral damage to the corneal surface appears to be one of the recognised triggers for this condition.
Uveitis
Uveitis and corneal sequestrum can both occur as consequences of feline herpesvirus infection, and in some cases uveitis may develop alongside or following chronic surface inflammation in the eye. The two conditions share overlapping triggers and may occasionally be seen in the same animal.
Keratoconjunctivitis Sicca (Dry Eye)
Keratoconjunctivitis sicca can predispose to sequestrum formation by reducing the protective tear film that normally keeps the cornea moist and healthy. Chronic dryness and irritation of the corneal surface may create the conditions in which dead tissue becomes isolated and visible.
Entropion
Entropion, where the eyelid rolls inward, causes ongoing friction and irritation to the corneal surface that can lead to chronic injury. This persistent mechanical trauma is recognised as one of the factors that may eventually trigger sequestrum formation in susceptible cats.
The presence of a corneal sequestrum often raises questions about the cat's broader eye health, including whether there is an underlying herpesvirus infection or a structural feature that predisposes to irritation. Understanding the timeline—how quickly the lesion appeared, whether it is stable or changing, and what degree of discomfort the cat is showing—can be useful context for conversations about next steps. The pages on chronic ocular surface disease and immune and inflammatory patterns in the eye may offer additional perspective on the factors that shape how these conditions unfold.