Moderate severity

Corneal Sequestrum

A brown or black plaque of dead tissue embedded in the clear surface of the eye. It is almost unique to cats, and it is one of the few eye problems where the appearance alone is close to diagnostic.

⚠️ Common symptoms

An amber, brown or black patch on the clear part of the eyeSquinting and holding the eye partly closedWatering, with tear staining down the facePawing or rubbing at the affected eyeThird eyelid drawn acrossVisible blood vessels growing in from the edge of the cornea

What It Looks Like

A corneal sequestrum starts as a faint amber haze in the centre of the cornea and darkens over weeks or months into a distinct brown or black plaque, sometimes with a well-defined edge that makes it look almost like a stone set into the eye. Owners often describe it as a piece of dirt that will not wash away. It is a striking enough appearance that many cats are brought in the same day it is noticed, which is exactly right.

The condition is essentially feline. It is described occasionally in horses and dogs, but a pigmented plaque of dead corneal tissue is otherwise a cat's problem, and the strong breed associations point squarely at facial anatomy.

Which Cats Get It

Persians and Himalayans are heavily overrepresented, and Burmese and Siamese cats follow. The common thread is a shallow orbit and a prominent eye: the more exposed the cornea, the faster its central tear film evaporates, and the more likely the eyelids are to close imperfectly during sleep. Add the very high prevalence of feline herpesvirus in the general cat population, and the ingredients are all present.

That said, sequestra appear in ordinary domestic shorthairs too, usually after an ulcer that took a long time to heal or an injury that was never noticed.

Why Waiting Is the Wrong Instinct

Because a sequestrum is dead tissue, it behaves as a foreign body embedded in a living structure. The cornea mounts an inflammatory response, blood vessels creep in from the edge to reach it, and the eye remains sore for as long as it stays. Left alone, some lesions do eventually slough — but the deeper ones take much of the corneal thickness with them when they go, and a cat that loses enough stroma is at risk of the eye perforating. That is the argument for planned surgery over hopeful monitoring in all but the smallest, most superficial cases.

Afterwards

Surgical outcomes are generally good, and most cats are comfortable within days. A degree of permanent corneal scarring is normal and rarely troubles the cat, since a small central haze affects feline vision far less than one might expect. Recurrence is the real issue — reported in a meaningful minority of cases, and considerably more likely if the underlying cause was never addressed. A cat with herpesvirus that has had one sequestrum should be watched carefully, and the second eye watched as well.

🔍 Causes

A sequestrum is a patch of corneal stroma that has died and become pigmented, and it forms where the cornea has been chronically irritated or poorly protected. Feline herpesvirus is the most frequently implicated trigger, since it causes recurrent corneal ulceration. Anatomy does much of the rest: brachycephalic breeds have prominent, shallow-set eyes that dry at the centre and close incompletely during sleep, and entropion — where the eyelid rolls inward and the lashes abrade the surface — produces constant low-grade damage. Chronic dry eye, previous trauma and long-standing ulcers all contribute. The dark pigment itself is not melanin from the cat's own pigment cells but a discolouration derived from tear film components deposited in the dead tissue, which is why even white cats develop black lesions.

🛡 Prevention

There is no way to prevent a sequestrum directly, but you can reduce the corneal insults that lead to one. Treat herpesvirus flare-ups promptly rather than waiting for a runny eye to settle, and have any recurrent squinting investigated instead of assumed to be a passing irritation. Persians, Himalayans and other flat-faced cats benefit from regular checks of the eyelid conformation, since entropion is correctable surgically and doing so early prevents years of abrasion. Never use leftover steroid eye drops in a cat with a sore eye — if there is an ulcer underneath, steroids can turn a superficial problem into a perforation.

💊 Treatment

Small, quiet sequestra are sometimes managed medically and monitored, since a proportion will loosen and slough out on their own over weeks to months — though the process is uncomfortable and leaves a defect that must then heal. Most vets recommend surgical removal, a lamellar keratectomy, in which the dead tissue is dissected out under an operating microscope. Deeper lesions may need the defect covered with a graft — a conjunctival flap, a corneal graft or a biological implant — to restore strength to the eye wall. Underlying causes are treated at the same time, which usually means managing feline herpesvirus, correcting entropion, or addressing a poor tear film. Pain relief matters throughout, and cats are usually sent home in a buff collar to prevent rubbing.

When to see a vet: Book an appointment for any dark spot appearing on the surface of a cat's eye, even if the cat seems comfortable. Go urgently for a suddenly painful eye, an eye held tightly shut, cloudiness spreading across the cornea, or any discharge that is thick rather than watery — and immediately if the eye looks like it is bulging, leaking, or has lost its smooth contour, which can indicate the cornea is perforating.

⚕️ Medical disclaimer

  • This information is educational only and is not a substitute for veterinary advice.
  • Symptoms overlap between conditions — only a vet can diagnose accurately.
  • Never withhold treatment or self-medicate based on information found online.
  • When in doubt, call your vet. Early intervention almost always leads to better outcomes.

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