A corneal sequestrum is a brown-to-black patch of dead tissue on a cat's cornea, a condition seen almost exclusively in cats. It usually develops after chronic corneal irritation and causes squinting, tearing, and a visible dark spot on the eye. Because it is painful and can deepen over time, a cat with a darkening cornea should be examined by a vet promptly.
Last reviewed: June 2026
What Is a Corneal Sequestrum?
A corneal sequestrum is an area of degenerated, dead corneal tissue that turns amber, brown, or black and is unique to cats. It forms when a portion of the cornea — the clear front surface of the eye — loses its blood-free vitality and the affected collagen becomes pigmented and necrotic. The discolored plaque is often surrounded by inflammation, blood-vessel ingrowth, and ulceration, and it is genuinely painful. Over time the dead tissue can either slough off on its own or, in deeper cases, threaten the structural integrity of the eye.
Sequestra most often follow chronic corneal irritation or injury, and certain flat-faced breeds such as Persians and Himalayans are predisposed because of their prominent eyes and shallow eye sockets. As described in Tilley's 5-Minute Veterinary Consult, corneal sequestrum is a distinctly feline disease frequently linked to prior corneal ulceration, feline herpesvirus infection, and conformational factors that leave the cornea chronically exposed.
Recognizing the Signs
The defining sign is a dark, well-defined patch on the surface of the eye, but discomfort often appears before the discoloration is obvious. Owners may first notice that the cat is bothered by one eye.
Common signs:
- A brown, amber, or black spot or plaque on the clear part of the eye
- Squinting or holding the eye partially closed
- Excessive tearing or watery discharge
- Pawing or rubbing at the eye
- Cloudiness or redness around the affected area
- Increased blood vessels visible on the eye surface
Because the early discomfort can resemble a simple irritation or conjunctivitis, the appearance of any persistent dark spot on the cornea should prompt a veterinary exam. The earlier a sequestrum is identified, the more treatment options are available.
Why It Happens
Corneal sequestra develop in response to ongoing corneal stress, and several factors commonly contribute. Chronic irritation from inward-rolling eyelids (entropion), hairs rubbing on the eye, or a poorly healing corneal ulcer can all trigger the degeneration. Feline herpesvirus, an extremely common cause of feline eye and respiratory disease, is strongly associated with sequestrum formation because it damages the corneal surface.
Breed conformation matters significantly. Flat-faced breeds have prominent eyes that are more exposed and a reduced ability to fully close the eyelids, leaving the central cornea chronically dried and irritated. Because herpesvirus is so prevalent in cats, addressing concurrent viral disease is often part of management. The role of herpesvirus in feline ocular and upper respiratory disease is well documented, including in Helps et al., 2005, JFMS.
Diagnosis and Treatment
Diagnosis is usually straightforward on examination, since the pigmented plaque is visually distinctive. A vet will apply fluorescein stain to check for accompanying ulceration, assess the depth of the lesion, and look for predisposing causes such as entropion or herpesvirus signs.
Treatment depends on the depth and severity of the sequestrum:
Medical management: Superficial, less painful sequestra may be monitored while treating the underlying cause — lubricating drops, antiviral therapy if herpesvirus is involved, and antibiotics to prevent infection. Some superficial sequestra eventually slough off on their own.
Surgical removal (keratectomy): Painful, deep, or progressing sequestra are best treated by surgically removing the dead tissue, often with a graft to reinforce the cornea. A study of corneoconjunctival transposition for feline sequestra reported good outcomes with a low recurrence rate across 97 cats (Featherstone et al., 2016, JFMS), supporting surgery as an effective option for significant lesions.
Pain control: Because sequestra are painful, comfort is a priority throughout treatment, consistent with the principles of the AAHA Pain Management Guidelines, 2022.
Surgery, when needed, is typically performed by a veterinary ophthalmologist and offers the most reliable resolution for deep lesions. Addressing the underlying irritation reduces the chance of recurrence.
When to See a Vet
Call your vet today if:
- You notice a brown, amber, or black spot developing on your cat's eye
- Your cat is squinting, tearing, or rubbing at one eye
- A flat-faced cat shows persistent eye irritation
- A previous corneal ulcer is not healing as expected
Go to the ER immediately if:
- The eye suddenly bulges, ruptures, or leaks fluid
- Your cat is in severe pain and holding the eye tightly shut
- There is sudden cloudiness with collapse of the eye's surface
What's going on with your pet?
Describe symptoms or snap a photo. Voyage tells you urgency, home care, and whether you need a vet.
First, tell us about your pet
Breed and age make a real difference in how Voyage interprets symptoms.
Describe the symptoms
Love it? See everything Voyage can do
Frequently Asked Questions
What does a corneal sequestrum look like in a cat?
It appears as a distinct amber, brown, or black patch on the clear surface of the eye, often surrounded by redness, cloudiness, and visible blood vessels. The affected cat usually squints, tears excessively, and may rub at the eye. The dark discoloration on the cornea is the most recognizable feature and is essentially unique to cats.
Is a corneal sequestrum painful for cats?
Yes. A corneal sequestrum is genuinely painful because the dead tissue irritates the sensitive cornea and is often accompanied by inflammation and ulceration. Cats typically show discomfort by squinting, tearing, and pawing at the eye. Pain control is an important part of treatment, and resolving the sequestrum — sometimes surgically — provides the most lasting relief.
How much does it cost to treat a corneal sequestrum?
An initial exam runs $50–150, with ophthalmic testing and fluorescein staining adding $50–150. Medical management with drops costs $30–80 per month. Surgical removal (keratectomy with a graft), usually done by a veterinary ophthalmologist, typically costs $1,500–3,500 per eye including anesthesia and follow-up. Treating the underlying cause early can reduce overall expense.
Which cats are most prone to corneal sequestra?
Flat-faced breeds such as Persians and Himalayans are most predisposed because their prominent eyes and shallow sockets leave the cornea chronically exposed and irritated. Cats with a history of corneal ulcers, entropion, or feline herpesvirus infection are also at higher risk. Any breed can be affected, but conformation and chronic irritation are the key drivers.
Can a corneal sequestrum go away on its own?
Superficial sequestra sometimes slough off naturally over weeks to months, leaving a healed cornea, especially when the underlying irritation is addressed. However, this process can be slow and painful, and deeper sequestra rarely resolve without surgery. Because of the discomfort and risk of the lesion deepening, veterinary evaluation is recommended rather than simply waiting it out.
Still Not Sure if Your Cat Needs a Vet?
When you're not sure if this is wait-and-see or call-tonight, Voyage AI Vet triages in under 2 minutes. Describe what you're seeing in chat, share close-up photos of the affected eye, any dark spot on the cornea, or how your cat is holding the eye, or hop on a live video call if you want a second pair of eyes. Every answer comes with citations to the actual veterinary literature it's pulling from — so you see exactly where the guidance comes from, not just a chatbot's word.