Corneal Ulcer

TL;DR. A corneal ulcer is a painful scrape or wound on the clear surface of your pet's eye that requires immediate veterinary attention to prevent serious complications, including vision loss.

The cornea is the clear, protective outer layer of your pet's eye.

What is it?

The cornea is the clear, dome-shaped window at the very front of the eye. It acts as a protective barrier against dirt, bacteria, and debris, while also helping to focus light as it enters the eye. To maintain its clarity, the cornea must remain perfectly smooth, hydrated, and free of blood vessels.

Structurally, the cornea is made up of multiple microscopic layers. The outermost layer is the epithelium, a thin sheet of rapidly dividing cells that acts as a shield. Beneath the epithelium lies the stroma, which makes up the vast majority of the cornea's thickness and is composed of highly organized collagen fibers. Underneath the stroma is a delicate membrane, and the innermost layer is the endothelium, which pump fluid out of the cornea to keep it clear.

A corneal ulcer, scientifically known as ulcerative keratitis, occurs when there is a loss of these outer epithelial cells, exposing the delicate layers underneath. If the damage is superficial and only affects the epithelium, it is considered an uncomplicated ulcer. However, if the injury penetrates deeper into the stroma, or if bacteria colonize the wound, it becomes a complicated ulcer.

In some cases, the cornea begins to dissolve due to destructive enzymes released by bacteria and inflammatory cells. This is known as a "melting" ulcer (malacia) and constitutes a true veterinary emergency. Another variation is the indolent ulcer, also known as a Spontaneous Chronic Corneal Epithelial Defect (SCCED). In these cases, the outer epithelial cells fail to stick to the underlying stroma, leaving loose edges of tissue that prevent the wound from healing.

Causes & risk factors

Corneal ulcers are most commonly caused by physical trauma. This can include a scratch from a cat's claw, contact with sharp grass or twigs, or self-trauma from a pet rubbing their face against carpet or furniture. Foreign objects, such as dirt, seeds, or loose hairs trapped under the eyelid, can also scrape the cornea every time the pet blinks.

Anatomical abnormalities are another major risk factor. Some pets are born with eyelashes that grow in abnormal directions, such as distichiasis (extra eyelashes growing from the eyelid margin) or ectopic cilia (eyelashes growing through the inside of the eyelid). Entropion, a condition where the eyelids roll inward, causes the outer hair of the eyelid to rub directly against the cornea.

Underlying medical conditions can also lead to ulceration. Keratoconjunctivitis sicca (KCS), commonly known as dry eye, occurs when a pet does not produce enough tears to lubricate the eye, leading to chronic friction and drying. Additionally, facial nerve paralysis can prevent a pet from blinking fully, leaving the center of the cornea exposed and vulnerable.

Finally, improper medication use is a major risk factor for severe complications. Applying leftover eye drops containing corticosteroids to a red eye without a veterinary exam can turn a simple scratch into a deep, melting ulcer. As noted in a leading veterinary critical care reference:

"Stromal loss, cellular infiltrate, moderate vascularization, and progression despite medical therapy indicate a complicated corneal ulcer. The leading cause of complicated ulcers is the use of topical steroids in a patient with a corneal defect."

Signs to watch for

Because the cornea is packed with highly sensitive nerve endings, corneal ulcers are incredibly painful. You will likely notice immediate changes in your pet's behavior and the appearance of their eye.

• Pain (Cardinal): Your pet may paw at their face, rub their eye against the floor, or whine when the area is touched.
• Blepharospasm (Cardinal): Squinting or holding the eye tightly shut to protect it from light and friction.
• Observable corneal defect (Cardinal): A visible dent, scratch, or rough patch on the normally smooth surface of the eye.
• Conjunctival hyperemia (Common): Severe redness of the white part of the eye (sclera) and the inner lining of the eyelids.
• Mucoid to mucopurulent discharge (Common): Watery, mucus-like, or thick yellow-green discharge pooling in the corner of the eye.
• Corneal edema (Common): A cloudy, bluish, or hazy appearance over the surface of the eye, caused by fluid leaking into the corneal layers.
• Episcleral congestion (Common): Engorged, prominent blood vessels visible on the white of the eye.
• Corneal vascularization (Occasional): Red blood vessels growing from the edges of the eye toward the center of the ulcer as the body attempts to heal itself.
• Malacia (Rare): A soft, gelatinous, or "melting" appearance of the cornea, indicating rapid tissue destruction.
• Abscess formation (Rare): A localized yellow or white pocket of pus trapped within the deeper layers of the cornea.

Squinting (blepharospasm) and watery discharge are classic signs of corneal pain in cats and dogs.

How vets diagnose it

Your vet will begin with a thorough ophthalmic examination to assess the structures of the eye and determine the depth of the ulcer.

The gold standard for diagnosing a corneal ulcer is fluorescein staining. Your vet will apply a small drop of a specialized orange dye to your pet's eye and gently rinse it out. Because the healthy outer epithelium is lipophilic (fat-loving), it repels the water-soluble dye. However, if the epithelium is damaged, the dye sticks to the underlying hydrophilic (water-loving) stroma. Under a blue light, any area of ulceration will glow a bright, vibrant green, clearly outlining the size, shape, and depth of the wound.

To evaluate the exact depth of the defect, your vet may use slit beam ophthalmoscopy, which projects a thin sliver of light across the cornea to create a cross-sectional view.

Your vet will also perform tonometry to measure the intraocular pressure (IOP) inside the eye. This is crucial because corneal ulcers often cause secondary inflammation inside the eye (anterior uveitis), which lowers the pressure. Conversely, high pressure could indicate glaucoma. As a leading veterinary critical care reference states:

"Epithelial cell loss usually results in focal corneal edema, although expansive defects can result in diffuse edema. Corneal endothelial cell dysfunction causes diffuse edema and is secondary to intraocular disease, specifically uveitis or glaucoma. A thorough ophthalmic examination including fluorescein staining and tonometry can aid in differentiating the underlying cause."

If the ulcer appears infected, deep, or is not responding to standard therapy, your vet will perform an aerobic bacterial culture and cytologic analysis. By gently scraping the edge of the ulcer, they can collect cells and bacteria to examine under a microscope and send to a laboratory, ensuring the most effective antibiotic is selected.

A fluorescein stain test is the gold standard for identifying corneal ulcers.

Treatment options

Treatment plans vary significantly depending on whether the ulcer is uncomplicated, complicated, or indolent.

Uncomplicated Ulcers

Uncomplicated ulcers are typically treated medically with topical medications. Your vet will prescribe a broad-spectrum topical antibiotic, such as Orbifloxacin (a fluoroquinolone antibiotic), to prevent secondary bacterial infections.

To manage the intense pain, your vet may prescribe Atropine (an anticholinergic/parasympatholytic ophthalmic drop). Atropine dilates the pupil and relaxes the painful spasms of the ciliary muscle inside the eye. Because Atropine dilates the pupil, your pet will be sensitive to bright light, so you should keep them in a dimly lit environment.

A protective Elizabethan collar (E-collar) is mandatory to prevent your pet from scratching or rubbing the eye, which can easily rupture a weakened cornea.

Complicated and Melting Ulcers

Complicated and melting ulcers require aggressive, round-the-clock medical therapy and potentially surgery. If the cornea is melting, your vet will use antiproteolytic agents to stop the enzymatic destruction of the stroma.

Autologous serum is a highly effective treatment for melting ulcers. Your vet will draw blood from your pet, spin it in a centrifuge to separate the red blood cells, and use the remaining golden serum as eye drops. As described in a prominent veterinary surgical reference:

"Autologous serum has antiproteolytic properties that inhibit corneal melting and supplies various growth factors that may assist in early post-operative healing, however, care must be taken to avoid microbial contamination of serum. The frequency of topical application varies from three to eight times daily, depending on the case."

Other treatments include Polysulfated Glycosaminoglycan (which has chondroprotective and healing properties), Sodium chloride ophthalmic drops (a hypertonic solution used to draw excess fluid out of a swollen, edematous cornea), and oral Doxycycline (a tetracycline antibiotic that, beyond its antibacterial properties, actively inhibits the destructive enzymes that cause corneal melting).

If the ulcer is very deep or has worn down to the final membrane (a descemetocele), surgical intervention is required. A veterinary ophthalmologist may perform a conjunctival graft, suturing a small flap of the pet's own conjunctiva over the ulcer to provide a permanent blood supply and structural support.

Indolent Ulcers (SCCEDs)

Because indolent ulcers have a loose lip of non-adherent epithelium, they will not heal with eye drops alone. Your vet must perform a debridement, using a sterile cotton swab to gently rub away the loose, dead epithelial cells.

To encourage new cells to stick, they may also perform a keratotomy (either a grid keratotomy or a diamond burr debridement). This procedure involves making microscopic scratches in the superficial stroma, creating a textured surface that allows the new epithelial cells to anchor securely.

Prognosis

The prognosis for a corneal ulcer depends entirely on its depth, cause, and how quickly treatment is initiated.

• Uncomplicated Ulcers: Excellent. With appropriate topical therapy and protection from rubbing, these superficial scratches typically heal completely within 3 to 5 days without leaving significant scars.
• Complicated or Melting Ulcers: Guarded to fair. These cases require intense, frequent medical therapy. While many can be saved with aggressive treatment or surgery, there is a risk of permanent corneal scarring (which can partially obstruct vision) or, in severe cases, rupture of the eye requiring surgical removal (enucleation).
• Indolent Ulcers (SCCEDs): Variable but ultimately good. While these ulcers are notoriously stubborn and can take several weeks or even months to heal, most will resolve after one or two debridement and keratotomy procedures.

Prevention

While accidents happen, you can take several steps to minimize the risk of corneal ulcers:

• Protect the eyes during baths: Always apply a protective ophthalmic lubricant to your pet's eyes before bathing them to prevent chemical burns from shampoo.
• Trim facial hair: Keep the hair around your pet's eyes trimmed short to prevent stray hairs from rubbing against the cornea.
• Manage underlying conditions: If your pet has been diagnosed with dry eye (KCS) or allergies, strictly adhere to their long-term medication schedule to keep the eyes healthy and lubricated.
• Never reuse old eye drops: If your pet's eye is red or squinting, do not use leftover medications from a previous illness. If the eye has an active ulcer and you apply a steroid-containing drop, you could cause rapid, irreversible damage.

When to call your vet

Any eye injury or sign of eye discomfort should be treated as an urgent matter. You should contact your veterinarian immediately if you notice any of the following red flags:

• Your pet is holding their eye tightly shut or squinting constantly
• There is a visible dent, crater, or cloudiness on the surface of the eye
• You see thick yellow or green discharge draining from the eye
• The white of the eye is dark red or highly swollen
• Your pet is actively pawing or rubbing at their face

Delaying treatment by even 24 hours can allow a simple scratch to progress into a deep, complicated ulcer that threatens your pet's sight.

For specific breeds

Boxers are highly predisposed to developing indolent ulcers, which are frequently referred to as "Boxer ulcers." As noted in a leading veterinary surgical text:

"These lesions are also known as indolent ulcers, indolent erosions, and boxer ulcers. Ophthalmic examination typically reveals a chronic (weeks in duration), superficial, variably painful, non-infected, and non-progressive erosion or ulceration with a characteristic lip of loose epithelium surrounding the border of the defect."

In Boxers, this condition is caused by an inherited abnormality in the basement membrane of the cornea, which prevents the outer epithelial cells from bonding to the deeper stroma. If you own a Boxer, be prepared for the possibility of a prolonged healing process, and ensure you seek veterinary care at the first sign of eye squinting or redness.

Sources

• Small Animal Critical Care Medicine, p. 893
• Current Techniques in Small Animal Surgery, p. 178, 183

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