Corneal Ulcer

A scrape on the eye surface will take up green stain, which fluoresces under a black light. Illustration by MarVistaVet

One of the classic eye problems veterinarians address is a red eye. The red eye may or may not be obviously painful, but when it is, the pet can be observed squinting or even rubbing at their face. The conjunctiva (the pink, moist tissue lining the inner surfaces of the eyelids) becomes an angry red and can even swell or puff up around the eye (a condition called chemosis).  This can happen when the eye is injured, infected, or irritated by allergies or coming into contact with various substances.

The cornea is the clear portion of the front surface of the eye and is made up of four layers.

Functions of the cornea:

• Protecting the eye from harmful substances (dust, pathogens, liquids, etc.), injury, UV radiation, etc.
• Refracting light: by bending light, the lens can focus light into the retina in the back of the eye, allowing images to be seen.
• Maintaining the eye’s fluid balance, making sure enough fluid and water are retained.

A corneal ulcer is a more severe form of erosion that affects the deeper layers of the cornea. It causes inflammation across an area of the cornea, which appears foggy or cloudy. It may also cause eye injury and scarring. Eye issues like these can be very painful and irritating for your pet and require veterinary attention.

Corneal erosion occurs when the outermost layers of the cornea are damaged, which may lead to inflammation and infection.

The Corneal Erosion

There are several causes of acute red and painful eyes, and one of the most common causes is a wound or scrape on the surface of the eye. Because the cornea is the outermost layer of the eye, it is prone to scrapes and tears. Common causes of corneal erosions include:

• Rough contact with plants, thorns, or bushes
• Scratches from another animal (note: the cat scratch wound can be especially serious as the wound quickly heals, sealing infection within the eye.)
• Self-trauma (rubbing or scratching at a painful ear or even at the eye due to some other eye problem can lead to an inadvertent scratch to the eye.)
• Chemical irritation (such as getting shampoo in the eye during a bath.)
• Foreign body injury (plant material can get stuck under an eyelid and can scrape the cornea.)

A special fluorescent stain is used to confirm if there is an ulcer or erosion. Normally, water will run smoothly off the surface of the cornea, like rain washing off a windshield. If the cornea is damaged, the stain will stick to the damaged area and look bright green under a fluorescent lamp.

Treatment

Antibiotics

A routine corneal ulcer or erosion should heal easily. Since the damaged cornea is at risk of becoming infected (or may even already be infected, as demonstrated by a purulent discharge), a topical antibiotic is needed and ideally should be used four times a day or more. Because it can be difficult to administer medication four times a day, three times can be acceptable, but to properly sterilize the eye surface, the antibiotic should be used four times a day. Either drops or ointment can be used depending on the owner’s preference.

Pain Relief

The second part of treatment is pain relief. Your veterinarian may recommend eye drops like atropine 1% drops or ointment, oral pain medications, non-steroidal anti-inflammatory medications, or a combination.  Your pet may also be prescribed eye drops to help keep the eye moist and comfortable and assist with tissue regrowth in some circumstances.

Atropine temporarily paralyzes the pupil’s ability to constrict (the main source of pain is spasms in the pupil). This medication causes the pupil to dilate, and your pet may be reluctant to experience bright sunlight. Because the tear duct system is connected to the nose and mouth, the patient will also taste the above medications, and atropine is famous for its bitter taste. Dogs do not seem to mind this too much, but cats will drool shortly after the medication is given in an effort to get the taste out of their mouths. This is a normal reaction to the atropine, as is the dilated pupil.

Anti-inflammatory drugs are often needed in cases of corneal injuries, and NSAIDs, such as carprofen, firocoxib, and meloxicam are often prescribed. If needed, pain relief medications like gabapentin, acetaminophen with codeine may be prescribed by your veterinarian.

An e-collar should prevent a pet from reaching and disturbing the eye. Photo courtesy of Nanette Walker Smith

An Elizabethan Collar may be needed to prevent eye self-trauma. If you think your pet will rub the eye, it is important to have the pet wear this special collar until the erosion is healed. Be sure to request one if you think your pet needs it, and if you are given one, be sure the pet wears it for the entire course of treatment.

Re-Check in One Week

It is important that the eye be stained again after one week of therapy. Most erosions will have healed in this time, but some will require an additional week. If the erosion has not healed after two weeks, it may be affecting the lower layers of the cornea, and may be a corneal ulcer. . Some other procedures, and possibly a visit to a veterinary ophthalmologist, may be necessary.

If the inflammation associated with the ulcer goes deeper into the eye, the situation becomes more serious; it is very important not to skip that one-week re-check. If there is any question about the eye’s healing progress, the eye should be re-checked sooner.

Types of Corneal Ulcers

Indolent Ulcer

Some ulcers form with a small lip on their edge. Since the ulcer is trying to heal from the bottom up, the lip interferes and creates an ulcer that seems to never get any smaller. Several techniques can be used to remedy this situation: the lip can be rubbed away, hyaluronan or PSGAG eye drops can be used to strengthen the cornea, or surgery can be performed. A technique that has gained popularity over recent years is called the grid keratectomy, where a needle is used to scratch a grid of lines on the cornea. The cornea is then able to heal in, grid by grid. Poodles and boxers are notorious for these types of ulcers, but they can occur in any breed. 

Melting Ulcers

When infection is present, the cornea will develop a yellow or tan gooey appearance because the bacteria or fungi causing the infection to develop enzymes that actually dissolve corneal collagen fibers. The cornea softens and appears to be melting, and can actually perforate. Culture and cell sampling for analysis are very helpful in determining the right antimicrobial therapy. In addition to antibiotic drops, the eye will need some sort of medication to inactivate the aforementioned collagen-dissolving enzymes. Often, this involves taking a blood sample from the patient and actually delivering the patient's own serum as an eye drop.

Descemetocele 

Descemet’s membrane (pronounced des'ĕ-met'ō-sēl) is one of the deeper layers of the cornea. A descemetocele is an ulcer that has penetrated through the cornea completely except for the last thin membrane. An eye with a descemetocele is at high risk for rupture, and measures must be taken to protect it. Usually, surgery is needed. The brachycephalic breeds (Pekingese, pug, etc.) are predisposed to this problem due to their prominent eyes.

Recovery and Prognosis (Outlook)

Corneal erosions usually heal routinely, but stay alert for any changes that could indicate a more serious turn of events, like an ulcer forming. Be sure self-trauma (rubbing the eye) is prevented and to attend recommended recheck appointments . Ulcers may require more frequent rechecks as they can lead to greater complications for your pet.

If anything seems not to be healing properly, be sure to contact your veterinarian. Again, your veterinarian may refer you and your pet to a veterinary ophthalmologist if your pet experiences complications during healing or has impacted vision.