The cornea is the outermost, transparent surface of the eye. You can see the pupil and colored iris through the cornea. The cornea is transparent, has no direct blood supply, and has sensitive nerve endings. The cornea receives its nutrition from a tear film. Diseases of the cornea are frequently recognized by owners because they result in pain and can cause changes in the transparency or color of the surface of the cornea.

Any abrasion to the cornea, including a bee sting, rub from a paw, a scratch from a claw or thorn or an invasive infection can abrade the cells on the surface of the dog or cat cornea. Once the surface cells are disrupted the smooth surface of the cornea becomes rough, infective organisms can invaded the spaces between the cells and the area becomes a source of pain and irritation to the animal. Dogs and cats with corneal ulcers commonly will have increased tear production, will squint and rub at their eye. The irritated tissues often become infected.

There are several causes of acutely red and painful eyes and one of the most common causes is a wound or scrape to 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 ulcers (also called 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 over, sealing infection within the eye)



• Self trauma (rubbing or scratching at a painful ear or an irritated eye due to another eye problem can lead to an inadvertent scratch to the eye)



• Chemical irritation (getting shampoo in the eye during a bath)



• Foreign body injury (plant material can get stuck under an eyelid and can scrape the cornea)

Materials Used In An Ocular Exam: Materials commonly used to diagnose a corneal ulcer are shown below. On the left is a topical anesthetic to temporarily eliminate the pain associated with the ulcer and to allow thorough examination of the eye. The Shirmer Tear Test is used to measure tear flow in the eye. Fluorets are the little paper strips that contain the stain that demonstrates the corneal defect. The ophthalmoscope is used to highlight the cornea and to allow examination of internal structures of the eye. The Schiotts Tonometer is at the bottom of the image and is used to evaluate intraocular pressure. It is not commonly used during the evaluation of the corneal ulcer unless there is evidence that there may be an underlying pressure problem with the eyes such as Glaucoma.


A special fluorescent stain is used to confirm the presence of the ulcer or erosion. If the cornea is damaged, the stain will stick to the damaged area and appear bright green under a fluorescent lamp.




Fluorescein strips are used to demonstrate if there is a break in the corneal surface. The stained strip is moistened with sterile water and the stain is flushed across the eye. Any break in the corneal surface takes up the stain and the veterinarian can record the dimensions of the defect.

Example of a case of an ulcerated cornea
This Lhasa Apso was presented because of squinting, watery eye, and pawing at the eye. The stain demonstrates on the right the extent of the ulcer and the new blood vessels (called neovascularization) that are supplying the area with healing nutrients.

   

Most uncomplicated corneal ulcers heal with treatment in about one week. Since the damaged cornea is at risk to become infected (or may even already be infected, as demonstrated by a purulent discharge), a topical antibiotic is needed and ideally should be used several times a day.

The second part of treatment is a pain reliever: An example of a pain reliever is Atropine 1% drops or ointment. The Atropine acts by temporarily paralyzing the pupil’s ability to constrict (the pupil’s spasm with the ulcer is the main source of pain). Pupillary dilation is to be expected when this medication is used and the pet may be reluctant to experience bright sunlight during treatment. Other anti-inflammatories such as Metacam or Buprenorphine may be used for pain relief.

A special collar, called an Elizabethan Collar, may be needed to prevent self trauma of the eye. 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. If your veterinarian gives you one, be sure the pet wears it for the entire course of treatment.

In some cases, surgery may be necessary. Complications of corneal ulceration that may require emergency surgery include keratomalacia (melting corneal ulcers), descemetocele (see below), corneal perforation (penetrating wounds), iris prolapse, corneal lacerations (tears) and corneal foreign bodies.

It is important that the eye be stained again after one week of therapy. Most ulcers will have healed in this time, but some will require additional time. If the ulcer has not healed after two weeks, additional procedures may be needed and/or a veterinary ophthalmologist may be consulted. If there is any question about the eye’s healing progress, the eye should be re-checked sooner.

IT IS VERY IMPORTANT THAT THE OWNER OBSERVE THE PROGRESSION OF HEALING AT HOME. IF THE EYE SUDDENLYBECOMES MORE PAINFUL, IF A DISCHARGE DEVELOPS, OR IF THE EYE CONDITION APPEARS TO WORSEN, HAVE YOUR VET RECHECK THE PET SOONER THAN THE PLANNED ONE WEEK APPOINTMENT.

These complicated ulcers can occur in any animal but are most often seen in dog breeds that have short noses and prominent eyes such as Pugs, Shih Tzu’s, Lhasa Apsos, Boston Terriers etc. These breeds have eyes that bulge out and are less sensitive to the external environment (i.e. they do not feel the discomfort of the eyes drying as other breeds do). Therefore, they do not blink as often as needed to spread the tear film properly across their eyes. The tears, in addition to lubricating the cornea, contain antibodies to help fight off infection.

Types of complicated ulcers:


INDOLENT ULCER: Some ulcers form with a small “lip” on the edge of the ulcer. 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. There are several techniques used to remedy this situation: the lip can be rubbed away, special Adequan eye drops can be used to strengthen the cornea, or even surgery can be performed. Indolent ulcers are seen more commonly in poodles and boxers, but they can occur in any breed.


DESCEMETOCOELE: Descemet’s membrane is the thin attachment of the cornea to the fluid of the eye below. A Descemetocole is an ulcer that has penetrated through the cornea completely except for the last thin membrane. An eye with a descemetocoele is high risk for rupture and special measures must be taken to protect the eye. Usually surgery is needed. The brachycephalic breeds (pekingese, pug etc.) are predisposed to this problem due to their prominent eyes.

KERATOMALACIA: Melting corneal ulcers - Keratomalacia or a melting corneal ulcer is the result of bacterial or fungal growth within the inner layers of the cornea after disruption of its outer surface. These organisms, as well as inflammatory cells in the corneal tear film, produce destructive enzymes that damage the inner corneal layers. Melting corneal ulcers appear blue-gray to tan or white and have a gelatinous or bubble-like appearance. They can progress to corneal perforation and rupture within a matter of hours. The eye is typically very painful.

When a corneal ulcer fails to heal or when a very deep or wide ulcer is present a third eyelid flap procedure is performed. Under general anesthesia the patient's Nictating Membrane (the third eyelid) that originates in the medial corner of the eye opening and under the lower lid, is pulled up and over the cornea. It is sutured to the inside of the upper eyelid, thus forming a protective and nourishing layer of tissue over the damaged cornea. Medications can still be applied to the eye between the eyelids, but the surface of the cornea will not be exposed and cannot be visualized while the third eyelid flap is in place. The sutures are removed in 10 to 28 days and the corneal healing is assessed. This procedure is commonly done and may be very helpful in generating a healing response in severely damaged corneas.

It is common for complicated corneal ulcers to cause significant corneal scarring. As with any disease, early treatment is key to decreasing this scarring. After the ulcer is completely healed, medications may be used to decrease scarring. In most cases, artificial tear supplements may be used on a permanent basis to keep the ulcer from returning, as well as being used prophylactically in the opposite eye. Early aggressive treatment can save vision in most patients.

ANY OCULAR INJURY IS AN EMERGENCY, PLEASE TRANSPORT YOUR PET TO A VETERINARIAN AS SOON AS POSSIBLE AFTER THE EYE INJURY OCCURS