A scrape on the eye surface will take up green stain, which fluoresces under a black light. Illustration by MarVistaVet
One of the classical eye problems veterinarians must 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 his 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). In short, it is clear when the eye suddenly hurts and that veterinary attention is needed.
The Corneal Erosion
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. The clear surface of the eye is called the cornea; because it 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 over, 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 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.
A routine corneal ulcer or erosion should heal easily. Since the damaged cornea is at risk for becoming infected (or may even already be infected, as demonstrated by a discharge of pus), a topical antibiotic is needed and ideally should be used four times a day or more. Since it is a rare pet owner that can accommodate any medication administration four times a day, we usually have to make do with three times a day 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.
The second part of treatment is pain relief: Atropine 1% drops or ointment. The atropine acts by temporarily paralyzing the pupil’s ability to contstrict (the main source of pain is spasm in the pupil). When this medication is used the pupil is expected to dilate (widen) and the pet may be reluctant to experience bright sunlight while taking this medication. 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 unduly 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 a dilated pupil.
An e-collar should prevent a pet from reaching and disturbing the eye. Photo courtesy of Nanette Walker Smith
An Elizabethan collar (cone) 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 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 ulcers will have healed in this time but some will require an additional week. If the ulcer has not healed after two weeks, it is no longer considered routine. 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 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.
It is important that the owner observe the progression of healing at home. If the eye is doing well but suddenly becomes more painful, if a discharge develops, or if the eye simply does not look right, have your vet recheck the pet sooner than the planned one week appointment.
Some Special Ulcer Conditions
Some ulcers form with a small lip on its 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 ulcers but they can occur in any breed. Middle-aged dogs in general are not as good at healing routine ulcers as younger dogs and may find themselves with an indolent ulcer.
When the cornea is infected, it will develop a yellow or tan gooey appearance because the bacteria or fungi causing the infection elaborate (induce) 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 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 delivering the patient's own serum as an eye drop.
(Pronounced des'ĕ-met'ō-sēl) Descemet’s membrane is the thin attachment of the cornea to the fluid of the eye below. A Descemetocoele 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 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.
Again, corneal ulcers and erosions usually heal routinely but be alert for any changes that could indicate a more serious turn of events. Be sure self-trauma (rubbing the eye) is prevented and be sure to go to a recheck at the proper time. If anything seems not to be proceeding properly, be sure to contact your veterinarian.