Eye to Eye

Kirsten Voigt, DVM

December 2006

Horses frequently develop eye problems, which is not too surprising given their tendencies to roll in the dirt and stick their head into heavy brush coupled with having large protuberant eyes placed on the sides of the head.  As an owner it is sometimes hard to tell if the problem is serious or painful to the horse.  Indications of pain are squinting, tearing, eyelid spasms, holding the eye closed and reluctance to having the eye touched.  If the horse is showing signs of pain it is always a good idea to immediately have the eye examined by your veterinarian.  The following are some of the more common eye conditions. 

Bacterial Infections:

This is a common cause for red, painful eyes with a lot of excessive tearing and goopy green to yellow discharge.  These are superficial infections and usually do well with topical antibiotic ointment and pain relief medication such as Banamine.  Persistent infections may require a culture of the eye to be done to more precisely identify the agent and determine a more targeted antibiotic.  In this case systemic antibiotics can be used as well. 

Allergies:

Allergens in the environment can cause the eyes to become quite swollen and red inside.  There may be tearing or a mucous type discharge and they are often very itchy or sore.  In order to fix the eye problem we need to stop the allergic reaction.  The allergen needs to be removed from the environment if it can be identified.  The condition is treated with systemic allergy relief medicine, anti-inflammatory eye ointment and pain relief medication.    

Corneal Ulcers:

An ulcer is a condition where damage is done to the outermost layer of the cornea, which is the clear surface of the eye.  Any eye with tearing, pain and redness should be stained with fluoroscein.  Fluoroscein is a fluorescent dye that is placed in the eye to diagnose corneal ulcers.  If there is a break in the surface of the cornea the dye will adhere to the defect and highlight the area.  By examining the size and shape of the highlighted ulcer we can monitor the healing process to make sure the ulcer is shrinking and healing during treatment.  A non-healing ulcer can progress into a melting ulcer where there is enough damage that the cornea actually melts off of the eye.  Ulcers require pain relief and antibiotic eye ointment to prevent infection and melting.  

Plugged Nasolacrimal Duct:

The nasolacrimal duct is an overflow drainage tube for the eye.  The duct starts at the inner corner of the eye, tracts along inside the tissues of the nasal passage and ends as an opening just inside the nostril.  Proper drainage allows the eye to flush which is an important function to prevent infections.  A plugged duct can be involved in two ways.  The first is that when it is plugged, fluid accumulates by the eye and this stagnant fluid can become contaminated leading to an infection.  The second is that a damaged eye produces more drainage which can be thicker than normal, plugging the duct.  Either way the result is a watery eye with large amounts of drainage down the face.  Five to ten minutes after staining an eye with fluoroscein, the dye should be seen dripping from the duct opening in the nostril.  Failure for this to happen confirms a plugged duct.  The duct can be cleared by inserting a small tube in the opening in the nostril and flushing with sterile water.  The procedure is simple but often requires twitching or sedation due to the sensitive, ticklish nature of the area. 

Corneal Abscess:

An abscess refers to a localized pocket of infection.  Bacteria, fungus or both can cause corneal abscesses.  It happens when the top layer of the cornea is broken and then quickly heals over trapping germs inside which then grow and multiply.  They can be difficult and time consuming to treat because the infection resides in the corneal tissue itself.  Abscesses often require special medications both topically and systemically.  Some may even require surgery. 

Equine Recurrent Uveitis:

There are several highly vascular (full of blood vessels) structures in the eye that are collectively referred to as the uvea.  Inflammation of these structures is called uveitis.  This causes pain, tearing, avoidance of light and can cause the eye to have a cloudy white to blue appearance. Uveitis can happen for a number of reasons, including the conditions listed above, and is also thought to be immune mediated (the body attacking itself) in some horses.  Equine recurrent uveitis, commonly known as moon blindness, is a syndrome in which a horse has multiple, recurrent episodes of uveitis. If left untreated the condition will inevitably lead to blindness due to progressive degeneration and scarring.  Treatment is aimed at reducing inflammation and alleviating pain with strong systemic and topical medications such as steroids, and preventing scarring that may lead to vision loss with pupil dilators.  Ultimately the goal is to prevent future episodes, which may mean life long eye medications, and since sunlight can aggravate the condition, the use of a fly mask is important.  

Treating an eye on your own by using an old ointment that has been lying around since the last time a horse had an eye issue is strongly discouraged.  Different ointments have different medications in them and not all conditions can be treated the same.  They can also become contaminated over time.  It is best to have the horse seen sooner than later to avoid further complications and the expense that goes with them.  The following are some helpful pointers to consider while treating any eye condition under the guidance of your veterinarian  

1)  Some eye medications have corticosteroids in them.  They are not the same kind of steroids that an athlete might use to build muscle and enhance performance. Corticosteroids work very well for quickly reducing inflammation and relieving pain.  They are most often used for the treatment of uveitis and allergies.  They do have a drawback however, which is that they delay or inhibit healing of a corneal ulcer.  For this reason it is imperative never to use a steroid containing eye medication in an eye until it has been stained and determined to be free of ulcers.  Using a steroid in an ulcerated eye can delay healing and worsen the condition. 

2)  It is very important to have your veterinarian do recheck examinations on eyes.  A lot can change in a short amount of time and it's important to adjust the treatment plan accordingly.  Some eye conditions may start out as one problem but quickly develop an additional one.  We see this frequently in horses that have itchy eye conditions.  Instead of using a tissue or clean finger to rub their eyes as we might do, horses use bacteria laden wooden posts and go at it as if using a brillo pad to remove egg from a baking dish.  This can quickly lead to ulcers or bacterial infections that were not there to begin with.  Bacterial infections are a common secondary problem because the initial condition impairs the natural defenses of the eye leaving it more susceptible. 

3)  Eye medications need to be applied several times a day.  Three to four times a day is common in field practice but in a hospital setting with serious eye conditions, treatments are done as often as every other hour around the clock. This is because the amount of medication that can be applied to the eye is very small.  Any extra will simply be washed away with tears. Even the amount that is absorbed does not stay in the eye for very long since there is constant turn over, a flushing type action, within the eye itself.  Since it is necessary for medication to be present for a continual length of time in order to be effective it must be re-applied frequently.

4)  Fly masks are valuable and inexpensive tools that serve a number of functions.  They keep bacteria carrying flies out of the eyes, reduce the amount of dust, allergens and hay particles that may come in contact with the eyes, and provide shade from bright light which can be painful to an eye that is already overly sensitive due to a condition or treatment.   

5)  Cleanliness is paramount.  As mentioned earlier the eye is vulnerable in a state of disease so we want to keep the area around the eyes clean, as well as fly masks, the applicator tips of medications and any other things that may be in close proximity.  This may mean cleaning several times a day since most eye conditions cause excessive discharge to run down the face and accumulate in the corners of the eyes and on fly masks.  When cleaning the face, warm water is sufficient as soap can be very irritating not only to the eyes but also to the sensitive skin around them. 

6)  To help with the pain and itchiness a cold pack can be held on the affected eye(s) for ten minutes a few times a day.   

Dealing with eye conditions can be a challenging experience for both horses and owners.  Patience and a rewards system for good behavior can help encourage a horse to accept the high frequency of treatment that is needed for eye conditions.  If you have a problematic patient talk to your veterinarian about the use of a subpalpebral lavage system which is a small tube that is temporarily inserted into the eyelid and delivers medication directly into the eye.