Sore eyes are true emergencies and it is important that your vet assesses and treats your horse's eye condition quickly.
If your horse has a sore eye, it is very likely it has corneal damage and you should contact your vet immediately. If you leave your horse's eye untreated, it can lead to severe pain and even blindness for your horse.
(This information was adapted from an article by Dr Brianna Clark BVSc (Hons), MANZCVS and UQ lecturer and Equine veterinary specialist Dr Allison Stewart BVSc (Hons), MS, DACVIM-LAIM, DACVECC, PhD, MANZCVS. Read the article (PDF, 570 KB))
What is a corneal ulcer?
A corneal ulcer is the most common cause of a painful eye in horses.
The cornea is the outer-most layer of the eye and is only 8-10 cells thick. This layer is an important protective barrier for preventing infection of the inner eye and is crucial for vision.
Corneal damage, infection and a horse's overzealous immune response can make ulcers much worse and threaten vision long term.
Infections are mainly caused by either bacteria and/or fungi. In Australia's warm and often humid climates, fungal infections are common.
Corneal ulcers can range from small and superficial to large, deep or melting.
Horse with a corneal ulcer
Identifying a corneal ulcer
It's important that your veterinarian assesses your horse's sore eye because a small defect in the cornea can deteriorate very quickly.
Your veterinarian will be able to sedate your horse, do nerve blocks and stain the eye to assess the size, severity and depth of the corneal damage.
Your veterinarian can carry out further tests, such as sampling of the cornea for viewing under the microscope or growing on a culture plate may identify the type of infection (bacteria or fungi) involved and tailor treatment.
Sometimes a gentle debridement of the ulcer will also be performed to remove unhealthy tissue and help drugs to penetrate.
What is a melting ulcer?
Horse with a melting ulcerA melting ulcer is when the cornea is very soft and appears to be melting off the surface of the eye.
Melting ulcers are caused by severe bacterial or fungal infection and uncontrolled inflammation. They can lead to rapid rupture of the eye and need immediate attention.
It is also not uncommon to have foreign objects lacerating or penetrating the cornea. These must be identified and carefully removed.
What is a stromal abscess?
A stromal abscess is a localised infection in the deeper layer of the cornea. Just like an abscess anywhere else in the body, it is when a bacterial or fungal infection is walled off.
A stromal abscess is often caused by an initial break in the surface of the cornea, then microorganisms gain entry, and the small ulcer on the surface of the cornea heals over.
This traps the bacteria or fungi under the surface, they then proliferate and cause inflammation.
Stromal abscesses have a characteristic cream cotton-bud-like appearance and are often associated with intense pain.
What is uveitis?
Uveitis is the inflammation of the middle layer of tissue within the eye. It has characteristic signs in horses and if left uncontrolled will cause intense pain and can lead to blindness.
Corneal damage in horses results in uveitis.
Uveitis develops in horses because the layers of the cornea have many sensitive nerve endings. When these nerve endings are activated or damaged it results in reflex inflammation. Often this reflex inflammation is overzealous.
Severe uveitis results in white cells and other inflammatory products such as fibrin, accumulating in the front chamber of the eye (anterior chamber).
Uveitis is very painful and if left untreated can lead to adhesions (scaring between the cornea, pupil, iris or lens) which can lead to blindness.
Signs of uveitis
a constricted pupil
corneal oedema (blue haze to the cornea)
squinting
tearing
swelling of the conjunctiva and around the eye.
Treating a corneal ulcer and uveitis
Your horse's treatment regime prescribed by your veterinarian will depend on the corneal ulcer's severity, type of suspected infection and your horse's compliance.
All corneal ulcers require topical broad-spectrum antibiotics which come either in ointment or drop form.
Ointments (eg. Tricin) are easier to apply directly to the eye and last longer than drops.
A subpalpebral lavage system (SPL) is used by a veterninarian when it is difficult to administer medication into a horse's eye.
The SPL is an extension set that deposits liquid medication onto the cornea's surface without having to pry the eye open.
Conjunctival graft
In some cases, particularly if the eye is at risk of rupture, surgery is recommended to provide immediate structural support.
The surgery is called a conjunctival graft and it will also bring blood vessels to the damaged area. If the deficit is large, a conjunctival graft will also assist healing.
Managing uveitis
In all cases of corneal damage, a veterinarian will also prescribe medication to manage the uveitis.
Topical atropine drops which dilate the pupil and non-steroidal anti-inflammatories such as phenylbutazone (Bute), flunixin or firocoxib can be prescribed.
It's crucial that owners treating your horse's eye condition administer medication as directed by your veterinarian and closely monitor the eye for any changes.
If you're unable to administer medication into the eye then your veterinarian may need to use an SPL.
Medications must be kept at room temperature or refrigerated (as directed) and should never be left in a barn or car. Ensure medications are kept very clean.
Never use medications previously prescribed for humans, cattle or small animals as these sometimes contain corticosteroids and this will likely lead to a fungal infection in horses.
Monitoring your horse's corneal treatment
As the corneal treatment takes effect, your horse will:
be more comfortable
be able to open their eye more
squint less
experience less tearing or discharge
show improvement in the blue haze of their cornea
have a dilated pupil.
If the treatments don't result in rapid improvement your horse will experience pain or get worse, the corneal surface may change, and the pupil will remain constricted.
Treatment time
There is no exact way to treat corneal disease in horses. It depends on the type, severity and individual horse.
A simple, small, superficial corneal ulcer should heal with topical antibiotics within 5-7days.
A deeper or larger ulcer may take much longer and your veterinarian may recommend surgery. In some cases, treatment may be months, especially with stromal abscesses.
Your horse's treatment regime prescribed by your veterinarian will depend on the corneal ulcer's severity, type of suspected infection and your horse's compliance.