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Uveitis in Horses

Uveitis is the most common eye disease that affects equines. It is also the leading cause of blindness in horses. The eye condition is also known as “Moon Blindness” Uveitis occurs when the horse’s immune system attacks the tissue of the eye. The uveal tract, which contains the iris in the front and the colored part of the eye in back, becomes inflamed. There are three known causes of uveitis: ocular, systemic, and immune-mediated.

Upon observing symptoms of uveitis, it is important to get the horse treated promptly. Quick treatment can prevent further eye damage, but there is no known cure for the disorder. Blindness is common with horses who have been diagnosed with uveitis or ERU. Left untreated, uveitis can lead to Equine Recurrent Uveitis (ERU) which increases the risk of the horse becoming blind.

Detecting uveitis symptoms in horses

There are several signs and symptoms of uveitis in equines.

  • Ocular pain – when the horse experiences eye pain, it will keep the affected eye closed. You may notice excessive watering redness and swelling of the eye.
  • Corneal edema –the eye turns a hazy, cloudy, or blue color
  • Constricted pupil – an eye spasm occurs, constricting the pupil in the affected eye
  • Shaking the head – a horse that continuously shakes their head may be signaling that they are in pain
  • Bloodshot eyes – a bloodshot eye is likely irritated
  • Loss of balance –if your horse is losing their balance or running into things, it may indicate a need for immediate treatment.
  • Rubbing eyes – constant eye rubbing is also a sign something is irritating the horse’s eyes.

If you notice these issues, act quickly. Damage from uveitis is preventable, but it is not reversible. Make an appointment with your veterinarian and begin treatment as soon as possible.

Understanding recurrent uveitis in horses

Equine Recurrent Uveitis is a recurring inflammation and pain in the eye of the horse who has uveitis. The recurrences of the disease are what can cause total blindness in the horse. Approximately 25 percent of horses in the United States are diagnosed with ERU. Certain breeds of horses are more prone to getting uveitis. They include Appaloosas, drafts, paint horses, and warmbloods. Standardbred and thoroughbred horses are less likely to be affected. Appaloosas are more susceptible to the disease, with an eight times higher risk of developing uveitis than other breeds.  They are also four times as likely to go blind from the condition. However, no horse is immune to this eye disease. Regular check-ups with your veterinarian can help prevent the disease from blinding your horse.

Types of Equine Recurrent Uveitis

There are three types of ERU in horses: classic, insidious and posterior. Classic ERU, also called anterior ERU, consists of an active period of approximately two weeks when there are symptoms present. During the inactive phase of Equine Recurrent Uveitis, the horse shows little to no active symptoms. This phase can last for any amount of time and is followed by another active phase.

Insidious ERU is more challenging to diagnose than classic ERU since horses are less likely to show signs and symptoms during an active phase. Although the horse may not show pain, low-grade inflammation remains present, damaging the animal’s eyes. Insidious ERU occurs in a continuous cycle and should be treated as soon as it is detected.

Cases of posterior ERU are rare in the United States. The vitreous humor, which is the clear fluid in the eye, may become clouded or stained. Retinal detachment is also common. Both issues can affect the horse’s vision.

Symptoms of active ERU

Your horse may exhibit one or more symptoms during an active phase of the disease. Talk to a large animal veterinarian if you notice the following symptoms.

  • Photophobia – sensitivity to light
  • Blepharospasm – squinting
  • Corneal edema – swelling of the red lining at the corner or edge of the eye
  • Aqueous flare – floaters in the eyes
  • Hypopyon - pus in the eye
  • Miosis – pupil construction
  • Vitreous haze – haze or cloudiness in the eye
  • Chorioretinitis – inflammation of the colored part of the eye.

Examining possible causes of uveitis

Though there is not a certain or specific cause for uveitis, there are several factors which can contribute to this eye condition. The horse’s environment, genetics, ocular injury, infections, and T-Cells called T-lymphocytes can all lead to uveitis. Ocular injuries can include direct trauma to the eye, corneal ulcers, lens-induced uveitis and immune-mediated uveitis. Bacterial, viral, and parasitic infections may trigger uveitis. There is no proof that allergies are a cause of uveitis; however, researchers note that the onset of uveitis has been seen in horses during high pollen and ragweed counts.

Diagnosing and treating uveitis

There are many tests the veterinarian can do to determine if your horse has uveitis or recurring uveitis. During the diagnosis, the veterinarian will do a blood count check, urinalysis, serum biochemical profile, leptospirosis, brucellosis titers, toxoplasmosis and fecal exam. The vet will also do an ophthalmic exam, to look at the horse’s eye to see signs and symptoms of uveitis and ERU.

Treatment for mild cases

Treatment of uveitis can be complicated when it is hard to determine the actual causes of the eye disease. Treating the underlying symptoms can help with the inflammation of the eye, and prevent the onset of more severe symptoms. For treatment, topical or non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin or meglumine are given to the horse. Pain medications may also be prescribed to ease the horse’s eye pain. Pain-relieving options include aspirin, phenylbutazone or herbal treatments. Your vet may also prescribe an antibiotic to reduce the chances of further infection. Treatment for a single bout of uveitis lasts for approximately four weeks. The vet will have you wean the horse off the medications, rather than stop at once.

Treating chronic uveitis in horses

In ERU, the treatment methods are the same, but trips to the vet are more frequent. Your horse’s doctor may prescribe a specific care regimen. It can take up to four weeks of daily treatment per active episode to control the disease.

For ERU, there is an option to treat the disease with a cyclosporine implant. The implant is a small disc filled with cyclosporine, an antibiotic. The veterinarian surgically implants the medicated disc into the sclera of the eye. The implant slowly administers the into the eye and reduces the requirements for daily treatment. There are risks to this type of treatment, including the development of cataracts, glaucoma, shrinking of the eye, and retinal damage. These conditions can also cause your horse to become blind.

Preventing and managing uveitis

 Preventing and managing uveitis symptoms will help the onset of uveitis. Some of these methods include:

  • Proper diet- the right nutrition can reduce the risk of infection and inflammation
  • Insect and rodent control – control disease infested rodents and insects with the proper chemicals
  • Decrease dust particles – eliminating large amounts of dust helps prevent allergies and eye injuries
  • Maintain common care – keep dental and hoof care, deworming, and vaccinations current
  • Change bedding – regular bedding changes help keep pests away
  • Sharp objects – make sure all sharp objects are out of the horse’s reach to prevent injuries
  • Decreased schedule – allowing the horse to rest properly ensures faster healing time
  • Sanitation – having proper sanitation when dealing with the horse helps prevent infections
  • Freshwater – never allow your horse to drink stagnant water
  • Vet visits –  schedule regular appointments with your veterinarian.

Maintaining your horse’s health is ideal for prevention, management, and treatment of uveitis and other diseases. Each case of uveitis is unique and may be treated differently. Taking action when you first notice signs of uveitis will help you manage the disease. It is important for the horse to receive medical attention from your veterinarian with the onset of these symptoms. Pain and irritation can be persistent for your horse, and early diagnosis is best for equine health. 

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