Eye Infections in Horses

Redness and Inflammation

Redness and inflammation is the most common indicator of any eye infection, and usually points to conjunctivitis or ERU. It can also indicate eye injury or allergies.

Causes of Eye Infections

There are several causes of eye infections in horses of varying severity. Visit your vet for a definitive diagnosis and a subsequent treatment plan.

• Bacterial and viral infection: Bacteria and viruses can get into your horses eye in a number of ways. Bacteria can enter the eye through insects and dirt, and viruses can be transported similarly.
• Fungus: It's normal to have some fungus living on the surface of a horse's eye, but when there is a wound that allows the fungus to enter inside of the cornea, infection can occur. Fungal infection in a horse's eye can lead to abscesses and blindness.
• Allergens: Allergens like pollen and dust can irritate the eye and lead to conjunctivitis. Conjunctivitis isn't always accompanied by pain and is especially prevalent in spring and summer months.
• Parasites: Infection with the parasite Thelazia, also known as the eye worm, is also a cause of eye infections in horses.2 Horses are infected with this parasite through flies, and they appear as thin worms in the eyes.
• Injury: Horses can develop an infection after having a foreign object lodged within the eye. If the eye's surface is scratched, environmental bacteria can quickly cause an infection. This could make the horse's eye appear cloudy and red. The horse will likely squint and tear profusely and may be reluctant to let you take a close look.

Diagnosing Eye Infections in Horses

A vet can usually diagnose an eye infection quickly through a physical examination of the eye, but the diagnosis doesn't always reveal a cause. Your horse may need to be sedated during this process. If the examination isn't conclusive, your vet may need to swab and test your horse's eye. Your vet will check for damage to the cornea as well as anything that may be lodged in the eye, such as splinters, awns from grasses, or grit. Developments in the microscopic corneal analysis have helped vets to identify funguses and bacteria in horses' eyes. A tool called an in vivo corneal confocal microscope is used to perform this type of exam.