Conjunctivitis in Horses

Updated Aug. 11, 2022
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What Is Conjunctivitis in Horses?

Conjunctivitis in horses is swelling of the conjunctiva, or pink mucus membranes of the eye. The swelling can be caused by an infection or have other non-infectious causes. Conjunctivitis is most commonly seen in young horses, but it can occur at any age.  

It is important to note that any abnormality with a horse's eye should be considered a medical emergency and a veterinarian should be called immediately. Eye issues can become serious quickly. 

Symptoms of Conjunctivitis in Horses

A horse with conjunctivitis may experience the following symptoms: 

  • Eye discharge/drainage 

  • Squinting  

  • Excessive itching or rubbing of the eye 

  • Head shaking 

  • Redness of eye or around the eye 

  • Swelling of any part of the eye or around the eye 

Causes of Conjunctivitis in Horses

Conjunctivitis can either be infectious or non-infectious. Common causes for each type include: 

  • Infectious 

    • Bacterial 

    • Parasitic 

    • Viral 

    • Fungal 

    • Protozoal  

  • Non-infectious 

    • Uveitis 

    • Trauma 

    • Allergic reaction/irritants 

    • Nasolacrimal duct obstruction 

    • Neoplastic/cancer  

Most commonly, horses get conjunctivitis due to trauma or through an infection. Young horses may get conjunctivitis if they have direct contact with a fly that has been in direct contact with another horse that is infected with a virus that causes conjunctivitis. Trauma can result from anything, ranging from a horse scratching its face to allergens or even dust getting in the eye and causing irritation.  

How Veterinarians Diagnose Conjunctivitis in Horses

To diagnose conjunctivitis in a horse, a veterinarian will take a thorough history and perform a physical exam and ophthalmic exam. They may also recommend diagnostic tests, including bloodwork.  

Veterinarians may ask questions such as:  

  • "How long have you noticed the new eye symptoms?” 

  • "Has the horse been traveling recently or been around any new horses?" 

  • "Is this the first time the horse has had any eye issues?" 

  • "Have you noticed your horse showing any other abnormal behaviors lately?" 

The veterinarian will also want to know the horse's vaccine and deworming history.  

Your veterinarian will also complete a physical exam by looking at the mucus membranes/gums, listening to the heart, lungs, and gastrointestinal tract, check body temperature, and look the horse over for any abnormal swellings or other physical abnormalities. Finally, your veterinarian may also ask you to hand-walk the horse to make sure there is no lameness or neurologic signs.  

Once the physical exam is complete, the veterinarian will perform an ophthalmic exam on the eye and the area surrounding the eye. First, they will look for any visual abnormalities, checking both eyes for comparison. After getting a good look at the structures in both eyes, the veterinarian will likely want to stain the eye (fluorescein eye stain) to look for any scratches or breaks in the cornea. Fluorescein eye stain will adhere to any damaged cells on the cornea. If there is any stain uptake, the veterinarian may diagnose the horse with a corneal ulcer and create a plan from there.  

Based on the eye exam findings, your veterinarian may advise further diagnostics such as:  

  • Culture and sensitivity testing to look for bacterial causes 

  • Conjunctival scraping or biopsy 

  • Viral testing 

  • Bloodwork such as a complete blood count 

  • Chemistry looking for systemic disease 

  • Specific testing for bacterial disease(s) 

Treatment of Conjunctivitis in Horses

Treatment for conjunctivitis will depend on the underlying cause, along with the severity of the condition. Commonly, horses are put on a combination of medications, including both topical and oral medications to treat the symptoms and the underlying cause. Topical broad-spectrum antibiotics such as Neopolybac are one of the most common medications used in the treatment of conjunctivitis.  

Conjunctivitis can be very painful due to the swelling and irritation of the eye, therefore oral systemic anti-inflammatories are commonly prescribed, such as Banamine (flunixin meglumine).  

Other medications that may be added include:  

  • Atropine ophthalmic drops 

  • Silver sulfadiazine cream solution 

  • Antifungal topical medications 

  • Topical steroids (such as dexamethasone) 

  • Serum (clear constituents of blood that the veterinarian can collect from the horse) 

It is very important to follow your veterinarian’s instructions, including the amount of medication to give, the number of times to give it per day, and how long to wait between medication administration if you’re instructed to give more than one medication in the eye at a time. Often, it is important to wait at least 5 minutes in between medications.  

Some medications, such as Atropine, are given to help with pain, but will also cause the eye to dilate and the horse to be extremely sensitive to light. During treatment, it may be important to keep your horse in a barn out of the sunlight during the day.  

The nasolacrimal duct is a duct or channel that passes from the inside corner of the eye to a small opening just inside the nostril. If the veterinarian has diagnosed the horse with an obstruction in the nasolacrimal duct that’s causing the conjunctivitis, the horse will likely need to be sedated. A small tube will be placed just inside the nasolacrimal duct opening in the nose, and sterile solution will be carefully pushed through the duct to clear away any obstruction. It is not uncommon for this duct to become plugged with debris and is generally an easy fix.  

There are over-the-counter eye wash solutions, such as Vetericyn eye wash, that may be helpful to clear away discharge from the eye. Before using any of these, ask your veterinarian if this would be appropriate to for your horse's current condition.

How to Apply Eye Drops to a Horse's Eye 

  1. Gently and carefully clear away any discharge with a wet tissue/cotton ball or eye wash solution.  

  1. Place the topical eye medication in one hand between your pointer finger and thumb with the tip down. If possible, rest your wrist against the horse so that if the horse throws his/her head, the eye medication bottle will not accidentally poke the eye and cause trauma to the eye.  

  1. Use your opposite hand to gently pull the lower lid of the eye down to show a little pocket in the inside of the lid.  

  1. Place the instructed amount of topical eye medication into the lower lid, being careful not to touch the tip of the medication to the eye. 

  1. Lastly, allow the lid to resume normal position. Your horse will likely blink a few times, allowing the eye medication to be distributed across the eye.  

Recovery and Management of Conjunctivitis in Horses

Conjunctivitis can heal in as short as 5-7 days, or it could take weeks depending on the underlying cause, severity, and how quickly treatment is started. If left untreated, conjunctivitis will likely get worse and may cause permanent damage to the eye as well as impairment of vision for the horse.  

Prevention of Conjunctivitis in Horses

In general, conjunctivitis can be prevented in several ways, including: 

  • Fly control in barns and pastures: If you live in an area where flies are abundant, using a fly mask is a great way to help keep the eyes clean and fly free. Flies not only can pass infectious agents from horse to horse, but can also cause irritation and trauma to the eye.  

  • Establish a preventive health program: It is important to keep horses up to date on vaccinations and deworming. Ask your primary veterinarian to help you develop the best protocol for your horse. 

  • Reduce environmental allergens: If horses are stalled, watering down dusty shavings can be helpful. 

  • Treat any underlying eye or systemic disease that could make the horse more prone to conjunctivitis.  

  • Limit sun exposure in lightly pigmented horses: This may decrease the incident of squamous cell carcinoma (SCC) of the eye and eyelid seen in horses. SCC is the most common form of tumor to affect the eye and eyelid in horses and second most common cancer seen in horses. 

Conjunctivitis in Horses FAQs

How long does equine conjunctivitis last? 

The duration of equine conjunctivitis will depend on the underlying cause and severity of the case. A mild, simple bacterial conjunctivitis may resolve in 5-7 days while a complicated severe case of conjunctivitis may take weeks to heal.  

Can conjunctivitis heal on its own?

Eye issues in all species, including horses, can quickly develop into very serious issues. Mild conjunctivitis can become a severe eye infection fast if medical intervention is not implemented.  

What is the best way to get rid of conjunctivitis?

Call your veterinarian as soon as you notice anything abnormal with your horse's eye. The sooner the eye is examined by the veterinarian, the sooner a treatment plan can be implemented and recovery can begin. Depending on the underlying cause of the conjunctivitis, recovery will be shorter and prognosis better the sooner medical therapy is started.  

Featured Image:

Jennifer Rice, DVM, CVSMT


Jennifer Rice, DVM, CVSMT


Dr. Jennifer Rice is a 2017 graduate from Purdue College of Veterinary Medicine where she specialized in Equine medicine. Since graduating...

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