Conjunctivitis in horses: causes, symptoms, prevention

Conjunctivitis is a common disorder in horses, causing pain and discomfort. It is crucial to identify it as early as possible, so that it can be treated at an early stage to avoid complications. Find out more about the causes and symptoms of conjunctivitis in horses, and how to prevent its onset.

A horse's eyes: a health asset worth preserving

As sensitive organs, the horse's eyes are exposed to many of the daily risks inherent in life outdoors. Environmental factors play a major role in triggering conjunctivitis. However, infectious causes can also be found, requiring more detailed examination by a veterinarian. Whatever the cause, the key to preventing conjunctivitis in horses is to take simple steps to ensure your pet's safety and peace of mind.

The horse's conjunctiva: a brief anatomical reminder

The horse's conjunctiva is a highly vascularized mucosa composed of :

• Palpebral conjunctiva(inner surface of the eyelids): borders the inner surface of the eyelids, the fornix (end of the conjunctival sac) and the anterior surface of the third eyelid.
• Bulbar conjunctiva(white of the eye): covers the anterior surface of the eyeball up to the corneal margin and the posterior surface of the third eyelid.

The conjunctiva's role is to lubricate the eye, thanks to its conjunctival glands, which produce mucus that makes up part of the tear film (Source: IMAIOS).
This film covers the conjunctiva and concentrates in its folds. It spreads over the eyeball with each movement of the upper and lower eyelids and the nictitating membrane (Source: Étude de la cytologie conjonctivale de cheval). The conjunctiva not only preserves the tear film, but also protects the eye against foreign bodies and micro-organisms that could potentially cause infection.

What is conjunctivitis?

Conjunctivitis is an inflammation of the conjunctiva that can affect one or both eyes. It may or may not be infectious, and is sometimes contagious. Common in horses, conjunctivitis must be identified and treated as soon as possible, as it can lead to serious complications, particularly in the case of conjunctivitis of bacterial or viral origin.

What are the symptoms of conjunctivitis in horses?

It's important to observe your horse's eyes regularly, as well as his behavior, to make sure they're healthy and that he's not suffering from a health problem.

Description

The symptoms of conjunctivitis are easy to identify:

• Red eye,
• Swelling of the eyelids,
• Frequent blinking,
• Eyelids half-closed,
• Tear-like or thick, purulent eye discharge,
• Glued eye,
• Light sensitivity,
• Rubbing of the eye on objects in the environment or on the leg,
• Head shaking,
• Possible agitation due to pain and stress.

Consequences of symptoms

The symptoms of conjunctivitis are painful: they create stressin the horse, which is expressed in its daily behavior. Your horse, usually so compliant, may show signs of impatience with activities normally enjoyed. Your horse may exhibit tics such as the bear tic. Some stressed horses become apathetic, while others may even show aggression and bite.

Possible complications

Untreated viral or bacterial conjunctivitis can spread to the cornea, causing ulcerative keratitis. Ulcerative keratitis refers to ruptures in the surface layer of the cornea, visible as rough patches on the surface of the eye. These corneal ulcers can be superficial or more profound, risking the loss of the eye. Horses can also cause these ulcers by rubbing their sore eyes a little too vigorously on injurious surfaces, resulting in trauma.

What causes conjunctivitis in horses?

There are many possible causes of conjunctivitis in horses, including environmental causes which account for a significant proportion of triggering factors. It's the origin of the disorder that determines the type of treatment applied by the veterinarian.

Pollen

Pollen is a frequent cause of conjunctivitis in horses, and more and more of them are becoming hypersensitive to it. From January to May, the wind blows pollen from particularly allergenic plants and trees such as grass, ragweed, juniper, birch and plane tree. Horses then develop an allergic reaction that affects both eyes, but can also cause coughing and breathing difficulties. Wearing a canvas eye protector can avoid this pitfall and protect your horse from allergic conjunctivitis.

UV

Sensitivity to UV rays (ultraviolet light) can also cause inflammation of the conjunctiva, with a considerable impact on the horse's quality of life. Here again, wearing UV protection means that your horse will no longer have to put up with the daily grind, and will be protected in all circumstances.

Wind

Wind can be aggressive to your horse's eyes, provoking an inflammatory reaction. As with UV rays, these external factors cannot be controlled, so it's essential to provide your horse with a wind protection mask.

Dust

Life in a stall means that your horse has to live in a dusty environment that is difficult to control. Straw and hay contain highly volatile particles that soon find their way into your horse's moist eyes. This can lead to irritation and conjunctivitis. What's more, some horses are more sensitive to dust than others, leading to a series of inflammatory reactions. If your horse's living environment is damp and poorly ventilated, fungi can also proliferate and cause infectious conjunctivitis.

Foreign body

Branches, plant debris, stones and insects can all find their way into a horse's eyes, causing inflammation of the conjunctiva. In severe cases, a sharp foreign body can perforate the cornea, leading to ulceration.

Chemical irritation

Numerous chemical pollutants pass through the air and can affect your horse's eyes. Be careful when choosing the disinfectants you use to maintain your horse's environment. Some are highly toxic, causing skin, respiratory or ophthalmic reactions.

Trauma

Horses can sometimes be a little too lively, rubbing their eyes energetically or banging their heads, causing injury. While this trauma can cause conjunctivitis, it can also lead to a corneal ulcer, which needs to be treated quickly.

Parasitosis

Parasite infestation can cause ocular symptoms, including inflammation of the conjunctiva. Among the most common ocular parasitoses in horses are :

• Habronemosis: also known as "summer blight", this parasitic disease transmitted by flies appears during the summer months. It can affect the eyes, skin and digestive system. In the conjunctival form, flies deposit their larvae on the conjunctiva, causing granular lesions at the inner angle of the eyelids and acute conjunctivitis.
• Onchocerciasis: also transmitted by mosquito bite during the summer months, onchocerciasis exists in both cutaneous and ocular forms. In the latter, symptoms are similar to those of uveitis. Lesions appear on the eyelids, conjunctiva (leading to conjunctivitis), cornea and retina.
• Thelaziosis: an eye disease caused by the pathogenic action of a nematode, transmissible to humans (zoonosis). The fly deposits the parasite in the horse's eye, frequently causing conjunctivitis (Source: Les parasitoses oculaires du cheval).

Bacteria

Bacterial eye infections in horses are often the result of eye injury or irritation. These are invaluable entry points for bacteria to proliferate and trigger ocular symptoms, including conjunctivitis.

Virus

Some viruses are responsible for eye disease in horses, such asequine herpesvirus, which causes viral rhinopneumonitis, a highly contagious disease. It can take three different forms: respiratory, neurological and abortive (responsible for spontaneous abortion). In the respiratory form, a flu-like syndrome appears, with nasal discharge and watery eyes. Your horse can be vaccinated against this viral infection.

Genetics

Some horses are genetically predisposed to ocular fragility. In such cases, they are more likely than other horses to develop localized damage, notably in the form of conjunctivitis.

Tear insufficiency

Lacrimal insufficiency, although rare, can cause conjunctivitis in horses, as in the case of keratoconjunctiva sicca, also known as "dry eye", which causes dehydration and inflammation of the conjunctiva and cornea, eye pain and possibly visual impairment (Source: Le Point Vétérinaire).

How is conjunctivitis treated in horses?

Treatment of conjunctivitis depends on its cause. It is therefore advisable to consult your vet as soon as possible, so that he can make a precise diagnosis and set up the most appropriate treatment protocol. This may involve purely symptomatic treatment, the administration of antibiotics, eye baths and the application of specific eye drops.

How to prevent conjunctivitis in horses?

As most of the causes of conjunctivitis are environmental, it's essential to take all necessary preventive measures. This includes protecting the horse's eyes with specific equipment such as eye masks and goggles. They offer the advantage of protecting the horse's eyes from all factors of aggression (UV, insects, wind, dust, pollen, etc.), as well as from injury during outdoor work and show jumping.

Flexible and comfortable, they can be worn by your horse in the pasture or during work sessions, without affecting his movements. It's also essential to clean your horse's eyes regularly It's also essential to clean your horse's eyes regularly, and to keep him under veterinary supervision to detect any ophthalmic damage as early as possible, the most common of which is conjunctivitis.