Conjunctivitis in Horses
- Conjunctivitis is inflammation of the tissues lining the eyelids and eye surface. In horses, it often causes redness, tearing, swelling, and discharge.
- A red or runny eye is not always 'just pink eye.' Corneal ulcers, foreign bodies, uveitis, and trauma can look similar and may threaten vision.
- See your vet promptly if your horse is squinting, holding the eye closed, has cloudy cornea, marked swelling, yellow-green discharge, or signs in both eyes with fever.
- Many mild cases improve well with timely care, but treatment depends on the cause. Your vet may recommend flushing, stain testing, and targeted medication.
What Is Conjunctivitis in Horses?
Conjunctivitis means inflammation of the conjunctiva, the thin membrane lining the inside of the eyelids and covering part of the eye surface. In horses, this tissue helps protect the eye and supports normal tear movement. When it becomes irritated or infected, the eye may look red, swollen, watery, or crusty.
Horse pet parents often call this condition pink eye, but that label can be misleading. Conjunctivitis may happen on its own, or it may be a sign of another eye problem such as a corneal ulcer, foreign material under the eyelid, blocked tear drainage, trauma, allergies, or a deeper inflammatory disease.
That is why any painful or suddenly abnormal eye deserves attention. Horses can develop serious eye complications quickly, and several different eye diseases can look similar at home. Early evaluation by your vet helps protect comfort and vision.
Symptoms of Conjunctivitis in Horses
- Red or bloodshot tissue around the eye
- Watery eyes or increased tearing
- Mucus or pus-like discharge
- Swollen eyelids or puffy conjunctiva
- Squinting or holding the eye partly closed
- Sensitivity to light
- Cloudiness on the eye surface
- Rubbing the eye or face
Watch closely if your horse has discharge, squinting, eyelid swelling, or cloudiness. These signs are not specific to conjunctivitis alone. Cornell Equine notes that eye changes should be acted on quickly because tearing and redness can range from a relatively minor issue to a vision-threatening disease.
See your vet immediately if the eye is painful, the cornea looks blue or cloudy, the horse will not open the eye, there is obvious trauma, or your horse also has fever, nasal discharge, or swelling around both eyes. Those findings can point to a deeper eye problem or a contagious systemic illness.
What Causes Conjunctivitis in Horses?
Conjunctivitis in horses has many possible causes. Common triggers include dust, wind, pollen, bedding particles, flies, smoke, and foreign material trapped under the eyelid. Trauma from hay stems, branches, fencing, or rubbing can also inflame the conjunctiva. In some horses, poor tear drainage or irritation from nearby eyelid problems contributes to repeated flare-ups.
Infectious causes are also possible. Merck notes that conjunctivitis affecting both eyes is more commonly linked to viral or bacterial infection, and herpesviruses have been associated with conjunctivitis in horses. Conjunctivitis may also appear as part of broader infectious disease, including equine viral arteritis, where eye reddening, tearing, and swelling around the eyes can occur along with respiratory signs.
One important point: conjunctivitis is sometimes the visible sign, not the whole problem. Corneal ulcers, keratitis, uveitis, blocked nasolacrimal ducts, and eyelid abnormalities can all cause a red, draining eye. Because treatment choices differ, your vet needs to identify the underlying cause before medication is selected.
How Is Conjunctivitis in Horses Diagnosed?
Your vet will start with a careful eye exam and a full history. They will want to know when the signs started, whether one or both eyes are affected, whether your horse has been rubbing the eye, and whether there has been dust exposure, fly pressure, trauma, or recent respiratory illness in the barn.
A proper equine eye workup often includes checking the eyelids and tissues under them for foreign material, evaluating the cornea, and looking for deeper inflammation. Fluorescein stain testing is especially important because it helps detect corneal ulcers, which can look very similar to conjunctivitis from a distance. AAEP ophthalmology guidance emphasizes fluorescein staining in horses with painful eyes, and Cornell highlights that many eye signs are nonspecific.
Depending on the case, your vet may also flush the tear duct, collect samples for cytology or culture, measure tear production or eye pressure, or recommend sedation for a safer and more complete exam. If there is concern for recurrent disease, severe infection, or vision-threatening changes, referral to an equine ophthalmology service may be the next step.
Treatment Options for Conjunctivitis in Horses
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Farm-call or clinic exam focused on the affected eye
- Basic eye stain test to rule out a corneal ulcer
- Eye flushing and removal of visible debris if present
- Short course of targeted topical medication if your vet feels it is appropriate
- Environmental changes such as fly mask use, dust reduction, and turnout adjustments
Recommended Standard Treatment
- Complete ophthalmic exam by your vet
- Fluorescein stain and eyelid/conjunctival inspection for foreign bodies
- Sedation if needed for a thorough exam
- Targeted topical medication plan based on exam findings
- Pain-control or anti-inflammatory plan when appropriate and safe
- Recheck visit to confirm healing and adjust treatment
Advanced / Critical Care
- Expanded ophthalmic testing and repeat exams
- Cytology and culture when infection is severe, unusual, or not responding
- Nasolacrimal duct evaluation or flushing
- Subpalpebral lavage system placement if frequent eye medication is needed
- Referral to an equine ophthalmology service for complicated or vision-threatening cases
- Treatment of underlying corneal ulcer, keratitis, uveitis, or systemic infectious disease if identified
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Conjunctivitis in Horses
Bring these questions to your vet appointment to get the most out of your visit.
- Does this look like uncomplicated conjunctivitis, or are you concerned about a corneal ulcer, uveitis, or trauma?
- Do you recommend fluorescein staining or any other eye tests today?
- Is the discharge pattern more consistent with irritation, allergy, infection, or a blocked tear duct?
- Should my horse wear a fly mask, stay out of dusty turnout, or have bedding changed while the eye heals?
- What signs would mean the eye is getting worse and needs recheck right away?
- If medication is prescribed, how often does it need to be given and for how many days?
- If this keeps coming back, what underlying causes should we investigate next?
- What cost range should I expect for today's plan versus additional testing if the eye does not improve?
How to Prevent Conjunctivitis in Horses
Not every case can be prevented, but daily eye checks make a real difference. Look for tearing, discharge, squinting, cloudiness, or eyelid swelling when you feed or groom. Early changes are easier to treat, and fast action can help protect vision.
Good barn management also matters. Reduce dust from bedding and hay when possible, keep stalls reasonably well ventilated, and control flies. Cornell recommends fly masks for protection from flies, wind, allergens, and sun, with daily removal so the eyes can be checked. A properly fitted mask can be especially helpful for horses that are sensitive to insects or environmental irritation.
Try to limit eye trauma by checking fencing, feeders, and turnout areas for sharp edges or poking branches. If your horse has repeated eye issues, ask your vet whether tear drainage, eyelid shape, allergies, recurrent corneal disease, or a contagious respiratory problem could be contributing. Prevention works best when it is tailored to your horse's environment and medical history.