Many horses have a slightly runny eye occasionally due to fly irritation in the summer or from dusty bedding, but remember eye problems can be more serious than you might initially think.  Don’t take any chances, as the eye is irreplaceable and some diseases can rapidly worsen over several hours. 

If an eye is painful, your horse will keep it partially or completely closed, there will probably be a discharge from the eye and the membranes may appear reddened.  A cloudy area on the surface of the eyeball indicates that an ulcer is present and treatment is required. 

To help make your horse more comfortable until the vet arrives, bathe around the eye with warm (boiled) water and remove any discharge.  Try not to let your horse rub his eye and if there is swelling, and if the horse is amenable, hold an icepack against the area for several minutes. 

It is better to contact your vet sooner rather than later to ensure prompt treatment.