A cornea scratch or other trauma to the eye would likely cause acute discharge and pain, rather than chronic weepiness. But, it’s best you have your horse’s eyes examined to rule out these possibilities. Upon examination, your vet may diagnose a blocked tear duct or a tear-duct infection. The tear ducts can easily be flushed, and an antibiotic ointment might be prescribed.
Some horses simply have face shapes that cause tears to constantly drip; others have tear ducts that don’t function perfectly. While these causes aren’t threatening to your horse’s health, they can cause discomfort if not managed properly. During fly season, keep a fly mask on your horse to prevent irritation from flies attracted to the watery runoff. As part of his regular grooming regimen, gently clean and coat the skin under his eyes (on the teary paths) with petroleum jelly to prevent the saline in the eye fluid from burning his skin. Your vet may also recommend a prescription cream to alleviate irritation.