What To Do
Assess your horse's eyes carefully. Look especially for grayness or any erosions in the clear surface of the eye (the cornea). Look for environmental causes such as dust, wind or flies. Manage those things as well as you can.
Place a fly mask, and control flies. It is safe to rinse eyes with saline if you feel confident doing so. Look for other signs of eye problems. Recognize that eye problems can worsen rapidly and be prepared to consult your vet if tearing continues.
What Not To Do
Do not apply steroid containing ophthalmic ointments or drops without vet guidance.