When your vet arrives, they will most likely sedate your horse and perform a couple of nerve blocks. These nerve blocks temporarily take away the sensory and the motor abilities of the skin and muscles. Once this has been performed, the horses tend to be a bit more relaxed and allow for full examination of the eye.
Treatment of superficial ulcers is aimed at reducing pain and minimizing infection. Oral bute or banamine is usually given for pain management. Topically, ophthalmic antibiotic ointment can be administered to help fight off any bacterial infection. Atropine, a mydriatic, dilates the pupil to decrease muscle spasm and pain within the eye. A weeklong course of this therapy is generally enough to combat a simple corneal ulcer.
One drug you never want to use on an ulcer is a steroid. A steroid (such as Prednisolone or Dexamethasone) eliminates the body's defense mechanisms and can make the situation much worse in a short amount of time. So do NOT use steroids in an eye unless directly told to do so by your veterinarian!
The cornea in the horse is a very fragile structure, but it has great capacity to heal. Early detection and treatment of problems is necessary to have a successful outcome. If you have any concerns at all regarding your horse's eye, contact your vet. We'd rather look at something like what's at the top of this post than at the bottom.