Yes, ulcers can ultimately lead to corneal rupture (burst eyeball!). It depends on how severe it is. Without seeing the dog myself and knowing what tests they've done, I can't really give more advice than that, but I always remind people to think about how irritating it is to have an eyelash in your eye, then imagine how terrible it must feel to have an actual HOLE and infection on the surface of your eye. Eye issues can be very painful, and if not treated correctly, can lead to loss of vision.
Not to scare you! Most superficial ulcers can be managed quite easily with antibiotic ointments, but first you have to know what you're dealing with.
Feel free to ask more questions when you have more information!
Endurance comes from exhaustion. Keep running!
--DH, aka "Coach"