Shelties are prone to a condition where they have a second row of eyelashes that rub against the outer surface of the eye. This can cause a lot of discharge from the eye that can turn solid. It can be either one eye or both.
My Neechee had this and it became a problem when he was about six months old, and he had it the rest of his life. I did consult a veterinary opthalmologist about it, and you can have a procedure done where they essentially freeze the extra row off. Since my little guy was so patient and would hold still for me, I was able to get by doing the plucking myself with a pair of tweezers every week. The freezing procedure causes them to lose the dark pigment around the eyelids, and I couldn't bear the thought of Neechee's sweet expression being altered. So I did the plucking thing 2-3 times per week for 17 years! He was so patient about it, it was no trouble at all.