Not sure where my original response to this post is, that I did just previously, however I will to it again.
Sorry to hear about the issue you are trying to solve about your almost 5yo yorkie. Unfortunately, I couldn't open the pic you uploaded
I'm sure that it's due to my lack of techology.
Although I am no expert, by any stretch of the imagination, after reading your post I have a few questions:
1) If the vet stated it may be hair, how does the other eye get affected, as you said the hair isn't long enough to reach the eyes? I could see if it was one eye effected, as cutting hair around the eyes, a small piece could get into the eye. and,
2) Have you looked at glaucoma as a possible cause?
I don't want to scare you, but thought I'd throw it out there.
Sending positive thoughts your and your sweet baby's way and hope that you find out the reason for your issue. Cheers!