Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before.Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Again I do apologize that my colleagues could not aid you sooner. If you would still like assistance, can you tell me:
Did they note any ulceration on the eye ball? Any clouding?
Is the mass growing? Does he ever catch it? Or does it make it hard for him to close his eyelids over the eye?
Have his vets noted a change in the eye's pressure?
What treatments is he on?
Do you seem him rub the eye? Does it tear more then the normal one?
Can you take a photo of this? If you can do so,this will let me see what you are seeing. To post them online, you can use the paperclip icon on the tool bar above your text box. Or if you can't see that on your computer/phone, then you can post them on any other site (ie Flickr,Photobucket, imgur, etc) and paste the web link here for me to check.