Thanks for all the responses guys! After meeting with specialist after specialist we've finally figured out what this "thing" is!
I got 2 different equine opthomologists to look at Robbie since the first guy wasn't too sure what it was. The tumor/cyst thing was biopsied and tested...not a tumor. No sign of cancer, etc. Good news! But they still didn't know what it was. So further testing was done and a vet was consulted from some univsersity in Toronto. And then we found out what it is!
Apparently, this "thing" on poor Robbie's eye is a rare type of allergic reation caused by an extremely rare fly landing in his eye.
Ummm...yeah so weird right? I guess there are only roughly 20 cases like this reported in Canada (not just in AB but all of Canada haha) because this type of fly is rare and the allergic reaction can only occur on certain membranes (eye, inner nose, bum) and this fly landing on one of the three areas is super rare. So all in all, Robbie got "bit" by this uber rare fly and now has a lovely growth because of it haha. But the extremely good news is that this can all be cured with steriod antibiotics! :) It will take 2-3 months for the bump to go away and I have to apply the eye ointment 3-4 times a day but his eye will be just fine with no damage or lasting effects! The only thing I must do come next year is keep a fly mask on the poor guy haha.
I'll take some updated pics of the growth, it's gone down so much already and I guess it'll kinda just fall off and then the origin of growth just needs to heal up. :) Yay!