Help with my sick dog!

[Flybyeme17]

I have a Maltese/American Eskimo 11 years old diagnosed with diabetes also his liver numbers extremely high in October 2016 treated with insulin took him in every week check and it was still high. Being at 10 (insulin) for 2 wks and his numbers not getting better I noticed his hair falling out they tested for Cushings and sure enough he had it. He's been on a Vetoryl since December 2016 with no positive change at all. Vet says he's not suffering bc he stilll eating and drinking (both a lot) and greeting me at the door but other than that he just lays around. Since I met with vet last week when he said that, now Riley has went blind! He walks into things and can't see the treats I try to give him unless I put them up to his nose. Him going blind happened in just cpl days so very fast! I'm so conflicting, I'm scared I'm going to make the wrong decision either way. I love and adore my dog, he's been thru so much with me in the 11 years! I know Cushings and diabetes can be controlled with meds, by again we are not sure about his liver many costly tests yet ??? Now he's blind! My heart is broke! I just need some honest guidance.