I will admit I put a dog to sleep (Harper, the one in my avatar photo) because I didn't have the time or the money nor did I feel 'right' about her diabetes.
She would have required several shots a day, at a specif time and her meals regulated, and according to the vet it would have taken some time to figure out the doses and her meals. In the meantime, the dog feels sick.
But then I had no money at that point, and my vet offered the medicine at no profit to herself, but it was still going to cost about $90.00 a month. I had just got out of a wheelchair, was fighting with disability and living off of my rapidly emptying savings.
But the thing that made me decide to put Harper to sleep was after reading all I could about diabetes, it seems like a majority of the dogs end up with pancreas cancer, or other vital organ issues within a year or two. A year or two where some of that time is spent trying to adjust the insulin dosage, and feeding program and if the diabetes changes...you are back to square 1 in trying to adjust insulin. Plus, you just can't explain to a dog why they are being 'pinched' or given a shot several times a day.
So, even if I had the money, I doubt I would have done that...because a dog just can't tell us how sick they are feeling...we can only guess and I would hate to guess wrong...and make her live like that for a few years only to see other issues arise...such as organ failures, blindness, and other issues that can come from having diabetes.
So, I put Harper to sleep at age 8. I only had her for 2 years but she was one of the best dogs I ever owned...just pure happiness all the time...her whole body would wiggle with joy. I miss her deeply, but don't regret my decision.
I love all my pets, and I'll spend quite a bit for vet help, but I just won't risk financial bankruptcy for one. I also don't like the idea of sending a medically dependent animal to a rescue group where it could end up living from foster family to foster family, or worse, end up in a kennel...getting treatment, yeah, but that's not the same as having a home. At least with Harper I know she's no longer in pain/feeling ill and I know I did my best for her which might not be as good as someone with a lot of money but it was my best, so I'm comfortable with that.
Only you can decide what to do with your dog...your own comfort level..as far as letting him live and keep paying for medical bills, or putting him to sleep or sending him out to a rescue. I hope what ever decision you make though, that you feel at ease with it.
On another note. I agree that with elderly dogs...their arthritis pain can be helped with inexpensive meds, and that being deaf or blind shouldn't be a reason to put one to sleep...deaf or blind isn't a painful condition and I've had elderly dogs do just fine with those handicaps. If the eye conditions heal up and are not causing pain....the dog should be ok as far as any sight loss.