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Here is my point of view:
Rex is 14 and yes I know he is getting old, but it's not the right time to put him down, and to be honest, I would rather get him put down than him suffer or be in any pain.
He isn't in pain and the crying is only for attention, as I work from early morning to quite late most nights, he doesn't get as much attention as I would like him to get.
As Lofty said, he's part of the family and you have to take the bad with the good, fair enough things haven't been as good as usual but the dog still has a quality of life.
With regards to him not being able to see, when I am walking him, it's quite obvious his eye-sight is still very good, not as good as what it was but he can still see dogs from the other side of the area where I walk him (approx 75 m distance).
I know the time will be coming soon but I am not going to get him put down until I know he is in pain or his quality of life is decreased enough that it is going to benefit him.
Although I know when the day comes it will actually kill me, I'll get it done cos I know it's the best for him, but not until then!!!