<human>: Can you summarize the given text in a few sentences?

I have a 10 year old Swiss Mountain Dog/mix (65 lbs).

*

About a year ago he was diagnosed with Sudden Acquired Retinal Degeneration Syndrome (completely blind), a Meningeal Tumor, a spot on his liver, & cyst on his kidney.  A few months after that he started having trouble urinating and the vet said the tumor was effecting his ability to go and prescribed him Valium.

*

Fast forward to today and we've had increase his does of Valium several times due to his issues going to the bathroom and have given him additional medications.
His on the following meds:

* Valium, 10 mg x 3/day (human adult dose is 2–10 mg x 2–4/day)
* Prazosin, 1 mg x 3/day
* Prednisone, 2.5 mg x 1/day
* Pepcid, 10 mg x 2/day

He is constantly stoned, listless, doesn't play anymore, has trouble walking, only affectionate when I first get home and only really moves with purpose when there is food involved.

*

I tried to go through the Quality Of Life Assessment, [here] and he scored an 11.  Although, I wish values where a bit more granular.  Another Quality of Life Assessment, [here] rate 1 category as great, 3 as good, 4 as decreased, & 5 as poor.  But, I'm not a vet, so I am unsure if my assessment of those categories are accurate.

*

My question is, am doing the right thing by keeping him alive.  He's not in pain all the time, but does seem to have discomfort when he gets up or goes up or down the stairs.  I do feel like he is just existing and not living.  I really think that only he enjoys now is eating.

*

I plan to speak to my vet about this, but would like your opinions as fellow dog owners.
<bot>: My blind dog is constantly stoned due to ever increasing medications for a terminal condition.  Is humane not to euthanize him?