Welcome to the board Julia and Blaze. Please bear with us, the weekend is often very quiet here. Others will be along.
I so understand your love for Blaze, I also have a black lab who was adopted as a pup from the pound. Her name is Halo. Halo is 12 years now, and also covered in lumps and bumps. Seems many breeds get them, but labs are very prone. Halo also has a large lump behind one of her front legs, but the vet assures me it doesn't hinder her mobility.
I am sorry to hear about the growth in Blaze's eye area. Trust your vet to steer you right, but trust your gut as well, and overall trust Blaze. If you read him well you will know when he is just going through the paces. I went through this just over a year ago with my 14 year old Akita X. Ultimately it was not the vet who told me when to have her pts, it was Shadow herself. The look in her eyes every day as she made the effort to do as I asked of her told me it was time. Not to sound hard, but if I can add this one last thought for you. Since losing Shadow (who literally was my shadow as she was with me 24 hours a day), many friends who had recently had their pets pts told me that they knew after the fact that they had waited too long. I had always promised my pups I would never keep them alive for me, but for them. Trust in the bond you and Blaze have to know when the time is right. Your vet may tell you a terrible truth, but Blaze will be honest if you read him well. Don't rush him to the door but when he's ready hold it open for him and guide him gently through it with love.
Positive thoughts for you and Blaze, you are among friends who truly understand here so feel free to question, vent, rage, and cry (as I am again now) and above all else share your love for Blaze with us.