I spent the day installing a bunch of locks into wooden doors and setting them up on a master key system. As the day progressed, my eyes became increasingly tired. My vision was very blurry and it was hard to see the pins and springs that I was working with. I started misplacing small lock parts and wasting time groping around for them like an old blind man. By late afternoon, the problem was seriously impeding my work. And it was getting me depressed about the future. My eyesight isn’t going to get better over time.