A family fossil

I have been going through some of my family history data. One of my GGG-Grandfathers was a prison turnkey for nearly twenty years, and he was blind in the 1860s. Turnkeys weren't very nice then, and I wonder if his blindness was down to natural causes. In 1847 he was earning £40 12/0, which was a decent wage then. This was topped up, of course, with all the money that he could extort from the prisoners. I'm sure he wasn't short of a bob or two.