Some scientists used to look at the beam emitter to adjust the aim of old particle accelerators. The story I heard was that some of them eventually developed cataracts as a result. Come to think of it, with today's medical technology that's a lot less awful than punching holes into your retina with a laser, but I think the result back then was eventually blindness.
I met a scientist who looked into a particle accelerator; it was intention, part of a self-experiment to establish whether high energy particles can cause scintillations in the eye. In his case he very carefully calculated how to get a safe dosage.
