Scenario (irrelevant details omitted):
Rather nervous horse has to be moved to a new stable, a few miles away. Two people do this...one to keep company on another horse.
On the way, they stop for some reason. Nervous horse is temporarily tethered to a fence post. The fence is made up of a series of posts linked by five strands of wire, stapled on as usual.
Horse gets spooked by something and pulls on post, tilting it quite a bit. Posts on either side hold firm, but the strain on the wire pops a few staples. One of the staples hits the guy right in the middle of the eye, and goes quite deep.
Rushed off to A&E, but eye is destroyed and has to be removed.
(Eye protection while riding???)