I can't think of the name or author of a short story that I read. It was about a man who was tracking down the last movements of an artist who went crazy. At the end he finds out that the artist was pierced in the eye by evil creatures, or fairies or something and thus, that is what drove him insane.
The story you're thinking of is "Orange is for Anguish, Blue for Insanity" by David Morrell. Synopsis lifted from this blog post:
A young artist becomes fixated to a 19th century impressionist named Van Dorn, who, despite being a genius in his time, was bypassed and unrecognized. Van Dorn’s frustration eventually shakes his sanity and by gouging his eyes, he met death.