Louis Wain loved to paint cats. He painted these over a period of time during which he developed schizophrenia.
Some psychiatrists have proposed that Van Gogh, who clearly suffered from some kind of mental illness in his last years, may have had absinthe or foxglove poisoning, which can cause a yellow tint to one's vison.
Others posit lead poisoning, which can cause one to see spots and halos.
Personally, my money is on schizophrenia, however.
Jackson Pollock had chronic migraines. His paintings certainly remind me of my own.