As I note in my book, the most famous impressionists all suffered from serious medical problems:
Monet became blind (but didn't stop painting the bridges of Giverny). Vincent Van Gogh, drinker of kerosene, turpentine, and absinthe, probably thought the coronas he painted around stars and streetlamps were real. Edgar Degas became severely myopic, which led him to do more and more sculpture ("I must learn a blind man's trade now," Degas said.) Auguste Renoir, poisoned by his pastel paints, became a rheumatic cripple.
Now scientists are able to simulate exactly what Monet would have seen through his cataracts:
Thanks to modern digital techniques, scientists and critics can have a better idea how cataracts changed what Monet saw. This year, an ophthalmologist at Stanford, Michael F. Marmor, described in The Archives of Ophthalmology creating computer simulations of Monet's world as his lenses yellowed, blurring vision and turning patterns of color and light into muddy, unfocused, yellow-green inkblots.
Although it is impossible to know how Monet wanted his canvases to look, Dr. Marmor's research suggests that understanding physical infirmity can help assess his work. Whatever Monet intended, his eyes provided little help. "He couldn't judge what he was seeing or see what he was painting," Dr. Marmor said. "It is a mystery how he worked."
Personally, I don't buy the strong version of this argument. I think it's rather naive to hold cataracts responsible for a work of art. It's like saying that El Greco had an astigmatism and that's why his figures are so extended. Lots of people have cataracts and never manage to paint like Monet. There are lots of astigmatics and yet there's only one El Greco.
However, I do think the art might have been indirectly inspired by the medical condition. Monet was fascinated by the process of sight, a fascination which was surely propelled by his own sensory difficulties. In general, I think illness makes us more sensitive to aspects of the body and the mind that we take for granted. I never think about my teeth until I get a toothache. And I would certainly spend a lot more time contemplating the reality of vision if I had eye problems.
Look, for example, at Virginia Woolf. All her life, Woolf suffered from periodic nervous breakdowns, those horrible moments when her depression became suffocating. As a result, she lived in fear of her own mind, exquisitely sensitive to its fevered "vibrations." Introspection was her only medicine. "My own psychology interests me," she confessed to her journal. "I intend to keep full notes of my ups and downs for my private information. And thus objectified, the pain and shame become at once much less. When all else failed, she used her sardonic humor to blunt the pain: "I feel my brains, like a pear, to see if it's ripe; it will be exquisite by September."
As I argue in my book, Woolf's mental illness that made her a passionate student of the mind. Her psychologically accurate writing style wasn't triggered by her disease but it was enriched by it. I bet a similar process was at work in the art of Monet. His blindness became a window, allowing him to see (and paint) in completely new and unexpected ways.
For an interesting angle involving rheumatology's possible influence on art, see: rheumatology.oxfordjournals.org/cgi/content/full/43/6/803#BIB13. To the list of sufferers one may add the Swiss expressionist painter Paul Klee.