From Galileo's Pendulum:
When he was 82 years old, Claude Monet suffered from such severe cataracts that he agreed to have the lens removed from his right eye. Cataracts that occur in elderly people turn the lens of the eye cloudy and yellowed, much like old glass can become discolored. The yellowing of the lens works as a filter, reducing the amount of blue light that reaches the retina. However, normal, healthy lenses filter out ultraviolet (UV) light, so when Monet’s lens was removed, he not only could see the blue hues again, he could also see a limited amount of UV—which he attempted to paint, as the images [above] demonstrate...The two images at top are crops from paintings by Monet of the same scene - "the house" as seen from "the rose garden."
Monet’s ultraviolet vision highlights this inherent subjectivity: he painted what he saw (and the Impressionists argued that their art was the most “objective”, since they attempted to paint without details missed by the eye), but all art is translation. We do not see the UV light in Monet’s painting because our eyes cannot receive it … yet those pigments were obviously important to the painter himself...
Via Not Exactly Rocket Science.