It’s long been noted that the impressionists steadily grew more abstract as the 19th century came to a close. One only has to compare an early Monet from the 1870′s to a late Monet landscape to understand the importance of this transition. The pretty pastels and dappling light gave way to thick impasto paints and blank spots on the canvas. In other words, the impressionists had become post-impressionists.
This transition is usually explained in terms of culture: the impressionists were simply reacting to the increasing acceptance of painterly abstraction. Modernism was beginning, verisimilitude was a thing of the past. But art historians are also beginning to explore a related hypothesis: perhaps the late works of the impressionists were partly due to eye troubles.