KEY POINTS:
Monet's series of paintings depicting the dappled light playing across the water-lilies at his home in Giverny are considered some of the towering achievements of French Impressionism.
But new research suggests that the famously blurred-effect achieved by the master's brush strokes may have been an all together more literal representation of how he saw the world.
Monet's deteriorating sight, caused by the onset of cataracts late on in his career, has long been the subject of speculation by art historians.
A computer simulation carried out by an opthalmologist at Stanford University has now cast new light on the state of Monet's vision and the effect it had on his work.
According to Professor Michael Marmor, the artist's failing sight was a source of ongoing frustration to him in the early decades of the 20th century.
"He wrote letters to friends, how colours were getting dull, and it was hard to tell them apart, and how he had to label tubes of paint," Prof Marmor said.
"He was very vocal about how his failing eyesight was affecting him."
Monet's cataracts caused the lens of his eye to become denser and increasingly more yellowish.
One immediate effect was to blur the difference between colours and reduce their intensity.
"His vision was becoming progressively more brownish in essence," Dr Marmor said.
"It was getting harder to see, it was getting blurrier, but he was probably more bothered by the progressive loss of colour vision than the blur alone."
The academic has illustrated how Monet's worldview changed by altering a photograph of his 1899 painting of the ornamental Japanese bridge in his garden.
The adjusted photo shows that as the sight gets worse the bright, floral shades of pink and blue disappear, leaving muddier browns, reds and dark yellows.
The study, published in the Archives of Ophthalmology, argues that two later paintings of the bridge with strong red-orange and green-blue tones would have appeared almost identical to him.
Monet eventually went under the knife in 1923 - just three years before his death from lung cancer at the age of 86.
But after surgery he complained incessantly- insisting the operation had left his sight at first too yellow and then too blue.
He destroyed much of the work he completed while suffering cataracts and the few pieces that survive were rescued by family or friends.
Meanwhile, Monet eventually went back to painting, completing the lily series that now hangs in the Orangerie.
Dr Marmor has also examined the life and work of the painter Edgar Degas, thought to have suffered from maculopathy - a condition which seriously affected his central vision.
Degas began experiencing difficulties earlier than Monet in the 1880s, suffering four decades of decline.
Unlike Monet there was no treatment and Professor Marmor believes that as his eyesight blurred, so the lines on his work grew indistinct too - an effect that did not pass unnoticed among his friends and critics.
"I think some of them were urging him to maybe quit. One of the interesting questions was: why did he continue to paint?" Prof Marmor said.
The evidence could force a dramatic reappraisal of both artists and their work, he believes.
"I think it points out very dramatically some physical limitations that they had, which both limited their ability to paint, to put paint on canvas directly, but also to interpret what they were putting on a canvas - they couldn't really judge what they were seeing."
Chris Riopelle, curator of 19th century painting at the National Gallery, described the research as a "great insight".
But he said: "It does not entirely answer the questions - after surgery, Monet's style did not alter radically. He also painted for 60 years before having problems, so developed a vast amount of skill. There will always be something of a mystery here."
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