What did Edgar Degas really see?

"Works by Edgar Degas in 1886, left, and 1905, center. Right, an image altered to show what Degas would have seen working on the 1905 piece"
-From NYT, A New Look at Impressionists’ Failing Vision

Related;
Ophthalmology and Art: Simulation of Monet's Cataracts and Degas' Retinal Disease

Eye Diseases Gave Great Painters Different Vision Of Their Work;

It's well-known that such artists as Monet, Degas, Rembrandt, Mary Cassatt and Georgia O'Keefe all reached their heights of artistic vision while facing a decline in their ocular vision. Marmor chose to focus on Degas and Monet for these simulations because both artists suffered from eye disease that was well-documented in historical records, journals and medical histories. Degas had retinal eye disease that frustrated him for the last 50 years of his long career. Monet complained of cataracts interfering with his ability to see colors for 10 years before he finally underwent surgery to have them removed