Whole libraries have been written trying to explain how Leonardo da Vinci produced some of the world's most revered paintings. Now a new study suggests he had a biological edge: an eye disorder that affected his depth perception. In JAMA Ophthalmology, researchers make the case that da Vinci had a rare condition known as strabismus, which allowed him to better present a 3D world on a 2D canvas, reports Ars Technica. The condition is known as being "walleyed," per the Washington Post. As Live Science explains, it generally means that one of da Vinci's eyes wandered instead of focusing on the same thing as the other eye, which led him to favor the non-wandering eye. He would thus be "seeing the world monocularly, with much reduced depth cues," says study author Christopher Tyler of City University of London.
That may not sound ideal for painters, but "the image they’re seeing is much closer to what they want to paint on the canvas," Tyler explains to the Post. Da Vinci could apparently control the wandering eye as needed, and thus "he’d be very aware of the 3D and 2D depth cues and the difference between them.” Other artists such as Rembrandt, Degas, and Picasso also were believed to have strabismus to some extent. Tyler's team figured this out by looking at six artworks, either by da Vinci or others, that are believed to be likenesses of da Vinci himself. (Among them was da Vinci's Salvator Mundi, the most expensive painting ever sold at auction.) Tyler took eye measurements of those images, and the results pointed to strabismus. (Elsewhere on the da Vinci front, it's possible that a physical condition also explains the most famous smile in art history.)