Creating 3D spaces with paint on a 2D canvas is very difficult, but it’s something that Leonardo da Vinci mastered during his long career. Christopher Tyler, a visual neuroscientist and professor, conducted a study and believes he knows why: da Vinci had an eye condition that made comparing the 2D and 3D world easier.
Known as strabismus, this condition makes it tricky for people to align both their eyes at once. One “wanders.” How much it moves depends on the severity of the condition. The eye that wanders has a broader view, but no depth perception, while the more stable eye sees in the usual 3D. For painters, this could make it easier to distinguish between 2D and 3D in a piece they’re working on.
There’s no way to know for sure if da Vinci had strabismus because so few confirmed pictures of him exist. However, Tyler looked at six portraits that are believed to have been inspired by the painter. These include the famous Vitruvian Man and a self-portrait late in his life. Tyler examined the eyes in the paintings, specifically the pupils, and claims that it appears they are turning outward. This would mean da Vinci had exotropia, a type of strabismus. In certain paintings, the extotropia is more obvious, possibly because the painter had “intermittent exotropia.” When da Vinci focused, his eyes would align normally, but when he was relaxed, his pupil would wander. While there is no way to confirm for sure da Vinci had extotropia, it wouldn’t be surprising.
Da Vinci isn’t the first artist believed to have some kind of eye condition. In 2004, two neuroscientists looked at self-portraits of Rembrandt and discovered that one eye is often wandering to the side, while the other looks directly out of the canvas. Assuming Rembrandt was being accurate in the depiction of himself, he most likely had some degree of stereo blindness, which would help him paint in 2D. While most have trouble translating the 3D world unto a flat surface, Rembrandt, da Vinci, and other artists with stereo blindness and other forms of strabismus don’t see a significant difference.