Exotropia is a type of strabismus, or squint, which affects 1% of the world population. A 2004 study theorized that Rembrandt was also affected by this condition. Researchers relied on studying the artist’s self-portraits, which they believe show one eye turned subtly outward.
A letter recently published in the journal JAMA Ophthalmology refutes this idea, claiming that the artists likely simply had a dominant eye, where one eye is favored, not unlike left- or right-handedness. Depicting one’s own eyes has always presented a challenge for artists working in self-portraits: one can only focus on the details of one eye at a time. While looking directly into one eye in the mirror, the other appears slightly off-center.