Was Rembrandt strabismic?

We studied a set of Rembrandt's self-portraits to reassess a previous claim, based on measurements of the centration of his painted irises, that Rembrandt had a large exotropia.

Of the 24 self-portraits that Rembrandt painted, with significant ocular detail to give an impression of the direction of his gaze, we scanned 10; the five with the largest difference in centration between the irises and the five with the smallest difference. The right and left eyes in each image were then occluded using Photoshop to produce two additional images that gave monocular gaze. Thirty observers then judged where the portraits appeared to be gazing within the plane of their face.

Although our observers did judge a significant outward deviation for gaze between the two eyes, part of this was caused by an outward deviation from central by the presumably nonstrabismic eye. Any greater amount of outward deviation from the "strabismic" than the nonstrabismic eye can then be explained by a gaze overshoot induced by head turn, painting with a mirror, and angle kappas. In addition, Rembrandt's apparent strabismus is seen only in those portraits painted during a few years early in his career, and portraits that Rembrandt and his students produced of other presumably nonstrabismic individuals often give a similar impression of strabismus.

There are several factors that can explain why some of Rembrandt's self-portraits make him look strabismic without concluding that he actually was. Rembrandt and his students may also have painted this appearance as an artistic style.