Importance: Strabismus is a binocular vision disorder characterized by the partial or complete inability to maintain eye alignment on the object that is the target of fixation, usually accompanied by suppression of the deviating eye and consequent 2-dimensional monocular vision. This cue has been used to infer the presence of strabismus in a substantial number of famous artists.
Objective: To provide evidence that Leonardo da Vinci had strabismus.
Design, setting, and participants: In exotropia, the divergent eye alignment is typically manifested as an outward shift in the locations of the pupils within the eyelid aperture. The condition was assessed by fitting circles and ellipses to the pupils, irises, and eyelid apertures images identified as portraits of Leonardo da Vinci and measuring their relative positions.
Main outcomes and measures: Geometric angle of alignment of depicted eyes.
Results: This study assesses 6 candidate images, including 2 sculptures, 2 oil paintings, and 2 drawings. The mean relative alignments of the pupils in the eyelid apertures (where divergence is indicated by negative numbers) showed estimates of -13.2° in David, -8.6° in Salvator Mundi, -9.1° in Young John the Baptist, -12.5° in Young Warrior, 5.9° in Vitruvian Man, and -8.3° in an elderly self-portrait. These findings are consistent with exotropia (t5 = 2.69; P = .04, 2-tailed).
Conclusions and relevance: The weight of converging evidence leads to the suggestion that da Vinci had intermittent exotropia with the resulting ability to switch to monocular vision, which would perhaps explain his great facility for depicting the 3-dimensional solidity of faces and objects in the world and the distant depth-recession of mountainous scenes.