"When I look at his work, I notice the pronounced divergence of the eyes in all of his paintings," said study author Christopher Tyler, a research professor at City University, London, and at the Smith-Kettlewell Eye Research Institute, San Francisco Francisco.
In six probable self-portraits of da Vinci – two sculptures, two oil paintings and two drawings – he analyzed the line of vision. Tyler found that some of the works showed signs of exotropia, with the eyes looking outward angles.
Not all six of these works were self-portraits, but in his own writings da Vinci pointed out that every portrait of a painter reflects the painter's own appearance.
Tyler judged the condition of the eyes by drawing circles on the pupils, irises and eyelids and measuring their positions on each image. When he converted the measurements to an angle, the results showed that Da Vinci had a tendency to exotropia, with one eye turning outward by -1
Tyler believes da Vinci's left eye was affected by the disease, but it's not easy to be sure.
Exlotropia of the eyes, a form of strabismus, affects about 1% of the world population, he said
Da Vinci's exotropia allowed him to view the world from a different angle. "What he saw would look more like a flat screen than a three-dimensional canvas for us," Tyler said; that made it "easier to translate things to the screen".
This condition contrasted with the regular view of his other eye to help him develop a strong understanding of three-dimensional objects. Tyler said that this ability enabled most of Da Vinci's artworks to have the exact shade for which he is known.
The study found that the difference in direction and size of students in some of Da Vinci's works can be interpreted as an anisocoria, a condition in which one student is greater than the other. But Tyler said that was "very unlikely". Rather, he believes that da Vinci uses this representation to show his experience of one eye more clearly than the other.
Dr. Julius Oatts, assistant professor at the Department of Ophthalmology, University of California, San Francisco, described the results as interesting. "There are many uncertainties as to whether the images are really da Vinci itself and whether they represent the eyes realistically," noted Oatts, who was not involved in the study.
Tyler said the artist is such a compelling figure historically It is very interesting to explore the roots of his genius. "