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3 Book structure 3

the brain. The pneuma would carry the shapes carried by the light to the brain, in a
bi-directional flow. In contrast, early functional theories of vision, including those by
Pythagoras and Euclid, who lived between the mid-5th and the mid-3rd century BC,
stated that the pneuma was emitted into the world and would bounce off objects car-
rying back their shapes into the eye. Democritus (4th–3rd century BC) had raised a
dissenting voice, postulating that objects emitted continuously images of themselves
(éidola, or “figures,” “representations”), that entered the eye (intromission theory)
making perception possible.
The eye model undergoes an idealization in the Middle Ages, seemingly to reflect
more the geometry of the divinely perfect, symmetric universe, in which the circle
represented the supreme geometric perfection. The anatomy of the eye was there-
fore inspired by the orbits of the known planets, that had to be rigorously circular.
Such models are found in the work by Roger Bacon (1214–92) and John Pecham
(1230–92), Archbishop of Canterbury. An eye model based on tradition, not anat-
omy, is found even in Leonardo da Vinci’s well-known section of a man’s head in his
Anatomical Studies, folio 32r. Here the eye is depicted as a spherical bulb containing
a central, spherical lens. Leonard’s eye is connected to the brain by a channel that
he believed was composed by many smaller ones, to keep separate the images of the
different things perceived simultaneously. Leonardo never took a definite position in
the controversy between emission and intromission theories.
Dissection and direct observations re-start in earnest with Andreas Vesalius, the
Flemish physician regarded as the father of modern anatomy. Vesalius’s drawing
of the eye in his De humani corporis fabrica (on the structure of the human body,
1543) suggests direct observation (e.g., the bulb is spherical, the anterior chamber
is present) but still reflects the burden of the tradition: the lens is central, the optic
nerve is hollow and aligned with the central axis of the bulb through the center of
the pupil.
In the work by Johann Kepler (1571–1630), the German astronomer and physi-
cist, optics plays a crucial role and allows Kepler to propose an explanation for the
paradox of the inverted image, which had puzzled Leonardo himself: if the pupil, as a
small aperture, makes the image appear inverted on a screen, why don’t we perceive
the world upside down? Kepler understands that an “opposite inversion” must hap-
pen in the brain. Finally, shortly after Kepler, Scheiner publishes the first anatomical
drawing of the eye which we can accept completely. A correct understanding of the
anatomy was finally achieved. Centuries would still be needed to attain accurate
physiological models, but this goes beyond the scope of this short historical note.

3 Book structure

The book is organized in five parts following logically from each other and taking
the reader from an introductory presentation of computational techniques for RIA
to cutting-edge topics, including of course the promises and challenges of artificial
intelligence for eye-related healthcare.