Page 13 - Computational Retinal Image Analysis

2 CHAPTER 1 A brief introduction and a glimpse into the past

a contemporary view on retinal imaging. We add here a brief summary of the ori-
gin of eye-related research in the West, which we hope may interest the reader; the
present cannot be understood completely but in the context of the past. Beyond the
western world, a concise history of ancient vision and eye-related theory in India and
some comparisons with western theories is given by Deshpande [2]. Our short ac-
count follows loosely Pierantoni’s detailed book [3], with elements from the history
of ophthalmology (anatomy and physiology) available on the UK Royal College of
Ophthalmologists website [4]. Bynum [5] is a concise, non-technical but informative
account of the history of medicine, including of course ophthalmology.
The curiosity of man for the eye goes back a long way. It may seem therefore
extraordinary that the first anatomically accurate drawing of the ocular bulb did not
appear before the early 17th century, in Rosa Ursina by the German Jesuit priest
and scientist Christoph Scheiner (1575–1650). Before then, all drawings of the eye
put religious or philosophical beliefs before anatomical observation. This fascinating
story starts, in the West, with the oldest known drawing of the ocular bulb and its
main component, due to the medieval arab scholar Hunain ibn Ishak, who lived in the
9th century BC, in his “Ten essays on the structure of the eye, its diseases and cures.”
The drawing was first reproduced by the neurologist Stephen Polyak during WWII
[6] and is itself a copy of an older drawing which did not reach us, perhaps a Greek
manuscript from many centuries before. Ibn Ishak’s eye looks very inaccurate to us:
it is almond-shaped; the lens is in the center; the optic nerve, the pupil and the lens
are aligned along the middle axis of the ocular bulb; the optic nerve is hollow. Vision
is explained through the flow of a “vital spirit” emitted by the eye (an idea already
found in Pythagoras and Euclid), which required the hollow optical nerve to flow out
of the eye and back. As Pierantoni observes, the drawing is best interpreted as a func-
tional diagram, as all functional elements are in place, but not anatomically accurate.
Yet dissecting an eye does not require particularly sophisticated instruments. But the
influence of the philosophical giants of the antiquity, in addition to the aversion to
cadaver dissection of religion and state, was obviously immense—and would last for
b
many centuries to come. Hence dissection was often practiced on animals, assuming
that their anatomy was similar or the same to the human one.
The first drawing showing a connection between the eye and the brain is due
to another arab scholar, Abu Ja’far Ahmad ibn Muhammad (906–963), again most
likely a copy of a previous Greek document. This drawing is also the first diagram
giving an account of binocular vision: it shows two ocular bulbs, now round but still
equipped with hollow channels carrying the “visual spirit” responsible for vision. A
relation of Ja’far, the scholar Ibn al-Haitam (also known as Alheizen, c.965–1040),
proposed however in his Book of Optics that vision was made possible by the rays of
light entering the eye. Precursors of this idea were already present in the work of the
highly regarded Greek physician and surgeon, Galen (129–c.200 AD), who thought
that the light entering the eye interacted with a “visual spirit” (pneuma) generated in

b Interestingly, some of the ideas from ancient Greece still permeate parts of contemporary western
medicine [5].