Book of the Ten Treatises of the Eye

Hunayn ibn Ishaq's Book of the Ten Treatises of the Eye is a 9th-century theory of vision based upon the cosmological natures of pathways from the brain to the object being perceived. This ophthalmic composition is heavily derived from Galen's De placitis Hippocratis at Platonis and De usu partium, both in terms of the anatomy and physiology being described. Hunayn's triumph comes from the systematic presentation of the parts of eye and the subsequent additions he made to the cosmological aspects of the work. Its early translation to Latin also provided a means for medieval ophthalmologists in the West to come into contact with the work of Galen.

There are four essential doctrines that shape Hunayn's dissertation on vision and the anatomy of the eye:

Hunayn relies on these principles to build up his conception of vision, which incorporates the anatomy of the eye in a way that makes discussion of one without the other unproductive.

The structure of the eye is presented as a hierarchy, starting first with the part that is most directly responsible for sight, and working down towards the parts which exists only to facilitate this function. The lens, described as white, transparent, and luminous have a composition which lends itself to quickly receive colors. As opposed to Galen's more mathematical conception of flat-like lens, Hunayn opts for a more spherical shape which allows for a larger field of vision. He describes the system behind the eyes that connects it to the brain, starting with the sclera, a thick, hard membrane which protects the inner parts of the nerves from injury. The chorioid, a thin and soft structure filled with veins and arteries, follows next and provides nourishment to the overall structure. Finally, the retina transmits nutrients to the lenses themselves. Hunayn then presents the system responsible for protecting the eye. From the outermost level, these are the conjunctiva, cornea, and uvea. While both the conjuctiva and cornea provide protection with minimizing hindrance to the lenses, the uvea has an extra function of concentrating the pneuma exiting out of the eye to prevent it from being dissipated by light.

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