Human eye of the size of the pupil, regulation and suppression of the hormone melatonin and entrainment of the body clock. The eye is not shaped like a perfect sphere, rather it is a fused two-piece unit, composed of the anterior segment and the posterior segment. The anterior segment is made up of the cornea, iris and lens. The cornea is transparent and more curved, and is linked to the larger posterior segment, composed of the vitreous, retina, choroid and the outer white shell called the sclera. The cornea is typically about 11.5 mm (0.3 in) in diameter, and 1/2 mm (500
Book of the Ten Treatises of the Eye 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