<P> The eye is made up of three coats, or layers, enclosing various anatomical structures . The outermost layer, known as the fibrous tunic, is composed of the cornea and sclera . The middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris . The innermost is the retina, which gets its oxygenation from the blood vessels of the choroid (posteriorly) as well as the retinal vessels (anteriorly). </P> <P> The spaces of the eye are filled with the aqueous humour anteriorly, between the cornea and lens, and the vitreous body, a jelly - like substance, behind the lens, filling the entire posterior cavity . The aqueous humour is a clear watery fluid that is contained in two areas: the anterior chamber between the cornea and the iris, and the posterior chamber between the iris and the lens . The lens is suspended to the ciliary body by the suspensory ligament (Zonule of Zinn), made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for accommodation (focusing). The vitreous body is a clear substance composed of water and proteins, which give it a jelly - like and sticky composition . </P> <P> The approximate field of view of an individual human eye (measured from the fixation point, i.e., the point at which one's gaze is directed) varies by facial anatomy, but is typically 30 ° superior (up, limited by the brow), 45 ° nasal (limited by the nose), 70 ° inferior (down), and 100 ° temporal (towards the temple). For both eyes combined (binocular) visual field is 135 ° vertical and 200 ° horizontal . When viewed at large angles from the side, the iris and pupil may still be visible by the viewer, indicating the person has peripheral vision possible at that angle . </P> <P> About 15 ° temporal and 1.5 ° below the horizontal is the blind spot created by the optic nerve nasally, which is roughly 7.5 ° high and 5.5 ° wide . </P>

List three characteristics of the iris of the eye