2 Structure of the Eyeball The wall of the eyeball has 3 layers the outer fibrous tunic the middle vascular tunic and the inner retina The fibrous tunic is composed of the comea and sclera The cornea is the transparent anterior portion that covers the iris and pupil and the sclera scler hard is the tough white part of the eye that forms the majority of the eyeball The scleral venous sinus canal of Schlemm is an opening found at the junction of the cornea and the sclera The middle vascular tunic is composed of the iris ciliary body and choroid The iris is the most anterior portion of the vascular tunic and contains pigmented cells It is made of circular smooth muscle and controls the pupil size The pupil is the opening in the middle of the iris that allows light to enter the eyeball and changes size in response to the intensity of light The ciliary body begins posterior to the iris at the junction of the cornea and choroid ciliary SIL ee air ee body ciliary muscle ciliary process comea KOR nee ah iris ora serrata ser RAH tah pupil retina sclera SKLER ah scleral venous sinus suspensory ligament zonular fibers Structure of the eyeball FIGURE 24 3 1 2 3 4 5 6 sclera and consists of the ciliary muscle and ciliary processes The ciliary muscle is a circular smooth muscle that contracts to control the shape of the lens Ciliary processes are folds that protrude from the ciliary body toward the lens They contain capillaries that secrete aque ous humor the fluid in the anterior chamber of the eyeball Suspensory ligaments zonular fibers are thin fibers that attach the lens to these processes The choroid is the most posterior part of the vascular tunic that lines most of the interior of the sclera It contains many blood vessels that nourish the retina The retina sensory tunic is the inner coat that begins at the ora serrata the serrated boundary between the ciliary muscle and the retina The retina continues posteri orly lining the interior of the choroid The pigmented layer of the retina is the outer portion and the neural layer is the inner portion that contains photoreceptors and asso ciated neurons 8 9 10 11 12 8 10 11 Lens 12