FIGURE 24.7 • Photomicrograph of the ciliary body and iridocorneal angle. This photomicrograph of the human eye shows the anterior portion of the ciliary body and parts of the iris and sclera. The inner surface of the ciliary body forms radially arranged, ridge-shaped elevations, the ciliary processes, to which the zonula fibers are anchored. The ciliary body contains the ciliary muscle, connective tissue with blood vessels of the vascular coat, and the ciliary epithelium, which is responsible for the production of aqueous humor. Anterior to the ciliary body, between the iris and the cornea, is the iridocorneal angle. The scleral venous sinus (canal of Schlemm) located in close proximity to this angle drains the aqueous humor to regulate intraocular pressure. 120. The inset shows that the ciliary epithelium consists of two layers, the outer pigmented layer and the inner nonpigmented layer. 480.
pupil to respond when light is shined into the eye— “pupil fxed and dilated”—is an important clinical sign showing lack of nerve or brain function.
 The dilator pupillae muscle is a thin sheet of radially oriented contractile processes of pigmented myoepithelial cells constituting the anterior pigment epithelium of the iris. This muscle is innervated by sympathetic nerves from the superior cervical ganglion and is responsible for increasing pupillary size in response to dim light.
Just before ophthalmoscopic examination, mydriatic agents such as atropine are given as eye drops to cause dilation of the pupil. Acetylcholine (ACh) is the neurotransmitter of the parasympathetic nervous system (it innervates the sphincter pupillae muscle); the addition of atropine blocks muscarinic acetylcholine receptors, temporally blocking the action of the sphincter muscle and leaving the pupil wide open and unreactive to light originating from ophthalmoscope.
The ciliary body is the thickened anterior portion of the vascular coat and is located between the iris and choroid.
The ciliary body extends about 6 mm from the root of the iris posterolaterally to the ora serrata (see Fig. 24.2). As seen from behind, the lateral edge of the ora serrata bears 17 to 34 grooves or crenulations. These grooves mark the anterior limit of both the retina and the choroid. The anterior third of the ciliary body has about 75 radial ridges or ciliary processes (see Fig. 24.7). The fibers of the zonule arise from the grooves between the ciliary processes.
The layers of the ciliary body are similar to those of the iris and consist of a stroma and an epithelium. The stroma is divided into two layers:  An outer layer of smooth muscle, the ciliary muscle, makes up the bulk of the ciliary body.  An inner vascular region extends into the ciliary processes.
The epithelial layer covering the internal surface of the ciliary body is a direct continuation of the two layers of the retinal epithelium (see Fig. 24.1).
The ciliary muscle is organized into three functional portions or groups of smooth muscle fibers.
The smooth muscle of the ciliary body has its origin in the scleral spur, a ridgelike projection on the inner surface of the sclera at the corneoscleral junction. The muscle fibers spread out in several directions and are classified into three functional groups on the basis of their direction and insertion: