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This has the effect of reducing the tension on the zonules, which allows the lens to assume a more spherical shape. It is generally believed that the ciliary muscle acts like a sphincter so that when it contracts, the central opening becomes smaller. Through contraction or relaxation, the ciliary muscle increases or decreases the tension on the zonules, causing them to pull more or less on the lens capsule. The lens is thus suspended in the open centre of the ciliary muscle. As the pupil expands (dilates) and contracts, the iris slides back and forth over the upper (anterior) surface of the lens.Ĭomposed of some 22,000 lamina of transparent fibrous material, the lens is enclosed within a transparent capsule which is attached by an array of non-elastic, hair-like filaments, called the zonules of Zinn, around the capsule’s rim (or ‘equator’) to the encircling ciliary muscle. The primary function of the ciliary muscle is to control the shape of the flexible, transparent lens, which is located directly underneath or behind the iris. The ciliary muscle is anchored around the perimeter of the circular opening to the choroid, a dark pigmented membrane beneath the sclera. In addition to the muscles of the iris, the ciliary body also includes the ciliary muscle. When the dilator muscle contracts, the diameter of the pupil can enlarge up to 9 mm. The contraction of the pupillary sphincter muscle can reduce the size of the pupil to as a little as 1.5 mm in diameter. The only way to ‘shut’ the eye is to close the eyelid. The eye is constantly open to the reception of electromagnetic rays. The opening in the iris never fully closes. The pupil is made smaller through the action of the pupillary sphincter muscle attached around the inner edge of the iris. Functioning in response to various stimuli, the iris will contract, causing the pupil to enlarge ( dilate). Most of the iris is a single dilator muscle comprising fibers arranged in concentric circles. These physical muscles operate the eye’s optical apparatus. The iris is the visible upper portion of the ciliary body, which is primarily a group of muscles anchored around the perimeter of the circular opening. Visible through the cornea is the iris, which fills most of the opening, and the pupil. Attached to the sclera around the perimeter of the opening is a dome-shaped, transparent membrane called the cornea.
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The outer membrane of the eyeball is called the sclera, of which a small part is visible as the ‘white-of-the-eye’. Imagine a hollow sphere about 20 mm in diameter with a circular opening about 12 mm in diameter cut into it. Its path to the retina is controlled by an apparatus of physical parts that fits neatly into a circular opening in the eyeball. In order for sight or vision to occur, radiation from the electromagnetic spectrum must enter the eye through the pupil and stimulate the photoreceptive rods and cones in the retina. Adie syndrome.The Visual Experience: Reading 2014 - ART HISTORY & IMAGE STUDIES -ĪRTH117 FALL 2014 SCHEDULE REQUIREMENTS ART HISTORY GUIDE National Organization for Rare Disorders. Parasympathetic innervation to the head and neck. Overview of the anatomy, physiology, and pharmacology of the autonomic nervous system. Anatomical variations of the ciliary ganglion with an emphasis on the location in the orbit. Walsh and Hoyt's clinical neuro-ophthalmology, 6th ed. Lippincott Williams & Wilkins 2005:673-674.
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Kardon R. Chapter 14: Anatomy and physiology of the autonomic nervous system. In: Miller NR, Newman NJ, Biousse V, Kerrison JB, eds. Anatomical study of the roots of cranial parasympathetic ganglia: a contribution to medical education. Lovasova K, Sulla IJ, Bolekova A, Sulla I, Kluchova D.