Ciliary Body & Iris Anatomy (PDF)

Ciliary Body & Iris Ciliary Body  ciliary body, - 3 main functions: 1. Produces Aqueous from blood; 2. Provides the muscles that change the curvature of the lens. Production and maintenance of the lens zonules 3.  The Ciliary body is continuous posteriorly with the choroid and anteriorly with the...

Ciliary Body & Iris Ciliary Body  ciliary body, - 3 main functions: 1. Produces Aqueous from blood; 2. Provides the muscles that change the curvature of the lens. Production and maintenance of the lens zonules 3.  The Ciliary body is continuous posteriorly with the choroid and anteriorly with the peripheral margin of the iris.  Ciliary body - a complete ring running around the inside of the anterior sclera.   ciliary body - about 6 mm wide (6.5 mm on the temporal side and 5.5 mm on the nasal side),  it extends forward to the scleral spur and backwards to the ora serrata of the retina.   ciliary body triangular in cross section.   Anterior surface - ridged or plicated - called pars plicata. Posterior surface is smooth and flat and is called pars plana.  The pars plicata surrounds the iris and give rise to the ciliary processes. Corona Ciliaris Folds in the pars plicata increase the surface area. Important As aqueous humour is produced here.   suspensory ligaments (fibres of the zonule) of the lens (zonules) – fibrillin protein attach to the surface of the pars plicata.  ciliary body - three parts: 1. The Ciliary Epithelium 1. The Ciliary Stroma 1. The Ciliary Muscle  The reason for division - understood better if one sees a histological section of the ciliary body cut along the eye’s horizontal plane   The ciliary epithelium 2 layers of cubical cells that cover the inner surface of the ciliary body.   Inner layer non pigmented - constitutes the anterior continuation of the nervous part of the retina. Covers the vitreous body   Outer layer Pigmented and constitutes the continuation of the retinal pigment epithelium.   Note - short distance between capillaries & outside of the ciliary processes. Both epithelial layers involved in producing aqueous humour.   The ciliary stroma bundles of loose connective tissue, rich in blood vessels and melanocytes The ciliary muscle forms the bulk of the substance of the ciliary body and consists of smooth muscle fibres.  What is the difference between Striated and Smooth muscle?   contraction of the ciliary muscles -pulls the ciliary body forward in accommodation. Forward movement - releaves tension in the suspensory ligaments, making the elastic lens more convex, increasing the refractive power of the lens.  Ciliary muscles - innervated by the parasympathetic and sympathetic nervous systems.  Parasympathetic stimulation -muscles contract sympathetic stimulation - muscle relaxed.   Changes in ciliary muscle tension affect both vision (by focusing light through the lens) and the outflow of aqueous humor in the eye. IRIS   The Iris is a thin contractile, pigmented diaphragm with a central aperture, the pupil. Suspended in aqueous humour between the cornea and the lens.   Periphery of the iris - attached to the anterior surface of the ciliary body called ciliary margin or root of the iris.   Pupil - surrounded by the pupillary margin of the iris Outlined with a ring of dark pigment known as the pupillary ruff.  Iris divides the space between the lens and the cornea  anterior and posterior chamber. Anterior Chamber Posterior Chamber  The iris measures about 12 mm in diameter  Pupil varies in diameter from 1 to 8 mm.   Colour of the iris varies from blue to dark brown. May vary in different parts of the same iris and from one eye to another in the same person.  Heterochromia – may be due to ocular disorders e.g. chronic iritis or diffuse iris melanoma  Or a normal genetic variant  More common in animals  The colour of the iris is produced mainly by the pigment in the melanocytes.  concentration of melanin determines eye colour  eg a blue iris has less pigment compared with the brown iris  Iris color - complex phenomenon combined effects of texture, pigmentation, fibrous tissue and blood vessels within the iris stroma   Anterior surface of iris - divided into a central pupillary zone and a peripheral ciliary zone. Line of demarcation - a ciliary ridge- collarette, about 2 mm from the pupillary margin.   Anterior surface of iris – no epithelium series of radial streaks caused by trabeculae of connective tissue that enclose oval shaped crypts (Fuch’s crypt).  Fuch’s crypts - series of openings located on either side of the collarette that allow the stroma and deeper iris tissues to be bathed in aqueous humour  Fuch’s crypts, between the tissues spaces of the stroma and the anterior chamber, allow the aqueous humour to have a direct communication with the tissue spaces of the iris.   Outer part of the ciliary region - concentric furrows known as contraction furrows, Caused by the folding of the iris as the pupil dilates.   Posterior surface of the iris - black a number of contraction folds which are most prominent in the pupillary region. Microscopically, the iris consists of two zones: the stroma and two epithelia layers.  The stroma of the iris consists of vascular connective tissue containing collagen fibres, fibroblasts, melanocytes, smooth muscles and nerve fibres.    In the pupillary zone - sphincter pupillae muscle. Ring of smooth muscle fibres around the pupil. Sphincter pupillae contracts - pupil constricts.    Dilator pupillae muscle - a thin layer of myoepithelium extends from the iris root to the sphincter pupillae dilator pupillae contacts - pupil dilates.  The two posterior epithelia layers consist of cells that are apposed to each other apex to apex.    The anterior layer is in contact with the stroma, Posterior layer is bathed with aqueous humour and faces the posterior chamber. Posterior cells - packed with melanin.  The blood vessels in the ciliary region produce long radial ridges The arterial supply of the iris is provided by radial vessels that lie in the iris stroma.  The vessels branch out in the vicinity of the sphincter and form an incomplete minor arterial circle.  The iris receives its nerve supply from ciliary nerves.  The ability of dilate and constrict the pupil permits the iris to control the amount of light entering the eye and impinging on the retina.  During accommodation for near vision the pupil constricts restricting the incoming light to the centre of the lens and diminishing spherical aberration.