Structure of the choroid may be divided into three layers: 1) the vessel layer 2) the capillary layer 3) Bruch’s membrane. It is also tethered to the sclera where the vortex veins leave the eyeball. It is firmly attached to the sclera in the region of the optic nerve and where the posterior ciliary arteries and ciliary nerves enter the eye. Its inner surface is smooth and firmly attached to the pigmented layer of the retina its outer surface is roughened.It is thickest at the posterior pole(about 0.22 mm) and gradually thins anteriorly (about 0.1mm ). The choroid extends from the optic nerve posteriorly to the ciliary body anteriorly. is a thin, soft, brown coat lining the inner surface of the sclera.It measures about 6mm wide(6.5mm on the temporal side and 5.5mm on the nasal side) and extends forward to the scleral spur and backward to the oraserrata of the retina. Considered as a whole, the ciliary body is a complete ring that runs around the inside of the anterior sclera. The ciliary body is continuous posteriorly with the choroid and anteriorly with the peripheral margin of the iris. Dilaterpupille muscle: sypatheticsuplying smooth.When the sphincter pupillae contracts, the pupil constricts.It forms a ring of smooth muscle fibers around the pupil, measuring about 1mm wide. The sphincter pupillae muscle is located in the pupillary zone of the iris.Microscopically, the iris consists of two layers: 1) the stroma, situated anteriorly and derived from mesenchyme, 2) two epithelial layers located posteriorly and derived from the neural ectoderm.The color results from the absorption of light, with long wavelengths and the reflection of the shorter blue waves that are seen by the observer The blue iris has less pigment in the melanocytes compared with the brown iris.The aqueous humor, formed by the ciliary processes in PC, circulate through the pupil into AC and finally exits into the sinus venosussclerae at the iridocorneal angle.The pupil varies in diameter from 1 to 8mm, and in about 25% of normal subjects the pupils differ slightly in size on the 2 sides.The anterior surface of the lens is convex and presses lightly against the iris, causing it to bulge antreiorly.The iris is thickest about 2mm from the pupillary margin and thinnest at the ciliary margin. The pupil is surrounded by the pupillary margin.The periphery of the iris is attached to the anterior surface of the ciliarybody (called the root of the iris).The iris is a thin, contractile, pigmented diaphragm with a central aperture (the pupil), between the cornea and the lens, dividing this space to an anterior chamber ( A.C)and posterior chamber (P.C.).VASCULAR PIGMENTED LAYER The uveal tract composed of the second (the vascular ) coat of the globe which consists, from back to front, of the choroids, the ciliary body, and the iris.Discus uveitis, its causes, clinical pictures, complications, associations & management.
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