Eye

Organ of sight situated in orbit or socket, consisting externally of a fibrous structure, sclerotic, of a spheroidal shape, which occupies posterior of eye and of the transparent cornea in front. Between posterior surface of cornea and iris, or visible colored portion, is anterior chamber which communicates with posterior chamber, or space between iris and lens, by opening in center of iris, the pupil, both of which contain a thin watery fluid, aqueous humor. Behind the lens is the chamber containing the vitreous humor, of gelatinous consistency. Next to the sclerotic lies the choroid, a vascular structure with numerous dark pigment cells, and between it and the vitreous humor is the retina or expansion of the optic nerve IMG:content-1397.jpg:[graphic] View of lower half of right Human Eye, divided horizontally: a, cornea; b . sclerotic; c, c, sheath of optic nerve pa ing into sclerotic: d, choroid; e, ci fary muscle; f . ciliary proce ; g . g, iris; h , optic nerve with artery in center; i, pa age of nerve into retina, called optic disk or papilla; k , fovea central is; 1, retina; m. anterior chamber of aqueous humor; n, posterior chamber of aqueous hu r; o, crystalline lens; p , zonute of Zinn; q, suspensory ligament of lens; 7, vitreous humor. IMG:content-1398.jpg:[ocr errors] Choroid and Iris, exposed by turning aside the sclerotic: c, c, ciliary nerves going to be distributed in iris; d, d, smaller ciliary nerves; e, e. veins known as vasa vorticosa: h , ciliary muscle; k, l, converging fibers of iris; o , optic nerve. which pierces the sclerotic at the posterior part of the eye. Motion is communicated by several muscles duplicated on each side which contract synchronously. Front portion is covered by the conjunctiva which also lines eyelids, and at the upper outer side is the lachrymal gland which secretes the tears which pa into the lachrymal duct, which terminates in the nose, by two small openings, one in the upper and lower lids respectively, at the inner angle of the orbit. Eyelids project from above and below, over the eye; made up of skin on the outer side, mucous membrane on the inner, and a fibrous framework in the interior. On the edges are the lashes and within are a number of small glands. Conjunctivitis, keratitis, iritis, cataract, retinitis, choroiditis, and glaucoma are the principal and most common diseases; hypermetropia, myopia, and presbyopia are defects in vision due to abnormalities of shape, disease, or advanced age.