Eye

(i) [AS., edge]. The organ of vision. It occupies the anterior part of the orbit, is nearly spheric in outline, and is composed of three concentric coats: the sclerotic and cornea, the choroid and iris, and the retina. The sclerotic is an opaque, dense, white, fibrous membrane, into the anterior part of which the transparent cornea is fitted. The choroid is the vascular ti ue, and is continuous with the iris in front. The latter is a circular membrane with a central perforation, the pupil. Within the choroid is the retina, a delicate transparent membrane containing the terminations of the optic nerve. The greater part of the eyeball is filled with a mucoid substance, the vitreous humor, against the anterior surface of which rests the crystalline lens. The space between the lens and the cornea is divided by the iris into two compartments, communicating through the pupillary opening, the anterior and posterior chambers, which contain the aqueous humor. Anteriorly the eye is covered by conjunctiva, posteriorly by a fibrous capsule (capsule of Tenon). The eyeball is moved by a series of muscles attached on the outer surface. Changes in the curvature of the lens are brought about by the ciliary muscle, while the size of the pupil is modified by the action of dilator and constrictor fibers in the iris. E., Diagrammatic, of Listing, a scheme for simplifying optic problems by representing the two nodal points and the two principal points of the eye by a mean nodal point and a mean principal point. E.-broW, the hair-covered skin on the upper margin of the orbit. E. -lashes, the hairs of the eyelid. E.-lid, the protective covering of the eyeball, composed of skin, glands, connective and muscular ti ue, the tarsus and conjunctiva, with the cilia at the free edge. E. -piece. Synonym of Ocular. E., Reduced, of Donders, a representation of the eye in such a way that all the F. I. Abbreviation of Fahrenheit. 2. Symbol for fiuorin. Ft. Abbreviation of fiat or f. ant, let there be made. ch313.xhtml f 272