eye

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“

'The deity called the eye is the attainer, may it attain this for me from him.

—Sacred Books of the East

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American Heritage Dictionary (39)

noun An organ of vision or of light sensitivity.
noun Either of a pair of hollow structures located in bony sockets of the skull, functioning together or independently, each having a lens capable of focusing incident light on an internal photosensitive retina from which nerve impulses are sent to the brain; the vertebrate organ of vision.
noun The external, visible portion of this organ together with its associated structures, especially the eyelids, eyelashes, and eyebrows.

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The organ of vision; the physiological mechanism of the sense of sight; an anatomical arrangement of parts by which optical images may be formed; in general, any part of an animal body by means of which the faculty of vision is exercised, or the impact of the light-rays is sensed as a visual impression or optical image. In most of the higher animals, as nearly all vertebrates, the eye is developed as a very special sense-organ of great structural complexity and functional delicacy. But from the point of view of comparative anatomy an eye is any part of an animal body which responds more readily than other parts to the special stimulus of light, or whose activity is specially excited by the impact of light-rays. Thus, an extremely rude eye in the form of a mere spot, often a pigment-spot sensitive*** light, is common in low animals, as in infusorians, a*** may be situated anywhere on the body, and may be indefinitely multiplied in number. These rudiments of eyes are commonly described as eye-specks, eye-points, or eye-spots. (See cut under Balanoglossus.) In various cœlenterates and echinoderms organs apparently responsive to the action of light occur in various parts of the body and in varying numbers. Somewhat higher in the scale of evolution, eyes become unmistakable in structural character, however dim or uncertain their actual visual function may be, as in worms, snails, etc. But in some of the Mollusca, as cuttlefishes, eyes are highly specialized as visual organs of conspicuous character, comparable to those of vertebrates, though constructed on a different plan. In the vast assemblage of arthropods, as crustaceans, insects proper, and arachnidans, constituting a large majority of the animal kingdom, eyes as a rule are well developed under one or both of two main modifications, namely, the simple eye or ocellus and the compound eye or oculus. (See compound eye, below, and cut under falx.) Such eyes are usually only two, but may be four, six, or eight in number. These higher numbers of eyes occur chiefly in arachuidans, as spiders. Crustaceans have normally a single pair, often mounted on movable eye-stalks or ophthalmites, which are modified limbs of one of the cephalic segments. (See cut under stalk-eyed.) A few crustaceans have a single median eye. In vertebrates, where the eyes are normally never more nor fewer than one pair, these organs are received in special formations of the skull, the sockets or orbits of the eyes; and the eyes are usually further defended from accidental injury by various contrivances, as eyelids, eyelashes, and eyebrows. (See these words.) Other appendages of the eye namable among its “defenses” are the lacrymal apparatus, which secretes tears to moisten the organ, and the glandular structures (Meibomian follicles), which serve for its lubrication by secreting a greasy substance. The front of the eye has usually a special mucous membrane, the conjunctiva. The most essential or intimate parts of the organ of vision are contained in a globe or disk, the eyeball (which see), which is freely movable in its socket in the higher vertebrates, and rolled about by the action of various muscles, as the four recti and two obliqui of man and the choanoid muscle of some mammals. Externally the eyeball consists for the most part of a tough opaque membrane, the sclerotic; but in front, of a hard transparent structure, the cornea. These together are the outermost of three tunics or coats of the eye; the second tunic consists of the choroid coat and ciliary processes and the iris, and the third and innermost of the retina, the expanded end of the optic nerve, which enters the ball from behind and spreads out upon the choroid to a varying extent. The retina receives optical impressions focused upon it by the crystalline lens, which are transmitted by the optic nerve to the brain, where they are sensed as visual images. The hollow eyeball with its several tunics forms a kind of camera filled with certain solid and fluid refractive media. Directly in the axis of vision in the interior of the ball is suspended a solid biconvex body, the crystalline lens, serving to bring rays of light to a focus on the retina. The lens, inclosed in its capsule, also divides the interior of the eye into two compartments. The larger rear compartment is filled with a glassy fluid, the vitreous humor, inclosed in a delicate hyaloid membrane, which may also send prolongations through its substance. In front of the lens, between this structure and the cornea, the space is filled with a more watery fluid, the aqueous humor. This anterior space is partly divided into an anterior and a posterior chamber by the iris, which hangs in front of the lens like a curtain with a hole in the middle, the pupil. Besides the optic nerve, or special nerve of sight, the eye is supplied with other motor, sensory, and sympathetic nerves, and has its appropriate blood-vessels. In man both eyes look directly forward, their axes being parallel, though the orbits in which they are contained present a little outward, or away from each other. The optic nerve follows the axis of the orbit, and consequently pierces the eyeball behind, a little on the inner side—that is, toward the nose. The muscles which move the ball are six, the rectus superior, rectus inferior, rectus externus, rectus internus, obliquus superior, and obliquus inferior. These muscles are innervated by three motor nerves, the oculomotor, trochlear or pathetic (distributed to the obliquus superior), and abducent (distributed to the rectus externus). The ball is embedded in a quantity of adipose tissue forming a soft cushion, but is also somewhat isolated by means of a thin membranous sac called the vaginal tunic or sheath of the eye. The ball is nearly spherical or globular, but is a little deeper and wider across than from before backward, measuring about an inch in each of the former axes and of an inch in the latter. (For the structure of the several tunics, see sclerotic, cornea, choroid, ciliary, iris, and retina.) The retina is an expansion of the optic nerve into a large, circular, concavo-convex sheet, which rests upon the choroid with its inner surface in contact with the body of vitreous humor in the back of the eye. In the middle of it and in the axis of the eye is a little rounded elevation, the yellow spot, or macula lutea, with a depression at its summit, the fovea centralis. To the nasal side of the yellow spot is the entrance of the optic nerve and of the central retinal artery; and here the retina lacks the visual function which characterizes all the rest of its surface. The lens is suspended in a transparent capsule in the axis of vision; it is biconvex, and more convex on its posterior than on its anterior surface. It is about ⅓ of an inch across and ¼ of an inch deep, and its structure presents concentric laminations. It tends to fiatten with age. (See crystalline lens, under crystalline.) The vitreous humor fills the hollow of the eyeball behind the lens. It is a glassy or jelly-like substance, consisting chiefly of water, with a little saline and albuminous material, inclosed in a delicate hyaloid membrane continuous in front with the capsule and suspensory ligament of the lens, and behind resting upon the retina. Some prolongations of the hyaloid enter the substance of this humor, and one of these is called the canal of Stilling. The quantity of vitreous humor, or bulk of the vitreous body, is about ⅘ of the entire mass of the eyeball. The aqueous humor is the slightly saline watery fluid which fills the eye in front of the lens, between this and the cornea, on both sides of the iris, consequently occupying the whole of the anterior and posterior chambers of the eye. Its bulk is very small. (See conjunctiva, lacrymal, Meibomian, nasal, ocular, ophthalmic, optic, palpebral, superciliary, tarsal, etc.) The eye agrees with other sense-organs in development in the embryo, in being partly formed by the inversion or involution of a portion of epiblast from without, and partly by protrusion or evolution from within of a primitive ocular vesicle, the two coming together in the situation where the lens is to be developed. The result is that a portion of epiblast from the back of the embryo, which had been shut into the hollow of the cerebrospinal tube, pushes out from one of the cerebral vesicles to meet another portion of epiblast from the face of the embryo. Thus, the retina and associate parts are an outgrowth from the undeveloped brain, while the lens and associate epithelial structures are an ingrowth of epidermis. In other mammals with well-formed eyes the structure is substantially the same as in man, though minor and incidental variations are numerous. The eyes of quadrupeds usually present laterally, and not directly forward. They are usually relatively larger and probably much more effective organs of vision than those of man. They frequently develop a special choanoid muscle or retractor of the eyeball. The iris is commonly black, brown, or of some dark tint, seldom bluish or pale. It often contracts in such a way that the pupil is linear, elliptical, or narrowly oval, instead of circular, as in man. This is well seen in the cat. In birds several modifications occur. The eyeball is strengthened and its shape molded by a set of splint-bones or small bony plates disposed in a circle in the sclerotic around the cornea. The ball is hemispherical with an anterior projection, somewhat like a short acorn in a large cup, and the cornea is very convex. The pupil is always circular, though the iris may be so motile as to present only a narrow ring round the pupil, or to reduce the pupil to a mere point. These changes are well seen in the eyes of owls. There is also in the vitreous humor a peculiar plaiting or folding of the choroid, called the marsupium or pecten. The visual range and power of the eye in some birds, if not in all, are much greater than in man. All birds have three eyelids, the third very fully developed and arranged so as to sweep entirely across the front of the eye by means of special muscles and tendons upon the back of the eyeball. No birds are eyeless. In reptiles the eyes are structurally more like those of birds than of mammals. Some reptiles are eyeless, or have very rudimentary eyes. Most have eyelids, but these are wanting in ophidians, a transparent cuticle being continued directly over the ball, and shed with the rest of the cuticle. In fishes the eyes are generally symmetrically lateral, but not infrequently dorsal and closely approximated to each other, and rarely inferior; in one type, the heterosomes or flat-fishes, they are, however, both on one side, that belonging to the side which rests on the ground being in the very young in the normal position, but soon actually penetrating through the integument, and with the circumocular cranial region twisting to the opposite side and assuming a permanent position above the regular eye of the colored or uppermost side. The accessories of the eyes of mammals are undeveloped in fishes, but the eyes themselves are sometimes covered by a fold of the integument, and sometimes, as in some sharks, by a peculiar nictitant membrane. Among the most characteristic features are the flattening of the cornea and the sphericity of the crystalline lens. In one group (Anableps) a remarkable deviation from all other forms occurs, in that the cornea is divided by a horizontal band of the conjunctiva into upper and lower halves, and two pupils are developed, the species consequently being known as four-eyed fishes. In the lowest of the vertebrates (Branchiostoma) the eye is represented by a very small spot, coated with dark pigment and receiving the end of a short nerve. See vision. For he beholdethe every man so scharply, with dreadfulle Eyen, that ben evere more mevynge and sparklynge, as Fuyr. Mandeville, Travels, p. 282. Our yeen ar made to looke; whi shulde we spare? Political Poems, etc. (ed. Furnivall), p. 60. Thane the worthy kynge wrythes, and wepede with his enghne. Morte Arthure (E. E. T. S.), l. 1920. There was he aware of a jolly beggàr, As ere he beheld with his eye. Robin Hood and the Beggar (Child's Ballads, V. 252).
In a restricted or specific use, some part or appurtenance of the physical eye, taken as representing the whole. The hole in the iris through which light enters; the pupil: as, owls' eyes contract in daylight; circular or oval eyes. The socket of the eye; the orbit: as, the empty eyes of a skull. The opening between the eyelids; the palpebral fissure: as, to close or shut the eyes.
Figuratively Vision; the act of seeing, or the field of sight; hence, observation; watch. Here will shee crosse the riuer; stand in her eye, That she may take some notice of our neglected duties. Heywood, If you Know not Me, i. After this jealousy he kept a strict eye upon him. Sir R. L'Estrange. Then said Evangelist, Keep that light in your eye, and go up directly thereto, so shalt thou see the gate. Banyan, Pilgrim's Progress, p. 86. The eye of the master will do more than both his hands. Franklin.

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For his eye was always across the Channel, calculating the domestic effect of each treaty provision. — Woodrow Wilson and the World War A Chronicle of Our Own Times.
Then again the eye is a delicate organ, but is fitted with an eyelid to keep guard over it, eye-lashes to strain off small particles, eyebrows to carry the sweat away from it. — The Prayer Book Explained
For the eye is always in search of beauty, and if we do not gratify its desire for pleasure by a proportionate enlargement in these measures, and thus make compensation for ocular deception, a clumsy and awkward appearance will be presented to the beholder. — The Ten Books on Architecture
It would be incomplete unless accompanied by such associates as the eye is accustomed to embrace in the full gratification of the sensations to which that organ is the conductor. — Rural Architecture Being a Complete Description of Farm Houses, Cottages, and Out Buildings
In the back of the eye is the retina, which acts as a film for the eye's picture Now, it was the part of the eye around that opening which got inflamed and began to exude. — The Sagebrusher A Story of the West

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face · voice · mind · light · life · ear · figure · man · gaze · hair · way

Roget's II: The New Thesaurus, Third Edition by the Editors of the American Heritage® Dictionary. Copyright © 2003, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Etymologies (4)

American Heritage Dictionary (1)

Middle English, from Old English ēge, ēage; see ok^w- in Indo-European roots.

Century Dictionary (3)

Early modern English also eie; from Middle English eye, eghe, eighe, ege, eie, ehe, ee, etc., plural eyen, eghen, eighen, egen, eien, eene, ein, iyen, ine, etc., also later eyes, etc., from Anglo-Saxon eáge, plural eágan = Old Saxon ōga = ÓFriesic āge, ōge = Middle Low German Low German ōge = Dutch oog = Old High German ouga, Middle High German ouge, German auge = Icelandic auga = Old Swedish auga, Swedish öga = Danish öie = Goth, augo, eye. The Teutonic forms do not quite agree with the other Aryan forms, which are somewhat irregular: L. oculus (later Italian occhio = Spanish ojo = Portuguese olho = Provencal olh = French œil: see œiliad, eyelet, ocular, etc.), diminutive of an assumed *ocus; = Greek ὅσσ, σ1ε, dual of an assumed *ὅσσ, σ1ος for *ὅκγος, (ὅκκος, in Hesychius) (cf. Bœotian ὅκταλλος, or ὅκκαλλος, reg. Greek ὀφθαλμός, eye); = Old Bulgarian Bulgarian Servian Bohemian Polish oko = Old Prussian agins = Lithuanian akis = Lettish acs = Sanskrit akshan, eye; apparently from the root (Greek *ὀκ, *ὀπ) of Greek ὅσσ, σ1εσθαι, see; ὅψεσθαι, future associated with ὁρᾶν, see, ὅπωπα, I have seen, ὀπτικός, pertaining to sight, ὀπτήρ, one who sees, ὅψ (ὀπ-), ω῎ψ (ὠπ-), the eye, countenance, etc.; cf. Sanskrit √ īksh, see. The word eye appears disguised in dais-y and wind-ow, q. v. See ocular, etc., ophthalmia, etc., optic, etc.
First in modern E.; = Dutch oogen = Danish öjne, eye, see; from the noun. Cf. ogle.
A corruption due to misdividing a nye as an eye, a nest, as eyas of nias, nyas: see nye, nide, nidus.

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