eyeglasses
eye·glass
E0309300 (ī′glăs′)eyeglasses
(ˈaɪˌɡlɑːsɪz)| Noun | 1. |  eyeglasses - optical instrument consisting of a frame that holds a pair of lenses for correcting defective vision |
| 单词 | eyeglasses | |||
| 释义 | eyeglasseseye·glassE0309300 (ī′glăs′)eyeglasses(ˈaɪˌɡlɑːsɪz)
eyeglasseseyeglassesorspectacles,instrument or device for aiding and correcting defective sight. Eyeglasses usually consist of a pair of lenseslens,device for forming an image of an object by the refraction of light. In its simplest form it is a disk of transparent substance, commonly glass, with its two surfaces curved or with one surface plane and the other curved. ..... Click the link for more information. mounted in a frame to hold them in position before the eyes. The first device of this kind was probably invented by Roger Bacon in the 13th cent. although similar devices are believed to have existed in ancient times in China and in the Mediterranean civilizations. Early forms were crude and clumsy and were not improved until the 18th cent. when the grinding of lenses was first based upon the principles of light refraction. Lenses are made of clear or rock crystal glass or plastic ground to suit the defect of the eye. Concave glass is used for nearsightednessnearsightedness or myopia, defect of vision in which far objects appear blurred but near objects are seen clearly. Because the eyeball is too long or the refractive power of the eye's lens is too strong, the image is focused in front of the retina rather than upon it. ..... Click the link for more information. , so that the rays of light are diverged. Convex lenses are used for farsightednessfarsightedness or hyperopia, condition in which far objects can be seen easily but there is difficulty in near vision. It is caused by a defect of refraction in which the image is focused behind the retina of the eye rather than upon it, either because the eyeball is ..... Click the link for more information. , so that the light rays are converged. Astigmatismastigmatism , type of faulty vision caused by a nonuniform curvature in the refractive surfaces—usually the cornea, less frequently the lens—of the eye. As a result, light rays do not all come to a single focal point on the retina. ..... Click the link for more information. is remedied by cylindrical lenses. Bifocal lenses, with a lower part for viewing objects near at hand (as in reading), were first devised by Benjamin Franklin; trifocal lenses have separate portions for near, middle distance, and distant viewing. In a progressive, multifocal, or varifocal lens, the lens is ground so as to permit viewing near objects through the lower portion and distant objects through the upper portion; in between, there in a progressive range of lens powers. Telescopic lenses are used by the near-blind. A contact lenscontact lens, thin plastic lens worn between the eye and eyelid that may be used instead of eyeglasses. Actors, models, and others wear them for appearance, and athletes use them for safety and convenience. ..... Click the link for more information. is shaped to fit the eye and is worn under the eyelid. Incorrect eyeglasses may do harm, and lenses should be prescribed by an ophthalmologist or optometrist and fitted by a skilled optician. Eyeglasses to protect the eyes from glare or from foreign bodies are made of tinted or polarized glass and of wire mesh. The Eskimo make and use wooden eyeglasses that have only narrow slits for eyepieces to protect the eyes from glare reflected by ice and snow. Eyeglassesthe most widely used optical device; eyeglasses with corrective lenses aid humans with visual defects of the eye, and protective eyeglasses (or goggles) protect the eyes from various harmful influences. The first reliable information on the use of eyeglasses is found in the 13th century in Italy and in England, where the British scientist R. Bacon described the effect of eyeglasses; however, accounts of the use of ground natural crystals for improving vision are found in ancient writings. The empirically developed technology for manufacturing eyeglass lenses was the impetus behind vigorous progress in the construction and manufacture of optical systems in the early 17th century. Discoveries in optics during this era where associated with such names as Galileo, J. Kepler, R. Descartes, and I. Newton. The human eye is a natural, complex, perfect optical system. Accommodation is the ability of the eye to focus images of objects on the retina as the distance between the retina and the objects changes. From every point on a distant object a nearly parallel bundle of rays enters the eye. If the image of such a distant object forms on the retina without accommodation, the eye is emmetropic, or normal; that is, its principal focus is on the retina. In an ametropic eye, normal refraction can be disturbed by several mechanisms. The principal focus, and consequently the surface upon which distant objects are represented, can shift to a position in front of the retina, in which case the eye is myopic, or nearsighted; if the focus lies behind the retina, the eye is hyperopic, or farsighted. Mild degrees of myopia and hyperopia are considered normal in ophthalmology. Astigmatism of the eye is another frequently encountered condition. The refractive capacity of the astigmatic eye changes along the various meridians of the eyeball—the imaginary planes that pass through the optic axis of the eye. The astigmatic eye cannot produce accurate images of point light sources. Corrective lenses. Disorders of ocular refraction and accommodation are treated with corrective lenses. When no astigmatism is present in the eye, eyeglasses that correct refractive disorders have spherical lenses whose refractive power is the same in all meridians. The principal focus of converging, or plus, lenses, which are prescribed for farsightedness, lies behind the glass; in dispersing, or minus, lenses, which are prescribed for nearsightedness, the focus is in front of the glass (see LENS). These lenses force the images of distant objects to be focused on the curved surface of the retina. Eyeglasses that correct ametropia are called distance glasses. The refractive power of the lenses in distance glasses depends on the degree of ametropia and is measured in diopters (m–1). Toric lenses are used for correcting ametropia that is complicated by astigmatism; these have a different refractive power for each meridian. With simple astigmatism, the eye is emmetropic in one of the mutually perpendicular principal meridians, which can have various angles of inclination to the vertical, and ametropic in another. However, astigmatism can often be compound, with a combination of nearsightedness or farsightedness of various degrees in the principal meridians, or mixed, with nearsightedness in one principal meridian and farsightedness in another. All types of astigmatism are corrected either with lenses that have one spherical surface and one toric surface or with lenses that have two curved surfaces, that is, lenses with various radii of curvature in the principal meridians. The capacity for accommodation decreases with age, until a condition known as presbyopia develops. In such cases, eyeglasses are necessary for distinct resolution of close objects and for reading; often, normal visual perception of distant objects is retained. Such eyeglasses have plus lenses and are called reading glasses. Bifocals are also prescribed for presbyopia and some other disorders of vision; the upper parts of the lenses of these eyeglasses are used for distance and have one refractive power (which can be zero), while the lower parts of the lenses have a different refractive power, for close vision. Two pairs of glasses —one for close and one for distant vision—can be used instead of bifocals. Eyeglasses with lenses that have a large number of foci, or multifocal eyeglasses, compensate for a loss of accommodation. Lenses with great refractive power have undesirable side effects: they do not produce a sharp image along the boundaries of the visual field, they distort shapes, they affect the size of the image on the retina, and they interfere with the correct perception of spatial perspective. Biconcave and biconvex lenses produce the most optical irregularities and are no longer used. Considerably fewer distortions arise with convexoconcave or concavoconvex lenses; these are called meniscus lenses and are the only eyeglass lenses commercially manufactured in the 1970’s. Any small optical distortions that are produced by meniscus lenses are usually compensated for by nervous mechanisms as the individual grows accustomed to the eyeglasses. Eyeglass lenses must clear the cornea by a specified distance, and the distance between lenses must strictly agree with the distance between pupils. For this reason eyeglasses require accurate fitting and careful manufacture. Specialized eyeglasses are used to correct severe combined visual disorders; for example, prismatic eyeglasses correct strabismus; mirror eyeglasses widen the field of vision; and telescopic eyeglasses with lenses arranged like those in small binoculars and are used to correct a severe decrease in visual acuity caused by diseases of the optic nerve, retina, or vascular tunic of the eye. In order to be of any benefit, eyeglass lenses must have the proper prescription, and this requires a comprehensive eye examination. The prescription, selection, and checking of the lenses are performed by an ophthalmologist. Contact lenses can be considered a type of eyeglasses; they are optically superior to ordinary eyeglasses in that they follow all the movements of the eyeballs, on which they are directly placed. They are manufactured either from glass or, more often, from flexible plastic, which conforms to the changing shape of the eyeball. Protective eyeglasses. These eyeglasses are designated to protect the eyes from mechanical influences, such as dust or metal shavings, from chemical injuries, and from excessively bright light or harmful regions of the light spectrum, which are encountered when welding or smelting metals, when working with lasers and other powerful light sources, and during prolonged exposure to brightly sunlit snow. Apart from fulfilling their specific requirements, eyeglasses for protection against mechanical and chemical injuries must not decrease visual acuity and must provide a sufficiently wide visual field. The space between the frames and face must be adequately ventilated and the eyeglasses must be lightweight and fit tightly and evenly to the face without injuring or irritating the skin. Finally, the glasses should not fog up. Light filters are used in glasses to protect against radiation; they can be neutral or, more often, selective. Selective light filters must eliminate as much useless—and often harmful—ultraviolet and infrared radiation as is possible while retaining as much of the visual-light spectrum as is absolutely necessary. A. V. LUIZOV What does it mean when you dream about eyeglasses?If not related to one’s eyeglasses in the real world, dream spectacles could indicate that something needs to be examined more clearly or attended to more carefully. Alternatively, looking at the world through “rose colored glasses” would indicate a reality check is in order. eyeglasses[′ī‚glas·əs]eyeglassesThe official term for "glasses," which are a pair of lenses mounted in a frame to improve a person's vision. See 3D glasses.Eyeglasses(dreams)eyeglassesglasses[glas´ez]spec·ta·cles(spek'tĭ-kĕlz),spec·ta·cles(spek'tă-kĕlz)Synonym(s): eyeglasses, glasses. eyeglasses
Synonyms for eyeglasses
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