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contact lens

(Encyclopedia)contact 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 conven...

contact process

(Encyclopedia)contact process: see sulfuric acid. ...

nearsightedness

(Encyclopedia)nearsightedness 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 stro...

cataract

(Encyclopedia)cataract, in medicine, opacity of the lens of the eye, which impairs vision. In the young, cataracts are generally congenital or hereditary; later they are usually the result of degenerative changes b...

Lens, city, France

(Encyclopedia)Lens läNs [key], city (1990 pop. 35,278), Pas-de-Calais dept., N France. During the 19th and 20th cent. it was one of the most important coal centers in N France, but its mines are now closed. Much o...

lens, in optics

(Encyclopedia)CE5 Lenses lens, 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 wi...

eyeglasses

(Encyclopedia)eyeglasses or spectacles, instrument or device for aiding and correcting defective sight. Eyeglasses usually consist of a pair of lenses mounted in a frame to hold them in position before the eyes. Th...

astigmatism

(Encyclopedia)astigmatism əstĭgˈmətĭzˌəm [key], 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, lig...

aberration

(Encyclopedia)CE5 A. Spherical aberration: Light rays near the edge of the lens are bent more and brought to focus nearer to the lens. B. Chromatic aberration: Shorter wavelengths (higher frequencies) are bent m...

image

(Encyclopedia)image, in optics, likeness or counterpart of an object produced when rays of light coming from that object are reflected from a mirror or are refracted by a lens. An image of an object is also formed ...