cylindrical lens

lens (lenz)

1. a piece of glass or other transparent material so shaped as to converge or scatter light rays; see also glasses.

Lenses: (A–F), Spherical lenses: (A), biconvex; (B), biconcave; (C), planoconvex; (D), planoconcave; (E), concavoconvex, periscopic convex, converging meniscus; (F), convexoconcave, periscopic concave, diverging meniscus; (G, H), cylindrical lenses, concave and convex.

2. crystalline l.; the transparent, biconvex body separating the posterior chamber and vitreous body, and constituting part of the refracting mechanism of the eye.

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achromatic lens  one corrected for chromatic aberration.

aplanatic lens  one for correcting spherical aberrations.

bandage lens  a soft contact lens worn on a diseased or injured cornea to protect or treat it.

biconcave lens  one concave on both faces.

biconvex lens  one convex on both faces.

bifocal lens  one with two parts of different refracting powers, the upper for distant and the lower for near vision.

concavoconvex lens  one with one concave and one convex face.

contact lens  a curved shell of glass or plastic applied directly over the globe or cornea to correct refractive errors. It may be a soft (hydrophilic) contact l., flexible and water absorbent, or a hard (hydrophobic) contact l., rigid and not water absorbent; the latter type is subdivided into gas permeable and non–gas permeable, usually polymethylmethacrylate (PMMA), lenses.

convexoconcave lens  one with one convex and one concave face.

crystalline lens  lens (2).

cylindrical lens  one for correcting astigmatism, with one plane surface and one cylindrical, or one spherical surface and one toroidal. Symbol C.

decentered lens  one whose optical axis does not pass through the center.

honeybee lens  a magnifying lens resembling the multifaceted eye of the honeybee, consisting of three or six small telescopes mounted in the upper part of the lens and directed toward the center and right and left visual fields. Prisms are included to provide a continuous, unbroken magnified field of view.

omnifocal lens  one whose power increases continuously and regularly in a downward direction, avoiding the discontinuity of bifocal and trifocal lenses.

planoconvex lens  a lens with one plane and one convex side.

spherical lens  (S) (sph) one that is a segment of a sphere.

trial lens  one used to test vision.

trifocal lens  one with three parts of different refracting powers, the upper for distant, the middle for intermediate, and the lower for near vision.

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cylindrical lens

n.

A lens in which one of the surfaces is curved in one meridian and less curved in the opposite meridian. Also called astigmatic lens.

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cylindrical lens,

a lens with at least one nonspherical surface, used to correct astigmatism.

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lens [lenz]

1. a piece of glass or other transparent material so shaped as to converge or scatter light rays. See also glasses.

2. the transparent, biconvex body separating the posterior chamber and the vitreous body of the eye; it refracts (bends) light rays so that they are focused on the retina. Called also crystalline lens. In order for the eye to see objects close at hand, light rays from the objects must be bent more sharply to bring them to focus on the retina; light rays from distant objects require much less refraction. It is the function of the lens to do accommodation, making of adjustments for viewing both near objects and more distant ones. To accomplish this it must be highly elastic so that its shape can be changed and made more or less convex. The more convex the lens, the greater the refraction. Small ciliary muscles create tension on the lens, making it less convex; as the tension is relaxed the lens becomes more spherical in shape and hence more convex.

With increasing age the lenses lose their elasticity; thus their ability to focus light rays in the retina becomes impaired. This condition is called presbyopia. In farsightedness (hyperopia) the image is focused behind the retina because the refractive power of the lens is too weak or the eyeball axis is too short. Nearsightedness (myopia) occurs when the refractive power of the lens is too strong or the eyeball is too long, so that the image is focused in front of the retina.

The biconvex lens of the eye. From Frazier et al., 1996.

achromatic lens one corrected for chromatic (color) aberration.

apochromatic lens one corrected for chromatic (color) and spheric aberration.

biconcave lens one concave on both faces.

biconvex lens one convex on both faces.

bifocal lens one having two segments with different refracting power, the upper for far vision and the lower for near vision. See also bifocal glasses.

concave lens one curved like a section of the interior of a hollow sphere; it disperses light rays. Called also diverging lens.

contact l's corrective lenses that fit directly over the cornea of the eye; see also contact lenses.

converging lens (convex lens) one curved like the exterior of a hollow sphere; it brings light to a focus.

convexoconcave lens one that has one convex and one concave face.

crystalline lens lens (def. 2).

cylindrical lens one with at least one nonspherical surface, used to correct astigmatism.

diverging lens concave lens.

honeybee lens a magnifying eyeglass lens designed to resemble the multifaceted eye of the honeybee. It consists of three or six small telescopes mounted in the upper portion, directed toward the center and right and left visual fields. Prisms are included to provide a continuous, unbroken magnified field of view.

omnifocal lens one whose power increases continuously and regularly in a downward direction, avoiding the discontinuity in field and power inherent in bifocal and trifocal lenses.

orthoscopic lens one that gives a flat and undistorted field of vision, especially at the periphery.

planoconcave lens a lens with one plane and one concave side.

planoconvex lens a lens with one plane and one convex side.

Stokes's l's an apparatus used in the diagnosis of astigmatism.

trial l's ones used in testing the vision.

trifocal lens one having three segments of different refracting powers, the upper for distant, the middle for intermediate, and the lower for near vision.