| lens | <physics> A transparent optical element, so constructed that it serves to change the degree of convergence or divergence of the transmitted rays. (05 Aug 1998) |
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| lens capsule | The capsule enclosing the lens of the eye. Synonym: capsula lentis, crystalline capsule, lenticular capsule, phacocyst. (05 Mar 2000) |
| lens capsule, crystalline | The noncellular outer covering of the crystalline lens, secreted by the embryonic anterior and posterior epithelium. The embryonic posterior epithelium later disappears. (12 Dec 1998) |
| lens clock | A device for measuring the radii of the curvature of a spectacle lens. Synonym: lens clock. Origin: Geneva, Switzerland (05 Mar 2000) |
| lens cortex, crystalline | The portion of the crystalline lens surrounding the nucleus and bound anteriorly by the epithelium and posteriorly by the capsule. It contains lens fibres and amorphous, intercellular substance. (12 Dec 1998) |
| lens implantation, intraocular | Insertion of an artificial lens following removal of the crystalline lens, usually after cataract extraction. (12 Dec 1998) |
| lens neutral proteinase | <enzyme> Degrades alpha 2-crystallin; requires ca and mg; cleaves phe-ser bond in bradykinin; similar enzyme found in human lung Registry number: EC 3.4.24.5 Synonym: neutral proteinase 24.5 (26 Jun 1999) |
| lens nucleus, crystalline | The core of the crystalline lens, surrounded by the cortex. (12 Dec 1998) |
| lens pits | The paired depressions formed in the superficial ectoderm of the embryonic head as the lens placodes sink in toward the optic cup; the external openings of the pit's are closed as the lens vesicles are formed. (05 Mar 2000) |
| lens placodes | Paired ectodermal placode's that become invaginated to form the embryonic lens vesicles. Synonym: optic placodes. (05 Mar 2000) |
| lens stars | Congenital cataracts with opacities along the suture lines of the lens; may be anterior or posterior or both. (05 Mar 2000) |
| lens subluxation | Incomplete rupture of the zonule with the displaced lens remaining behind the pupil. In dislocation, or complete rupture, the lens is displaced forward into the anterior chamber or backward into the vitreous body. When congenital, this condition is known as ectopia lentis. (12 Dec 1998) |
| lens sutures | 9 to 12 faint lines on the anterior and posterior surfaces of the lens that radiate from the poles toward the equator; they mark the lines along which the ends of lens fibres abut. Synonym: lens stars, lens sutures. (05 Mar 2000) |
| lens vesicle | In the embryo, the ectodermal invagination that forms opposite the optic cup; it is the primordium of the lens of the eye. Synonym: lenticular vesicle. (05 Mar 2000) |
| lens, Bertrand | <microscopy> A small convergent lens placed between objectives and eyepiece. The lens focuses an image of the upper focal plane of the objective on the focal plane of the eyepiece. It is chiefly used with polarized light for inspecting the interference figure. It is also convenient for quickly verifying centreing, size, and uniform illumination of an aperture. (05 Aug 1998) |
| achromatic lens | A compound lens made of two or more lens's having different indices of refraction, so correlated as to minimise chromatic aberration. (05 Mar 2000) |
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| acoustic lens | In ultrasonography, a lens used to focus or diverge a sound beam; may be simulated by electronic manipulation of signals. (05 Mar 2000) |
| anterior pole of lens | The central point on the anterior surface of the lens of the eye. Synonym: polus anterior lentis. (05 Mar 2000) |
| anterior surface of lens | The anterior surface of the lens of the eye. Synonym: facies anterior lentis. (05 Mar 2000) |
| aplanatic lens | A lens designed to correct spherical aberration and coma (q.v.). Synonym: periscopic meniscus. (05 Mar 2000) |
| apochromatic lens | A compound lens designed to correct both spherical and chromatic aberrations. (05 Mar 2000) |
| asphenc lens | <physics> A lens made aplanatic by grinding the outer zones to a greater radius than the inner zones. Aplanatic condensers can be made in this way. A simple aspheric lens is widely used as a lamp condenser because of its efficiency in converging light rays to one focal plane. (05 Aug 1998) |
| aspheric lens | A lens with a paraboloidal surface that eliminates spherical aberration. (05 Mar 2000) |
| astigmatic lens | A lens in which one of the surfaces is curved in one meridian and less curved in the opposite meridian; e.g., a teaspoon or a football. Synonym: astigmatic lens. (05 Mar 2000) |
| axis of lens | A line connecting the anterior and posterior poles of the lens of the eye. Synonym: axis lentis. (05 Mar 2000) |
| back lens | <physics> In any compound lens (a lens system composed of more than one lens element), the last lens through which the light passes is called the back lens. It may be a single simple lens, a doublet, or triplet. See: front lens (05 Aug 1998) |
| Bertrand lens | <physics> A small, low-power lens, usually on a slide for insertion into the drawtube between analyser and ocular. It is used to observe the back focal plane of the objective so as to examine interference figures or as an aid in achieving interference figures. It is apt to be strongly astigmatic. It is used to image the lamp filament in setting up Kohler illumination as well as for centreing dispersion staining stops to the substage aperture diaphragm. (05 Aug 1998) |
| biconcave lens | A lens that is concave on two opposing surfaces. Synonym: concavoconcave lens, double concave lens. (05 Mar 2000) |
| biconvex lens | A lens with both surfaces convex. Synonym: convexoconvex lens, double convex lens. (05 Mar 2000) |
| bifocal lens | A lens used in cases of presbyopia, in which one portion is suited for distant vision, the other for reading and close work in general; the reading addition may be cemented to the lens, fused to the front surface, or ground in one-piece form; other bifocal lens's are the flat-top Franklin type, or blended invisible. (05 Mar 2000) |