lens

[L. a lentil.] piece of gla , quartz, or other transparent substance with one or both surfaces curved, either concave or convex; used for acting upon the rays of light in the way of convergence or dispersal, collec'tive 1., field 1. crys'talline 1., 1. crystal lin a. cylindrical 1.. one which is a segment of a cylinder parallel to its axis; see cylindrical, eye 1., ocular 1., the upper of the two planoconvex lenses of Huygens* ocular, field I., collective the lower of the two planoconvex lenses of Huygens' ocular. 1. crystalli'na [BNA], crystalline a transparent biconvex body lying between the iris and the vitreous, the principal refracting medium of the eye; it consists of ct soft outer part {cortical substance) with a denser central part (nucleus). surrounded by a fine membrane (capsule). mi'nus 1., a concave or reducing 1. oc'ular 1., eye 1. plus 1., a convex or magnifying 1. spher'ical 1., one the curved surfaces of which are segments of spheres, see spherical, spherocylin'drical see spherocylinder. to'ric 1., a. curved lens corresponding in shape to the surface of a torus.