a piece of transparent material (as glass) that has two opposite regular surfaces either both curved or one curved and the other plane and that is used either singly or combined in an optical instrument for forming an image by focusing rays of light
combination of two or more simple lenses
piece of glass or plastic used (as in safety goggles or sunglasses) to protect the eye
device for directing or focusing radiation other than light (as sound waves, radio microwaves, or electrons)
highly transparent biconvex lens-shaped or nearly spherical body in the eye that focuses light rays (as upon the retina) see eye illustration