The Goldmann contact lens and other fundus lenses work by nullifying the dioptric power of the cornea, thereby bringing the retina into the depth of field of the slit-lamp biomicroscope. These lenses are plano-concave contact lenses. Placed on the cornea, they form a virtual, erect, and minified image of the illuminated retina near the pupillary plane and within the range of view of the slit-lamp biomicroscope
http://creativecommons.org/licenses/by-sa/3.0/
