title: Biconcave contact lenses: a critical analysis of their optical properties.
abstract: OBJECTIVE
  The purpose of this experiment was to compare biconcave contact lenses with other contact lenses already used for observation and irradiation of the retina and choroid.
  
  
  METHODS
  The optical performance of different biconcave lenses is described in terms of magnification, resolution, and field of view. The optical properties of the eye were taken into account using the Gullstrand's model of the human eye.
  
  
  RESULTS
  The performance of biconcave contact lenses represents a compromise between that of Goldmann's and wide angle indirect contact lenses. An upright image, with good peripheral image quality and an intermediate field of view is characteristic of such design. In addition, laser irradiation with large spot sizes is less hazardous when using such negative contact lenses compared to positive lenses of the same absolute refractive power.
  
  
  CONCLUSIONS
  Biconcave contact lenses qualify as a complement to planoconcave lenses for chorioretinal observation and irradiation tasks. For the same magnification factor, the field of view is smaller than that obtained with indirect contact lenses but the image degradation in the periphery of the retina is reduced.
authors.affiliation: Department of Ophthalmology, University of Zurich, Switzerland.
authors.forename: P
authors.initials: P
authors.lastname: Rol
authors.forename: F
authors.initials: F
authors.lastname: Fankhauser
authors.forename: P
authors.initials: P
authors.lastname: Niederer
mesh_terms: D003261:Contact Lenses / Q000592:standards*; D006801:Humans; D055095:Optics and Photonics; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000628:therapy