title: Error cells for spherical powers in symmetric dioptric power space.
abstract: OBJECTIVE
  : The purpose of this article is to analyze the geometry and examine the implications of the error cells of purely spherical powers in symmetric dioptric power space.
  
  
  METHODS
  : In the context of spherocylindrical data spherical data typically implies a cylindrical component that is less than some particular amount (often 0.125 D) in magnitude. This error or uncertainty in cylinder is over and above the error in sphere itself. The two components of error are used to define the error cells in symmetric dioptric power space.
  
  
  RESULTS
  : Error cells of spherical powers are constructed and presented as stereopairs. They are also shown in relation to error cells of powers in general.
  
  
  CONCLUSIONS
  : An understanding of error cells can help the researcher avoid pitfalls in the analysis of spherocylindrical data. Perhaps surprisingly, the error cells of spherical powers are not invariant under spherocylindrical transposition.
authors.affiliation: Optometric Science Research Group, Department of Optometry, University of Johannesburg, Johannesburg, South Africa.
authors.forename: W F
authors.initials: WF
authors.lastname: Harris
authors.forename: A
authors.initials: A
authors.lastname: Rubin
mesh_terms: D006801:Humans; D008433:Mathematics; D009799:Ocular Physiological Phenomena; D055095:Optics and Photonics; D009907:Optometry; D012029:Refraction, Ocular / Q000502:physiology