title: A simple variable prism with a linear scale.
abstract: OBJECTIVE
  To build a simple, low cost, variable-power prism with a linear scale.
  
  
  METHODS
  A sliding lens system, using the prismatic effect of ophthalmic lenses, was constructed.
  
  
  RESULTS
  The system functions well at low powers using conventional curved form ophthalmic lenses.
  
  
  CONCLUSIONS
  The sliding lens variable prism is a useful alternative to the conventional rotating variable-power prism.
authors.affiliation: Division of Vision Sciences, Glasgow Caledonian University, Glasgow, Scotland, United Kingdom.
authors.forename: Glyn
authors.initials: G
authors.lastname: Walsh
authors.forename: Peter
authors.initials: P
authors.lastname: Rafferty
authors.forename: E Ian
authors.initials: EI
authors.lastname: Pearce
mesh_terms: D004867:Equipment Design; D005139:Eyeglasses; D006801:Humans; D012030:Refractive Errors / Q000628:therapy