title: Calculating the error in refractive error.
abstract: OBJECTIVE
  To demonstrate a quick way of calculating the optical difference between two refractions using vector analysis, and to express this as a score for examination purposes.
  
  
  METHODS
  An existing formula is applied, converted to a defocus equivalent, and then converted to a score. The formula is set out in an Excel spreadsheet.
  
  
  RESULTS
  The spreadsheet enabled rapid assessment of the difference between two refractive errors. Examples are demonstrated.
  
  
  CONCLUSIONS
  The spreadsheet was successful in enabling a comparison of any two refractions, expressing the difference either as a correcting (third) refraction, a defocus equivalent or a one-figure score.
authors.affiliation: York Teaching Hospital NHS Foundation Trust, York, UK. robert.taylor@york.nhs.uk
authors.forename: R H
authors.initials: RH
authors.lastname: Taylor
authors.forename: R B
authors.initials: RB
authors.lastname: Ellingham
authors.forename: S
authors.initials: S
authors.lastname: Subramaniam
authors.forename: L A
authors.initials: LA
authors.lastname: Wakely
mesh_terms: D000465:Algorithms; D003627:Data Interpretation, Statistical; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008297:Male; D011237:Predictive Value of Tests; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000175:diagnosis* / Q000503:physiopathology