title: Exploring the optimum step size for defocus curves.
abstract: OBJECTIVE
  To evaluate the effect of reducing the number of visual acuity measurements made in a defocus curve on the quality of data quantified.
  
  
  METHODS
  Midland Eye, Solihull, United Kingdom.
  
  
  METHODS
  Evaluation of a technique.
  
  
  METHODS
  Defocus curves were constructed by measuring visual acuity on a distance logMAR letter chart, randomizing the test letters between lens presentations. The lens powers evaluated ranged between +1.50 diopters (D) and -5.00 D in 0.50 D steps, which were also presented in a randomized order. Defocus curves were measured binocularly with the Tecnis diffractive, Rezoom refractive, Lentis rotationally asymmetric segmented (+3.00 D addition [add]), and Finevision trifocal multifocal intraocular lenses (IOLs) implanted bilaterally, and also for the diffractive IOL and refractive or rotationally asymmetric segmented (+3.00 D and +1.50 D adds) multifocal IOLs implanted contralaterally. Relative and absolute range of clear-focus metrics and area metrics were calculated for curves fitted using 0.50 D, 1.00 D, and 1.50 D steps and a near add-specific profile (ie, distance, half the near add, and the full near-add powers).
  
  
  RESULTS
  A significant difference in simulated results was found in at least 1 of the relative or absolute range of clear-focus or area metrics for each of the multifocal designs examined when the defocus-curve step size was increased (P<.05).
  
  
  CONCLUSIONS
  Faster methods of capturing defocus curves from multifocal IOL designs appear to distort the metric results and are therefore not valid.
  
  
  BACKGROUND
  No author has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: Ophthalmic Research Group Life and Health Sciences, Aston University, Birmingham, United Kingdom. j.s.w.wolffsohn@aston.ac.uk
authors.forename: James S
authors.initials: JS
authors.lastname: Wolffsohn
authors.forename: Amit N
authors.initials: AN
authors.lastname: Jinabhai
authors.forename: Alec
authors.initials: A
authors.lastname: Kingsnorth
authors.forename: Amy L
authors.initials: AL
authors.lastname: Sheppard
authors.forename: Shehzad A
authors.initials: SA
authors.lastname: Naroo
authors.forename: Sunil
authors.initials: S
authors.lastname: Shah
authors.forename: Phillip
authors.initials: P
authors.lastname: Buckhurst
authors.forename: Lee A
authors.initials: LA
authors.lastname: Hall
authors.forename: Graeme
authors.initials: G
authors.lastname: Young
mesh_terms: D057128:Aberrometry; D000368:Aged; D058452:Axial Length, Eye; D019781:Corneal Topography; D005139:Eyeglasses; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D055095:Optics and Photonics; D018918:Phacoemulsification; D011305:Presbyopia / Q000175:diagnosis* / Q000628:therapy; D012029:Refraction, Ocular / Q000502:physiology; D014787:Vision Tests; D014792:Visual Acuity / Q000502:physiology*