title: A logistics evaluation of visual acuity as applied to the Bailey-Lovie chart.
abstract: OBJECTIVE
  To discover whether as a result of the increasing use of the Bailey-Lovie chart some classes of patients may not be affected by the crowding of the smaller test characters, whose spacing is proportional to their size; and to determine acuities with a logistic function so that all of a patient's responses may be utilized.
  
  
  METHODS
  112 patients were tested both with the original chart and one in which the horizontal distance is kept constant, i.e., the letters are arranged in vertical columns. All of a patient's responses were recorded so that the constants of the logistic function might be determined.
  
  
  RESULTS
  No difference was found for very high and very low acuity scores, but, for intermediate ones, the vertical columns yielded acuity ratings increased by some 13%.
  
  
  CONCLUSIONS
  The use of the logistics function was successful in that the correlation between stimulus and response was between 0.9 and 1 for some 80% of those examined. A constant horizontal spacing may be of advantage to some patients with a conventionally measured visual acuity of approximately 0.9.
authors.affiliation: Department of Optometry, University of Bradford, W Yorks, UK.
authors.forename: B K
authors.initials: BK
authors.lastname: Pierscionek
authors.forename: R A
authors.initials: RA
authors.lastname: Weale
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D004867:Equipment Design; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D014787:Vision Tests / Q000295:instrumentation* / Q000706:statistics & numerical data; D014792:Visual Acuity