title: Comparing the Shape of Contrast Sensitivity Functions for Normal and Low Vision.
abstract: OBJECTIVE
  The contrast sensitivity function (CSF) provides a detailed description of an individual's spatial-pattern detection capability. We tested the hypothesis that the CSFs of people with low vision differ from a "normal" CSF only in their horizontal and vertical positions along the spatial frequency (SF) and contrast sensitivity (CS) axes.
  
  
  METHODS
  Contrast sensitivity for detecting horizontal sinewave gratings was measured with a two temporal-interval forced-choice staircase procedure, for a range of SFs spanning 5 to 6 octaves, for 20 low-vision observers and five adults with normal vision. An asymmetric parabolic function was used to fit the aggregate data of the normal-vision observers, yielding the "normal template." Each of the 20 low-vision CSFs was fit in two ways, by using a shape-invariant version of the normal template (with the width parameters fixed) that was shifted along the log-SF and log-CS axes, and by an unconstrained asymmetric parabolic function ("free-fit").
  
  
  RESULTS
  The two fitting methods yielded values of the peak CS, the SF corresponding to peak CS, and the high cut-off SF that were highly correlated and in good agreement with each other. In addition, the width parameters of the low-vision CSFs were comparable with those of the normal template, implying that low-vision CSFs are similar in shape to the normal CSF.
  
  
  CONCLUSIONS
  The excellent agreement of parameters estimated by the two fitting methods suggests that low-vision CSFs can be approximated by a normal CSF shifted along the log-SF and log-CS axes to account for the impaired acuity and contrast sensitivity.
authors.affiliation: School of Optometry University of California, Berkeley, Berkeley, California, United States.
authors.forename: Susana T L
authors.initials: ST
authors.lastname: Chung
authors.affiliation: Department of Psychology, University of Minnesota, Minneapolis, Minnesota, United States.
authors.forename: Gordon E
authors.initials: GE
authors.lastname: Legge
mesh_terms: D000328:Adult; D000368:Aged; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D012684:Sensory Thresholds / Q000502:physiology*; D015354:Vision, Low / Q000503:physiopathology*