title: A method to determine the impact of reduced visual function on nodule detection performance.
abstract: OBJECTIVE
  In this study we aim to validate a method to assess the impact of reduced visual function and observer performance concurrently with a nodule detection task.
  
  
  METHODS
  Three consultant radiologists completed a nodule detection task under three conditions: without visual defocus (0.00 Dioptres; D), and with two different magnitudes of visual defocus (-1.00 D and -2.00 D). Defocus was applied with lenses and visual function was assessed prior to each image evaluation. Observers evaluated the same cases on each occasion; this comprised of 50 abnormal cases containing 1-4 simulated nodules (5, 8, 10 and 12 mm spherical diameter, 100 HU) placed within a phantom, and 25 normal cases (images containing no nodules). Data was collected under the free-response paradigm and analysed using Rjafroc. A difference in nodule detection performance would be considered significant at p < 0.05.
  
  
  RESULTS
  All observers had acceptable visual function prior to beginning the nodule detection task. Visual acuity was reduced to an unacceptable level for two observers when defocussed to -1.00 D and for one observer when defocussed to -2.00 D. Stereoacuity was unacceptable for one observer when defocussed to -2.00 D. Despite unsatisfactory visual function in the presence of defocus we were unable to find a statistically significant difference in nodule detection performance (F(2,4) = 3.55, p = 0.130).
  
  
  CONCLUSIONS
  A method to assess visual function and observer performance is proposed. In this pilot evaluation we were unable to detect any difference in nodule detection performance when using lenses to reduce visual function.
authors.affiliation: University of Salford, Salford M6 6PU, UK. Electronic address: j.d.thompson@salford.ac.uk.
authors.forename: J D
authors.initials: JD
authors.lastname: Thompson
authors.affiliation: Lisbon School of Health Technology, 1990-096 Lisbon, Portugal; Public Health Research Center, National School of Public Health, NOVA University of Lisbon, Portugal.
authors.forename: C
authors.initials: C
authors.lastname: Lança
authors.affiliation: Lisbon School of Health Technology, 1990-096 Lisbon, Portugal; Karolinska Institute, SE-171 77 Stockholm, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Lança
authors.affiliation: University of Salford, Salford M6 6PU, UK; Karolinska Institute, SE-171 77 Stockholm, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Hogg
mesh_terms: D000328:Adult; D002983:Clinical Competence; D006801:Humans; D008875:Middle Aged; D015588:Observer Variation; D019047:Phantoms, Imaging; D000072177:Radiologists; D003074:Solitary Pulmonary Nodule / Q000000981:diagnostic imaging*; D014792:Visual Acuity
keywords: JAFROC; Observer performance; Visual acuity