title: Image Scaling Difference Between a Confocal Scanning Laser Ophthalmoscope and a Flash Fundus Camera.
abstract: OBJECTIVE
  To evaluate scaling and measurement differences between flash and scanning laser fundus images.
  
  
  METHODS
  The authors analyzed fundus autofluorescence images of patients with geographic atrophy secondary to age-related macular degeneration imaged with both 30º confocal scanning laser ophthalmoscope (cSLO) and 50º flash fundus camera (FFC). Multiple vessel-crossing points served as landmarks.
  
  
  RESULTS
  The mean (±SD; range) scaling factor between cSLO and FFC images (by GRADOR) for the horizontal dimension was 1.217 (±0.0487; 1.0474-1.272) versus 1.138 (±0.0311; 1.0841-1.193) for the vertical dimension. The mean percentage difference between horizontal and vertical scaling factors was 7.48 (±2.29; 2.30-10.70). Refractive error (focus) and aperture size (or field of view of the image) were positively correlated and aspect ratio was negatively correlated with landmark pair measurements.
  
  
  CONCLUSIONS
  Inherent image-scaling differences between fundus autofluorescence imaging systems are not restricted to simple pixel-to-millimeter calibration variances, but appear to vary depending on measurement orientation. Differences should be considered when comparing measurements obtained using different imaging systems, particularly for clinical trials.
authors.forename: Muneeswar G
authors.initials: MG
authors.lastname: Nittala
authors.forename: Amirhossein
authors.initials: A
authors.lastname: Hariri
authors.forename: Wai T
authors.initials: WT
authors.lastname: Wong
authors.forename: Emily Y
authors.initials: EY
authors.lastname: Chew
authors.forename: Frederick L
authors.initials: FL
authors.lastname: Ferris
authors.forename: Srinivas R
authors.initials: SR
authors.lastname: Sadda
mesh_terms: D057092:Geographic Atrophy / Q000175:diagnosis*; D006801:Humans; D008268:Macular Degeneration / Q000175:diagnosis*; D015588:Observer Variation; D019721:Ophthalmoscopes; D010781:Photography / Q000295:instrumentation*; D015203:Reproducibility of Results; D012160:Retina / Q000473:pathology*