title: Distortion and size calibration of the scanning laser ophthalmoscope (SLO) laser-beam raster.
abstract: OBJECTIVE
  The Rodenstock scanning laser ophthalmoscope (SLO) is useful for mapping retinal function and for developing and evaluating visual rehabilitation methods. It is essential to know the visual angle subtended by stimuli in the SLO laser-beam raster and to accurately measure angular distances between objects in the final SLO image. To accomplish this, the angular extent of the SLO laser-beam raster must be calibrated.
  
  
  METHODS
  We developed a simple method and apparatus for calibrating the raster and used it for repeated calibrations during a 3-month period.
  
  
  RESULTS
  The laser-beam raster is quite stable in shape and size, but it is trapezoidally distorted in the vertical direction. Consequently, SLO images are distorted.
  
  
  CONCLUSIONS
  Trapezoidal distortion of the SLO laser-beam raster can cause stimulus size to change as much as 10% from the top to the bottom of the raster. Measurements of fixed horizontal retinal landmark distances in SLO images can also vary as much as 10%. We developed a straightforward mathematical method for correcting distortion in SLO image measurements.
authors: Department of Ophthalmology, University of Kansas Medical Center, Kansas City, KS 66160, USA. gtimberl@kumc.edu
authors: George T
authors: GT
authors: Timberlake
authors: Manjo K
authors: MK
authors: Sharma
authors: Denise V
authors: DV
authors: Gobert
authors: Joseph H
authors: JH
authors: Maino
mesh_terms: D002138:Calibration; D006801:Humans; D007834:Lasers; D008433:Mathematics; D019721:Ophthalmoscopes; D009887:Ophthalmoscopy / Q000592:standards*