title: Computerized stereochronoscopy and alternation flicker to detect optic nerve head contour change.
abstract: OBJECTIVE
  Stereochronoscopy, a technique previously explored but abandoned for glaucoma diagnosis, viewed optic nerve images acquired at separate points in time as if a stereo pair. Prior efforts to exploit this technique were impaired by a lack of superimposability for sequential optic nerve images. We investigated computerized registration techniques for aligning sequential, monoscopic optic disc images to facilitate sensitive detection of optic nerve head contour changes in glaucoma.
  
  
  METHODS
  Algorithm and software development. Comparisons with standard techniques.
  
  
  METHODS
  Existing patient records from the Glaucoma Service, Scheie Eye Institute, University of Pennsylvania.
  
  
  METHODS
  Two sets of optic disc photographs, separated in time by 1 to 18 years, of 25 eyes with and without glaucomatous optic disc progression were digitized. We developed custom software for accurate image alignment. Change in disc morphology was then judged by digital stereochronoscopy and user-controlled alternation flicker of superimposed, time-separated images on a computer monitor. Comparisons were made with standard stereoscopic comparison.
  
  
  METHODS
  Identification of change or no change in optic nerve head contour for images acquired at separate points in time.
  
  
  RESULTS
  Image processing and registration permits accurate alignment of optic disc photographs. Alternation flicker of superimposed, sequential images facilitates image comparison and detection of change as indicated by change in vessel position, color, and other cues for contour change. A high concordance was found between standard stereoscopic comparison and alternation flicker. In several cases, reinspection of stereo comparison led to a revised judgment on the basis of disc changes rendered more obvious with alternation flicker. Digital stereochronoscopy was less concordant with standard techniques.
  
  
  CONCLUSIONS
  Digital image processing techniques and alternation flicker provide a simple, sensitive, software-based method for detecting glaucomatous optic disc change.
authors.affiliation: Computer Vision Laboratory, Scheie Eye Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Berger
authors.forename: T R
authors.initials: TR
authors.lastname: Patel
authors.forename: D S
authors.initials: DS
authors.lastname: Shin
authors.forename: J R
authors.initials: JR
authors.lastname: Piltz
authors.forename: R A
authors.initials: RA
authors.lastname: Stone
mesh_terms: D000465:Algorithms; D003941:Diagnostic Techniques, Ophthalmological; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009898:Optic Disk / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis*; D010781:Photography / Q000379:methods