title: Clinical monitoring of ocular physiology using digital image analysis.
abstract: OBJECTIVE
  To examine the use of image analysis to quantify changes in ocular physiology.
  
  
  METHODS
  A purpose designed computer program was written to objectively quantify bulbar hyperaemia, tarsal redness, corneal staining and tarsal staining. Thresholding, colour extraction and edge detection paradigms were investigated. The repeatability (stability) of each technique to changes in image luminance was assessed. A clinical pictorial grading scale was analysed to examine the repeatability and validity of the chosen image analysis technique.
  
  
  RESULTS
  Edge detection using a 3 x 3 kernel was found to be the most stable to changes in image luminance (2.6% over a +60 to -90% luminance range) and correlated well with the CCLRU scale images of bulbar hyperaemia (r=0.96), corneal staining (r=0.85) and the staining of palpebral roughness (r=0.96). Extraction of the red colour plane demonstrated the best correlation-sensitivity combination for palpebral hyperaemia (r=0.96). Repeatability variability was <0.5%.
  
  
  CONCLUSIONS
  Digital imaging, in conjunction with computerised image analysis, allows objective, clinically valid and repeatable quantification of ocular features. It offers the possibility of improved diagnosis and monitoring of changes in ocular physiology in clinical practice.
authors.affiliation: Neurosciences Research Institute, School of Life and Health Sciences, Aston University, Aston Triangle, Birmingham B4 7ET, UK. j.s.w.wolfsohn@aston.ac.uk
authors.forename: James S
authors.initials: JS
authors.lastname: Wolffsohn
authors.forename: Christine
authors.initials: C
authors.lastname: Purslow