title: New clinical grading scales and objective measurement for conjunctival injection.
abstract: OBJECTIVE
  To establish a new clinical grading scale and objective measurement method to evaluate conjunctival injection.
  
  
  METHODS
  Photographs of conjunctival injection with variable ocular diseases in 429 eyes were reviewed. Seventy-three images with concordance by three ophthalmologists were classified into a 4-step and 10-step subjective grading scale, and used as standard photographs. Each image was quantified in four ways: the relative magnitude of the redness component of each red-green-blue (RGB) pixel; two different algorithms based on the occupied area by blood vessels (K-means clustering with LAB color model and contrast-limited adaptive histogram equalization [CLAHE] algorithm); and the presence of blood vessel edges, based on the Canny edge-detection algorithm. Area under the receiver operating characteristic curves (AUCs) were calculated to summarize diagnostic accuracies of the four algorithms.
  
  
  RESULTS
  The RGB color model, K-means clustering with LAB color model, and CLAHE algorithm showed good correlation with the clinical 10-step grading scale (R = 0.741, 0.784, 0.919, respectively) and with the clinical 4-step grading scale (R = 0.645, 0.702, 0.838, respectively). The CLAHE method showed the largest AUC, best distinction power (P < 0.001, ANOVA, Bonferroni multiple comparison test), and high reproducibility (R = 0.996).
  
  
  CONCLUSIONS
  CLAHE algorithm showed the best correlation with the 10-step and 4-step subjective clinical grading scales together with high distinction power and reproducibility. CLAHE algorithm can be a useful for method for assessment of conjunctival injection.
authors.affiliation: Department of Ophthalmology, Kyung Hee University College of Medicine, Kyung Hee University Hospital, Seoul, Korea.
authors.forename: In Ki
authors.initials: IK
authors.lastname: Park
authors.forename: Yeoun Sook
authors.initials: YS
authors.lastname: Chun
authors.forename: Kwang Gi
authors.initials: KG
authors.lastname: Kim
authors.forename: Hee Kyung
authors.initials: HK
authors.lastname: Yang
authors.forename: Jeong-Min
authors.initials: JM
authors.lastname: Hwang
mesh_terms: D000465:Algorithms; D003228:Conjunctiva / Q000473:pathology*; D003231:Conjunctivitis / Q000175:diagnosis*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D010781:Photography; D012372:ROC Curve; D015203:Reproducibility of Results; D012720:Severity of Illness Index
keywords: clinical grading; conjunctival injection; contrast-limited adaptive histogram equalization (CLAHE); objective measurement; standard photograph