title: Pointwise linear progression criteria and the detection of visual field change in a glaucoma trial.
abstract: BACKGROUND
  Current pointwise linear regression (PLR) change criteria for visual field analysis are largely empirical.
  
  
  METHODS
  Two independent sets of Humphrey Field Analyzer fields were analysed using PLR. Set i, 56 patients, and set ii, 97 patients, were followed over 16 months. Criteria were tested against set i, and then validated using set ii. Each criterion specified a fixed critical slope of 1 dB/year and with a range of significance from P<0.001 to 0.05. The criteria were varied by altering location number, cluster arrangement, and by requiring points to show change over both 12 and 16 months. True glaucomatous change was differentiated from noise by looking for exclusive progression (EP), the detection of progression without detection of improvement.
  
  
  RESULTS
  Set i required 1 point to have a slope of 1 dB/year and P<0.05 labelled 64% progressing and 58% improving, whereas several stricter criteria were capable of detecting EP. Two points in a perimetric nerve fibre bundle (PNFB) cluster gave optimal EP detection, labelling 8.9% progressing in set i and 7.2% progressing in set ii with a cutoff P-value of 0.026 inset i and 0.013 inset ii.
  
  
  CONCLUSIONS
  Lax PLR criteria detect large amounts of change. Validating criteria using two data sets allow selection of better criteria, capable of detecting EP. The criterion involving 2 points changing in a PNFB cluster offers the best option for exclusively detecting progression.
authors.affiliation: Wound Healing Research Unit, Institute of Ophthalmology, London, UK. mail@markwilkins.co.uk
authors.forename: M R
authors.initials: MR
authors.lastname: Wilkins
authors.forename: F W
authors.initials: FW
authors.lastname: Fitzke
authors.forename: P T
authors.initials: PT
authors.lastname: Khaw
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001331:Automation; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D005901:Glaucoma / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity; D014130:Trabeculectomy; D016896:Treatment Outcome; D058609:Visual Field Tests / Q000379:methods; D014794:Visual Fields