title: A novel strategy for the estimation of the general height of the visual field in patients with glaucoma.
abstract: BACKGROUND
  More accurate estimation of the general height of the visual field may improve our ability to detect and monitor progression of diseases affecting visual function such as glaucoma. General height (GH) can be affected by factors such as cataracts, pupillary miosis, refractive error, and learning and fatigue effects. The conventional GH index, consisting of subtracting the 85th largest value from the total-deviation map, has been shown to overestimate the height in patients with moderate and advanced glaucoma. We aimed at developing an improved estimator for general height based on ranking of total-deviation values that are within normal limits (GHr).
  
  
  METHODS
  Two datasets were used for the comparisons between GH and GHr estimates: one with 369 visual fields for 102 controls, and another with 500 visual fields for 124 patients. For controls, we compared the distributions of mean of total deviation (MD) and of mean of pattern deviation (MPD) derived from both the GH and the GHr estimates. For patients, we assessed agreement between both estimates and between pairs of consecutive visits. We also compared linear fits in progression analyses. All data were collected with 24-2 SITA Standard.
  
  
  RESULTS
  For control subjects and patients with MD above -5.5 dB, estimates with the GHr estimator were not significantly different than with the GH estimator. For patients with glaucoma with MD below -5.5 dB, as MD became more negative the GH estimates were increasingly greater than GHr estimates. For patients with glaucoma, test-retest variability was lower with the GHr estimator: between visits agreement was better for GHr estimates than for GH estimates (SD of 0.8 dB versus 1.5 dB; p < 0.0001). Linear-regression analysis fitted better estimates obtained with the GHr estimator. Root mean square error for GHr was 0.4 dB; lower than the 0.8 dB for GH (p < 0.0001).
  
  
  CONCLUSIONS
  The novel GHr estimator is very different from the conventional GH estimator, has more solid foundations, and better statistical properties. Nevertheless, it is not always better than the GH estimator, in particular if no focal loss is present. Pattern-deviation maps obtained with GHr reduce systematic underestimation of glaucomatous damage.
authors.affiliation: Grupo de Investigación en Optometría, Departamento de Óptica, Facultad de Física, Universitat de València, C/Dr. Moliner 50. Burjassot, Valencia, 46100, Spain, ivan.marin@uv.es.
authors.forename: Iván
authors.initials: I
authors.lastname: Marín-Franch
authors.forename: William H
authors.initials: WH
authors.lastname: Swanson
authors.forename: Victor E
authors.initials: VE
authors.lastname: Malinovsky
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D018450:Disease Progression; D005260:Female; D005901:Glaucoma / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D012720:Severity of Illness Index; D014786:Vision Disorders / Q000175:diagnosis* / Q000503:physiopathology; D058609:Visual Field Tests / Q000379:methods*; D014794:Visual Fields