title: Clinical classification of glaucomatous visual field loss by frequency doubling perimetry.
abstract: OBJECTIVE
  To determine whether the frequency doubling perimeter (FDP) can grade glaucomatous visual function loss in a clinically relevant manner. Sinusoidal gratings < 1 cpd that undergo counterphase flicker > 15 Hz appear to have twice as many bands of light, a phenomenon referred to as the "frequency doubling illusion." Evidence suggests that this psychophysical effect is mediated in part by large-diameter ganglion cells, which are reported to be lost early in the glaucomatous disease process. A portable, commercially available FDP has already demonstrated high diagnostic potential for glaucoma screening.
  
  
  METHODS
  Sixty-four eyes of 42 glaucomatous patients and 22 eyes of 14 normal subjects were evaluated by means of both frequency doubling perimetry and Humphrey perimetry. A clinical scoring algorithm modeled after the Hodapp-Parrish-Anderson criteria for scoring Humphrey visual field defects was derived for the FDP at the halfway point of the study, and all participants were reassessed with this algorithm upon its completion.
  
  
  RESULTS
  FDP mean and pattern deviation showed strong linear correlations with Humphrey 30-2 mean deviation (R = 0.75; P < .0001) and corrected pattern standard deviation values (R = 0.64; P < .0001). Despite this, neither global index could consistently categorize the graded glaucomatous visual fields in a manner consistent with the Hodapp-Parrish-Anderson criteria. The new FDP scoring algorithm did provide good segregation (73% precise parity, 93% parity within one Humphrey grade).
  
  
  CONCLUSIONS
  Sixteen-zone frequency doubling perimetry can segregate glaucomatous visual field loss into pathologic categories approximating those obtained with Humphrey 30-2 perimetry by means of a formula modeled after the Hodapp-Parrish-Anderson criteria.
authors.affiliation: South Texas Ocular Imaging Center, University of Texas Health Science Center, San Antonio, USA. sponsel@uthscsa.edu
authors.forename: W E
authors.initials: WE
authors.lastname: Sponsel
authors.forename: S
authors.initials: S
authors.lastname: Arango
authors.forename: Y
authors.initials: Y
authors.lastname: Trigo
authors.forename: J
authors.initials: J
authors.lastname: Mensah
mesh_terms: D000465:Algorithms; D005901:Glaucoma / Q000145:classification* / Q000473:pathology; D006801:Humans; D008875:Middle Aged; D014786:Vision Disorders / Q000145:classification* / Q000473:pathology; D014792:Visual Acuity; D058609:Visual Field Tests / Q000379:methods*; D014794:Visual Fields