title: Vergence facility and target type.
abstract: OBJECTIVE
  Target suppression-cues are considered important for valid binocular accommodative facility response. However, there are no comparable recommendations concerning the effect of target type on vergence facility response.
  
  
  METHODS
  Ten subjects ages 16 to 19 years of either sex and any race were pooled, based on the lack of any asthenopic symptoms determined by a verbal interview with the investigator. Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, and near-normal phorias. Vergence facility response was tested over a 1-min period using 8 delta base-in (BI) and 20 delta base-out (BO) loose prisms at near (0.4 M) for 3 different vertically oriented targets: 6/9 (20/30) Snellen letters, back-illuminated anaglyphic shapes, and modified Wirt circles.
  
  
  RESULTS
  For the group, the mean facility response was similar among the target types [Snellen letters: 9.5 cycles per minute (cpm) +/- 5.6; anaglyphic shapes: 9.0 cpm +/- 6.3; and Wirt circles: 9.4 cpm +/- 4.5]. Group response-differences were not significantly different by one-way ANOVA polynomial regression testing at the 0.05 level (F-value = 0.03, p = 0.97, df = 2).
  
  
  CONCLUSIONS
  Whereas a binocular accommodative facility target must have additional vectographic or anaglyphic suppression-cues, vergence facility testing may incorporate a simple and available vertical row of 6/9 (20/30) Snellen letters, which provide inherent fusional suppression-cues, for a valid binocular response.
authors.affiliation: College of Optometry, University of Houston, Texas, USA.
authors.forename: R
authors.initials: R
authors.lastname: Gall
authors.forename: B
authors.initials: B
authors.lastname: Wick
authors.forename: H
authors.initials: H
authors.lastname: Bedell
mesh_terms: D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D003290:Convergence, Ocular / Q000502:physiology*; D003463:Cues; D005260:Female; D006801:Humans; D008297:Male; D012044:Regression Analysis; D013285:Strabismus / Q000503:physiopathology; D014787:Vision Tests; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology