R Gall1, B Wick, H Bedell. 1. College of Optometry, University of Houston, Texas, USA.
Abstract
PURPOSE: 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.
PURPOSE: 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.