VERGENCE FACILITY AND TARGET TYPE

Purpose. Target suppression-cues are considered important for valid bi nocular accommodative facility response. However, there are no compara ble recommendations concerning the effect of target type on vergence f acility response. Methods. Ten subjects ages 16 to 19 years of either sex and any race were pooled, based on the lack of any asthenopic symp toms 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 facil ity response was tested over a 1-min period using 8 Delta base-in (BI) and 20 Delta base-out (EO) loose prisms at near (0.4 M) for 3 differe nt vertically oriented targets: 6/9 (20/30) Snellen letters, back-illu minated 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 shap es: 9.0 cpm +/- 6.3; and Wirt circles: 9.4 cpm +/- 4.5]. Group respons e-differences were not significantly different by one-way ANOVA polyno mial regression testing at the 0.05 level (F-value = 0.03, p = 0.97, d f = 2). Conclusions. Whereas a binocular accommodative facility target must have additional vectographic or anaglyphic suppression-cues, ver gence facility testing may incorporate a simple and available vertical row of 6/9 (20/30) Snellen letters, which provide inherent fusional s uppression-cues, for a valid binocular response.