The effect of induced fusional vergence on stereopsis

Context: Time taken to complete the task with induced fusional vergence. Aims: To identify the time taken to complete the task with and without fusional demand with different object sizes and contrast levels. Settings and Design: Prospective cross-sectional study. Subjects and Methods: In this study, we included the patient between the age of 18 and 30 years. All the patients underwent a complete eye examination. Heterophoria were calculated by using the prism bar cover test. For each participant, prism power equivalent to the blur point of base-in (BI) and base-out (BO) fusional vergence at 40 cm was divided and placed in front of both eyes. At 0, 3, 6, 9, and 12 min after prism introduction, the stereo acuity was measured. Time taken to complete the task was calculated by asking the patient to identify the difference between the two images in both modes of gameplay with and without BI and BO fusional vergence using 4 different contrast level and 3 target size. Statistical Analysis Used: The data were analyzed by using SPSS statistical software version 20. Wilcoxon signed-rank test and one-way ANOVA test with post hoc analysis were performed to see comparison between multiple groups. Results: A total of 20 patients with a mean age of 20.70 ± 3.52 participated in the study. In experiment 1, the stereoacuity was reduced immediately after prism introduction and slowly it got adapted after 6 min and came to the baseline at 12 min. For experiment 2, after the 12 min of adaptation with BI and BO prism is showing the similar results as normal mode of game play. Conclusions: The stereoacuity can be regained to baseline after 9 min for BI and 12 min for BO prism. Stereoacuity can be achieved back to the baseline without the orthophoria also.