Clinical relevance: The vergence facility (VF) test is important in a complete optometric examination, but there is still controversy over which prismatic power combinations to use according to the patient age, especially in children.
Background: The aim of this work is to study the VF test using three different prismatic power combinations in four age groups, with a view to determine the best prismatic power for performing the test.
Methods: The VF of 122 healthy subjects was evaluated using three prismatic flippers with different powers: 8∆ base-in with 8∆ base-out (8BI/8BO∆), 3BI/12BO∆ and 5BI/15BO∆. The number of cycles per minute (cpm) was counted.
Results: The participants were divided into four age groups. The mean age of group 1 was 6.69 ± 0.65 years, that of group 2 was 9.36 ± 0.87 years, that of group 3 was 12.08 ± 0.79 years and that of group 4 was 28.67 ± 8.11 years. The mean cpm value in VF was higher for near vision than in distance vision. The lowest cpm values were observed in the youngest group (group 1) (far vision: 8BI/8BO∆: 2.32 cpm, 3BI/12BO∆: 2.68 cpm and 5BI/15BO∆: 1.59 cpm; near vision: 8/8∆: 6.59 cpm, 3BI/12BO∆: 7.77 cpm and 5BI/15BO∆: 5.27 cpm). The cpm values increased progressively with age, with group 4 achieving the highest cpm values (far vision: 8BI/8BO∆: 3.61 cpm, 3BI/12BO∆: 8.56 cpm and 5BI/15BO∆: 5.28 cpm; near vision: 8BI/8BO∆: 10.22 cpm, 3BI/12BO∆: 12.28 cpm and 5BI/15BO∆: 10.89 cpm).
Conclusions: VF increased with age. The youngest children achieved the lowest cpm values, which progressively increased until the highest cpm values were achieved in adults. The best results were found with 3BI/12BO∆ in all groups in near and far vision. Higher cpm values were achieved in near vision than in far vision with all flippers in all groups.
Keywords: Binocular vision; fusional vergences; prismatic flippers; prismatic power; vergence facility.