Analysis of the vergence facility test using different prismatic dioptric powers

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.

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.

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.

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).

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.