Association between interpupillary distance and fusional convergence-divergence amplitudes

PURPOSE: The purpose of the study was to evaluate the effect of individual differences in interpupillary distance (IPD) on convergence and divergence amplitudes measured at near and at distant fixation targets.
METHODS: Ninety-three healthy subjects were enrolled. Group 1 included subjects with smaller than normal IPD (mean IPD = 58.2±1.4; 27 subjects), Group 2 included those with larger than normal IPD (mean IPD = 69.5±1.6; 31 subjects), and Group 3 included those with normal IPD (mean IPD = 63.10±2.22; 35 subjects). Outcome measures were best corrected visual acuity, binocular vision level (TNO test), convergence, and divergence amplitudes at near and at distance.
RESULTS: There was no statistically significant difference between Group 1, 2, and 3 regarding age or clinical characteristics. The differences in gender distribution between Groups 2 and 3 and between Groups 1 and 2 were significant (Chi-square test, p=0.001 for both). There was no statistically significant difference between the groups in the values of near conver-gence amplitude, near divergence amplitude, and distant convergence amplitude. There was a statistically significant differ-ence between in mean distant divergence amplitude between Groups 2 and 3 (p=0.01).
CONCLUSION: Differences in IPD can affect an individual’s vergence amplitudes and binocular vision level. Especially, the in-dividuals with IPD larger than normal limits have the lowest mean values for all vergence amplitudes, while the normal IPD group had the highest.