Changes in Accommodative and Vergence Responses When Viewing Through Near Addition Lenses

Purpose: Progressive addition lenses (PALs) have been shown to slow myopia progression. It has been proposed that PALs reduces the subject's lag of accommodation. In this study, we investigated the differences in accommodative response and near phoria in subjects with and without addition lenses. Methods: Fourteen subjects (7 emmetropic and 7 myopic) participated in the study.Monocular and binocular accommodative responses to a target at 40 cm were measured with and without +2 D addition lenses using a Canon R–1 optometer. Near phorias were measured with three methods: Maddox rod, Cover test, and Risley prism. Repeated measures ANOVA was used to determine the significance of the results. Results: No significant difference was found in accommodative response and near phoria between refractive error groups. The accommodative responses were significantly different between the two viewing conditions with and without the addition lens (p < 0.0001). For near phoria, the difference was also significant between the two viewing conditions (p < 0.0001). There was no difference between the three measurement methods. Under binocular viewing condition with the +2 D addition, the average accommodative responses were 2.74 ± 0.22 (S.D.) D for the emmetropic group and 2.71 ± 0.32 D for the myopic group. The near phoria shifted to exo when the subject viewed through the +2 D addition. For the emmetropic group, the average shifts were –6.00 ± 2.89 Pd (Maddox rod), –4.43 ± 1.24 Pd (Cover test), and –7.71 ± 4.27 Pd (Phoropter). For myopic group, the averageshifts were –5.86 ± 3.20 Pd (Maddox rod), –4.79 ± 1.91 Pd (Cover test), and –6.14 ± 3.34 Pd (Risley prism). Conclusions: When the subject viewed with the +2 D addition lens, the accommodative response showed a lead. At the same time, the subjects experienced large exo shifts increasing fusional convergence demand. Based on these results, we question whether PALs slow myopia progression by improving the accommodative response and speculate that inappropriately prescribed PALs may instead increase stress on the visual system leading to reduced visual performance at near.