Correlation of the Interactions between Accommodation and Vergence in Different Refraction Groups

Abstract

Objective: To investigate stimulus and response accommodative convergence to accommodation (AC/A) and stimulus and response convergence accommodation to convergence (CA/C ) ratios between different refractive groups and heterophoria groups. The correlations between the four parameters were also investigated. Methods: In this case control study, 20 emmetropes (EMM) and 27 early-onset myopes (EOM) aged 9 to 14 years participated in this descriptive study from October 2016 to January 2017 at Eye Hospital, Wenzhou Medical University. The accommodative response and phoria through five accommodative stimuli and 6 convergence stimuli levels were measured at 25 cm under binocular viewing conditions with a Grand Seiko WAM-5500 autorefractor and a modified Thorington card. Data were analyzed using t-tests and Pearson correlation analysis. Results: Response AC/A ratios of the EMM and the EOM groups were 4.07±1.47 Δ/D and 5.13±1.95 Δ/D, respectively; the difference between the two groups was significant (t=2.12, P=0.04). A significant linear correlation was found between the stimulus and response AC/A ratios in both the EMM and EOM groups (r=0.903, P<0.001; r=0.880, P<0.001). A negative correlation was found between the response AC/A and CA/C ratios in the EMM group (r=-0.450, P=0.04), while no correlation was found between these two ratios in the EOM group (r=-0.367, P=0.06). Conclusions: EOM has a higher response AC/A ratio compared to EMM. The negative correlation between AC/A and CA/C was only found between the response ratios of EMM, indicating that the AC/A ratio cannot provide a true representation of both cross-link interactions. Key words: accommodative convergence to accommodation ratio; convergence accommodation to convergence ratio; accommodative vergence; vergence accommodation