Comparison of CA/C Ratio with Different Measuring Methods

Abstract

································································································································································································································Purpose: To compare the convergence accommodation to convergence (CA/C) ratios with varying prismatic powers and base among three clinical methods. Methods: 52 young adult subjects (mean age of 21.68±2.57 years, 32 males and 20 females) with normal binocular vision participated in this study. After measure diatance and near binocular function include phoria test and accomodation, accommodative response was measured using the open-field autorefractor (NVision K-5001, Shin-Nippon, Japan), the Streak Retinoscope (WEL18245, Welch Allyn, America) and the BCC (binocular crossed cylinder). While accommodative response was measuring, prismatic powers and base were also varied. CA/C ratios was calculated base on the accommodative response. Results: Accommodative response were high in the order of BCC, AR, and Nott method at all prismatic power and base. As the prismatic power was increased from the prismatic base of the BI to the BO, accommodative response was also gradually increased. The mean of the CA/C ratios in all prismatic powers and bases was higher in the order of BCC, AR, and Nott method. For persons with normal binocular function, the mean of the CA/C ratios measured by 6 Δ, BI was 0.095±0.012 D/Δ in BCC, 0.093±0.012 D/Δ in AR, 0.088±0.009 D/Δ in Nott method, respectively. The mean and standard deviation for 6 Δ, BI was the smallest in all methods and there was no statistically significant difference (F = 2.532, p = 0.085). Conclusions: When the CA/C ratios was measured by the Nott method, the most consistent result was obtained regardless of the prismatic power and the base.