comparison of gradient ac/a ratio with different deviation measurement techniques

purpose: to compare the effect of different deviation measurement techniques and different lens powers on gradient accommodative convergence to accommodation (ac/a) ratio. methods: we randomly selected 78 eligible students of different majors from zahedan university of medical sciences. following retinoscopy for refractive errors, alternate prism cover test, von graefe and maddox rod without additional lenses and with ±1, ±2 and ±3 d lenses were performed for measurement of deviation at near and determination of gradient ac/a ratio. data were analyzed using within subject factorial repeated measurement anova and correlation tests. results: mean ac/a ratio was 3.6, 3.7 and 4 prism diopter to diopter using alternate cover test, maddox rod and von graefe methods, respectively (p=0.2). the highest and lowest ac/a ratios were related to von graefe method with +3d and cover test with -1d lens power, respectively. only differences between ac/a ratios with -1 and +2 lenses as well as with -1 and +3d were significant (p<0.05). for all different deviation measurement methods, ac/a ratios with plus lenses were higher than minus lenses. conclusions: the type of deviation measurement method had no effect on ac/a ratio but selected lens power affected the results. we recommend using 2 or 3 diopter instead of 1 diopter lenses to avoid possible effects of depth of focus.