Investigation Of The AC/A Ratio Measured By Phoria Method?Gradient Method And Synoptophore Method

ObjectiveAC/A ratio is widely used in the clinical work of ophthalmology and optometry.There are many measurements to measure AC/A ratio and the commonly methods in the clinic are Phoria method,Gradient method and Synoptophore method,however,there's only one normal range of AC/A ratio for reference.In order to analyze whether the normal range of AC/A ratio measured by the three methods are the same or not.This study use Phoria method,Gradient method and Synoptophore method which is different additional accommodative stimulus to measure AC/A ratio.The findings in this study could provide a more accurate range of AC/A ratio for clinical application.Methods(1)Subjects: Selecting 57 students of Tianjin Medical University who are between 18~25 years old,including 23 males and 34 females.Excluding the volunteers with history of illness or eye disease.(2)Refractive examination: All volunteers are refractive corrected by computer refractormeter and comprehensive refractormeter.The monocular best corrected visual acuity and binocular best corrected visual acuity are both ? 0.9,effective spherical degree are between 0.00 DS and-5.00 DS,cylindrical degree are between 0DC and-1.00 DC,anisometropia are between 0DS and 1.00 DS.(3)Accommodation function examination and evaluation: Using comprehensive refractormeter with near vision chart,flip with near vision card to exam all subjects' monocular/binocular accommodative amplitude ? positive/negative related accommodation?accommodative sensitivity to evaluate their accommodative ability.(4)Convergence and divergence function examination and evaluation: Using comprehensive refractor with rotary prism and distance vision chart?near vision chart to measure positive and negative fusional convergence and divergence to evaluate fusional function of binocular visual function.(5)Stereopsis examination and evaluation: Titmus stereogram with polarized glasses was used to exam stereoscopic vision sensitivity to evaluate their stereopsis.(6)To measure AC/A ratio: Phoria method,Gradient method and Synoptophore method with different accommodative stimulus were used to measure subjects' AC/A ratio to evaluate whether the results were the same or not.Results(1)All the subjects' function of the eye are within the normal range and at a higher level including monocular/binocular accommodative amplitude ?positive/negative related accommodation?accommodative sensitivity?positive and negative fusional convergence and divergence and stereoscopic vision sensitivity.(2)Different results are measured by different methods.The AC/A ratio measured by Phoria method is higher than the AC/A ratio measured by Gradient method,and the AC/A ratio measured by Gradient method is higher than the AC/A ratio measured by Synoptophore method.The AC/A ratios measured by different accommodative stimulus added in the same method are not same.(3)The AC/A ratio measured by Phoria method with staring distance of 40 cm is higher than the ratio measured by Phoria method with staring distance of 33 cm.(4)In the Gradient method,there were no difference between the ratio measured by different accommodative stimulus lens while the results measured by plus lens are higher than with minus lens.(5)Compared Phoria method and Gradient method with the same staring distance,the results of Phoria method are higher than Gradient method.(6)There were no difference between different accommodative stimulus lens with Synoptophore method.And results in Synoptophore method with the same accommodative stimulus lens compared with Phoria method were no difference.Conclusion(1)Phoria method is influenced by the proximal or psychic convergence,so the AC/A ratio was larger than Gradient method.(2)In the Phoria method,while the target was closer to the subject the AC/A ratio measured was smaller for influenced by proximal or psychic convergence and the lag of accommodation.(3)In the Gradient method,the AC/A ratio measured for adding minus lens would cause more lag of accommodation,and the higher the degree minus lens added the greater the lag of accommodation caused,which resulting in smaller AC/A ratio.(4)The results measured by Synoptophore method were same to Gradient method for it was less influenced by the accommodation and convergence for the subjects were at a distant state.(5)The normal range of AC/A ratio is 3~5?/D clinically.However,this study indicate that the results are different measured with different methods while the ratio measured by the Gradient method is most close to the reference on clinic.the Gradient method with plus stimulus lens would cause less lag of accommodation and the subject would be more comfortable for they use less accommodation during the examination.Therefore,it is suggested that using Gradient method with plus stimulus lens as the method of AC/A ratio could be appropriately,and when AC/A ratio was measured clinically,results should be compared with the normal range of AC / A ratio measured by the same method in order to assess the visual status of the subject more accurately.