Evaluating Stereoacuity With 3D Shutter Glasses Technology

Stereopsis is the measurement of the ability to estimate distance precisely.Moreover,it is an important index for evaluating binocular vision in ophthalmology.Stereopsis is quantified as the minimum geometric disparity that elicits the perception of depth termed stereoacuity.The smaller the detectable parallax is,the better will be the stereoacuity.Howard-Dolman test was a traditional method,however,it is seldom used in a clinical setting at present.The majority of measurements are performed using polarization technology or red and green glasses.Although the instruments were used simply,the problem with relatively poor accuracy,large error,and limited measuring range still existed.We established a stereoacuity measurement system using 3D shutter glasses technology and carried out the following three parts work:(1)Designing different test targets in order to assess the effects of different factors on stereoacuity.We also applied two methods to evaluate those factors: the fixed distance test and the variable distance test.The aim of our study was to investigate the effect of different target shapes and sizes on stereoacuity.(2)Exploring the variation in the stereoacuity threshold under different symbols and background contrasts,evaluate the tolerance range of an acceptable result,and subsequently,judge whether the contrast is an essential influence factor in normal 3D computer displays.(3)Exploring whether the ambient luminance affects the result of computer-aided stereoacuity tests.A total of 30 subjects,aged 20–28 years,were recruited.The equipment including a 3D laptop(ASUS G750Y47JX)with an NVidia 3D Vision 2 wireless glasses kit,laser rangefinder,color calibration instrument,screen luminance meter and photometer.A program written in C# produced all test targets.The research including(1)36 sets of test patterns were designed in the fixed distance test system set at 4.1 m,which were composed of three symbol types(tumbling "E",tumbling "C",and "□")containing crossed and uncrossed disparity,with each having six sizes,corresponding to 0.5,0.4,0.3,0.2,0.1,and 0 logMAR visual acuities.Six test pattern sets,composed of three types of crossed and uncrossed symbols,were drawn and used to test the subjects in the variable distance test system.(2)The variable distance test system was used for measuring the stereoacuity of 19 pages,with their respective grayscale contrast being 100%,90%,80%,70%,60%,50%,40%,30%,24%,20%,18%,16%,14%,12%,10%,8%,6%,4%,and 2% while the symbols were dimmer than the background.(3)The ambient luminance was set at no greater than 3 lux,approximately 150 lux,approximately 800 lux and approximately 10,000 respectively,and the stereoacuity was tested with the variable distance test system.All data were processed using PASW Statistic 18.0.Results:(1)Using the Kruskal-Wallis test,no significant difference was found among the 36 groups(Chi-square=29.844,P=0.715)with the fixed distance test system.These results showed that stereoacuity was consistent among the study population,regardless of the size of the symbols(ranging from 0.5 to 0 logMAR),the symbol shape("C","E",or "□"),and the types of disparity(either crossed or uncrossed).The shape of the targets and the types of disparity were not significant factors affecting stereoacuity while measured with the variable distance test system.(2)One-way ANOVA test resulted in significant differences among all 19 different grayscale contrast groups(F = 39.750,P < 0.001).Then,the Bonferroni test was used for evaluating the difference between groups,and no significant difference was observed among the first 12 groups(grayscale contrast 100%–16%,actual contrast 99.8%-36.4%).(3)One-way ANOVA test exhibited no significant difference among the four different ambient luminance groups(F = 0.773,P = 0.512).Evaluating stereoacuity with 3D shutter glasses technology was convenient and effective.Changes in target shape and size and disparity types had no significant effect on stereoacuity.The contrast of images and ambient luminance are not critical factors to stereoacuity under normal circumstances.The 3D laptop stereoacuity test system is portable,adaptive,and versatile,and thus valuable in research and clinical practice.