The Effect Of Induced Aniseikonia On Stereopsis And Accommodation

ObjectiveTo study the effects of induced aniseikonia by size lenses on stereopsis, positive and negative relative accommodation, and accommodative response. To determine at which level does the induced aniseikonia have an effect on stereopsis and accommodation significantly, and to provide a reference for clinical test and diagnosis of aniseikonia.MethodsProspective randomized block design was used in this study.Forty-five observers, which was consist of12males and33females, aging from17to28, were selected randomly. The average spherical equivalent of these observers is-2.52±1.92D. Then they were divided into three groups by degree of ametropia:the emetropia group(+0.75≤SE<-0.50), including8persons; low myopia group (-0.50≤SE<-3.00), including19persons; median myopia group (-3.00≤SE<-6.00), including18persoins. All observers, before participating in the study, gave their informed consent in accordance with the Declaration of Helsinki.Two percent,3%,5%,8%,10%aniseikonia was induced by placing size lenses in front of the right eyes of the observers. Then the stereopsis was tested utilizing the Stereo-Fly Test and Digital Stereoscopic Test Charts(DSTC) under normal binocular vision and induced aniseikonia. The effect of induced aniseikonia on stereopsis then was analyzed based on the data collected.Thirty-five observers, aging from18to27, were selected randomly. The average spherical equivalent of these observers is (-2.31±1.58D). All observers, before participating in the study, gave their informed consent in accordance with the Declaration of Helsinki.The negative relative accommodation, accommodative response and positive relative accommodation were tested under normal condition and after inducing different degree of aniseikonia(2%,3%,5%and8%) in the right eye.SPSS version13.0statistics software was used. The data was analyzed by Friedman’s M test, Spearman rank correlation, Wilcoxon rank sum test an, Kruskal-Wallis H test, randomized block design analysis of variance and student-newman-keuls test.Results1.Stereopsis was significantly affected by induced aniseikonia[FLY(x2=210.113, P<0.01), DSTC(x2=162.237,P<0.01)]; And there is a positive correlation between the degree of the induced aniseikonia and decline of stereoacuity. Stereopsis will be affected by only2%aniseikonia, and will drop drastically when aniseikonia is more than5%.2.There was not significant difference between male and female, in the study of the effects of induced aniseikonia on stereopsis[FLYT(Z=-1.870, P=0.061>0.05), DSTC(Z=-1.600, P=0.110>0.05)].3.There was significant difference between different ametropia groups when tested stereopsis with FLYT, at2%and3%aniseikonia, in the study of the effects of induced aniseikonia on stereopsis.4.There was significant difference between normal(0%) condition and different level of induced aniseikonia, for the measurement of NRA, AR and PRA [NRA(F=4.69,P=0.001),AR(F=4.89,P=0.001)and PRA(F=32.90, P<0.01)]. When the induced aniseikonia was2%, PRA was significantly declined compare with0%condition; when the induced aniseikonia was5%,NRA and AR began to incress significantly.Conclusion1. When induced aniseikonia reach5%, stereopsis would be affected significantly. However the visual system will maintain the function of stereopsis at median level.2. Accommodation would be affected by5%induced aniseikonia, too.3. There was not difference between male and female in the test of stereopsis.4. Ametropia would not have profound effect on stereopsis, at least in the normal people and people who only have median myopia.5. Aniseikonia should be considered and tested more frequently in clinical practice. And aniseikonia should be controlled under5%,when prescribing a lenses prescription.