The effects of myopic anisometropia on binocular vision function

Abstract

Background Nomal binocular vision is achieved through accommodation and vergence.Anisometropia is associated with abnormal visual development,but its impact on accommodation and vergence is unknown.This study is helpful to make a reaonable correction plan for anisometropia.Objective This clinical study was to examine the binocular vision function in myopic anisometropia and evaluate the influence of myopic anisometropia on binocular vision function.Methods Seventy subjects with myopic anisometropia ≥ 1.0 D were recruited in Tianjin Eye Hospital and Tianjin Vocational Institute from 2006 to 2009.The subjects were assigned to the low anisometropia group with the 1.0 D ≤ spherical equivalent difference ＜ 2.5 D and the moderate and high anisometropia group with spherical equivalent difference ≥2.5D,and other 35 individuals with spherical equivalent difference ＜ 1.0 D were enrolled as the without anisometropia group.Binocular vision function parameters were examined in all the individuals,including comprehensive refractometer to check the diopter,Worth 4 dot to examine the binocular vision function,different distance of vertical fusional amplitudes,accommodative convergence/accommodation (AC/A) and stereoscopic vision.Written informed consent was obtained from each subject prior to the study.Results After anisometropia was completely corrected,the normal rate of Worth 4 dot examination was 94.3％,80.0％ and 60.0％ in the without anisometropia group,low anisometropia group,moderate and high anisometropia group,respectively,showing a statistical difference among groups (x2 =12.137,P＜0.05),and the normal rate of 4 dot was less,and that of 5 dot was higher in the moderate and high anisometropia group compared with the without anisometropia group and low anisometropia group (P＜0.05).No significant difference was found in the normal rate for phoria of distance among the three groups (x2 =4.489,P=0.344).The normal rate for near phoria of distance was 65.7％,42.9％ and 37.1％ in the without anisometropia group,low anisometropia group,moderate and high anisometropia group,respectively,with significant difference among them (x2 =6.045,P＜0.05).The normal rate of stereopsis was 91.4％,77.1％ and 54.3％ in the without anisometropia group,low anisometropia group,moderate and high anisometropia group,respectively,which was statistically different among groups (x2 =12.863,P =0.002),and that in the moderate and high anisometropia group was significant declined in comparison with the without anisometropia group (x2 =12.208,P ＜ 0.05).The difference of distance phoria,AC/A,negative relative accommodation (NRA),positive relative accommodation (PRA),accommodation amplitude and binocular accommodative lag were statistically different among groups (P＞0.05).Conclusions The normal rate of the stereopsis,Worth 4 dot and the phoria of near distance are decreased with the increase of anisometropia,but other ocular motor parameters are normal in anisometropic subject. Key words: Anisometropia; Myopia; Binocular vision