Effect of heterophoria on binocular accommodation response and vergence adaptation of adult with myopia

Abstract

Objective To study the effects of heterophoria type on binocular accommodation response and vergence adaptation of adult with myopia and to explore the related fact between heterophoria and the development of myopia.Methods Clinical case control study.There were 116 voluntary undergraduate or postgraduate with myopia from Tianjin Medical University investigated during September to November 2013.Participants were assigned to three groups according to near phorias (NP),including exophoria group (EXO) 42 participants (NP＜-6△),esophoria group (ESO) 26 participants (NP＞0△),normal phoria group (N) 48 participants (-6△≤NP≤0△).They were continuous to read vedio display terminal (VDT) at 40cm for 20 minutes.Operations including subjective refraction,distance (5m) and near (40cm) horizontal heterophoria,AC/A value,monocular (MA) and binocular (BA) accommodation response using Shin-Nippon WR-5100K open vision automatic infrared refractometer were performed before and after reading.Results The results demonstrated that the difference of MA and BA of the three groups had statistically significant difference.EXO group:BA＞MA (t 9.264,P ＜0.001); N group:BA＞MA (t =840,P ＜0.001); ESO group:MA＞BA (t-6.064,P ＜0.001).The vergence adaptation of three groups had statistically significant difference (x2=4.026,P ＜0.001).EXO group showed convergence adaptation (less exophoria); ESO group and N group showed divergence adaptation (less esophoria in ESO group and more exophoria in N group).Conclusions The heterophoria type has effects on binocular accommodation response by vergence accommodation.The different types of heterophoria show vergence adaption with different direction in the effect of varying fusional vergence demands.There is a relationship between the esophoria with higher lag of binocular accommodation and the development of myopia. Key words: Heterophoria; Vergence adaptation; Accommodation response