Normative Value of Accommodative Convergence to Accommodation in Indian Population Measured by Heterophoria Method

Abstract

Abstract Introduction: Near response is a complex synkinesis required for a good binocular vision. accommodative convergence per diopter of accommodation (AC/A ratio) is a value of significance in this synkinetic movement. In addition, the value is used to classify and treat ocular movement abnormalities. The two commonly used methods for determining the AC/A ratio are Gradient Method and Heterophoria method. The normative data for Indian population by gradient method was described in two studies. However, the normative data for heterophoria method is lacking in Indian population. Objective: The purpose of this cross-sectional study is to generate the normative value for AC/A ratio for the Indian population by heterophoria method. One hundred healthy ophthalmologically normal adults with no presbyopia or refractive error were chosen consecutively among the attendants of patients visiting the center. Materials and Methods: After thorough ophthalmic evaluation, the participants were subjected to AC/A ratio calculation by heterophoria method using 6/9 fixation target and PMMA Prism bar. Results: One hundred healthy adults with no refractive error or ocular abnormality were selected with a mean age of 25.70 years (standard deviation [SD] = 4.92) and equal gender distribution. The mean Inter Pupillary Distance (IPD) was found to be 62.88 mm with a SD of 3.91 mm. The average phoria at distance was 1.82 prism diopters (SD = 2.03pd) of exophoria and for near at 33 cm was 4.20pd (SD = 1.92pd). The mean AC/A ratio by heterophoria method was found to be 5.49PD/D with an SD of 0.54PD/D. The highest being 6.90PD/D and the lowest being 4.27PD/D with no statistically significant difference between genders. Conclusion and Relevance: According to the previous studies, the normative data arrived is lesser than the value reached in the current study for similar population groups when considering both methodologies of testing. This variation between the gradient method and heterophoria method accounted for by the involvement of proximal convergence during the heterophoria method.