THE RELATIONSHIP BETWEEN SPHERICAL EQUIVALENT REFRACTIVE ERRORS, AMPLITUDE OF ACCOMMODATION AND RELATIVE ACCOMMODATION IN YOUNG ADULTS

ABSTRACT

Background: Refractive error has been shown to be influenced by an interwoven interaction of genetic as well as environmental factors. It has been suggested that accommodation plays a huge role in refractive development and as such, there would be fundamental differences in the accommodative responses of emmetropes and ametropes. Purpose: To explore the possible associations between spherical equivalent of refractive errors, amplitude of accommodation and relative accommodation. Method: An observational, prospective cross-sectional study was carried out using at least 100 subjects between the ages of 18-35 years at The Optometry Clinic, Department of Optometry, University of Benin, Nigeria. Refractive error was measured using static retinoscopy and subjective refraction. Amplitude of accommodation was assessed by minus-lens to blur (AAMLB), push-up to blur (AAPUB) and modified push-up to blur methods. Relative accommodation was assessed by measuring the Negative Relative Accommodation (NRA) and Positive Relative Accommodation (PRA). The external adnexa of the subjects was examined using a penlight and handheld magnifier while an ophthalmoscope was used to examine the internal structures of the eye. Static retinoscopy and subjective refraction were carried out to ascertain the magnitude of the spherical equivalent refractive error. For this study, subjects with +/- 0.50DS were classified as emmetropes, while subjects with greater than or equal to +0.75DS and -0.75DS were considered as hyperopes and myopes respectively. A comprehensive case history was taken to ensure that the subjects fell within the required age range and to rule out any systemic condition. Data analysis: Data obtained was analyzed in the Statistical Package for Social Sciences, SPSS ver. 24.0 (SPSS Inc., Chicago, IL, USA). The measured variables were tested for normality using the Kolmogorov-Smirnov Z test. Comparison of amplitude of accommodation obtained by the minus-lens and push-up to blur techniques was done by analysis of variance (ANOVA). Contribution to Optometry: this study will help eye care practitioners to predict changes in relative accommodation with respect to refractive errors and this will possibly guide them in making clinical diagnosis of convergence and accommodative dysfunction. It will also help eye care practitioners to determine which of these methods (push-up to blur, minus-lens to blur or modified push-up to blur) would give a hypothetically more reliable measurement of amplitude of accommodation in young adults and as such guide them on the best techniques for measuring amplitude of accommodation.