Effects of Refractive Errors on Visual Functional Magnetic Resonance Imaging

Abstract

Objective: The purpose of our study is to evaluate the effects of refractive errors on functional magnetic resonance imaging (fMRI) of visual cortex. Methods and Materials: We performed a prospective study. The study included 13 patients with refractive error (group 1) and 30 emetropic volunteers (group 2). Group 2 was also subgrouped as 20-32 years old (young) and over 45 years old (old) to analyse accommodation effect. fMRI data were acquired with a block design paradigm with 3 Tesla MR system. In both groups, images initially were acquired in normal refractive state. fMRI was performed again in both groups during refractive error. Activation areas on visual cortex were calculated as square centimeter. Total activated areas on visual cortex was compared between normal refractive state and induced/ uncorrected refractive error. Results: In group 1, activation areas of visual cortex during uncorrected refractive error revealed significantly decrease compared with activation areas during corrected refractive error (p=0.001). In group 2, induced myopia resulted significant decrease in activation areas compared with normal refractive state. Decrease in activation areas were significant both in 2 and 4 diopters (D) of myopia compared with normal refractive state (p=0.003, p<0.001 respectively). Both in young and old subgroup, activation areas were significantly decreased during induced myopia. We revealed no difference between young and old subgroups. Conclusion: The refractive errors have a clear effect on fMRI of visual cortex. Thus, to achieve accurate results they should be corrected in patients that included in the visual fMRI study.