Abstract
Myopia is a type of refractive error that blurs retinal image and in turn can change neural signals transferred from retina to visual cortex. The purpose of this study was to evaluate the effect of induced myopia on occipital visual cortex activity by fMRI results. BOLD fMRI was performed in 13 emmetropic volunteers (refractive error, <±0.50D) with normal visual acuity, good binocular vision, and no history of neurologic illness. Visual stimulus was counterphasing vertical luminance sinusoidal grating with spatiotemporal frequency of 1.84 cycles per degree/8 Hz and contrast of 60%. The functional images were acquired in block design, during normal refractive state and induced myopia produced by convex noncoating plastic lenses of +1D, +3D, +5D, by using an EPI gradient-echo sequence in a 1.5T MR imaging scanner. fMRI data were processed by using FSL software. fMRI responses to visual stimuli demonstrated that percentage of BOLD signal intensity change and number of activated voxels within occipital visual cortex were reduced remarkably in induced myopic states of 1D, 3D, and 5D in comparison with normal refractive state; the results did not show a significant and regular decreasing trend in number of activated voxels and BOLD signal intensity change in these 3 different values of induced myopia. The findings suggest that induced myopia has a considerable effect on visual cortex activity, because myopia induced by lens of +1D is sufficient to change fMRI results significantly. Accordingly, it is essential to correct myopia before visual fMRI studies, even if it is at low levels.
Highlights
AND PURPOSE: Myopia is a type of refractive error that blurs retinal image and in turn can change neural signals transferred from retina to visual cortex
The findings suggest that induced myopia has a considerable effect on visual cortex activity, because myopia induced by lens of ϩ1D is sufficient to change fMRI results significantly
ABBREVIATIONS: AC/PC ϭ anterior/posterior commissure; ANOVA ϭ analysis of variance; BOLD ϭ blood oxygenation level– dependent; EPI ϭ echo-planar imaging; fMRI ϭ functional MR imaging; FSL ϭ Functional MR Imaging Software Library; VEP ϭ visual-evoked potential fMRI is a powerful, noninvasive neuroimaging technique that allows studying many different aspects of the human visual system, because of the robust and reliable BOLD responses elicited by visual stimuli. fMRI has been widely used for clinical assessments of visual impairments and neurologic disorders, and in physiologic studies, where it is useful for delineation of visual cortical area borders and for examining the functional specialization of these areas
Summary
The purpose of this study was to evaluate the effect of induced myopia on occipital visual cortex activity by fMRI results
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