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Scott A Read, Alex R Wade, Patrick Johnston, David Alonso-Caneiro, Stephen Vincent, Samaneh Delshad; Changes in visual cortical activity during image blur in myopes and emmetropes. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1920.
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© ARVO (1962-2015); The Authors (2016-present)
The ocular response to blur is one of the primary factors guiding the eye’s normal growth and the development of myopia. In this study we examined the influence of myopic optical blur and simulated blur upon functional activity in the primary visual cortex (V1) of young adult myopes and emmetropes, using functional MRI (fMRI).
Twenty young adults (mean ± SD age 23 ± 3.6 years) had fMRI scans on a 3.0 T MRI scanner, to determine changes in blood oxygen level dependent (BOLD) responses to visual stimuli with optimal focus, simulated +1.50 D myopic blur, and optical +1.50 D myopic blur. Ten subjects had (corrected) myopic refractive errors (mean spherical equivalent refraction -2.92 ± 1.20 D) and ten were emmetropic (mean -0.05 ± 0.19 D). Scanning was undertaken while participants viewed flickering black and white checkerboards (9° x 9° visual angle) of two different spatial frequencies (0.24 CPD and 4.8 CPD) and two different contrasts (50% and 90%) presented in a block design (21s stimulation, 15s rest). fMRI data analysis was performed with FEAT software (FMRI Expert Analysis Tool), Version 6.00.
Stimulus spatial frequency, stimulus contrast and blur condition all affected BOLD responses in V1 (p < 0.05) (Figure 1). Compared to optimum focus (mean BOLD signal change 0.56 % ± 0.28), both optical (0.31 ± 0.21) and simulated blur (0.33 ± 0.27) caused a significant attenuation of the BOLD signal in V1. A significant blur condition by refractive group interaction (p = 0.014) was observed, with a significant reduction in BOLD signal with blur found for myopic subjects, but not for emmetropic subjects (Figure 1A). BOLD changes in response to blur were only significant at the higher spatial frequency (p < 0.01) (Figure 1B).
Neuronal activity in V1 appears to be significantly attenuated by both optical and simulated image blur. As expected, these effects are most prominent for high spatial frequency stimuli. Surprisingly, the attenuation of neural activity was most pronounced in subjects with myopia. Our findings suggest that there are differences in the visual cortical response to image blur associated with the presence of refractive error.
This is a 2020 ARVO Annual Meeting abstract.
Figure 1: Changes in BOLD signal in primary visual cortex associated with blur in myopes and emmetropes (A), with different spatial frequency visual stimuli (B) and contrasts (C). *indicates significant difference (p < 0.05).
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