Abstract
BackgroundThe latency and amplitude of visual evoked cortical responses are known to be affected by refractive states, suggesting that they may be used as an objective index of refractive errors. In order to establish an easy and reliable method for this purpose, we herein examined the effects of refractive errors on visual evoked magnetic fields (VEFs).MethodsBinocular VEFs following the presentation of a simple grating of 0.16 cd/m2 in the lower visual field were recorded in 12 healthy volunteers and compared among four refractive states: 0D, +1D, +2D, and +4D, by using plus lenses.ResultsThe low-luminance visual stimulus evoked a main MEG response at approximately 120 ms (M100) that reversed its polarity between the upper and lower visual field stimulations and originated from the occipital midline area. When refractive errors were induced by plus lenses, the latency of M100 increased, while its amplitude decreased with an increase in power of the lens. Differences from the control condition (+0D) were significant for all three lenses examined. The results of dipole analyses showed that evoked fields for the control (+0D) condition were explainable by one dipole in the primary visual cortex (V1), while other sources, presumably in V3 or V6, slightly contributed to shape M100 for the +2D or +4D condition.ConclusionsThe present results showed that the latency and amplitude of M100 are both useful indicators for assessing refractive states. The contribution of neural sources other than V1 to M100 was modest under the 0D and +1D conditions. By considering the nature of the activity of M100 including its high sensitivity to a spatial frequency and lower visual field dominance, a simple low-luminance grating stimulus at an optimal spatial frequency in the lower visual field appears appropriate for obtaining data on high S/N ratios and reducing the load on subjects.
Highlights
The latency and amplitude of visual evoked cortical responses are known to be affected by refractive states, suggesting that they may be used as an objective index of refractive errors
In order to establish an easy and reliable method to objectively assess the eyes of a subject, we conducted a series of experiments using visual evoked potential (VEP) and visual evoked magnetic field (VEF)
Generator of M100 The field distribution in isocontour maps, polarity reversal between the upper and lower visual fields, and dipole location around the calcarine fissure indicate that the main generator of M100 was the primary visual cortex (V1), which is consistent with previous findings observed using VEP [16] and VEF [17]
Summary
The latency and amplitude of visual evoked cortical responses are known to be affected by refractive states, suggesting that they may be used as an objective index of refractive errors. In order to establish an easy and reliable method for this purpose, we examined the effects of refractive errors on visual evoked magnetic fields (VEFs). VEPs are affected by non-pathological factors such as age, sex, and refractive states as well as visual stimulus parameters such as spatial frequency, contrast, and luminance. In order to establish an easy and reliable method to objectively assess the eyes of a subject, we conducted a series of experiments using VEPs and VEFs. We described one of these experiments using transient VEFs. two fMRI studies previously demonstrated that induced myopia reduced visual evoked cortical activity in Brodmann’a areas 17 and 18 [11] or in V1 and Suzuki et al BMC Ophthalmology (2015) 15:162
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