title: Effects of refractive errors on visual evoked magnetic fields.
abstract: BACKGROUND
  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 herein examined the effects of refractive errors on visual evoked magnetic fields (VEFs).
  
  
  METHODS
  Binocular VEFs following the presentation of a simple grating of 0.16 cd/m(2) 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: R&D Department, Tokai Optical Co., Ltd, Okazaki, 444-2192, Japan. ma-suzuki@tokaiopt.co.jp.
authors.forename: Masaya
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: R&D Department, Tokai Optical Co., Ltd, Okazaki, 444-2192, Japan. n.mizpyon@gmail.com.
authors.forename: Mizuki
authors.initials: M
authors.lastname: Nagae
authors.affiliation: R&D Department, Tokai Optical Co., Ltd, Okazaki, 444-2192, Japan. y.nagata.chibiko@gmail.com.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Nagata
authors.affiliation: R&D Department, Tokai Optical Co., Ltd, Okazaki, 444-2192, Japan. n-kumagai@tokaiopt.co.jp.
authors.forename: Naoya
authors.initials: N
authors.lastname: Kumagai
authors.affiliation: Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan. inui@nips.ac.jp.
authors.forename: Koji
authors.initials: K
authors.lastname: Inui
authors.affiliation: Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan. kakigi@nips.ac.jp.
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Kakigi
mesh_terms: D000328:Adult; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D060526:Magnetic Fields; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D012030:Refractive Errors / Q000503:physiopathology*; D014793:Visual Cortex / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology; D055815:Young Adult