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Computational analysis of thresholds for magnetophosphenes
1Department of Computer Science and Engineering, Nagoya Institute of Technology, Nagoya, Japan. laakso.ilkka@nitech.ac.jp
Physics in Medicine and Biology
|September 14, 2012
Summary
This study computationally models magnetophosphenes, estimating retinal threshold current density for low-frequency magnetic fields. Current limits for occupational exposure may not be sufficiently conservative for preventing visual disturbances.
Area of Science:
- Biophysics
- Neuroscience
- Electromagnetism
Background:
- International guidelines set exposure limits for low-frequency electric and magnetic fields to prevent magnetophosphenes.
- Magnetophosphenes are visual sensations caused by magnetically induced electric fields on the retina.
- Existing methods lack a straightforward way to determine retinal thresholds from magnetic flux density measurements.
Purpose of the Study:
- To computationally reproduce a magnetophosphene generation experiment.
- To determine the induced electric field and current density in the retina using finite-element analysis.
- To estimate the macroscopic retinal threshold current density for magnetophosphenes.
Main Methods:
- Computational reproduction of a previous experimental setup involving magnetic field exposure.
- Finite-element method (FEM) applied to five MRI-based head models.
- Analysis of induced electric fields and current densities within the retinal tissue.
Main Results:
- Induced current density is predominantly radial in the retina, peaking superiorly and inferiorly.
- Estimated macroscopic retinal threshold current density for 20 Hz phosphenes is 10 mA m⁻².
- The International Commission on Non-Ionizing Radiation Protection (ICNIRP) basic restriction limit may not be sufficiently conservative due to calculation methods.
Conclusions:
- The study provides a computational method to estimate retinal current density thresholds for magnetophosphenes.
- Current exposure limits might underestimate risks due to technical aspects of their application.
- Further refinement is needed for accurate application of basic restriction limits for retinal electric fields.
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