Study type: Medical/biological study (experimental study)

Magnetophosphenes: a quantitative analysis of thresholds. med./bio.

Published in: Med Biol Eng Comput 1980; 18 (3): 326-334

Aim of study (acc. to author)

The aim of this study was to describe quantitatively the nature of magnetophosphenes (magnetic field-induced phosphenes).

Background/further details

Particular interest has been focused on threshold values and the way in which they are affected by background light.
Time-variable very low frequency (10-50 Hz) electromagnetic fields of moderate magnetic flux densities (0-40 mT) were used.
The study comprised four different test groups: 1) 11 healthy volunteers; phosphene threshold values were determined in darkness as well against background light; 2) 8 healthy subjects; thresholds were recorded at frequencies of 20, 30 and 35 Hz during dark-adaptation; 3) 6 healthy volunteers with normal colour vision; threshold values were recorded with three different background colours; 4) 9 healthy but colour defective subjects; same conditions as for group 3.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 10–50 Hz
Exposure duration: 28 min

Exposure 1

Main characteristics
Frequency 10–50 Hz
Type
Waveform
Exposure duration 28 min
Exposure setup
Exposure source
Distance between measurement device and exposure object 2 cm
Setup each coil with 115 turns of insulated copper wire, coils connected in series, distance between the poles adjustable; magnet placed with the poles near the temporal area of the test person
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 40 mT mean measured - 0 - 40 mT

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure

Main outcome of study (acc. to author)

Maximum sensitivity occured at a frequency of approximately 20-30 Hz, and with broad-spectrum light the threshold magnetic flux density was 10-12 mT. The threshold values depended upon the intensity and the spectral distribution of the background light. Sensitivity decreased during dark adaptation. In certain respects colour defective volunteers differed from subjects with normal colour vision.

Study character:

Study funded by

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