Medical/biological study (experimental study)

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

By: Lovsund P, Oberg PA, Nilsson SE, Reuter T

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

phosphene threshold determination

Exposure

- magnetic field

Exposure	Parameters
Exposure 1: 10–50 Hz Exposure duration: 28 min	magnetic flux density: 40 mT mean (0 - 40 mT)

Exposure 1

Main characteristics

Frequency	10–50 Hz
Type	magnetic field
Waveform	sinusoidal
Exposure duration	28 min

Exposure setup

Exposure source	U-shaped electromagnet consisting of laminated iron plates with a coil on each arm
Distance between measurement device and exposed 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:

human
partial body: head

Methods Endpoint/measurement parameters/methodology

phosphene threshold determination (interrogation)

Investigated system:

investigation on living organism

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:

medical/biological study
experimental study
full/main study

Study funded by

Swedish Medical Research Council (SMRC), Sweden
Swedish Work Environment Fund

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