The increased movement of eyes and eyelids is characteristic of the rapid eye movement (REM) sleep stage, making it an important indicator in sleep monitoring. A device was designed to detect this activity in a non-invasive way by means of measuring infrared light intensity reflected off the eyelid. The system converts the light intensity into current through a photodetector, performs analog signal processing and analog to digital conversion (ADC). The data is transmitted wirelessly to a computer, where the results can be displayed, stored and analyzed with a dedicated software, which also provides control over the device. The hardware is embedded in a mask, which is put over the patient's eyes. User safety in terms of mechanical, electrical and optical dangers has been ensured. The device was tested on a napping subject.
 Achim Westermann. JChart2D, precise visualization of data [Internet]. [place
unknown: publisher unknown]; [updated 2010 Jun 19; cited 2013 Jun 23].
Available from: http://jchart2d.sourceforge.net/.
 Below K, Dietrich K.: Medizinische Gerätetechnik. 1st ed. Haan-Gruiten: Verlag
Europa-Lehrmittel; 2006. p. 126. German.
 Directive 2006/25/EC of the European Parliament and of the Council of 5 April
2006 on the minimum health and safety requirements regarding the exposure
of workers to risks arising from physical agents. OJ L114/38. 2003.
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