Does low power laser light used in laser Doppler systems affect the sensory nerves?

Many subjects have stated that they can sense the laser light during cutaneous laser Doppler recordings. The aim of the study was therefore to investigate if low power laser light used in laser Doppler systems affects the sensory nerves.

Single point recording as well as imaging was performed with the laser Doppler perfusion imager at the finger pulp, dorsal and ventral side of the hand and the forearm skin in 12 healthy volunteers. The hypothesis "the subject can not sense the laser beam" was tested by double blind random control of the on-off pattern of the laser light reaching the skin. In total, 96 trials (each including 12 recordings) were performed. Furthermore, it was investigated if the blood flow level was influenced by the subjects "sense" of being measured.

The hypothesis was rejected in 92 out of 96 trials. Three of the trials that could not be rejected were recorded from the same subject. In further trials no reproducibility was found. The blood flow level was not influenced by the subjects "sense" of being measured.

In general, the laser light used in laser Doppler imaging systems does not influence the sensory nerves. However, it can not be excluded that the laser light used in laser Soppier perfusion imaging (LDPI) affects sensory nerves under unknown circumstances and at specific spots in cutaneous tissue.