In vivo attenuation profile of 660 nm and 830 nm wavelengths on human elbow skin and calcaneus tendon of different phototypes.
Level 4 - case-series / case-control
Cross-sectional in vivo physiological measurement study comparing two pigmentation groups.
PubMed 38194210 · doi:10.1007/s10103-023-03955-3
What was done
Thirty young male and female participants were stratified into two groups based on melanin index. Photobiomodulation using 660 nm and 830 nm laser wavelengths was applied to two anatomical sites: the posterior elbow (skin-skin) and the calcaneus tendon (skin-tendon-skin). Transmitted power and the resulting irradiation field were measured in vivo using a custom linear array of five optical sensors.
What was found
Transmitted light power differed significantly across melanin indices and wavelengths (p < 0.0001). For the 660 nm laser, average scattering distance was 14 mm in the higher melanin index group compared to 21 mm in the lower melanin index group. For the 830 nm laser, average scattering was 20 mm in the higher melanin group versus 26 mm in the lower melanin group. The 830 nm wavelength demonstrated greater overall light transmission through skin than 660 nm, and transmitted power at 830 nm also varied significantly between different laser devices.
Why it matters
Photobiomodulation dosing often assumes uniform tissue penetration; these findings demonstrate that patient skin phototype and wavelength substantially alter light attenuation and lateral scattering, indicating that laser application point spacing and energy delivery must be adjusted for individual pigmentation.
Limits
The sample was small (n = 30) and limited to young individuals, preventing generalization to older populations or varied anatomical sites. Measurements were gathered using a custom-built sensor array rather than standardized optical equipment. Absolute values for delivered power, tissue thickness, and exact melanin ranges were not reported in the abstract.
Cited by
- supports Long-wavelength light between approximately 620 nm and 850 nm from red light or near-infrared light devices penetrates deep into the skin.