Laurie's Blogs.


May 2024

Laser Light Reflection, Eye Exposure, and Random Musings

Laurie Edge-Hughes, BScPT, MAnimSt, CAFCI, CCRT, Cert. Sm. Anim. Acup / Dry Needling

Here’s the story kids:  At the conference I was at most recently, a couple of the sales people came up to the Animal Rehab Division booth to ask our opinion on their Class 4 laser for animals.  (To be clear, it was a human physiotherapy conference, so they were legitimately wanting to discuss lasers and not just ‘sales pitch us’, which I found refreshing!)  I said, sure, I love talking about lasers!


So, they came back with their product to show us.  I actually liked it, as far as a class 4 laser goes, and we gave them some feedback, especially as it pertained to portability and functionality of the head.  They were pleased with the information.  (I was even told that if I ever wanted to become a salesperson for lasers, that their company would love to have me!  Hilarious!  Maybe I might just quit my day job!  But I digress…)


The point of this intro is that we got talking about dosage, being able to press the laser head into the body to improve penetration, eyewear, and REFLECTION of light.  The sales guy had never heard that.  He never knew that the laser light had the potential to reflect off of the skin.  He was shocked, and shocked to the point that I questioned whether I had made up that fact!  I did not, however, I thought it might be interesting to ‘reflect’ here on the ‘reflection’ of laser light in therapeutic applications.  (See what I did there?  Reflect and reflection?)


Reflection occurs at all interfaces of media through which the laser beam is travelling, such as optical glass or sapphire tip, air, water jelly and skin surface. For example, the stratum corneum (the outermost layer of the epidermis) reflects approximately 4% to 7% of visible light that encounters the skin surface.1,2  The remaining 93–96% of the radiation entering the skin is either scattered or absorbed.


Now, just from a practical standpoint.  Contact application is likely to have less reflection of light than non-contact application.  Reflection and accidental exposure are the main reasons that practitioners (and others in the room) would wear special glasses (or shield their eyes).  Closing the eyes is sufficient to protect them from the damaging effects of laser to the retina.

Fun facts about deciding the type of eye protection needed:

  1. Our therapeutic lasers with wavelengths between 400 – 780nm (visible) and 780-1400nm (near-infrared) have the ability to pass through the cornea and lens to potentially cause damage to the retina.3
  2. Maximal permissible exposure (MPE) limits to determine need for eye protection are as follows: (i) unintentional accidental exposure to a visible beam where MPE may exceed 0.25 sec (the blink-aversion reflex); (ii) unintentional, accidental viewing of a near-infrared laser beam for up to 10 seconds; (iii) intentional viewing of diffuse reflection for up to 600 seconds.3
  3. The eyewear needs to be specific  to the wavelength of light and the exposure conditions.3



Not much else to conclude.  Honestly, I thought and hoped I’d find more information and studies on this topic. I tried a number of different search terms even!  Ah well, to be honest, the reflection percentage was less than I thought it was, and the maximal permissible exposure times were longer than I thought they were.  So, I guess I learned a little from doing this search myself!



1.  Patil UA, Dhami LD. Overview of lasers. Indian J Plast Surg. 2008 Oct;41(Suppl):S101-13. 

2.  Randall V, Lanigan S, Hamzavi I, Chamberlain J. New dimensions in hirsutism. Lasers Med Sci. 2006;21(3):126–133. 

3.  Bartels KE.  Therapy Laser Safety.  In Laser Therapy in Veterinary Medicine: Photobiomodulation, 1st Ed.  Riegel RJ & Godbold JC eds.. John Wiley & Sons Inc. 2017: 31-32.