Introduction
Choosing the right safety glasses for both you and your patient doesn’t have to be confusing. Terms like optical density (OD), wavelength, and visible light transmission (VLT) conjure up memories from high school physics class. Have no fear though, as we are about to explain how to select the right protective glasses for the job.
Safety Glasses for Technicians
For the technician, protective glasses are always a trade-off between being able to clearly see the treatment area and protecting the eyes from harmful laser light. For the patient, the choice of glasses is much simpler as the only concern is protecting the patient’s eyes, since the patient doesn’t need great visibility during treatment. This leads to two different types of protective glasses used in laser hair removal: technician glasses and patient glasses.
Technician glasses are almost always specific to the wavelength of the laser being used in the treatment. For example, an Alexandrite laser, which is commonly used in laser hair removal, has a wavelength of about 750nm. Therefore, the protective glasses should be specified to greatly reduce light in the frequency range of 750nm, while letting most other frequencies pass through. You may be asking, “but why would I want other frequencies to pass through?” The answer is that the technician needs to clearly see the patient's skin and hair during treatment. A lens that blocks a wide range of wavelengths, say from 200nm to 1000nm, is also going to block most visible light, which means you as the technician won't be able to clearly see the area of the patient you are working on. This is why as a technician, you will need special safety glasses for each wavelength of laser you work with.
Safety Glasses for Patients
The patient, on the other hand, doesn’t have a need to see clearly during treatment, and so a lens that blocks out a very wide range of laser wavelengths is ideal. So while a technician would typically switch glasses when switching from YAG to Alexandrite treatment, the patient will keep the same glasses on, as the patient glasses are designed to block all the major laser frequencies.
Safety Elements
Block
Now that we understand the basics between technician glasses and patient glasses, let’s talk about how much laser light safety glasses block. In fact, "block" isn’t really the best description since laser safety glasses don’t completely stop laser light, they "reduce" laser light in a specific frequency range. The amount of light that safety glasses reduce is called Optical Density or OD. Most laser safety glasses will have an OD rating between OD4 and OD6 for a specific range of light frequencies. OD is a logarithmic scale which means for each whole number increase in OD, the light is reduced 10 times. This means that OD5 glasses block out 10 times more laser light than OD4 glasses. Likewise, OD6 glasses block out 10 times more than OD5 glasses. Again, it’s important to remember that the OD rating is always for a specific range of wavelengths, not all wavelengths. So the specifications for Alexandrite laser safety glasses might read "OD4 for wavelengths between 750-850nm." Outside of that specific frequency range (750-850nm), the glasses may not block any laser light at all, which is why it’s critical that the technician always wears the right glasses for the laser they are using!
Visible Light Transmission (VLT)
The next element of laser safety glasses to understand is Visible Light Transmission or VLT. Visible light is the normal light we see with our eyes every day and has a wavelength that ranges from 400-700nm. For the technician, we want VLT to be as high as possible so that the patient's skin and hair are clearly visible during treatment. VLT is measured between 100% and 0%. It's a pretty simple measurement: a VLT of 50% means that 50% of visible light passes through the lens, while a VLT of 20% means 20% of light passes through the lens.
Deciding what's right for you
Now let’s put it all together with a general rule of thumb for selecting safety glasses. A technician working with multiple lasers is going to need multiple glasses with an OD value of 4 or greater specific to the laser they are working with. For example, 1 pair of glasses for Alexandrite, 1 pair for YAG, and 1 pair for Diode laser. The technician should switch glasses every time they switch laser types. The patient will need 1 pair of glasses with the highest possible OD value that covers the frequencies used by all major laser types.
There are a couple of exceptions to our rule of thumb above. The first pertains to treating a patient's face. When doing a facial laser treatment, the patient should be outfitted with either metal or elastomer eye shields that block out all light (approximately OD 8). Remember that hair removal lasers are very powerful and even a small amount of laser light could permanently damage a patient's eyes. The second exception is Intense Pulsed Light (IPL) treatment. Unlike lasers, which have a very narrow frequency range, IPL has a relatively wide frequency range. This means that protective glasses for IPL must also have a wide frequency range to keep the technician safe. Therefore, there are specific technician glasses for IPL that cover a wider but specific frequency range used by IPL machines.
Conclusion
Remember that technicians are exposed all day to laser light that can be very dangerous to human eyes. It’s, therefore, critical that technicians use high-quality glasses with documented specifications for OD and VLT and contain all needed certifications, including the CE Mark. Any glasses without clear certification, documented specifications, or that do not fully cover the eye area should not be used. Nothing is as important as maintaining safety for you and your patient!