Scientific Principles of Lasers

Scientific Principles of Lasers
Scientific Principles of Lasers
A laser is a high energy light, which can only represent a single wavelength, generally
measured in nanometers (nm). The Electromagnetic Spectrum describes the entire range of
wavelengths. Light below 400 nm is called ultra-violet and is invisible. Light in the visible portion
of the spectrum ranges between 400 and 700 nm. Light over 700 nm is infra-red and is invisible.
Each laser wavelength has its own characteristics, mainly differentiated by the organic tissue in
which it is absorbed. Three primary organic chromophores (tissue in which light is absorbed) are
water, oxy-hemoglobin (HbO), deoxy-hemoglobin (HbR), and melanin.
Light in the visible portion of the spectrum is generally strongly absorbed by either melanin or
oxy-hemoglobin or both. Light in the near infra-red range is absorbed well by high
concentrations of dark pigments. Light in the far infra-red spectrum is generally well absorbed
by water.
Based on its individual absorption characteristics, laser light penetrates shallower or deeper. For
instance, a KTP 532 nm laser is highly absorbed in oxy-hemoglobin. When it is applied to skin
that has the chromophore located near the surface (e.g., superficial blood vessels), the laser
light will be immediately absorbed by the chromophore and will not travel deep into the
surrounding tissue. If the wavelength is highly absorbed in melanin and is applied to tissue that
has little to no melanin, it will continue travelling until it either finds its chromophore within the
tissue or scatters to non-significant levels. Thus, it’s important to find the optimal laser
wavelength for the chosen procedure.
When light energy is absorbed it immediately turns into heat which, in turn, destroys the target
tissue (e.g., blood vessel). As soon as the heat is created, it begins to dissipate into surrounding
tissue. Thus, it’s important to deposit light into the target tissue faster than the time it takes for
the target structure to transmit the created heat into the surrounding structures or in other
©2009 IRIDEX. All rights reserved.
Part No. 0112-7270, Rev. D 31/07/2009
Page 3.1
Scientific Principles of Lasers
words, for the tissue to relax. Consequently, the larger the target structure, the longer it will take
to cool and the longer the laser light can be applied to it.
The opposite is true for smaller target structures. So, it’s important to determine the appropriate
time period of laser application for the target tissue. This time is called Thermal Relaxation Time
(TRT) and is measured in nano- or milli-seconds.
Each structure in tissue is destroyed at a certain temperature. This temperature is achieved by
applying sufficient energy. If too little energy is applied, the target structure will heat but not
reach destructive temperatures. If too much energy is applied, excess energy will immediately
dissipate beyond the target and destroy adjacent tissue. Thus, it’s important to transmit the right
amount of energy [measured in Joules per centimeter squared (J/cm2)] to the target.
These three principles, optimal wavelength, appropriate time and sufficient energy, are the
basics of Selective Photo-Thermolysis and are the foundation for laser applications in medicine.
532 nm treatments are preferred for small and superficial vessels
Superficial and small-diameter vessels are most selectively treated with wavelengths that are
strongly absorbed by oxyhemoglobin as the vessels can be heated to clinical response
temperatures with minimal incident energy. High oxyhemoglobin absorption can limit the depth
to which laser light penetrates into skin, making it difficult to treat large or deep vessels with
these wavelengths.
940 nm treatments are preferred for larger and deeper facial vessels, and some leg veins
Less strongly absorbed wavelengths penetrate more deeply, and can more uniformly heat
through larger diameter vessels. Higher fluences are used to overcome the lower absorption
coefficient and successful treatments can be achieved with good selectivity. Of the near infrared
wavelengths, 940 nm is optimal having the highest oxyhemoglobin absorption coefficient
(9.0 cm-1). This is 35 times lower than the absorption coefficient of 532 nm (320 cm-1) allowing
the treatment of larger and deeper vessels, but 40% higher than 810 nm (6.5 cm-1), and 80%
higher than 1064 nm (5.0 cm-1) for improved selectivity, reduced discomfort, and fewer
side effects.
1064 nm treatments are preferred for hair removal, and larger and deeper vessels
including leg veins
Induces less energy absorption by other cutaneous structures, leading to less collateral damage
and more efficient deep penetration. The decreased epidermal absorption accounts for the
reduction in side effects. The penetration of the 1064 nm Nd:YAG laser is 5 to 10 mm, causing
diffuse heating of the dermal tissue.
2940 nm treatments are preferred for skin resurfacing
The 2940 nm erbium wavelength is highly absorbed by water and is typically used for ablating
and coagulating tissue in many surgical and aesthetic procedures. The 2940 nm wavelength is
optimal for removing wrinkled, scarred, rough, or uneven skin without the downtime seen with
other methods of resurfacing.
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©2009 IRIDEX. All rights reserved.
Part No. 0112-7270, Rev. D 31/07/2009
Laser Safety
The treatment room is considered the “Nominal Hazard Zone”. This room must be maintained
by having all entryway doors closed. Laser energy may pass through glass; therefore, protective
barriers should be placed over all windows. Reflective objects should be reduced and/or
eliminated in the room.
Warning Sign
A “Laser in Use” warning sign must be posted outside all entryways warning any person who
may enter that appropriate eyewear must be worn.
Protective Eyeware
All persons in the room must wear protective eyewear labeled with an OD (optical density) and
wavelength appropriate for the system being used. This includes glasses, goggles, or occlusive
metal eye shields.
Handpiece Use
The handpiece should never be pointed towards the eye/orbit of the patient or user, even when
wearing appropriate eyewear. Careful consideration is necessary when treating around the eye.
The laser should always be fired in a direction away from and outside the periorbital region of
the eye.
Standby Mode
The unit should be placed in Standby mode when the unit is not in use to prevent unintended
exposure. There is a Red Emergency Shut Off button located on the front of the laser that may
be used when necessary. There is also a remote door interlock that can be used to disable the
unit if the treatment room door is opened during a procedure. The key must be removed and
kept in a controlled area when the system is unattended or not in use.
Fire Hazards
To reduce the risk of fire hazards, flammable liquids (alcohol, etc.), dark colored drapes or
clothing should not be present in the treatment area. A basin of water and a fire extinguisher
should be available in the treatment area during treatment. To reduce the risk of electrical
hazards, the covers enclosing the components of the unit should not be removed. Liquids
should never be placed on, or sprayed onto the laser system. Never operate the unit in an area
of leaking or spilled fluid. The system should not be operated if the power cable is frayed or
faulty. If using the Gemini, Aura i, or Lyra i systems, the chiller fluid level should be checked
daily or more frequently during periods of heavy use. As an added precaution, manually check
the temperature of the chiller tip before treating. It should be cold to the touch.
Patient Selection
The proper patient selection is important and specific to the type of laser used. Also consider
lowering the energy when treating over bone and in areas of darker pigment. All patients should
have their skin type evaluated. Always perform a test spot prior to a full treatment when treating
a patient for the first time, use the lowest energy levels recommended for that patient’s skin
type. In the case of hair reduction, do a range of settings as test spots. And after the appropriate
waiting period, treat the patient at the highest energies that are tolerated by the patient’s skin.
Contact cooling, where indicated, is vital in preventing possible skin burns.
Cautions
Remember, never treat within the periorbital ridge, and take care when treating near eyebrows,
moles, or tattoos.
©2009 IRIDEX. All rights reserved.
Part No. 0112-7270, Rev. D 31/07/2009
Page 3.3
Laser Safety
An excellent source of reference material for laser policies and procedures is www.AORN.org.
This site has representative policies and procedures for Operating Room laser use that you may
want to write for your facility.
Note: This is a brief overview of laser safety. Users are advised to read the operator’s manual
before operation.
Page 3.4
©2009 IRIDEX. All rights reserved.
Part No. 0112-7270, Rev. D 31/07/2009
Care for Eyeware and Handpieces
How to Care for Your Laser Eyewear
Care for your laser eyewear as you would prescription glasses.
Never use harsh or abrasive cleaners.
Wipe eyewear with a slightly damp gauze. If smudged, you may use soap and water, then rinse.
Gel antibiotic hand wash can be used as well. Clean eyewear; then dry and put in a protective
case that came with the eyewear.
How to Care for Your Handpieces
Handpieces cannot be sterilized. Never use harsh or abrasive cleaners. Do not use heat,
immersion or chemical sterilization.
NEVER pour water or other liquids on the handpieces.
Gemini, Aura i, and Lyra i
Clean handpieces and the handpiece tubing with a mild detergent and wipe dry immediately.
Clean the lens of the handpieces with 90% or higher concentration of alcohol or gel antibiotic
hand wash. Clean the lens window or lens and dry immediately.
Never remove the lens cell on the Versistat i. This will allow liquids to reach the inner workings of
the handpiece. If that happens, immediately TURN OFF the laser and report the incident to the
Customer Response Center.
DioLite, DioLiteXP, VariLite
The handpieces can be used with either non-contact conical tips, or with a removable contact
distance gauge tip. The removable distance gauge is the only portion of the handpiece intended
to come into patient contact. The distance gauge should be removed between usages, and
cleaned and disinfected.
The handpieces themselves should be cleaned if they become soiled using a soft cloth
dampened with either a mild detergent or alcohol. Aloe or other water-based gels may cause
staining. To prevent this carefully remove all traces of gel after each use. A nickel polishing
cloth or liquid may be used to remove stains.
©2009 IRIDEX. All rights reserved.
Part No. 0112-7270, Rev. D 31/07/2009
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©2009 IRIDEX. All rights reserved.
Part No. 0112-7270, Rev. D 31/07/2009
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