Q: What is lllt, LPLT, low level laser therapy, low power laser, bio stimulation?
Q: Is there a physical difference between laser and LED/or other light sources?
Q: Is laser therapy scientifically well documented?
Q: Which lasers can be used in medicine?
Q: Can therapeutic lasers damage the eye?
Q: How come some LLLT equipment has power in watts and some only in mill watts?
Q: How deep into the tissue can a laser penetrate?
Q: Can LLLT cause cancer?
Q: What happens if I use a too high dose?
Q: Are there any counter indications?
Q: Does LLLT cause a heating of the tissue?
Q: Does it have to be a laser? Why not use monochromatic non coherent light?
Q: Does the coherence of the laser light disappear when entering the tissue?

Q: What is LLLT, LPLT, therapeutic laser, soft laser, MID laser?
Ans: Regarding the therapy, we have chosen to use the term LLLT (Low Level Laser Therapy). This is the dominant term in use today, but there is still a lack of consensus. In the literature LPLT (Low Power Laser Therapy) is also frequently used. Regarding the laser instrument, we have chosen to use the term “therapeutic laser” rather than “low level laser” or “low power laser”, since high-level lasers are also used for laser therapy. The term “soft laser” was originally used to differentiate therapeutic lasers from “hard lasers”, i.e. surgical lasers. Several different designations then emerged, such as “MID laser” and “medical laser”. “Biostimulating laser” is another term, with the disadvantage that one can also give inhibiting doses. The term “bioregulating laser” has thus been proposed. An unsuitable name is “low-energy laser”. The energy transferred to tissue is the product of laser output power and treatment time, which is why a “low-energy laser”, over a long period of time, can actually emit a large amount of energy. Other suggested names are “low-reactive-level laser”, “low-intensity-level laser”, “photobiostimulation laser” and “photobiomodulation laser”. Thus, it is obvious that the question of nomenclature is far from solved. This is because there is a lack of full agreement internationally, and the names proposed thus far have been rather unwieldy. Feel free to forget them, but remember LLLT until agreement is reached on something else. 

Q: Is there a physical difference between laser and LED/or other lightsources?
Ans: Yes there is, Laserlight has unique physical properties, that no ordinary light has. This is the key to why laserlight is so effective compared to other kinds of light in healing. See Editorial by Rubinov and prima-books.com for more detail info.

Q: Is laser therapy scientifically well documented?
Ans: Basicly yes. There are more than 100 double-blind positive studies confirming the clinical effect of LLLT. More than 2500 research reports are published. Looking at the limited LLLT dental literature alone (370 studies), more than 90% of these studies do verify the clinical value of laser therapy.

Q: Which lasers can be used in medicine?
Ans: Examples of lasers which can be used in medicine: Laser name Wavelength Pulsed/continuous Use in medicine.
Crystalline laser medium:
Ruby 694 nm p holograms, tattoo coagulation, hair removal
Nd:YAG 1 064 nm p coagulation, dentistry
Ho:YAG 2 130 nm p surgery, root cana
l Er:YAG 2 940 nm p surgery, dental drill
KTP/532 532 nm p/c dermatology
Alexandrite 720-800 nm p bone cutting, hair removal

Semiconductor lasers:
GaAs 904 nm p biostimulation
GaAlAs 780-820-870 nm c biostimulation, surgery
InGaAlP 630-685 nm c biostimulation

Liquid laser:
Dye laser (tuneable) p kidney stones
Rhodamine: 560-650 nm c/p PDT, dermatology

Gas lasers:
HeNe 633, 3 390 nm c biostimulation
Argon 350-514 nm c dermatology, eye
CO2 10 600 nm c/p dermatology, surgery
Excimer 193, 248, 308 nm p eye, vascular surgery
Copper vapour 578 nm c/p dermatology
There are many other types, but those mentioned above are the most common ones.

Q: Can therapeutic lasers damage the eye? 
Ans: Yes and no! Read the following:
The following factors are of importance regarding the eye risk of different lasers:
The divergence of the light beam. A parallel light beam with a small diameter is by far the most dangerous type of beam. It can enter the pupil, in its entirety, and be focused by the eye’s lens to a spot with a diameter of hundredths of a millimetre. The entire light output is concentrated on this small area. With a 10 mW beam, the power density can be up to 12,000 W/cm2

The output power (strength) of the laser. It is fairly obvious that a powerful laser (many watts) is more hazardous to stare into than a weak laser. The wavelength of the light. Within the visible wavelength range, we respond to strong light with a quick blinking reflex. This reduces the exposure time and thereby the light energy which enters the eye. Light sources which emit invisible radiation, whether an infra-red laser or an infra-red diode, always entail a higher risk than the equivalent source of visible light. Radiation at wavelengths over 1400 nm is absorbed by the eye’s lens and is thus rendered safe, provided the power of the beam is not too high. Radiation at wavelengths over 3,000 nm is absorbed by the cornea and is less dangerous.

The distribution of the light source. If the light source is concentrated, which is often the case in the context of lasers, an image of the source is projected on the retina as a point, provided it lies within our accommodation range, i.e. the area in which we can see clearly. A widely spread light source is projected onto the retina in a correspondingly wide image, in which the light is spread over a larger area, i.e. with a lower power density as a consequence. For example: a clear light bulb (which is apprehended as a more concentrated light source) penetrates the eye more than a so-called “pearl” light bulb. A laser system with several light sources placed separately, such as a multiprobe (the probe is the part of the laser you hold and apply to the area to be treated: a single probe means there is only one laser diode in the probe, as opposed to a multiprobe, which has several laser diodes) with several laser diodes, can, seen as a whole, be very powerful but at the same time constitute a smaller hazard to the eye than if the entire power output was from one laser diode, because the diodes’ separate placement means that they are reproduced in different places on the retina.

We have often heard this kind of remark: “If it’s a class 3B laser then it’s fine, otherwise it has no effect….” This is of course entirely incorrect and has lead to a situation where manufacturers have produced lasers to meet the 3B classification, so that they will sell in greater volumes. Let us look at a couple of examples: * A GaAlAs laser with a wavelength of 830 nm, an output of 1 mW and a well collimated beam (1 mrad divergence) is classified as laser class 3B as it is judged to be hazardous to the eye. The reason for this is partly the collimated beam, and partly the wavelength, which is just outside the visible range and hence provokes no blink reflex in strong light.

* A HeNe laser with a wavelength of 633 nm, an output of 10 mW and divergent beams (1 rad divergence, which corresponds to a cone of light with a top angle of about 57°) is classified as laser class 3A because, owing to its divergence, it cannot damage the eye.

With the recent advent of “high power low power lasers”, i.e. GaAlAs lasers in the range 100-500 mW there is another story. These lasers are indeed dangerous for the eye and should only be used by qualified persons and with proper protective measures taken.

Q: How come some LLLT equipment has power in watts and some only in milliWatts?
Ans: This applies to GaAs lasers. When a GaAs laser works in a pulsed fashion, the laser light power varies between the peak pulse output power and zero. Then usually the laser’s average power output is of importance, especially in terms of dosage calculation. The peak pulse power value is of some relevance for the maximum penetration depth of the light. Some manufacturers specify only the peak pulse output in their technical specifications. “70 millwatt peak pulse output” naturally seems more impressive than 35 milliwatts average output! Rule of thumb is: Take the “watt peak pulse” figure, divide by 2, and you have the average output in mW. This rule of thumb is not valid for GaAs-lasers when these lasers are pulse-train arranged). Then the average power is independent of the frequency.

Q: How deep into the tissue can a laser penetrate?
A: The depth of penetration of laser light depends on the light’s wavelength, on whether the laser is super-pulsed, and on the power output, but also on the technical design of the apparatus and the treatment technique used. A laser designed for the treatment of humans is rarely suitable for treating animals with fur. There are, in fact, lasers specially made for this purpose. The special design feature here is that the laser diode(s) obtrude from the treatment probe rather like the teeth on a comb. By delving between the animal’s “hair”, the laser diode’s glass surface comes in contact with the skin and all the light from the laser is “forced” into the tissue.

A factor of importance here is the compressive removal of blood in the target tissue. When you press lightly with a laser probe against skin, the blood flows to the sides, so that the tissue right in front of the probe (and some distance into the tissue) is fairly empty of blood. As the haemoglobin in the blood is responsible for most of the absorption, this mechanical removal of blood greatly increases the depth of penetration of the laser light. It is of no importance whether the light from a laser probe, held in contact with skin is a parallel beam or not.

There is no exact limit with respect to the penetration of the light. The light gets weaker and weaker the further from the surface it penetrates. There is, however, a limit at which the light intensity is so low that no biological effect of the light can be registered. This limit, where the effect ceases, is called the greatest active depth. In addition to the factors mentioned above, this depth is also contingent on tissue type, pigmentation, and dirt on the skin. It is worth noting that laser light can even penetrate bone (as well as it can penetrate muscle tissue). Fat tissue is more transparent than muscle tissue.

For example: a HeNe laser with a power output of 3.5 mW has a greatest active depth of 6-8 mm depending on the type of tissue involved. A HeNe laser with an output of 7 mW has a greatest active depth of 8-10 mm. A GaAlAs probe of some strength has a penetration of 35 mm with a 55 mm lateral spread. A GaAs laser has a greatest active depth of between 20 and 30 mm (sometimes down to 40-50 mm), depending on its peak pulse output (around a thousand times greater than its average power output). If you are working in direct contact with the skin, and press the probe against the skin, then the greatest active depth will be achieved.

Q: Can LLLT cause cancer?
Ans: The answer is no. No mutational effects have been observed resulting from light with wavelengths in the red or infra-red range and of doses used within LLLT. But what happens if I treat someone who has cancer and is unaware of it? Can the cancer’s growth be stimulated? The effects of LLLT on cancer cells in vitro have been studied, and it was observed that they can be stimulated by laser light. However, with respect to a cancer in vivo, the situation is rather different. Experiments on rats have shown that small tumours treated with LLLT can recede and completely disappear, although laser treatment had no effect on tumours over a certain size. It is probably the local immune system which is stimulated more than the tumour.

The situation is the same for bacteria and virus in culture. These are stimulated in vitro by laser light in certain doses, while a bacterial or viral infection is cured much quicker after the treatment with LLLT

Q: What happens if I use a too high dose?
Ans: You will have a biosuppressive effect. That means that, for instance, the healing of a wound will take longer time than normally. Very high doses on healthy tissues will not damage them.

Q: Are there any counter indications?
Ans: You should not treat cancer for legal reasons. Pregnant women are not a counter indication, if used with common sense. Pacemakers are electronical, do not respond to light. Epilepsy may be a counter indication. The most valid counter indication is lack of medical training

Q: Does LLLT cause a heating of the tissue?
Ans: Due to increased circulation there is usually an increase of 0.5-1 centigrade locally. The biological effects have nothing to do with heat. GaAlAs lasers in the 300-500 mW range will cause a noticeable heat sensation, particularly in hairy areas and on sensitive tissues such as lips.

Q: Does it have to be a laser? Why not use monochromatic non coherent light/LED/other types of standard light?
Ans: Monochromatic non coherent light, such as light from LED’s is useful for superficial tissues such as wounds. In comparative studies, however, lasers have shown to be more effective than monochromatic non coherent light sources. Non coherent light will not be as effective in deeper areas. LED based systems have gradually improved during the years and are now better documented. Because of lack of scientific support in the past, some manufacturers have quoted laser research as proof of the effectiveness of LED therapy, meaning that they are one and the same. Such argumentation should be a “warning lamp” to the customer. LED’s can easily be arranged in “clusters” to cover large areas, while this is quite possible but less common with lasers. Combining LED’s and lasers in the same cluster is sometimes found, but the usefulness has not been documented. 

Q: Does the coherence of the laser light disappear when entering the tissue?
Ans: No. The length of coherence, though, is shortened. Through interference between laser rays in the tissue, very small “islands” of more intense light, called speckles occur. These speckles will be created as deep as the light reaches in the tissue and within a speckle volume, the light is partially polarized. It is easy to show that speckles are formed rather deep down in tissue and the existence of real speckles proves that the light is coherent. The polarisation of polarised light, though, is lost soon after entering tissue.


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