LLLT, lllt, laser therapy - biostimulation
The Low Level Laser Therapy -
LLLT Internet Guide


The following text is taken from
chapter 13 of the new book
"Low Level Laser Therapy"
by Tunér-Hode.
Part 1
Part 2

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1998 Copyright © Prima Books

13.1 Are all the negative lllt studies really negative?

The authors of this book have performed an analysis of a number of frequently cited studies on the effects of low-power-laser therapy. In many of these studies, analysis uncovered one or more reasons for the negative findings reported, the most common being the use of extremely low doses. Other reasons are: faulty inclusion criteria, inaccurate control group definition, ineffective methods of therapy, inadequate attention to systemic effects and tissue condition, and low power density. A weakness often encountered in these studies is their failure to provide sufficient data on laser parameters. Since negatively inclined studies such as these are often quoted as "proof" of the ineffectiveness of LLLT, it is important that they be subjected to a proper critical analysis. 1.400 articles were reviewed for this analysis, the emphasis being on double-blind studies. Of the 135 localised double-blind studies, 85 reported positive findings.

Though important, the critical examination of scientific literature is decidedly unglamorous. It involves hours and days of searching through a wide variety of different sources, and by no means all information is yet available on-line. There are numerous pitfalls, too, especially for those who opt to read abstracts only - criticism of sources is impossible unless an article can be studied in its entirety. Basing an opinion from abstracts obtained from e.g. Medline is risky. In addition, only a minority of the early LLLT research reports are available from the major databases.

In the following analysis of the available literature, we have chosen to analyse those studies unable to demonstrate the effectiveness of LLLT. Although priority was given to double-blind studies, non-double-blind studies were also included in certain typical cases. Certain studies were also included merely on the grounds that they are among the most frequently cited. The 1.400 articles reviewed for this analysis are now being stored in computerised form.

"I heard it through the grapewine"

A recognisable pattern is often distinguishable in the bibliographies accompanying scientific reports. The manner in which these patterns arise goes something like this: Researcher A is the man or woman behind some pioneering achievement and is therefore extensively quoted by researcher B, as well as by C, D, E and several others. Researcher K, however, is content to read what E has written about A and B, while researcher Z treats the work of A and B as a simple historical reference point previously described by researcher P. And, like a rumour, word spreads: everyone knows about A, B and C, but no-one has actually read their published work. Although generally known, therefore, older studies are not always relevant and it may sometimes be rewarding to go back and review them in detail. Often, especially in the light of new findings, the impression given is quite unlike that suggested in later, second-hand reports.

Positive from negative

Having traditionally concentrated on studies positive to LLLT, over the last few years we found ourselves becoming more and more interested in those studies with a negative spin: provided they have been properly carried out, they may be able to show us the parameters that do not appear to work. Naturally, negative reports must always be taken seriously, but the fact that a given study has been unable to demonstrate the effectiveness of LLLT does not necessarily mean that the method studied is incapable per se of producing results within the indication in question. All that it shows is that the parameters selected for the study were not sufficiently effective. Therefore, it is illogical to conclude that LLLT is ineffective simply because no effect was reported in that particular study. A number of studies reporting negative results are marred by such startling illogicality.

Negative from negative

LLLT is a relatively young science that has only just emerged from its Sturm und Drang period, and it might perhaps be unfair to criticise the earlier negative studies. Many medical researchers then had - and indeed still have - a rather diffuse knowledge of physics, and qualified books on the physics of laser therapy were long in appearing. In many cases, the only information available to researchers on doses, methods of treatment and suitable indications came from the manufacturers or agents, while over-optimistic, ignorant salesmen often laid traps that would ensnare both themselves and the researchers.

Many studies will come in for criticism in the following paragraphs, although the researchers involved need not always take this to heart. As often as not they pioneered new territory, seeking either to retain an open mind towards the examination of new methods or reacting to what they perceived as a lack of objectivity. The purpose of our criticism is described in the Introduction - we wish to draw the reader's attention to the fact that many negative studies are poorly structured and are therefore largely irrelevant, even though they constantly feature in bibliographies and reading lists and are cited as "evidence" that LLLT does not work. Few people appear to have actually read them. As we see it, it is high time they were weeded out so that they can no longer function as traveller's tales in the future.

Important parameters

A. Wavelength
That biological effect is significantly related to the wavelength of the light emitted by the laser has been demonstrated in numerous studies. Today, the wavelengths most commonly used for therapeutic purposes are 633 nm (HeNe lasers), 635 nm, 650 nm, 660 nm, 670 nm (InGaAIP lasers), 780 nm, 820 nm, 830 nm (GaAIAs lasers), 904 nm (GaAs lasers), and 10600 nm (CO2 lasers). Except for GaAs and CO2 lasers, all these lasers usually produce a continuous beam but may also be pulsed.
B. Dose
The most important parameter in LLLT is always the dose, often referred to as "fluence". By dose (D) is meant the energy (E) of the light directed at a given unit of area (A) during a given session of therapy. The energy is measured in J (joules), the area in cm2, and, consequently, the dose in J/cm2. Mathematically, this may be expressed as follows:
D = ----     [J/cm2]
Assuming that the power (P) output of the laser probe remains constant during treatment, the energy (E) of the light will be equal to the power multiplied by the time (t) during which the light is emitted. The dose may then be calculated as follows:
          P t
D =   ----         [J/cm2]

Sometimes, however, the power output is not constant, such as when the laser is pulsed or modulated, which may be achieved in several ways. The preferred method of pulsing a HeNe laser is to use some form of mechanical switching device or shutter, such as a rotating pierced disc, the useful proportion of the time during which light is emitted by the laser normally being fixed at a given value (duty cycle), most often 50%. In other words, light is permitted to pass through the disc for 50% of the total operating time (and is blocked for the remaining 50%). This enables use of the concepts of mean power (Pm) and maximum power. In the example given here, the mean power is 50% of the maximum power. If the laser is pulsed at mean power, the above formula will apply, giving:
         Pm t
D =  -------     [J/cm2]

GaAs lasers always pulse, the duration of each pulse being extremely short, and in these lasers the maximum power is always much, much greater than the mean power. This type of pulsing is often referred to as super-pulsing. In GaAs lasers, the duration of the pulse is normally in the region of 100-200 ns (nanoseconds) and the maximum power is typically 1 - 20 W (watts). Assuming, for example, that the duration of the pulse is 150 ns and that the maximum power is 10 W, each pulse emitted by the laser will have an energy of 1.5 µ J (microjoules).
If the laser emits 100 such pulses per second (a pulse frequency of 100 Hz), its mean power output will be 0.15 mW (milliwatts). A pulse frequency of 1000 Hz gives a mean output of 1.5 mW, etc. In other words, the mean power output varies with the number of pulses emitted per second.
By applying these relationships, it is often possible to obtains doses or other parameters not explicitly stated in the article under review.

C. Power density
Power density, indicating the degree of concentration of the power output, has also increasingly proved to play a major role. It is measured in watts per square centimetre (W/cm2). If, for example, a circular area having a diameter of 5 mm (approx. 0.2 cm2) is illuminated with a laser operating at a power output of 100 mW, the biological effects are quite different from those produced by illuminating a circular area of 5 cm diameter (approx. 20 cm2) with the same laser. In the first case, the power density is 100 times greater than the second. Some studies have concluded that the power density may be of even greater significance than the dose. This parameter is very seldom indicated in the articles we have studied. It must also be remembered that the power density varies within the area illuminated - normally, it will be greatest at the centre.

Typical traditional laser instruments
Whenever possible, we also reviewed the brochure or brochures describing the instrument used for the study. The power output of the first commercial therapeutic lasers was very low. HeNe instruments often achieved an output of 1 - 2 mW at the laser tube, while the losses sustained in the optical fibres were frequently 50% or more. Further-more, the laser was sometimes pulsed (usually switched to produce a duty cycle of about 50%), thereby reducing the power/mean output power sent to the tissue by another half.
Brochures describing GaAs lasers often only specify the maximum pulse power, whereas the mean output power, which is of the greatest significance for LLLT, is often not named at all.
In the following we were often obliged to make a number of assumptions, since it was only very seldom that all the parameters were indicated in the studies. For example, unless otherwise stated, we have assumed that the fibre incurred a 50% loss; if the light was pulsed we assumed a duty cycle of 50%; and, unless otherwise indicated, we assumed that the mW values quoted envisage power output at the laser rather than at the fibre opening. For GaAs lasers, we sometimes had to make several assumptions at once, since here there are more parameters to be taken into account and they were often incompletely reported.
During the eighties, considerable discrepancies between actual outputs and those stated in manufacturers' brochures were not unusual. Only a handful of authors stated whether they themselves measured actual output at the tissue or whether they merely relied on the figure quoted in the brochure. Clearly, we must expect the dark figure to be quite large here.

Dose development
A number of early positive reports on the clinical effects of very weak HeNe lasers suggested that there was cause for some optimism - and scepticism, too. Among them are Walker (1983) [E1] (calculated at approx. 0.005 J per point) and Snyder-Mackler (1988) [E2, 3] (calculated at approx. 0.01 J per point), reporting on the effect of very weak HeNe lasers.
It must be remembered that Mester had been working with doses of around 1 J as far back as the early seventies. Later, in an article published in 1971 [E4] he recommended a dose of 1.5 J/cm2 as conducive to wound healing. The HeNe laser he used had an output of 25 mW at the laser. For a long time Mester's papers attracted little attention in the West, since they were published in relatively unknown journals. Later, in 1981, Kana [E5] published a study on the healing of open skin wounds in which he presented an analysis of the biological effect of 4, 10 and 20 J therapy.
The instrument he used was an HeNe laser producing an output of 25 mW from the laser tube. Mester's and Kana's experience of doses suitable for wound healing still hold good today. Although HeNe lasers with a power output of 25 mW were extremely expensive at the time, it cannot be held that information on suitable doses was not then available. It should be noted, too, that the treatment of pain requires larger doses than does the healing of open wounds. It seems that a large proportion of the negative studies concentrated mainly on testing the reliability of studies such as [E1, 2 and 3] without regard to existing knowledge of reasonable doses.


1. Low outputs
In the following we review some of the studies in which low dose can plainly be identified as the most significant negative factor. We have also listed the parameters that we consider should always be specified in studies of this nature. It is not unusual for an author to criticise previous studies for inadequate specification of parameters, then himself to be found guilty of the same sort of omission.
In the following examples, the parameters are summarised in tabular form. It should be noted that the power output is here to be understood as mean output on pulsing, since this is the figure required in order to calculate the dose.
Author: Waylonis G.W. et al: Ref no: [E6]  
Title: Chronic Myofascial Pain: Management by Low-Output Helium-Neon Laser Therapy.
Published in: Arch Phys Med Rehab. 1988; 69: 1017-1020.
Laser type: HeNe-laser (633 nm) Output: Not specified
Pulsing: Not specified Pulse frequency: Not specified
Dose: Not specified  
Power density: Not specified Treatment distance: Not specified
Laser model: Dynatron (model 1120), with fiberoptics  
Treated area: All together 12 acupuncture points  
Treatment time: 15 sek per point No of patientes: 62
No of treatments: 2 x 5 (6 weeks inbetween) Time between treatm: Not specified
Our comments:
This study is frequently quoted. No dose is specified. However, other sources state that the tube output of the HeNe laser (Dynatron 1120) is less than 1 mW. Assuming that losses in the fibre-optic set-up reduce this to 0.5 mW, and given an irradiation time per point of 15 seconds, the dose will be 0.5 mW x 15 sec = 0.0075 J. Since a normal dose today is 0.5 - 2 J per acupuncture point and 1 - 4 J per trigger point, it is hardly surprising that no significant effect was observed. And since the instrument used can be pulsed, the dose and the effect may actually have been reduced still further.
The study is said to have been double-blind, although there is no description of how this was achieved. This would, in fact, have been valuable information, since double-blind studies are normally quite difficult to carry out with HeNe lasers - they use red, visible light that is immediately distinguishable from conventional red light by its characteristic laser speckles.


Author: Jensen H. et al: Ref no: [E7]  
Title: Is Infrared laser effective in painful arthroses of the knee?
Published in: Ugeskr L¾ ger. 1987; 149: 3102-3106.
Laser type: GaAs-laser (904 nm) Output: 0,3 mW
Pulsing: Yes. 200 ns puls width Pulse frequency: 190-250 Hz
Dose: Not specified  
Power density: Not specified Treatment distance: Not specified
Laser model: Space Laser IR CEB    
Treated area: All together 4 points per knee  
Treatment time: 180 sek per point No of patientes: 29
No of treatments: 5 Time between treatm: 1 day
Our comments:
Although the dose is not explicitly stated, approximate figures may be calculated from other data. The power output is given as 0.3 mW, although in Space's instruments (as in many other GaAs lasers), the output is directly proportional to the pulse frequency. At 1000 Hz, these Space instruments usually produce an output of 1 mW. The pulse frequency interval is stated as being 195 - 250 Hz. On the basis of the power output stated, the dose may be estimated as 0.0003 W x 3 x 60 sec = 0.054 J. Four points were treated on each knee, giving a total dosage per session of 0.2 J. This dose is totally inadequate for a part of the body as large as the knee. This was a double-blind cross-over study.
Author: Basford J R et al: Ref no: [E9]  
Title: Low-energy Helium Neon laser treatment of thumb osteoarthritis.
Published in: Arch Phys Med Rehab. 1987; 68: 794-797.
Laser type: HeNe-laser (633 nm) Output: 0.9 mW
Pulsing: Continuous Pulse frequency: -
Dose: Not specified  
Power density: Not specified Treatment distance: Not specified
Laser model: Dynatronics (modell not specified), via fiberoptics    
Treated area: 4 different points around 3 joints (All together 12 points)  
Treatment time: 180 sek per point No of patientes: Not specified
No of treatments: 9 Time between treatm: Not specified
Our comments:
Assuming that the fibre loss is about 50%, the dose will here be 15 sec x 0.9 mW x 0.50 = 0.007 J per point. No obvious effect can be expected from such a low dose. This was a single-blind study.
Author: Taube S et al: Ref no: [E10]  
Title: Helium-neon laser therapy in the prevention of postoperative swelling and pain after wisdom tooth extraction
Published in: Proc. Finn Dent Soc. 1990 (86) 1: 23-27
Laser type: HeNe-laser (633 nm) Output: 8 mW (tube)
Pulsing: Pulsed Pulse frequency: 50 Hz
Dose: Not specified  
Power density: Not specified Treatment distance: Not specified
Laser model: Biotronical Laser MC-8    
Treated area: Not specified  
Treatment time: 120 sek before suturing and day 2 No of patientes: 17
No of treatments: 2 Time between treatm: 24 hrs
Our comments:
Assuming a 50% fibre loss and a 50% pulsing loss, the total dose will be 2 mW x 120 sec x 2= 0.48 J. This is a low total dose for such major surgery. Also the number of treatments are low.
Author: Lundeberg T, Haker E, Thomas M Ref no: [E11]  
Title: Effect of laser versus placebo in tennis elbow
Published in: Scand J Rehab Med. 1987; 19: 135-138.
Laser type: HeNe-laser (633 nm) Output: 1.56 mW
Pulsing: Continuous Pulse frequency: -
Laser type2: GaAs-laser (904) Output: 0.07 mW
Pulsing: Pulsed Pulse frequency: 73 Hz
Dose: 0.09 J/point (HeNe), 0,004 J/point (GaAs)  
Power density: Not specified Treatment distance: 1 mm
Laser model: Modell was not specified, nor if fiberoptics was used    
Treated area: 10 different acupuncture points through a 1 mm transparent plastic disc  
Treatment time: 60 sek per point No of patientes: 82
No of treatments: 10 per point Time between treatm: 2 treatm / week
Our comments:
The doses are so low that significant effects can hardly be expected.
Author: Masse J-F et al Ref no: [E12]  
Title: Effectiveness of soft laser treatment in periodontal surgery
Published in: Internat Den J. 1993; 43: 121-127.
Laser type: HeNe-laser (633 nm) Output: 0.27 mW
Pulsing: Continuous Pulse frequency: -
Laser type2: GaAs-laser (904 nm) Output: 0.8 mW
Pulsing: Pulsed, 200 ns pulse width Pulse frequency: 47.5-3040
Dose: Not specified  
Power density: Not specified Treatment distance: 1 mm
Laser model: Stomalaser, independent measuring of power    
Treated area: Not specified  
Treatment time: 2 min 30 sek No of patientes: 28
No of treatments: 1 Time between treatm:  
Our comments:
In this report, the authors studied the effect of combined HeNe/GaAs therapy on bilateral free autogenous gingival grafts and, commendably, performed independent measurement of the output specified by the manufacturer. The HeNe output, specified as 4 mW, proved actually to be 2 mW and a mere 0.27 mW after sustaining heavy losses in the fibre-optic rig. The maximum peak power output of the GaAs laser, given as 2 watts, was found to be only 0.8 watts. The size of the area treated is not specified, but assuming it was 1 cm2, the dose will be 0.0022 J/cm2 GaAs, plus 0.04 J/cm2 HeNe, that is, a total dose of 0.0422 J/cm2. Further, a single treatment is not likely to give significant results.
Author: Smith R J et al Ref no: [E13]  
Title: The effect of low-energy laser on skin-flap survival in the rat and porcaine animal model
Published in: Plastic and Reconstructive Surgery, 1992; 89 (2): 306-309
Laser type: HeNe-laser (633 nm) Output: 2.75 mW
Pulsing: Continuous Pulse frequency: -
Dose: Not specified  
Power density: 310 mW/cm2 at probe tip Treatment distance: 1 mm
Laser model: Biostim 2000    
Treated area: Four dorsally based skin flaps with distal demarcation of necrosis  
Treatment time: 30 sek/cm2 No of patientes: 82
No of treatments: 5 Time between treatm: 24 hours
Our comments:
This study specifies just about everything but the dose, although this may be calculated as being 0.0825 J/cm2 per day. Five sessions of treatment were given before the skin flaps were prepared, five afterwards. Therapeutic treatment carried out before surgical invasion of healthy tissue is probably of questionable value. The total dose per flap will therefore be 5 x 0.0825 J/cm2 = 0.4125 J/cm2. This dose is quite low. The control procedure may also be called into question since symmetrical flaps were prepared on the right and left sides of the animal and only one side was irradiated. This procedure ignores the systemic effects of laser treatment (see below).
Author: Klein R G et al Ref no: [E14 ]  
Title: Low-energy laser treatment and exercise for chronic low back pain: double-blind controlled trial.
Published in: Arch Phys Med Rehab. 1990; 71: 34-37
Laser type: GaAs (904 nm) Output: 10 diodes of each 0.4 mW
Pulsing: Pulsed Pulse frequency: 1000 Hz
Dose: Stated : 1.3 J/cm2 per point. Calculated: 0.1 J/cm2  
Power density: Not specified Treatment distance: Not specified
Laser model: Omniprobe    
Treated area: Not specified  
Treatment time: 4 min per point No of patientes: 20
No of treatments: 12 Time between treatm: Three times per week
Our comments:
The authors state that a GaAs laser was used to produce a point dose of 1.3 J/cm2, the indication being the heterogeneous diagnosis of "low back pain". However, analysis of the parameters given show that the dose was in fact only 0.1 J/cm2 (Pm = 2 W x 2 x 10 -7 sec x 1000 Hz = 0.4 mW; t = 240 sec; D = Pm x t = 0.1 J/cm2) and that the total dose was 5 J. In our experience, this recalcitrant indication calls for 2 - 4 J/cm2.
Author: Seichert N. et al: Ref no: [E8]  
Title: Wirkung einer Infrarot-Laser-Therapie bei weichteilrheumatischen Beschwerden
Published in: Therapiewoche, 1987; 37: 1375-1379.
Laser type1: GaAs-laser (904 nm) Output: (each of 5 diodes): 1.2 mW
Pulsing: Yes. 200 ns pulse width Pulse frequency: 1200 Hz
Laser type2: HeNe-laser (633 nm) Output: 6.5 mW
Pulsing: Continuous Pulse frequency: -
Dose: Not specified  
Power density: Not specified Treatment distance: 15 cm
Laser model: Space Laser MIX 5    
Treated area: Circular area, 6 cm diameter = 28 cm2  
Treatment time: 10 min = 600 sek No of patientes: 18
No of treatments: 5 Time between treatm: Once per day
Our comments:
Although the author claims that his instrument is a GaAlAs laser, it is clear from the wavelength (as from the brand) that it is actually a GaAs laser. The dose is not explicitly stated, but, for the GaAs laser, can be calculated to 600 x 0.0012 x 5/28=0.128 J/cm2. On top of this comes the NeHe dose, which is more or less the same (0.139 J/cm2). See below for the purported double-blind procedure.
Author: Mulcahy D et al Ref no: [E41]  
Title: Low level laser therpy: a prospective double blind trial of its use in an orthopaedich population.
Published in: Injury. 1995; 26 (5): 315-317.
Laser type: Not stated Output: 35 mW
Pulsing: Not stated Pulse frequency: Not stated
Dose: 1 J/cm2 “of skin”  
Power density: Not specified Treatment distance: Not specified
Laser model: Not stated    
Treated area: Not specified  
Treatment time: Not stated No of patientes: 20
No of treatments: 8 Time between treatm: 2-4 days

Our comments:
Very little is known about the parameters, such as wavelength, pulsing/continous and treatment technique. The indications are plantar fasciitis, trochanteric bursitis, tendonitis, lateral epicondylitis, knee pain, cervical pain and lumbar pain. If applied in the compressive mode, 1 J/cm2 may be a reasonable dose (but of the low side) for some of the indications but certainly subclinical for indications such as cervical pain and lumbago. The list could be made much longer.

For example, Krikorian [E15] used a HeNe laser and a dose of 0.05 J/cm2 to study wound healing in rats. Zarkovic [E16] used a GaAs laser and a dose of 0.0004 J/cm2 to study pain perception in mice. Using a HeNe laser and a dose of 0.004 J/cm2, Jarvis [E17] could (naturally) find no evidence of stimulation of thermoreceptors in humans.

It is interesting to quote the abstract of the negative study by Siebert [E40] and then compare it to the analysis made by Baxter [E35].

Siebert: “The efficacy of "athermic" lasers (HeNe/GaAs) in the treatment of tendinopathies was investigated in a randomized double-blind study. On 10 consecutive days, 64 patients (32 therapy, 32 placebo) were treated for 15 minutes each with a switched-on or switched-off laser under otherwise identical conditions. The extent of movement in involved joints (neutral 0 method) and rating on a pain scale for rest in pain, movement pain, and pressure pain before treatment, after treatment, and 2 weeks after conclusion of therapy, as well as infrared thermography, served to check therapy.
After the end of therapy, a significant reduction (P = < 0.001) of 50% was shown for resting pain as well as reductions of 30% for movement an 30% for pressure pain. This result was identical in the therapy group and in the placebo group. There was also no indication of a different result of therapy between the therapy and placebo groups with regard to the thermographic control and the extent of movement.
The breakdown of the data in terms of age, sex, and duration of disease did not provide any indications of different results for placebo or therapy. It was striking that the patients who reported sensations during or after the treatment (irrespective of whether pleasant or unpleasant) had a greater reduction of pain than the patients without sensations. This laser therapy thus did not show any effect above and beyond that in the untreated group”.

Baxter: “Despite being highly critical of the standard of previous laser research, these investigators employed a non-contact technique in their trial, irradiating the patients’ skin from a distance of 10 cm. Given the beam divergence of clinical LLLT apparatus, the use of such a distance would appear to be inappropriate, producing minimal power and energy densities on the irradiated tissue. This, coupled with the apparent inaccuracies in calculation of doasge (by a factor of 10), casts serious doubts upon the reliability and validity of the reported findings”.


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