Can Compact Lasers Have An Impact For Onychomycosis?

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What You Should Know About The Science Behind Lasers

The main characteristic of the laser’s electromagnetic waves is the wavelength, which is measured in nanometers. For clinical purposes, a second characteristic of lasers that is very relevant is the average power, which is measured in watts.

As with many other types of waves, laser energy can be reflected, transmitted, absorbed, scattered or refracted. A chemical reaction occurs only when cells absorb light. When absorbed by cells, laser light converts into either heat or biochemical energy. Different wavelengths affect the conversion in different proportions. For example, a wavelength such as 1,064 nm will interact with soft tissues to optimally convert into heat for an ablative effect. Another wavelength such as 2,400 nm will interact more effectively with bone. The amount of light energy that converts into biochemical energy is minimal, which ensures maximum ablative efficiency.

Most human tissues are poor absorbers of lasers with wavelengths of 600 nm and 1000 nm, which would produce less conversion to heat and would allow for deeper tissue penetration. As all of the therapeutic lasers in the market today have wavelengths in the therapeutic window (between 600 and 1,000 nm), they all meet the first criterion to be able to deliver light energy into the tissue. It is for these reasons that the Nexus line of lasers have either 810 nm or 980 nm wavelengths.

The power of the laser device is the second factor for effective delivery of light energy into the target tissue for absorption. A laser device could have the appropriate wavelength and still be unable to drive the light energy to the tissue that needs treatment. This is not unlike standard radiography equipment. Therapeutic lasers need to have the appropriate wavelength and power to produce the desired therapeutic effects in the tissue one is treating.

Numerous researchers have stated that therapeutic lasers do not provide positive clinical effects and provide no negative side effects.2,3 By analyzing the articles that reported no clinical effects, one easily finds a pattern: most of these researchers in these studies used low doses in their clinical trials and this was usually due to using a low-powered laser instrument.

The dose in laser therapy is the amount of light energy, measured in joules, delivered to a given unit area during a treatment session. Simply stated, 1 J of energy is delivered by a 1-W laser emitter for one second or other combinations of the two parameters laser power (in watts) and time (in seconds). Therefore, energy density is the energy per cm2 (J/cm2).

Power density is the amount of power (watts) delivered to 1 cm2 of tissue area. One determines this by the size of the treatment applicator and the emitted power. One can conclude that the larger the applicator, the lower the power density because the treated area is larger. Likewise, the lower the average power of the device, the lower the power density because the beam is not as intense. The same results are present in lasers with multiple diodes with the same average power. The power density of a laser with multiple diodes is lower than lasers with a single diode. Research has determined that power density plays a major role in the therapeutic process.4

Tuner and Hode demonstrated that the optimum dose necessary to obtain therapeutic effects at the treated tissue should be at least 4 J per cm2.5 To estimate the energy reaching the target tissue, one must consider the depth of the treated area and the composition of the layers of tissues between the laser applicator and the treated tissue.

A typical laser device in the United States emits approximately 7 milliwatts of power using a 635-nm laser diode (red light). As a comparison, a laser pointer commonly used for presentations typically emits 3 to 5 milliwatts of power in the 660-nm range. On a per-milliwatt basis, the cost comparison between them is staggering. In terms of energy density, the same typical therapeutic laser, as reported by the manufacturer, delivers 0.0002 to 0.0003 J per minute/cm2. As an illustrative example, to deliver the minimum necessary energy at a skin target tissue (no tissue penetration needed) to obtain therapeutic value would take approximately 2,500 minutes.

Author(s): 
David Zuckerman, DPM, FACFAS

   Of the pulsed format lasers, there are several types that are distinguished by the duration of the laser pulses. The most common are long-pulsed lasers and Q-switched lasers. Long-pulsed lasers have typical pulse durations in the millisecond (10-3 s) to microsecond (10-6 s) range and Q-switched lasers have pulse durations in the nanosecond (10-9) range. For a given pulse energy, generally expressed in units of millijoules or joules, the shorter the pulse duration, the higher the laser’s peak power. Continuous wave and long-pulse lasers interact with biological materials (“biomatter”) dominantly through photothermal means. In other words, the energy in the light absorbed rapidly converts into heat, causing a temperature rise in the material illuminated. Q-switched laser pulses additionally can interact more disruptively, causing photoacoustic, photoablative and other photomechanical effects.

   With lasers, selectivity is key as the anti-targeting of its surroundings can be every bit as important targeting a specific bio-entity. Selective photothermolysis is a process that uses differential light absorption to selectively heat and kill a targeted cell type. One can use this process when there is a wavelength at which the bio-target has stronger specific absorption than the surrounding tissue and when the absorbed energy can be confined within the target for times long enough for thermal necrosis to occur in the target. This process is abetted by poor thermal transport between the target and its surrounding tissue and by good cooling of the anti-targeted tissue due to blood circulation or, when possible, by external means.

In Conclusion

There are several lasers on the market that unfortunately are not well designed for the podiatric market. They are too large, too expensive and cost patients more money than they are willing to spend. The future of podiatry is compact, multi-task lasers that the doctor is able to offer to patients at a reasonable price without extensive marketing. These lasers can also make very nice revenue for the practice.

   Dr. Zuckerman is a Fellow of the American College of Foot and Ankle Surgeons. He practices at Foot Specialists in Woodbury, N.J. and is the Medical Director and CEO of Clearly Beautiful Nails Mobile Laser in Cherry Hill, N.J.

   The author acknowledges Nelson Marquina, MSc, PhD, DC, and Donald Heller, PhD, for their assistance in laser research.

   Editor’s note: Dr. Zuckerman is a consultant to Light Age, Inc.

References

1. Prescribing information, terbinafine (Lamisil, Novartis).

2. Joensen J, Demmink JH, Johnson MI, et al. The thermal effects of therapeutic lasers with 810 and 904 nm wavelengths on human skin. Photomed Laser Surg. 2011; 29(3):145-53.

3. Venezian GC, da Silva MA, Mazzetto RG, Mazzetto MO. Low level laser effects on pain to palpation and electromyographic activity in TMD patients: a double-blind, randomized, placebo-controlled study. Cranio. 2010; 28(2):84-91.

4. Bjordal JM, Couppé C, Chow RT, Tunér J, Ljunggren EA. A systematic review of low level laser therapy with location-specific doses for pain from chronic joint disorders. Aust J Physiother. 2003; 49(2):107-16.

5. Tunér J, Hode L. Laser therapy, clinical practice and scientific background. Prima Books, Sweden, 2002.

6. Data on file, Light Age.

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Dr. Eric Bornsteinsays: November 18, 2011 at 1:24 pm

There are two major factors that need to be taken into account when discussing lasers and podiatric therapeutic indications that are missing here for this discussion of onychomycosis.

First, the perimeter of a human nail is made up of three right angles (a three sided square) with a rounded edge at the proximal tip.

For an area like this to be correctly and adequately irradiated with laser energy, there needs to be a Uniform Beam Dosimetry across the entire diameter of the treatment spot. Only this will deliver a uniform therapeutic dose across the entire area of a nail being treated. The only device that accomplishes this task is the Noveon Podiatric Laser.

A uniform beam dosimetry is also known as a “flat-top projection” of laser energy. This is in contrast to a “Gaussian projection," which contains a hot spot and is non-uniform in its energy delivery, which is the delivery mechanism of most commercial near-IR devices.

Also, the Noveon treatment spot geometry is a larger flat-top circle. Hence with this difference in beam geometry, there is always a small area of paronychial tissue surrounding the nail that is included within the treatment area spot size. With distal lateral onychomycosis, this is necessary to help prevent re-infection.

Second, one should carefully review the peer-reviewed literature describing IRB approved human clinical trials before making any treatment decisions with lasers for their patients. In this way, good evidence based medicine can be practiced for potential patients. The largest body of this literature can be found below.

When a laser company tells you the data "is on file" and not published, one should ask the question why? If they do not have data, one should ask "Then how do I know what amount of energy to use?" and "Who has evaluated the use of this energy?"

Dr. Eric Bornstein
Chief Science Officer
Nomir Medical Technologies

Landsman, A. et al. (2010) Treatment of Mild, Moderate and Severe Onychomycosis Using 870nm and 930nm Light Exposure J. of the Am. Pod. Med. Assoc. 2010 100:166-177

Bornstein E., S. Gridley, and P. Wegender (2010) Photodamage to Multidrug-resistant Gram-positive and Gram-negative Bacteria by 870 nm/930 nm Light Potentiates Erythromycin, Tetracycline and Ciprofloxacin. Photochem. and Photobiol Volume 86 Issue 3, Pages 617 - 627

Bornstein E.S. (2009) A Review of current research in light-based technologies for treatment of podiatric infectious disease states. J. of the Am. Pod. Med. Assoc. 99 (4), 348-352.

Bornstein E., W. Hermans, S. Gridley, and J. Manni (2009) Near infrared Photo-inactivation of bacteria and fungi at physiologic temperatures. Photochem. and Photobiol. 85, 1364–1374

Bornstein E.S. (2009) Treatment of onychomycosis using the noveon® dual-wavelength laser. FDA Pivotal Study data presented at Council for Nail Disorders 13th Annual Meeting, San Francisco, CA, March 5, 2009.

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