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

In recent years, laser therapy has emerged as a possible treatment option for onychomycosis. Given the variety of available lasers, this author offers insights on a couple of compact laser systems and provides a helpful primer on the technology behind laser therapy modalities.

Onychomycosis has been a historic problem because fungi are hardy and robust organisms with spores and hyphae that can survive under conditions and at temperatures more extreme than most human cells can tolerate. Many species are anaerobic or require little oxygen, and most flourish under the conditions of warm temperature and high moisture. Regions beneath the nail plate and within the nail bed and matrix form a nearly ideal environment, providing fungal colonies the ideal environment for growth.

   Topical antifungal agents have a hard time getting through and maintaining a presence long enough to be effective. Systemic antifungal medications, such as terbinafine (Lamisil, Novartis), can attack the colony from below but terbinafine can have unpleasant and sometimes serious side effects. These include liver damage, severe skin reactions and, in some cases, reported death.1 Manufacturers of oral antifungals recommend repeated blood tests, which is the standard of care.

   Most thermal therapies, including some laser therapies, are limited because dermal cells and pain sensors under the nail plate are more sensitive to temperature rises than the fungi. In addition, the use of laser therapy is contraindicated in patients with compromised circulation and a lack of sensation as it may cause burning and tissue injury.

   Light in the near infrared spectrum and specifically at wavelengths around 1 µm transmits well through the nail plate, even when it is reasonably compromised by infection. Most dermal tissues absorb such wavelengths as 1,064 nm but the penetration is less than 1 cm. The fungi that colonize the nail more strongly absorb these wavelengths. (For more insights on how lasers function, see the sidebar “What You Should Know About The Science Behind Lasers” at the right.)

A Closer Look At The Potential Benefits Of Compact Laser Systems

Unfortunately, in my experience, there is currently no insurance coverage for the use of laser therapy to treat onychomycosis. We are currently in a market where it is crucial to offer a reasonably priced treatment to the public. When purchasing a laser, it is essential to acquire one that is cost-effective, offers multiple treatment functions for podiatry and is affordable at the same time.

   Granted, there are many choices when it comes to offering laser therapy to our patients. The use of diode lasers provides the perfect opportunity for podiatrists to treat pain and inflammation without the use of local steroid injections and/or non-steroidal anti-inflammatory drugs (NSAIDs). Over the years, hundreds of patients have received referrals to or sought out my practice due to this physical medicine aspect of diode lasers.

   Today, there are therapeutic lasers available with average power levels, typically in the range of 5 W to 30 W per diode, which deliver the necessary dose at the needed depth of penetration in a reasonable amount of time. The cost per average watt per treatment minute at the needed depth of penetration is well within the financial model of the average patient.

   Nexus lasers (USA Laser) provide the necessary power density and dose at all levels of tissue depth to produce excellent clinical results that increase patient referrals. The Nexus laser weighs less than 3 pounds and is essentially a combination of a diode laser and a surgical laser. It has two hand-pieces, one for pain and inflammation and one for soft tissue ablation, which includes warts and toenail fungus. It is a replacement for our old CO2 lasers.

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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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