Fluorescence Photobiomodulation

Annette Lundberg, DVM and Amelia White, DVM, MS, DACVD | Auburn University College of Veterinary Medicine | Published: Issue 3 2023

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Photobiomodulation is the use of visible to near-infrared light waves to create therapeutic changes in the skin. Fluorescence photobiomodulation is a subset of this and has been used to treat cutaneous infections, inflammatory conditions, and wounds. It has a favorable safety profile and offers another option in the treatment of dermatologic diseases in veterinary species.

Photobiomodulation and Fluorescence

Photobiomodulation

Photobiomodulation uses the interaction of visible (400-750nm) to near-infrared light waves with endogenous cellular chromophores such as water, melanin, porphyrin, flavins, and cytochrome C oxidase to create a desired effect (e.g. reduction of inflammatory mediators, activation of fibroblasts and keratinocytes, decreased bacterial adhesion to keratinocytes, bacterial killing, etc.). The wavelength, intensity, and duration of illumination influence the effects of light on tissue.

Blue light (400-495 nm) has the shallowest penetration into the skin, reaching the epidermis and superficial dermis. Bluelight primarily has been studied for its antimicrobial effect. The antimicrobial effect is thought to be due to blue light triggering the production of reactive oxygen species within the bacterial cells resulting in cell death. Blue light phototherapy has been shown to alter the structure of methicillin-resistantS. aureus(MRSA), which disrupts the cell membrane and decreases its ability to replicate. Human studies have found efficacy against fungal species such as Candida sp., Malasseziasp., and dermatophytes.

Green light (495- 570 nm) can penetrate the mid-dermis. It has been studied for its effects on wound healing, osteoblast differentiation, alteration of melanogenesis, and regulation of intracellular calcium. Yellow and orange light (570-600 nm)can stimulate collagen synthesis, improve wound healing, and reduce skin pathogens. Red light (600-750 nm) can reach the deep dermis or hypodermis depending on the thickness of the skin. This set of wavelengths has been studied for its effect on wound healing and demonstrated to reduce inflammation, increase collagen synthesis, and induce the proliferation of mesenchymal stem cells and epithelial cells. The primary proposed mechanism of the effects of red light on wound healing is the stimulation of adenosine triphosphate within the mitochondria.

Fluorescence Photobiomodulation

Fluorescence photobiomodulation is a form of photobiomodulation in which the light emitted from the initial light source is altered by an exogenous chromophore. This creates longer wavelength photons and expands the therapeutic potential. The commercially available form of fluorescence photobiomodulation is called the Phovia™ System made by Vetoquinol. This system uses a topical photoconverting hydrogel

and a blue light-emitting diode (LED) lamp. The interaction of the light from the LED lamp and photoconverting hydrogelemits low-energy fluorescence within the 500-700 nm range. Fluorescence photobiomodulation has been studied in a number of conditions in dogs including superficial pyoderma, deep pyoderma, interdigital pyoderma, perianal sinuses, otitis external, acute traumatic wounds, chronic wounds, and surgical wounds. It has also been used by the authors as an adjunct treatment in the management of feline eosinophilic granulomas, inflammation associated with allergies, and anal sac rupture. Additionally, the authors have implemented Phovia™ light therapy in the treatment of dermatological diseases in birds, small mammals, horses, and cats. The primary proposed mechanism of fluorescence photobiomodulation in wound healing is the stimulation of adenosine triphosphate within the mitochondria. The blue-green wavelengths may also help regulate intracellular calcium. In a study on canine deep pyoderma, areas treated with fluorescence photobiomodulation showed less tissue inflammation when compared to systemic antibiotics alone. A similar finding was demonstrated in a study on canine surgical wounds. In both studies, this was evidenced on a molecular level with a decrease in the pro-inflammatory marker tumor necrosis factor-∝and an increase in the anti-inflammatory markers such as epidermal growth factor and collagen III.

Clinical Use

Application

The use of Phovia™ System is typically well tolerated by patients. In most cases, it can be performed without the need for sedation. However, in cases where the patient is in pain or does not allow contact with the affected area, sedation may be required. The photoconverting hydrogel comes in two parts: a jar of clear hydrogel and an ampule of orange photoconverter liquid. The two parts are combined prior to application. Once combined the photoconverting hydrogel is only stable for 24 hours at refrigeration and should be kept in a dark area.

If any debris or crusting is present on the lesion, the area should be gently cleaned prior to treatment to avoid any impedance to the ability of the light to reach the skin. The photoconverting hydrogel is then applied to the affected area such that it is approximately 2 mm thick. The LED lamp is positioned above the lesion as close to the skin as possible without touching it. Once the “on” button on the LED lamp is pressed, the light turns on for two minutes. Following the two minutes, the LED lamp will automatically turn off. The hydrogel should be removed from the skin using gauze soaked in sterile saline. As blue light is emitted by the LED lamp, the users should wear appropriate blue-light filtering protective goggles and the patient’s head should be facing away or their eyes covered while illumination occurs.

The manufacturer recommends that the treatment be performed twice per week. This can either occur as a single treatment once every three to four days. Alternatively, the treatments can be performed consecutively with a one-minute resting period. When using consecutive treatments, the hydrogel should be removed and reapplied between illuminations. The treatment has a favorable safety profile; however, topical reactions occur rarely.

Role in Treating Skin Infections

Antibiotic resistance is a growing concern in both human and veterinary medicine. It represents the largest health concern worldwide. Due to this, there is an increasing need for effective alternatives to systemic antibiotics. Topical antimicrobial therapy treatments are excellent alternatives in the case of surface or superficial skin infections with bacteria or yeast. These reach high concentrations on the skin with few systemic side effects and are available in many formulations including shampoos, conditioners, mousses, and wipes. However, the application of topical antimicrobial therapies can result in complex treatment plans and high caretaker burden. Additionally, topical therapy is not typically effective for deep skin infections. Therefore, therapy that decreases owner burden but still limits the use of systemic antibiotics is crucial.

Fluorescence photobiomodulation is an example of this. For many clients, bringing their pet to the veterinary office once twice weekly may be more convenient than administering oral medication or applying topical medications once to twice daily. An appointment for two consecutive treatments typically takes 15 minutes and can be performed as a technician appointment. It is important to communicate with clients that superficial skin infections can take three to four treatments to achieve resolution and deep infections typically take longer. Combining fluorescence photobiomodulation with other topical treatments and addressing the underlying cause of the infection can lead to even higher success rates.

Studies in dogs demonstrated that Phovia™ as a sole therapy even speeds the time to healing by 36% in canine superficial pyoderma as compared to dogs receiving oral antibiotics alone. In one study, dogs with superficial pyoderma were treated with Phovia™ alone or with an oral antibiotic alone. Dogs treated twice weekly with Phovia™ demonstrated complete clinical healing 2.3±0.7 (p<0.05) whereas dogs receiving oral antibiotics healed in 3.75±1 weeks. Additionally, it has been demonstrated to speed time to healing by nearly 50% in deep pyoderma when used with an oral antibiotic (5.7 weeks of treatment) compared to dogs receiving only oral antibiotics (11.7 weeks of treatment).

Role in Wound Treatment

Fluorescence photobiomodulation can aid in wound healing. The authors typically use it in conjunction with other wound management therapies. It has been used successfully in the management of wounds in dogs, cats, and horses. In a study on canine surgical wounds, fluorescence photobiomodulation was found to increase the expression of factors that play a role in epithelial growth and collagen deposition such as factor VIII, epidermal growth factor, decorin, and collagen III, while increasing the expression of the pro-inflammatory marker, TNF-∝, when compared to untreated skin. On histological evaluation, the treated skin was found to have less inflammation of the dermis, greater and more regular collagen deposition, and high neoangiogenesis.

Conclusion

Studies over the last 50 years have demonstrated photobiomodulation as an effective and safe treatment for dermatological conditions. The ability of fluorescence photobiomodulation to eliminate or significantly reduce the duration of exposure to antibiotics in veterinary species will decrease the spread of antibiotic-resistant bacterial strains within pets and people. Veterinarians continue to play an important role in the One Health initiative, and application of Phovia™ in everyday cases will contribute to this standard of care.

Annette Lundberg, DVM

Dr. Annette Lundberg obtained her DVM degree from the University of Minnesota. She completed a rotating internship at the ASPCA Animal Hospital in New York City and a specialty internship in dermatology at the University of Minnesota before coming to Auburn University for her residency.

Amelia White, DVM, MS, DACVD

Dr. Amelia White received her DVM degree from the University of Georgia College of Veterinary Medicine. She was accepted to a dermatology residency at the University of Illinois at Champaign-Urbana the following year. Dr. White became a diplomate of the American College of VeterinaryDermatology in 2014 and is an associate clinical professor of dermatology at Auburn University College of Veterinary Medicine.

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