Photomedicine

Medical discipline involving the application of light in health and disease

Photomedicine is an interdisciplinary field of medicine that focuses on the interaction of light with biological tissues for the purposes of diagnosis, therapy, and research. It encompasses a broad spectrum of techniques and technologies involving the application of light—from ultraviolet (UV) to near-infrared (NIR)—in the management of a wide range of medical conditions.

Photomedicine is used across various specialties, including dermatology, oncology, cardiology, ophthalmology, surgery, psychiatry, interventional radiology, and sleep medicine.

History and Principles

The origins of photomedicine can be traced to ancient civilizations, where sunlight was used therapeutically—a practice known as heliotherapy. With the advancement of optical physics and medical imaging in the 20th century, the modern practice of photomedicine emerged, incorporating devices such as lasers, light-emitting diode (LED) systems, and other sources of therapeutic light.

Light used in photomedicine can produce effects through various mechanisms including:

• **Photochemical reactions**, such as in photodynamic therapy
• **Photothermal effects**, seen in laser surgery
• **Photomechanical effects**, such as in laser lithotripsy
• **Photobiomodulation**, where light influences cellular function without heating or destruction

Applications

Dermatology

Photomedicine is extensively used in dermatology for both diagnostic and therapeutic purposes:

• PUVA therapy (psoralen + UVA) is a form of photochemotherapy used in treating psoriasis, vitiligo, and eczema.
• Photodynamic therapy (PDT) is used for the treatment of precancerous lesions, acne, and non-melanoma skin cancers. Photosensitizing agents are activated by light to produce reactive oxygen species that destroy abnormal cells.
• Laser hair removal and other aesthetic dermatological procedures use selective photothermolysis to target hair follicles or pigmented lesions.
• Light therapy for acne or alopecia involves LED-based systems emitting red or blue light.

Oncology

In oncology, photodynamic therapy (PDT) is used for selective destruction of cancerous tissues. PDT involves the administration of a photosensitizing compound that accumulates in malignant cells. These cells are then exposed to light at specific wavelengths, initiating a cytotoxic reaction that destroys the tumor while sparing surrounding healthy tissue.

Psychiatry and Sleep Medicine

Light therapy is a first-line treatment for:

• Seasonal affective disorder (SAD)
• Delayed sleep phase disorder
• Circadian rhythm misalignment due to shift work or jet lag

Therapeutic light is administered using light boxes or dawn simulators that deliver high-intensity white or blue-enriched light to the retina to reset the body's circadian clock.

Cardiology

Advanced optical imaging methods like optical coherence tomography (OCT) allow high-resolution visualization of coronary arteries to assess plaque composition, aiding in the management of atherosclerosis and coronary artery disease.

Ophthalmology

• Photocoagulation using laser therapy is a common treatment for diabetic retinopathy and age-related macular degeneration.
• PDT with verteporfin is used for choroidal neovascularization.

Diagnostics and Imaging

Photomedicine enables non-invasive, real-time tissue analysis:

• Confocal microscopy and fluorescence microscopy for cellular-level examination of skin lesions and mucosal surfaces.
• Diffuse reflectance spectroscopy and Fourier-transform infrared spectroscopy (FTIR) for quantitative measurement of pigments and hemoglobin levels in tissues.
• Photoplethysmography for monitoring blood volume changes.

Emerging Technologies

• Free-electron lasers (FEL) are under research for their tunable wavelength properties in medical applications.
• Photobiomodulation (low-level light therapy) is being investigated for wound healing, inflammation reduction, and tissue regeneration.
• Intense Pulsed Light (IPL) is used for vascular and pigmented lesion treatment, and hair removal.

Advantages of Photomedicine

• Minimally invasive or non-invasive procedures
• High precision and tissue selectivity
• Minimal systemic side effects
• Real-time diagnostics and rapid therapeutic response

Limitations

• Requires careful selection of wavelength, dose, and delivery method
• Photosensitizing agents can cause sensitivity to sunlight
• Not suitable for all tissue depths or disease types

See also

• Laser medicine
• Phototherapy
• Biophotonics
• Optogenetics
• Medical imaging

External links

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