Laser Therapy Basics

Laser Principles - Light Fantastic!

• LASER: Light Amplification by Stimulated Emission of Radiation.
• Key Properties:
  • Monochromaticity: Single wavelength/color. Allows selective targeting of chromophores.
  • Coherence: Light waves in phase (spatial & temporal). Enhances power density.
  • Collimation: Parallel beams, minimal divergence. Maintains intensity over distance.
• These properties enable precise tissue interaction.

⭐ LASER: Light Amplification by Stimulated Emission of Radiation. Key properties: Monochromaticity, Coherence, Collimation.

Laser-Tissue Interaction - Skin's Reaction

⭐ Selective Photothermolysis: Targets specific chromophores (e.g., melanin, hemoglobin, water) using appropriate wavelength, pulse duration (ideally ≤ Thermal Relaxation Time of target), and fluence to minimize damage to surrounding tissue.

• Primary Interactions:

  • Photothermal: Heat (coagulation, vaporization); most common.
  • Photomechanical: Shockwaves (e.g., tattoo removal).
  • Photoablative: Vaporization/ablation (precise cutting).
  • Photochemical: Chemical reaction (e.g., PDT).

• Determinants of Effect:

  • Target Chromophore: Melanin, Hb, H₂O, ink.
  • Wavelength ($ ext{\lambda}$): Governs depth & target absorption.
  • Pulse Duration ($t_p$): For selectivity, $t_p ext{ \le TRT}$ (Thermal Relaxation Time).
  • Fluence (J/cm²): Energy density.
  • Spot Size: Influences penetration depth (larger = deeper).

• Light Propagation in Tissue:
  • Absorption (by chromophores): Key for effect.
  • Scattering: Influences light distribution & depth.
  • Reflection, Transmission.

Dermatology Lasers - Zap Masters

• Laser Types & Primary Targets:
  • CO₂ Laser (10600 nm): Ablative. Skin resurfacing, warts, scars, rhinophyma. High water absorption.
  • Er:YAG Laser (2940 nm): Ablative. Superficial resurfacing, pigmented lesions. More precise, less thermal damage than CO₂.
  • Nd:YAG Laser (1064 nm):
    • Q-switched: Tattoo removal (dark inks), pigmented lesions.
    • Long-pulsed: Hair removal (darker skin), vascular lesions (deeper vessels).
  • Pulsed Dye Laser (PDL) (585 nm, 595 nm): Vascular lesions (port-wine stains, telangiectasias), scars, warts.

    ⭐ Pulsed Dye Laser (PDL), typically 585 nm or 595 nm, is the gold standard for treating port-wine stains and other superficial vascular lesions like telangiectasias.

  • Alexandrite Laser (755 nm): Hair removal (lighter skin), tattoo removal (green/blue inks), pigmented lesions.
  • Diode Laser (800-980 nm): Hair removal, vascular lesions.
  • Fractional Lasers: Create microscopic treatment zones; ablative or non-ablative. For resurfacing, scars, pigmentation.

📌 Mnemonic: Cold Eskimos Never Prefer Apple Drinks (CO₂, Er:YAG, Nd:YAG, PDL, Alexandrite, Diode for common lasers).

Laser Parameters & Safety - Handle With Care

• Key Parameters:
  • Wavelength (nm): Targets specific chromophore (e.g., melanin, Hb); dictates penetration depth.
  • Fluence (J/cm²): Energy density ($E/A$); determines thermal effect & therapeutic outcome.
  • Pulse Duration (ms, ns, ps): Laser exposure time; vital for selective photothermolysis, matching Thermal Relaxation Time (TRT).
  • Spot Size (mm): Diameter of laser beam; larger spots generally penetrate deeper.
• Safety Essentials: (📌 L.A.S.E.R.)
  • Light Hazard: MANDATORY wavelength-specific eye protection (patient & all staff).
  • Access Control: Restricted area, clear warning signs, Laser Safety Officer (LSO) oversight.
  • Smoke Evacuation: Use evacuator for plume (infectious/toxic risk).
  • Electrical & Fire Safety: Non-flammable preps, wet drapes, check equipment; avoid O₂ enrichment.
  • Responsible Personnel: Trained operators & designated LSO.

⭐ Laser Safety: Mandatory eye protection specific to the laser's wavelength for both patient and operator is the most critical safety measure to prevent irreversible ocular damage. ANSI Z136 standards are key.

• Key Risks: Burns, dyspigmentation (hyper/hypo-), scarring, infection, ocular injury.

High‑Yield Points - ⚡ Biggest Takeaways

• Selective photothermolysis: Specific chromophores absorb distinct laser wavelengths for effect.
• TRT (Thermal Relaxation Time) dictates pulse duration to confine thermal damage.
• Key chromophores: melanin (pigment), oxyhemoglobin (vessels), water (ablative resurfacing).
• Q-switched lasers (nanosecond pulses) effectively treat tattoos and pigmented lesions.
• Pulsed Dye Laser (PDL) (585/595 nm) targets oxyhemoglobin for vascular lesions.
• Ablative lasers (CO2, Er:YAG) target water for skin resurfacing and scar revision.
• Laser safety is crucial: wavelength-specific eye protection mandatory for all present.