Biological Effects

The potential injury to the skin or eye can be significant and permanent, so every precaution must be taken to avoid this. These precautions are outline in the Control Measures section of this web site. It is also important to understand the bioeffects of exposure to the different types of lasers.

Skin Exposure is a combination of primary absorption and secondary absorption associated with internal reflection / backscatter of the beam.

Risk factors associated with skin characteristics:

- tissue texture

- absorption characteristics

- tissue density

- degree of hydration

- skin pigmentation

- chronic exposure

- phototoxic and photosensitizing chemical in skin 

- Biological effects:  

  • thermal - denaturation of proteins, coagulation, vapourization
  • ablation -  breaking of molecular bonds
  • photodisruption - plasma formation with resulting vapourization and ablation
  • acoustic shock - plasma creation with acoustic waves break structural components.
  • photochemical – energerized molecules either fluoresce or react chemically
  • absorption – when associated with low power lasers biostimulation occurs.

Eye Exposure:

  • the risk of eye damage is significant, and hence an understanding of how the location of exposure in the eye will determine the severity of the damage is required.

    Image of eye

Wavelength Band (nm)

Eye

Skin

UV-C (200-280)

Photokeratitis

Erthyema  & Cancer

UV-B (280 – 315)

Photokeratitis

Accelerated skin aging and increase pigmentation

UV-A (315-400)

Photochemical reaction

Pigment darkening, photosensitive reaction, and sunburn

Visible (400 – 780)

Photochemical cataract and thermal retinal injury

Photosensitive reaction, and skin burn

IR-A (780 – 1400)

 Cataract retinal burn

Skin burn

IR-B  (1400 – 3000)

Corneal burn, aqueous flare, possible cataract.

Skin burn

IR-C (3000 – 10,000)

Corneal burn only

Skin burn

Summary of Basic Laser Biological Effects

Courtesy of: Rockwell Laser Industries – Industrial Laser Safety 1999

Minimal Reactive Dose Levels for Skin Damage

Laser

Wavelength (nm)

Radiant Exposure* (J/cm2)

Exposure Times (sec)

Ruby

694

11 - 20 (unpigmented) 2.2 - 6.9 (pigmented)

2.5 x 10-3

Ruby (Q-switch)

694

0.25 – 0.24

7.5 x 10-8

Argon ion gas (CW)

514

4.0 – 8.2

1.0

CO2 (CW)

10,600

2.8

1.0

Neodymium glass (long pulse)

1060

2.5 – 5.7

7.5 x 10-8

Neodymium – YAG (Q-switched)

1064

46 – 78

1.0

Excimer (xenon chloride)

308

0.50

 -

* at 50% probability levels for minimal tissue reaction, except for excimer which is minimal level for tissue ablation.

Courtesy of: Rockwell Laser Industries – Industrial Laser Safety 1999

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