Risk Management Services

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Laser Safety and Program Development

Laser Beam Injuries

Laser Beam Injuries

High power lasers can cause skin burns and severe eye injuries resulting in permanent vision loss.

Laser Bioeffects: Skin

Skin Sensitivity: - Epidermis (UV-B, UV-C) - Dermis (IR-A)

1)Thermal:

Most laser skin injuries are thermal in nature. Exposure to high power beams at all wavelengths can result in skin burns. These burns usually do not lead to long-term disability, but they can have painful short-term consequences. Far IR light, such as that from CO2 lasers, is absorbed strongly by water in the skin and results in a surface burn. Near IR light with wavelengths close to 1 mm, such as that from a Nd:YAG laser, penetrates more deeply into tissue and can result in deeper, more painful burns.

Skin Sensitivity: - Epidermis (UV-B, UV-C) - Dermis (IR-A)

(Thermal continued)

If a high power laser beam is focused on the skin, it can vaporize tissue and drill a hole or produce a cut if the beam or tissue is moving. CW beams will cauterize the tissue preventing bleeding. Focused short pulses form repetitive pulse Q-switched lasers vaporize tissue without heating the surrounding tissue enough to cauterize. Exposures to focused Q-switched beams can result in cuts several millimeters deep that bleed freely.

Laser Bioeffects: Skin

Skin Burn from CO2 Laser Exposure

Accidental exposure to partial reflection of 2000 W CO2 laser beam from metal surface during cutting

2) Acoustic: Localized vaporization of tissue can create a mechanical shockwave to be propagated through the tissue. These shockwaves can cause tearing of surrounding tissue. 3) Photochemical Effects: Causes changes to the chemistry of cells, which can result in changes to tissue. Photochemical skin injuries include sunburn and the possibility of promoting skin cancer by repeated low level exposures over long periods of time. Chronic effects can include cataract formation and skin aging. The best way to avoid these issues is to enclose high power UV beams.

Laser Bio-effects: Skin

Visual Response

Laser Bioeffects: Eye

Laser Spectrum

10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102

LASERS

200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 10600

Ultraviolet Visible Near Infrared Far Infrared

Gamma Rays X-Rays Ultra- Visible Infrared Micro- Radar TV Radio

violet waves waves waves waves

Wavelength (m)

Wavelength (nm)

Nd:YAG

1064

GaAs

905

HeNe

633

Ar

488/515

CO2

10600

XeCl

308

KrF

248

2w

Nd:YAG

532

Retinal Hazard Region

ArF

193 Communication

Diode

1550

Ruby

694

Lasers operate in the ultraviolet, visible, near infrared, and far infrared regions of the spectrum.

Alexandrite

755

Eye Anatomy of Concern in Laser Injury

Microwaves and Gamma Rays

• Wavelength of microwaves are too large to interact with the eye

• Wavelength of Gamma waves are too small to interact with the eye (at the cellular level)

400-1400nm Affects the retina

The Retinal Hazard Region

Optical Portion of Electromagnetic Spectrum

UV-C (Extreme) 1 - 280 nm

UV-B (Far) 280 - 315 nm

UV-A (Near) 315 - 380 nm

Visible Light 380 - 780 nm

Near IR (IR-A) 780 - 4000 nm

Middle IR (IR-B) 4um - 14 um

Far IR (IR-C) 14um – 100 um

UV-C (100-280nm) Cornea surface

UV-A (315-400nm) Affects the lens

UV-B (280-315nm) Absorbed by the cornea

Ultraviolet region

λ nm

280

300

320

340

360

% UV

Absorption

100

92

45

37

34

6

16

14

12

2

36

48 52

1

1

2

Absorption of UV on Different Parts of The Eye

Ultraviolet Effects on the Eye

UV-A Lens Absorption:

(315-380nm) - Injuries permanent - Cataractogenisis - Elasticity loss Retinal Absorption: - Not normally affected - Possible if photosensitized

UV-B/C Corneal Absorption:

(280-315nm) - Photokeratitis (6-12hr onset) (1-280nm) - Conjunctivitis - Photochemical reaction - Permanent scarring

Far IR

Affects cornea and aqueous humor

Near IR (< 1400nm) Affects the retina

Infra-red Region

Visible and Near Infrared Effects on the Eye

Retinal Hazard Region: 400-1400nm

• Elevated irradiance at retina

• Partially a function of pupil size

• Exposure duration is critical

• Thermal injury by protein denaturation

• Acoustical damage

Middle and Far Infrared Effects on the Eye

• Cataractogenisis: acute exposure

• Cataractogenisis: chronic exposure

• Corneal flash burns

• Thermal injury to conjunctiva, iris etc.

25 m

Photo courtesy of U S Air Force

THERMAL BURNS

ON PRIMATE RETINA

This image shows the macula of the eye of a rhesus monkey. The light spots on this retina were produced by 0.25 s exposures to a green laser beam with a power of 10 mW. Each of these exposures heated the retinal tissue to the point that the protein cooked, producing a “white burn”. This is the most common type of laser eye injury in humans. It is likely that thousands of people have received these small retinal burns. They are permanent blind spots. If the burn is outside the macula, the effect on vision is small. If the burn is inside the macula, the effect is much greater. One such burn in the center of the macula will mean that you cannot thread a needle using that eye. A slightly larger spot or multiple spots will make reading difficult. This type of injury can be prevented by wearing laser safety eyewear.

Multiple Pulse Retinal Injury

This is an image of the retina of a human who experienced an eye injury from a repetitive pulse near infrared laser. The beam was invisible. In such cases people do not usually realize they are being exposed until their vision has been severely effected. The person’s eye was moving during this exposure. This resulted in a line of laser burns on the retina. This is a color enhanced image to better show the laser damage. The macula of the eye is located out of the photo to the lower left. This individual was lucky that the damage did not extend into the macula. The correct laser safety eyewear would have prevented this injury.

Photo courtesy of U S Army Center for Health Promotion and Preventive Medicine

Eye Injury by Q-Switched Laser

This is a human eye injury resulting from four pulses into the macular region from an AN/GVS-5 Nd:YAG laser rangefinder. The pulse duration was about 20 ns and the pulse energy was about 15 J. The safe exposure limit for this pulse duration is 2 mJ per pulse. Thus, this exposure was 7500 times the safe level. Short pulse lasers produce the greatest eye hazards. Each short pulse results in a tiny explosion in the retina. The resulting shockwave causes severe damage to the retinal tissue. This photo was taken three weeks after the exposure. It shows the permanent destruction of the macular region. Visual acuity in the eye is approximately 20/400 and will not improve.

Corneal Burn from CO2 Laser Exposure of Rabbit Eye

This is a surface burn on the cornea of a rabbit’s eye caused by exposure to a CO2 laser beam of a few watts. All the laser energy was absorbed by water on the surface of the cornea. This heated the cornea causing the protein in the corneal tissue to cook. Human eye injuries from far infrared lasers have been rare, but they have occurred.