Eyes Must Be Protected During Laser/Light Treatments!

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Eyes Must Be Protected During Laser/Light Treatments!

PostPosted by DCNGA » Sun Jan 15, 2012 12:48 pm

http://www.wickedlasers.com/laser-tech/ ... afety.html

Laser Safety and the Eye:

THE UNPROTECTED HUMAN EYE is extremely sensitive to laser radiation and can be permanently damaged from direct or reflected beams. The site of ocular damage for any given laser depends upon its output wavelength. Laser light in the visible and near infrared spectrum 400 - 1400 nm (the majority of lasers used in dermatology) contributes to the so-called "retinal hazard region" and can cause damage to the retina, while wavelengths outside this region (i.e., ultraviolet and far infrared spectrum) are absorbed by the anterior segment of the eye causing damage to the cornea and/or to the lens.

The extent of ocular damage is determined by the laser irradiance, exposure duration, and beam size. As laser retinal burns may be painless and the damaging beam sometimes invisible, maximal care should be taken to provide protection for all persons in the laser suite including the patient, laser operator, assistants, and observers.

Protective eyewear in the form of goggle, glasses, and shields provides the principal means to ensure against ocular injury, and must be worn at all times during laser operation. Laser safety eyewear (LSE) is designed to reduce the amount of incident light of specific wavelength(s) to safe levels, while transmitting sufficient light for good vision.

The site of damage depends on the wavelength of the incident or reflected laser beam:


Laser light in the visible to near infrared spectrum (i.e., 400 - 1400 nm) can cause damage to the retina resulting in scotoma (blind spot in the fovea). This wave band is also know as the "retinal hazard region".

Laser light in the ultraviolet (290 - 400 nm) or far infrared (1400 - 10,600 nm) spectrum can cause damage to the cornea and/or to the lens.

Eye Absorption Site vs. Wavelength:

Different wavelengths of light are absorbed in different parts of the eye. Visible light reaches the retina for image perception. Other wavelengths interact with eye tissue differently. Where the laser energy will be absorbed in the eye depends on the light's wavelength.

Notice that visible and near infrared light are focused onto the retina by the eye's lens. This makes the eye much more sensitive to injury from light in this wavelength range (400 nm ? 1400 nm) because the focusing by the lens increases the power density in the laser beam.


The damage mechanisms are similar no matter where the light is absorbed. The basic types of damage are thermal burns, photochemical reactions, and acoustic shock. The last mechanism, acoustic shock, is caused by high-intensity short-pulse lasers when the laser light causes a sudden vaporization of tissue which then causes a shock wave to spread, tearing other tissues in the eye. Photochemical reactions either cause cloudiness in eye tissues or a loss of light sensitivity.

Near UV light that is absorbed in the lens changes proteins there causing them to become cloudy (cataracts) which blurs and dims vision. Blue light which is focused on the retina can also induce a photochemical reaction which causes the light receptors in the eye to loose sensitivity. This is known as photo bleaching and mostly effects blue color vision.

Long exposure to bright sunlight can cause this type of vision loss. Infrared and far UV light that is absorbed in the cornea produces an effect called photo keratitis, which can be an irritation to the eye that causes pain and watering in the eye, or it can cause some pigmentation to occur in the cornea (welder's flash) in the case of UV light.

The effect is similar to cataracts. Injuries to the outer parts of the eye or tearing of the eye's back wall can be corrected by surgery (and with contact lenses.) Photo bleaching or thermal burns to the retina cannot be healed and result in permanent loss of vision.

Specific symptoms of laser eye injuries:
The site of damage depends on the wavelength of the incident or reflected laser beam:

•Exposure to the invisible carbon dioxide laser beam (10,600 nm) can be detected by a burning pain at the site of exposure on the cornea or sclera.
•Exposure to a visible laser beam can be detected by a bright color flash of the emitted wavelength and an after-image of its complementary color (e.g., a green 532 nm laser light would produce a green flash followed by a red after-image).
•When the retina is affected, there may be difficulty in detecting blue or green colors secondary to cone damage, and pigmentation of the retina may be detected.
•Exposure to the Q-switched Nd:YAG laser beam (1064 nm) is especially hazardous and may initially go undetected because the beam is invisible and the retina lacks pain sensory nerves. Photoacoustic retinal damage may be associated with an audible "pop" at the time of exposure. Visual disorientation due to retinal damage may not be apparent to the operator until considerable thermal damage has occurred.

The part of the electromagnetic spectrum relevant to lasers is divided into seven wavelength regions as follows:

Wavelength Regions relevant to Lasers Ultraviolet C: 100-280 nm B: 280-315 nm A: 315-400 nm

Visible 400-760 nm
Infrared A: 760-1400 nm B: 1400-3000 nm C: 3000-106 nm

•Ultraviolet C radiation is responsible for photokeratitis of the cornea and erythema of the skin (sunburn).
•Ultraviolet B radiation is responsible for photokeratitis of the cornea, skin cancer, and accelerated aging.
•Ultraviolet A radiation is responsible for photochemical cataracts, pigment darkening and skin burn.
•Visible radiation is responsible for photochemical and thermal retinal injury, photosensitive skin reactions and skin burn.
•Infrared A radiation is responsible for cataracts and retinal burns and skin burns.
•Infrared B radiation is responsible for corneal burns, cataracts, damage to the aqueous humor, and skin burns.
•Infrared C radiation is responsible for corneal and skin burns.
Factors to considered in laser safety eyewear selection:
•Laser wavelength at which protection is afforded.
•Optical density (OD) of the laser safety eyewear for the wavelength being used. OD refers to the ability of a material to reduce laser energy of a specific wavelength to a safe level below the MPE. It can be expressed by the following formula:

OD = log10(Ei /Et) Ei = incident beam irradiance (W/cm2) for a "worse case exposure"
Et = transmitted beam irradiance (MPE limit in W/cm2)

Example: OD of 4.0 allows 1/10,000 of the laser light energy to be transmitted.

The required OD for any given laser can be determined by:

(a) calculation,
(b) consulting nomograms or tables (e.g., ANSI 136.1 guidelines), or
(c) consulting the laser manufacturer.

The OD of the laser safety eyewear will decrease if the LSE is damaged. The damage threshold refers to the maximum protection that the LSE will provide for at least 5 - 10 seconds following noticeable melting or flame.
•Comfort of the laser safety eyewear design to enhance compliance.
•Field of view provided by the design of the eyewear.
•Absence of irreversible bleaching when the laser safety eyewear filter is exposed to high peak irradiance.
•Effect on color vision: the colored filter material may reduce color vision and contrast, creating additional hazards.
•Impact resistance. laser safety eyewear must be resistant to dust, heat, etc., so that they will not loose their effectiveness.
"It is a good thing to learn caution from the misfortunes of others."

"If you wish to succeed in life, make perseverance your bosom friend, experience your wise counselor, caution your elder brother, and hope your guardian genius."
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