Safety and the Eye:
Hidden Hazards and
Osama Bader, MD, and , MD,
From the Lions Laser Skin Centre, Division of Dermatology,
Vancouver Hospital & Health Sciences Centre,
and University of British Columbia, Vancouver, B.C.
Presented at the American Academy of Dermatology
Annual Meeting Poster Session,
February 10-15, 1996
What are the effects of laser
energy on the eye?
Are there any specific symptoms of
laser eye injuries?
What types of laser safety
eyewear are available?
What are the technical
considerations for eye safety?
What factors should be
considered when selecting specific eyewear?
Practical Pearls in Laser
- (Click the images below for a
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.
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. In accordance with the ANSI
Z136.3 (1988) guidelines, each laser requires a
specific type of protective eyewear, and factors that
must be considered when selecting LSE include: laser
wavelength and peak irradiance, optical density (OD),
visual transmittance, field of view, effects on color
vision, absence of irreversible bleaching of the filter,
comfort, and impact resistance. Ignorance of any of these
factors may result in serious eye injury. As LSE often
look alike in style and color, it is important to
specifically check both the wavelength and
OD imprinted on all LSE prior to laser use, especially in
multi-wavelength facilities where more than one laser may
be located in the same room. Color coding of laser
handpieces and LSE may help to minimize confusion. LSE
should not move between laser rooms, nor should they be
carried in lab coat pockets between use. The integrity of
LSE must be inspected regularly since small cracks or
loose fitting filters may transmit laser light directly
to the eye. With the enormous expansion of laser use in
medicine, industry and research, every facility must
formulate and adhere to specific safety policies that
appropriately address eye protection.
What are the effects of laser energy on
The site of damage depends
on the wavelength of the incident or reflected laser
- 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.
Are there any specific symptoms of
laser eye injuries?
- 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
What types of laser safety eyewear are
- fit tightly on the face
- typically worn over vision-correcting
prescription eye glasses
- usually constructed with frame vents to
minimize lens fogging
- larger, heavier than spectacles or wraps
- a frame that usually has two separate
lenses with side shields
- can be made with vision-correcting
prescription eye glasses
- a frame with a single lens that covers
- usually lighter than spectacles/goggles
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What are the technical considerations for eye safety?
There are two important
1. Maximum permissible exposure (MPE),
is the level of laser radiation to which a person may be
exposed without hazardous effects or biological changes
in the eye. MPE levels are determined as a function of
laser wavelength, exposure time and pulse repetition. The
MPE is usually expressed either in terms of radiant
exposure in J/cm2 or as
irradiance in W/cm2 for
a given wavelength and exposure duration.
- Exposure to laser energy above the MPE can result
in tissue damage.
- The ANSI 136.1 standard defines MPE levels for
specific laser wavelengths and exposure
durations. Generally, the longer the wavelength,
the higher the MPE; the longer the exposure time,
the lower the MPE.
2. The Nominal Hazard Zone (NHZ)
is the physical space in which direct, reflected or
scattered laser radiation exceeds the MPE. LSE must be
worn within the NHZ.
- In practical terms, when using dermatologic
lasers the entire laser procedure room should be
considered to be within the NHZ because the laser
fiber or handpiece can be directed anywhere in
What factors should be considered when
selecting specific eyewear?
- Laser wavelength at which
protection is afforded.
- Optical density (OD) of the LSE
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
||OD = log10(Ei /Et)
= incident beam irradiance (W/cm2) for a "worse
= 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
nomograms or tables (e.g., ANSI 136.1
||(c) consulting the laser manufacturer.
- The OD of the LSE 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 design to
- Field of view provided by
the design of the eyewear.
- Absence of irreversible bleaching
when the LSE filter is exposed to high peak
- Effect on color vision: the
colored filter material may reduce color vision
and contrast, creating additional hazards. For
example, certain LSE may interfere with
visualizing monitoring equipment or detecting
cyanosis during general anesthesia.
- Impact resistance. LSE must be
resistant to dust, heat, etc., so that they will
not loose their effectiveness.
Practical Pearls in Laser Eye Safety
- Laser warning signs must be
placed at the entrance to laser operating rooms.
- Access to the laser operating room should only be
granted to those individuals who have been
appropriately educated in laser safety.
Each laser facility must develop its own Safety
Procedures to be enforced by an appropriately
trained Laser Safety Officer for
the facility. Safety procedures should be in
accordance with ANSI and OSHA guidelines (and
others, where appropriate).
- As LSE often looks alike in style and color, it
is mandatory to check the wavelength and
imprinted on each pair of LSE prior to its use.
- Color coding of the laser
handpiece and LSE may help to minimize confusion
especially in facilities where multiple laser
wavelengths are available.
- LSE should not move between laser rooms,
nor should they be carried in lab coat pockets
can be very expensive, so proper care and
handling is mandatory. The integrity of the LSE
must beinspected regularly since
small cracks or loose fitting filters may permit
the laser beam to reach the eye directly.
- The patient's eyes must always be
protected from laser energy. If the
patient is awake, appropriate opaque
"mini" goggles must be worn. Great care
must be taken to avoid accidentally exposing the
straps of the patient goggles to laser light,
since this can ignite them.
- Whenever laser energy is used in the immediate
vicinity of the eye (e.g. treating eyelids) a
steel or lead eye shield
should be positioned on the surface of the orbit
after the application of a topical ophthalmic
local anesthetic. Plastic patient eye shields
cannot be expected to withstand the thermal and
mechanical effects of pulsed lasers, and should
never be used.
- Anonymous. Laser energy and its dangers to eyes.
Health Devices 1993; 22:159-204.
- ANSI 136.1 (American National Standards Institute
) American National Standard for the safe use of
lasers. Laser Institute of America, Orlando FL,
- ANSI 136.3 (American National Standards Institute
) The safe use of lasers in health care
facilities. Laser Institute of America, Orlando
FL, 1988. [1995 revision will be released soon]
- OSHA Instruction PUB 8-1.7. Guidelines for laser
safety and hazard assessment. Occupational Safety
and Health Administration. United States
Department of Labor, Washington DC, 1991.
- Sliney DH. Laser safety. Lasers in Surg Med 1995;
We thank the Massachusetts General Hospital
Dermatology Laser Center for providing us with some of
the photographs used in this poster.
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