Adjustment of guidelines for exposure of the eye to optical radiation from ocular instruments: statement from a task group of the International Commission on Non-Ionizing Radiation Protection (ICNIRP)
David Sliney, Danielle Aron-Rosa, Francois DeLori, Franz Fankhauser, Robert Landry, Martin Mainster, John Marshall, Bernard Rassow, Bruce Stuck, Stephen Trokel, Teresa Motz West, and Michael Wolffe
David Sliney,1,2
Danielle Aron-Rosa,1
Francois DeLori,1
Franz Fankhauser,1
Robert Landry,1
Martin Mainster,1
John Marshall,1
Bernard Rassow,1
Bruce Stuck,1
Stephen Trokel,1
Teresa Motz West,1
and Michael Wolffe1
2chair of the task group, U.S. Army Center for Health Promotion and Preventative Medicine, Laser/Optical Radiation Program, Aberdeen Proving Ground, Maryland 21010-5422 USA
David Sliney, Danielle Aron-Rosa, Francois DeLori, Franz Fankhauser, Robert Landry, Martin Mainster, John Marshall, Bernard Rassow, Bruce Stuck, Stephen Trokel, Teresa Motz West, and Michael Wolffe, "Adjustment of guidelines for exposure of the eye to optical radiation from ocular instruments: statement from a task group of the International Commission on Non-Ionizing Radiation Protection (ICNIRP)," Appl. Opt. 44, 2162-2176 (2005)
A variety of optical and electro-optical instruments are used for both diagnostic and therapeutic applications to the human eye. These generally expose ocular structures to either coherent or incoherent optical radiation (ultraviolet, visible, or infrared radiation) under unique conditions. We convert both laser and incoherent exposure guidelines derived for normal exposure conditions to the application of ophthalmic sources.
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Table 2 is a chart that covers representative instruments and key characteristics that would influence the potential hazard and the exposure at each of the three planes of concern.
The maximum cumulative time is given in square brackets.
TH, tungsten–halogen lamp.
SLO, scanning laser ophthalmoscope. The SLO beam focal spot is the retina but the highest averaged irradiance at the nodal point.
Exposure durations apply to the time of exposure on the same tissue location.
Table 3
Exposure Limits for Unrestricted Instrument Use: Photochemical Limitsa
Hazard and Wavelength Range
Exposure Guideline Limit
Comments
UV cornea and lens
λ = 315–400 nm
HUV-A = 1 J/cm2 for t < 1000 s and EUV-A = 1 mW/cm2 for t ≥ 1000 s
Total UV irradiance limit to protect cornea and lens tissues; no spectral weighting; 1-mm aperture for irradiance averaging.
λ = 180–400 nm
EUV = 0.1 μW/cm2 (8 h). EUV = 0.4 μW/cm2 (2 h)
S(λ) spectrally weighted irradiance for cw sources used for lengthy or repeated exposures based on a maximal 2-h or 8-h exposure; 1-mm aperture for irradiance averaging.
UV cornea pulsed hazard
(single or multiple pulses) λ < 400 nm
HUV = 3 mJ/cm2
For pulsed sources in which the total integrated S(λ)-weighted radiant exposure should remain below the limit for the maximal number of daily exposures; 1-mm aperture.
Retinal photochemical hazard
λ = 305–700 nm
LB = 2 mW/(cm2 sr) for t > 10,000 s, or LV = 1 cd/cm2 external
Radiance of light source spectrally weighted against the aphakic A(λ) or phakic B(λ) function based on t > 10,000-s exposure.
Expressed alternatively as a luminance limit for a white-light source
Hr = 2.2 J/cm2 or Er = 0.22 mW/cm2 for t > 10,000 s; or 0.3 mW/cm2 for t = 2h A(λ) or B(λ) weighted
Retinal radiant exposure or irradiance for light source spectrally weighted against the aphakic A(λ) or phakic B(λ) function. Basic limit assumes 0.9 maximum transmittance of the ocular media and t > 10,000-s exposure. Averaged over 1.75 mrad or 30 μm.
In cases in which spectral weighting is noted in the Comments column, more complex spectroradiometric measurements are needed for a rigorous measurement.
Table 4
Exposure Limits for Unrestricted Instrument Use: Thermal Limitsa
Hazard and Wavelength Range
Exposure Guideline Limit
Comments
Retinal thermal hazard for
Pulsed sources
L = (5/α)t−0.25 W/(cm2 sr) or 50 t−0.25 W/(cm2 sr) for sources where α > 0.1 rad and for t < 10 s.
Applied to pulsed-light sources to protect against retinal thermal injury; R(λ) spectrally weighted radiance per pulse, or L = 50 t−0.25 W/(cm2 sr) when α > 0.1 rad. Assumes that pupil diameter constricts from 7 to 3 mm between 0.25 and 1.0 s.
λ = 380–1400 nm
At the retinal plane, Etherm = ΣEλR(λ)Δλ ≤ (0.6/α) t−0.25 W/cm2 or Etherm = (10/dr)t−0.25 W/cm2.
Applied to pulsed-light sources or very brief exposures expressed as a retinal irradiance. The angular subtense is expressed in radians. The retinal image diameter dr is in millimeters.
Continuous sources
Lttherm = 6 W/(cm2 sr) for dr > 1.7 mm. Therefore, for smaller dr,
Retinal radiant exposure or irradiance, R(λ) spectrally weighted, basic limit assumes 0.9 maximum transmittance of the ocular media.
λ = 380–1400 nm
Etherm = 0.7 W/cm2 for t ≫ 10 s and dr > 1.7 mm. Etherm = 1.2/dr W/cm2 for t ≫ 10 s and dr < 1.7mm
Lengthy exposure limit was based on near-IR limit for large retinal image areas. Retinal image diameter dr is expressed in millimeters.
IR cornea–lens thermal hazard
λ = 770–3000 nm
Ec = 1.8 t−0.75 W/cm2 for t < 20 s. Ec = 0.1 W/cm2 for t > 20 s.
cw exposure based on corneal heating of small, local areas of the cornea and lens for periods greater than 45 s and at least to 1000 s; 1-mm aperture for averaging irradiance.
λ = 770–3000 nm
H = 1.8 t0.25 J/cm2
Total radiant exposure for pulsed source or from any exposure up to 45 s.
E = 25 t−0.75 W/cm2 for pulsed sources t ≤ 10 s. E = 4 W/cm2 (i.e., 32 mW in a 1-mm-diameter zone) for cw sources.
New limit with no spectral weighting and 0.5-mm aperture for irradiance averaging for pulsed sources; and 1.0-mm aperture for irradiance averaging for cw sources. Higher irradiances up to 20 W/cm2 could be used under controlled conditions for t < 1000 s.
In cases in which spectral weighting is noted in the Comments column, more complex spectroradiometric measurements are needed for a rigorous measurement.
Tables (4)
Table 1
Current General Exposure Guidance and Hazard Thresholds at Each Relevant Ocular Plane
Ocular Plane and Guideline
Exposure Guideline
Damage
Pupil Dilation
Eye Movement Relative to Source
Measurement Aperture-to-Average Irradiance
Photosensitivity
Cornea
UV
3 mJ/cm2 effective for S(λ)
4 mJ/cm2 at 270 nm
N/A
Yes, moderate
1 mm (250 nm ≤ λ ≤ 400 nm)
UV only
Lens
UV-B
3 mJ/cm2 effective for S(λ)
600 mJ/cm2 at 300 nm
Possible increase in risk
Yes, moderate
1 mm (315 nm ≥ λ ≤ 400 nm)
UV only
UV-A
1.0 J/cm2
Photochem > 2 J/cm2 at > 315 nm. Thermal at 351–364 nm: 33 J/cm2, 1s
Possible
Yes, moderate
1 mm
UV only
IR
0.1 W cm2
4 W/cm2
Possible
Yes, moderate
1 mm
No
Retina
Photochemistry
100 J/cm2 sr effective for B(λ) or A(λ)
3 J/cm2 at the retina at 320 nm and 22 J/cm2 at 442 nm
Constricted, 3-mm pupil
Yes, very important
7 mm at cornea, but derived for 3-mm pupil and 11-mrad acceptance angle, corresponding to 180 μm at the retina
Possible
Thermal
5/αt0.25 W/cm2 sr effective for R(λ)
1–1000 W/cm2 with retinal spot size
7 mm for pulsed, but transition to 3 mm by 10 s
Yes, very important
7 mm at cornea, but variable with t and for image diameters greater than 25 μm
Table 2 is a chart that covers representative instruments and key characteristics that would influence the potential hazard and the exposure at each of the three planes of concern.
The maximum cumulative time is given in square brackets.
TH, tungsten–halogen lamp.
SLO, scanning laser ophthalmoscope. The SLO beam focal spot is the retina but the highest averaged irradiance at the nodal point.
Exposure durations apply to the time of exposure on the same tissue location.
Table 3
Exposure Limits for Unrestricted Instrument Use: Photochemical Limitsa
Hazard and Wavelength Range
Exposure Guideline Limit
Comments
UV cornea and lens
λ = 315–400 nm
HUV-A = 1 J/cm2 for t < 1000 s and EUV-A = 1 mW/cm2 for t ≥ 1000 s
Total UV irradiance limit to protect cornea and lens tissues; no spectral weighting; 1-mm aperture for irradiance averaging.
λ = 180–400 nm
EUV = 0.1 μW/cm2 (8 h). EUV = 0.4 μW/cm2 (2 h)
S(λ) spectrally weighted irradiance for cw sources used for lengthy or repeated exposures based on a maximal 2-h or 8-h exposure; 1-mm aperture for irradiance averaging.
UV cornea pulsed hazard
(single or multiple pulses) λ < 400 nm
HUV = 3 mJ/cm2
For pulsed sources in which the total integrated S(λ)-weighted radiant exposure should remain below the limit for the maximal number of daily exposures; 1-mm aperture.
Retinal photochemical hazard
λ = 305–700 nm
LB = 2 mW/(cm2 sr) for t > 10,000 s, or LV = 1 cd/cm2 external
Radiance of light source spectrally weighted against the aphakic A(λ) or phakic B(λ) function based on t > 10,000-s exposure.
Expressed alternatively as a luminance limit for a white-light source
Hr = 2.2 J/cm2 or Er = 0.22 mW/cm2 for t > 10,000 s; or 0.3 mW/cm2 for t = 2h A(λ) or B(λ) weighted
Retinal radiant exposure or irradiance for light source spectrally weighted against the aphakic A(λ) or phakic B(λ) function. Basic limit assumes 0.9 maximum transmittance of the ocular media and t > 10,000-s exposure. Averaged over 1.75 mrad or 30 μm.
In cases in which spectral weighting is noted in the Comments column, more complex spectroradiometric measurements are needed for a rigorous measurement.
Table 4
Exposure Limits for Unrestricted Instrument Use: Thermal Limitsa
Hazard and Wavelength Range
Exposure Guideline Limit
Comments
Retinal thermal hazard for
Pulsed sources
L = (5/α)t−0.25 W/(cm2 sr) or 50 t−0.25 W/(cm2 sr) for sources where α > 0.1 rad and for t < 10 s.
Applied to pulsed-light sources to protect against retinal thermal injury; R(λ) spectrally weighted radiance per pulse, or L = 50 t−0.25 W/(cm2 sr) when α > 0.1 rad. Assumes that pupil diameter constricts from 7 to 3 mm between 0.25 and 1.0 s.
λ = 380–1400 nm
At the retinal plane, Etherm = ΣEλR(λ)Δλ ≤ (0.6/α) t−0.25 W/cm2 or Etherm = (10/dr)t−0.25 W/cm2.
Applied to pulsed-light sources or very brief exposures expressed as a retinal irradiance. The angular subtense is expressed in radians. The retinal image diameter dr is in millimeters.
Continuous sources
Lttherm = 6 W/(cm2 sr) for dr > 1.7 mm. Therefore, for smaller dr,
Retinal radiant exposure or irradiance, R(λ) spectrally weighted, basic limit assumes 0.9 maximum transmittance of the ocular media.
λ = 380–1400 nm
Etherm = 0.7 W/cm2 for t ≫ 10 s and dr > 1.7 mm. Etherm = 1.2/dr W/cm2 for t ≫ 10 s and dr < 1.7mm
Lengthy exposure limit was based on near-IR limit for large retinal image areas. Retinal image diameter dr is expressed in millimeters.
IR cornea–lens thermal hazard
λ = 770–3000 nm
Ec = 1.8 t−0.75 W/cm2 for t < 20 s. Ec = 0.1 W/cm2 for t > 20 s.
cw exposure based on corneal heating of small, local areas of the cornea and lens for periods greater than 45 s and at least to 1000 s; 1-mm aperture for averaging irradiance.
λ = 770–3000 nm
H = 1.8 t0.25 J/cm2
Total radiant exposure for pulsed source or from any exposure up to 45 s.
E = 25 t−0.75 W/cm2 for pulsed sources t ≤ 10 s. E = 4 W/cm2 (i.e., 32 mW in a 1-mm-diameter zone) for cw sources.
New limit with no spectral weighting and 0.5-mm aperture for irradiance averaging for pulsed sources; and 1.0-mm aperture for irradiance averaging for cw sources. Higher irradiances up to 20 W/cm2 could be used under controlled conditions for t < 1000 s.
In cases in which spectral weighting is noted in the Comments column, more complex spectroradiometric measurements are needed for a rigorous measurement.