United States Naval Flight Surgeon Handbook
2nd Edition 1998

Laser Exposure

References:

• SPAWAR 5100.12A

Points of Contact

• Unit Intelligence Officer/Safety Officer

• Armed Forces Medical Intelligence Center

• NOMI Ophthalmology, DSN: 922-3938 / 4558

Definition:

LASER - Light Amplification by Stimulated Emission of Radiation

General:
Lasers are of military usefulness by all nations for range finding, target designation and tracking. They may also be used as weapons for harassment and physical injury of opposing forces. They may be disruptive of operations by:

• Obscuring dim lights, such as Heads Up Displays

• Causing glare and interference with dark adaptation and target acquisition

• Causing damage to canopies, cameras and weapons

• Causing temporary or permanent eye damage

Laser Physics:
If energy is applied to a substance causing electrons to jump from the basal to the excited state, the same amount of energy is released as electrons return to the basal state. If that energy is released as light, the light will be of the wavelength (color) characteristic for that substance and the energy required to excite it. Thus, only a single wavelength is produced when an electron in a given molecule returns to its basal state. If that light is collimated by mirrors into a unidirectional beam, it will tend to retain its energy until dissipated by distance through the atmosphere, each wavelength absorbed by the atmosphere at different rates. So, some wavelengths will retain their energy and focus over greater distances than others. How intense the laser beam is depends upon the energy applied to excite the electrons (and therefore that released) and the excitability of the substance used. Therefore, a ruby laser is not necessarily stronger or more energetic than a neodymium laser, but the wavelengths produced have quite different properties. Each LASER will function at a discrete frequency (depending on the substance used), some of which are in the visible range, some not. Some LASER substances have more than one energy level capability on excitation, and therefore may radiate at more than one discrete frequency if different energy levels are applied.

Optical Media:
Atmospheric conditions will have an effect on LASER beams by diffusion or absorption by water vapor, smoke, etc., again depending on wavelength. Generally all LASER beams widen at least a small amount with distance. Unfortunately, the human eye has the capability of concentrating the LASER beam by a factor of about 100,000 times and focusing it on the retina. The temperature at the point of focus at the retina may be in the neighborhood of 1000 degrees, causing coagulation and destruction of that small area or, if a blood vessel is involved, a rupture of that vessel and hemorrhage into the vitreous with subsequent loss of vision. Or, since there are no pain fibers in the retina, damage may go undetected until it is discovered that there is a loss of some portion of the visual field. It is also worth noting that LASER beams may be reflected off mirror-like surfaces and picked up by the eye, losing some energy in transmission, but still dangerous. Skin burns are quite unlikely given the powers used and distances on the battlefield, and since skin does not concentrate the beam as the eye does.

The cornea will not allow all wavelengths to pass through, but acts somewhat like a filter. Wavelengths above 1300 nm (far infrared) are absorbed by the cornea and lens and may produce damage to these structures while the retina is undamaged. Thus, visible and near infrared LASERs may cause damage to the retina while far infrared LASERs cause damage to the cornea and lens structures ultimately leading to corneal scarring and cataract formation.

LASER Eye Protection
Just as with any other optical media, filters may be employed to absorb LASER light before it reaches the eye to cause damage. Unfortunately, if one were to filter out all the LASER wavelengths available, the result would be a filter which no one would be able to see through. The compromise is to filter out those frequencies most likely to be used in LASER operations, leaving as much usable visible spectrum as possible. Two examples of LASER protective goggles are shown with their absorption spectra.

Note that while the EEK-3/P would only block the Neodymium wavelength, but the aircraft canopy would block the far infrared and provide some additional protection. The LG-B goggle provides protection against several wavelengths, but would also block out considerable amounts of visible violet and blue-green wavelengths, degrading normal vision and particularly night vision. Unfortunately, there are literally hundreds of different LASERs with different wavelengths available.

The Practicalities of LASER Protection
When operating in the neighborhood (5 mi) of U.S. deployed neodymium LASERs, eye protection at the 1040 nm wavelength is needed to prevent eye damage from this invisible wavelength device. This does not help much when confronted by opposing forces who may use different wavelength devices or multiple devices. The fact is that there is no good way to predict what might be used. We do know that there have been a number of incidents reported in which the Soviets have practiced their target designation on our aircraft and ships.

At this time the recommendations are to use protection against neodymium when that is the one most likely to be used, and LG-Bs when unknown frequency LASERs are the potential threat. At night, there is greater threat of eye damage due to enlarged pupillary opening, and so LASER protection is recommended when operating within 10 miles of suspected systems.

It is also recommended that people not fixate on a target with LASER use potential, but rather to one side of it. The rational for that is to minimize the possibility of central retinal burn and complete visual loss. Obviously, when LASERs are being used around friendly forces, they cannot be trained on ships, aircraft or uncleared ground.

It is very important that LASER exposure incidents be evaluated and reported in order to gather as much data as possible in an attempt to determine wavelengths being used, allowing use of appropriate protection.

Laser Incidents
The flight surgeon should be alert to the possibility of laser incidents which may be encountered. A high index of suspicion is necessary because laser damage may be produced without any particular immediate awareness of the event by the patient. Any such events need to be evaluated and reported.

Questions Following Potential Exposure to Lasers

1. What did the patient describe as the initial event which caused him/her to seek care. How long ago did incident occur?
   

2. Was the patient wearing any type of goggles, sunglasses or other eye protection during this incident? Identify if possible.
   

3. Was there a flash of light? Have the patient describe the light to the best of his/her ability...color, intensity, continuous or pulsed source, number of pulses observed (if any)? etc.
   

4. Was the patient's vision disrupted or disturbed during or after the sighting? Any flashblindness or afterimage? Have patient describe to the best of his ability. If there was an after image what color was it or the surrounding background when the patient tried to see through it? Was the color of the image the same if the patient closed his eyes? (Positive vs. Negative after image)
   

5. Is there any lingering visual problem?

   1. visual acuity

   2. visual field defects - define limits

   3. color defects

   4. photophobia/photopsia

6. Gross physiological defects? Describe and diagram to the best of your ability.
   

7. Slit lamp defects? Describe and diagram to the best of your ability.

   1. fluorescein - corneal lesions or anterior chamber abnormalities.

8. Ophthalmoscopic defects? Describe and diagram to the best of your ability.

   1. vitreous

   2. retina

   3. hemorrhage/hole/windows

   4. edema

   PLEASE QUALIFY AND QUANTIFY THE ABOVE TO THE BEST OF YOUR ABILITY.

   DESCRIBE ANY OTHER OBSERVATIONS YOU FEEL MAY BE PERTINENT TO THE LIGHT INCIDENT BASED ON YOUR EXAMINATION, TESTING, TREATMENT, AND INTERACTION WITH THE PATIENT.

9. What is the estimated distance from the source taking into account slant angle and altitude?
   

10. Was the light directed at the patient? Did it follow the platform or did the patient move through the beam of light?
    

11. Is the patient aware of any others exposed to the light? Have they been examined by the flight surgeon?
    

12. Were any evasive maneuvers attempted by the individual? Describe please.