The crux of aerospace medicine is the identification of medical conditions that lead to sudden and unanticipated incapacitation of the flyer. Screening for disease is performed during the initial flight physical and then reviewed annually for concerning changes in health and wellness. This is the flight physical. There are, however, a number of external threats that can arise without warning. One common source for a potential in-flight incapacitation is acute ocular injury secondary to LASER exposure- Laser eye injury.
A visually impaired pilot is clearly at considerable risk for catastrophic loss of aircraft and crew. While weaponized laser technology remains a real threat in the combat arena, the more common source for exposure is through commercially available laser pointers. These exposures are much less likely to cause actual ocular injury, but may distract or cause temporary visual disturbance to a pilot increasing the risk of crashing. Many pilots and aerospace medicine specialists have legitimate concerns regarding possible injury from LASER sources.
The word L.A.S.E.R. is actually an acronym- Light Amplification by Stimulated Emission of Radiation. A LASER is a spatially and temporally coherent light source which allows it to be focused on a point and also emit energy at a narrow range of wavelengths. Each LASER operates within its unique wavelength based on where it falls on the optical spectrum: red & infrared (IR) sources have longer wavelengths (around 650 nm or longer), while ultraviolet (UV) frequency emissions are much shorter (< 280 nm in length). Irradiance is another measure by which to categorize LASERs and refers to the amount of radiant energy per unit area (1).
Lasers pose a unique risk to the eye due to their energy characteristics. In the United States, lasers are classified from the FDA and ANSI going from class 1 to 4 with class 4 having the highest power. Laser pointers are required to be between class 1-3A for commercial sale (1).
Lasers cause tissue injury through either mechanical, thermal, or phototoxic mechanisms dependent on irradiance, wavelength, duration of exposure, and tissue absorption. Mechanical injuries are commonly seen in high irradiance, short duration injuries. These injuries are due to the mechanical stripping of electrons from the respective atoms at the cellular level, leading to atomic instability and tissue death. Thermal injuries are noted in medium irradiance, longer duration, longer wavelength exposures where the tissue becomes warmed and eventually coagulates, leading to necrosis (cell death). In the retina specifically, even increases in temperature of 10-20 Celsius can lead to damage. Low irradiance, short wavelength, and long duration are characteric of phototoxic injuries. In these cases, the tissue never gets heated enough to cause coagulation but does impart enough energy to the electrons of the recipient tissue that it causes downstream toxicity and a delayed cell death. Often, these injuries will present with visible damage 1-2 days after exposure or even later in rare cases (1).
The retina is the part of the eye most at risk for LASER injury due to its absorptive pigment epithelium and sensitivity to relatively small changes in temperature. Phototoxic retinopathy refers to retinal injury secondary to a light source. These injuries can occur from a variety of light exposures- sun exposure, lighted equipment (operating microscopes), and lasers. Retinal pigment epithelial (RPE) injury can be reversible; however, if significant tissue damage and necrosis occur, more permanent deficits may remain. Classic patterns of damage include retinal hemorrhage, retinal detachment, and vitreous hemorrhage. The cornea, being transparent, is less likely to be injured as many lasers will pass through the cornea and up to 60% of incidental, non-perpendicular light reflects off of the surface. UV and low-energy IR radiation, however, can damage the corneal epithelium. Higher energy radiation can lead to burns of corneal layers – again typically in the far IR range – and lead to scarring or even perforation (1, 2).
INJURY INCIDENCE & POLICY
Case reports of laser eye injury from incidental contact are, thankfully, rare. There have been no reports of significant or permanent eye injury from laser pointer exposure. Temporary symptoms have been noted in both red (650nm) and green (532nm) laser pointer exposures but these cases have always been in cases of intentional, direct ocular, overexposure (10 sec – 15 minutes) and have healed within 10 weeks (2). Unintentional military-grade LASER exposure has been noted with significant retinal injury in a series of cases described in the U.S. Army database with one of those exposures occurring secondary to hostile LASER exposure in the Persian Gulf. In all these cases; however, no personal protective equipment was being used and all injuries occurred on ground level (4).
The literature regarding aviation-specific laser exposure is very limited but anecdotally supported. A report of data from the UK showed that about 2,300 cases of laser pointer light exposure were reported in 2011. None of these cases were associated with significant ocular injury or an aviation mishap (3). The FAA reported 5,352 exposures in 2015.
Military Policies: The DoD has established a 24/7 Tri-Service Laser Hotline (1-800-473-3549) whose sole purpose is to help triage and manage laser exposures. In addition to this resource, each branch has developed its own laser-exposure and surveillance policy.
US NAVY: BUMEDINST 6470.23 covers laser injury management and safety protocols. This guidance recommends that visual acuity, slit lamp exam, and dilated fundal examination be done immediately for anyone with LASER exposure. PPE is required for people who routinely work with class 3 or greater lasers. Evacuation from deployment is recommended for any exposed person in which visual acuity is worse than 20/40 in best eye. There is no specific recommendation on return to flying duty for exposed aircrew.
US ARMY: FM 8-50 “Prevention and Medical Management of Laser Injuries” covers the aspects of laser injury, both ocular and extra-ocular. Annual screening is required in members working with class 3 or greater lasers. The policy recommends a post-exposure full eye exam and immediate evacuation of members with any visual impairment or retinal injury. Eventual return to duty disposition is not addressed.
USAF: AF148-139 establishes safety protocols with monitoring of all class 3B and 4 lasers in addition to all military specific lasers in a unit. Active surveillance for individuals working with class 3B or 4 lasers recommended. The USAF School of Aerospace Medicine Laser Injury Guidebook published since 2008 provides an excellent, laser-specific resource for all aircrew. The Laser Beam Incident Questionnaire helps with the assessment of the injury and the guide follows through with recommended reporting. Recommend full eye exam to include slit lamp and dilated fundal examination. No specific disposition recommendation for return to flying duty.
US COAST GUARD: COMDTINST M5100.47A. Active surveillance of personnel working with class 3B and 4 lasers only with annual ocular screenings. There is a specific Laser Ocular Strike Aeromedical Policy Letter regarding aeromedical management. Self-assessment is recommended using ALESA to help gauge the need for immediate vs. deferred medical evaluation. Full ophthalmologic examination is recommended but if no findings are present, the member can return to full flying duties.
Based on the current literature and knowledge pertaining to lasers, a few general recommendations can be made:
- Typically incidental, non-sustained laser pointer exposure in any asymptomatic person poses no concern for long-term ocular injury.
- A rapid and focused ocular assessment of the eye is required for any exposed aircrew member. The UK Civil Aviation Authority has helped develop a rapid self-assessment tool (ALESA) to help pilots self-screen if exposure was suspected (4). Deferred examination would be reasonable in benign exposures given no symptoms and favorable ALESA assessement in order to meet operational concerns.
- LASER eye protection (LEPs) should be the mainstay for laser injury mitigation for military personnel whenever the potential for exposure to more powerful lasers exist. Active surveillance of members who routinely work with class 3 or greater lasers is reasonable and would provide good sensitivity for screening potential injuries.
- Return to flying duty without waiver is reasonable and safe in the context of no symptoms and a benign evaluation by a flight surgeon or aerospace medical examiner.
- Baumai, C.R. (2013) Light and Laser Injury, Yanoff, M & Duker, J (2013) Ophthalmology 4th Edition (pp 461-466), London: Elsevier/Saunders.
- Ajudua, Stephanie, and Michael J. Mello. ‘Shedding Some Light On Laser Pointer Eye Injuries’. Pediatric Emergency Care 23.9 (2007): 669-672. Web.
- Waggel, Stephanie E., and Ewan J. Hutchison. ‘Design And Acceptability Of The Aviation Laser Exposure Self-Assessment (ALESA)’. Aviation, Space, and Environmental Medicine 84.3 (2013): 246-251. Web.
- Harris, M.D., Lincoln, A.E., Amoroso, P.J., et al. ‘Laser Eye Injuries In Military Occupations’. Aviation Space and Environmental Medicine 74.9 (2003): 947-52. Print.