Blinding laser weaponsBMJ 1997; 315 doi: https://doi.org/10.1136/bmj.315.7120.1392 (Published 29 November 1997) Cite this as: BMJ 1997;315:1392
Still available on the battlefield
- John Marshall, Frost professor of ophthalmogya
Ever since the publication of H G Wells's War of the Worlds military strategists have dreamt of using beams as weapons. Weapons using optical radiationhave the advantages of having unlimited, weightless ammunition; a huge range; almost instantaneous delivery of energy; silence; and under certain circumstances, self targeting. With the advent of the laser in 1960, the possibility of beam weapons became a reality. Present laser systems can deliver terawatts of power to remote targets at the speed of light. Although military designers soon determined that laser systems that would destroy armoured targets or aircraft required huge amounts of power and resulted in large, unwieldy systems, they rapidly appreciated that soldiers' eyes were a relatively easy target.
The human eye is vulnerable for three reasons. Firstly, it is the only organ that allows optical radiation to penetrate deep within it.1 Secondly, the optical properties of the surface of the eye, the cornea, and to a lesser extent the lens increase the irradiance (power per unit area) in the passage of optical radiation between the cornea and retina by up to 500 000 times. Finally, the eye is consciously directed to any area of interest in the visual scene and thus presents the central and most sensitive area of the retina, the fovea, to the image of interest. If the fovea is destroyed the individual is legally registerable as blind, as he or she would have no high acuity vision.2 A single exposure to a rangefinder laser could destroy the fovea in 10−9 seconds.
Military propagandists have been coy about antipersonnel weapon systems, claiming that such systems are designed merely to dazzle enemy troops. In fact, when the eye perceives bright light one of four reactions may take place.1 These are, in order of increasing brightness: dazzle, after image formation, flash blindness, and irreversible damage. Most individuals will have experienced dazzle as a result of oncoming car headlights and persistent after images from accidentally staring at the filament of an incandescent bulb. Both dazzle and after images will distort vision for some seconds to minutes. Flash blindness occurs when an extremely bright flash is discharged, usually at night, and again vision is temporarily lost. All three reactions would be useful in temporarily disabling a pilot and causing him to abort close approach to a target. If even higher irradiances reach the retina then irreversible damage may occur. In practice, a laser system that will dazzle at one mile may permanently blind at closer range.
On the modern battlefield five classes of optical radiation sources may be deployed: rangefinders and target designators, antimaterial systems, antisensor systems, antipersonnel systems, and non-laser optical systems.3 All modern tanks have laser rangefinders and target designators, which, although primarily designed to measure distances and mark targets, are potentially blinding to support infantry. Antimaterial systems are the high energy systems designed to destroy aircraft or, indeed, satellites. Antisensor systems are designed to destroy optical sensors deployed by the enemy. Unfortunately, optical sensors have almost the same response parameters as the human eye, so antisensor systems are potentially blinding.4 Several countries have developed antipersonnel systems to be carried by infantry, specifically designed to blind enemy troops. Finally, non-laser optical systems have been deployed in such devices as the “Dragon,” a high-intensity light source for crowd control, and the flash discharge units used by special forces. This plethora of eye threatening sources of radiation may account for the increase in eye injuries as a percentage of total injures in warfare from 1% in the last century to 13% in the Gulf war, where such laser devices were deployed.5
Originally, it was thought that the eye could be protected against laser systems by goggles. However, many laser devices switch wavelengths between pulses, so protective goggles would have to be opaque and are therefore self defeating. Blinding weapons have a huge psychological impact on troops.6 There is no treatment and, if the fovea is destroyed, then the individual is permanently blind in that eye.2 They also have an impact on support services and media coverage. A dead soldier ties down no personnel behind the lines. A maimed soldier requires on average 40 personnel in the medivac chain. With TV coverage civilian morale is further eroded by viewing masses of young men rendered blind.
Against this scenario, the International Red Cross initiated meetings of experts, starting in 1989, to try to formulate a protocol to prevent deployment of antipersonnel weapons.7 In 1995 protocols were signed by 40 nations in Vienna. Unfortunately, although antipersonnel systems should now not be manufactured or deployed by signatory countries, the efficiency of rangefinders, target illuminators, and antisensor systems is such that no countries will relinquish them and these are still effectively antipersonnel laser weapons.