ArticlesLaser Eye Injuries
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Lasers and vulnerability of the eye to laser radiation
The term laser is an acronym for light amplification by stimulated emission of radiation. A laser device produces a light beam that, unlike ordinary light, is coherent, monochromatic, unidirectional, and minimally divergent. Consequently, such a device can direct most of its radiant power over very small areas, even at great distances. Light radiation in the visible and near-IR part of the electromagnetic spectrum is gathered and focused by the refractive media of the eye to a retinal image
Laser-Related Factors
An important determinant of damage is the wavelength of the radiation. Optical radiation (visible and near-IR, between 380 and 1,400 nm) is transmitted by the optical media of the eye38, 79 and focused on the retina, which may be damaged by radiation doses at or above a certain threshold value. Photons of shorter wavelengths (ultraviolet [UV]) are rapidly absorbed by organic molecules in tissues and may cause corneal injury via a photochemical process.109, 125, 196 Longer wavelengths, such as
Retina
Many studies have documented the energy required to produce retinal damage (Table 2). Most of them report the minimal, or threshold energy required to produce an ophthalmoscopically detectable lesion, typically a small, gray-white spot (Fig. 1). The threshold value is usually recorded as the ED50 for the total energy entering the eye, i.e., the energy level that will produce the lesion in 50% of cases. These values, with additional safety factors and extrapolations, form the basis for laser
Clinical Aspects of Laser Accidents
The vulnerability of the eye to laser radiation has resulted in a significant number of accidents, reported and unreported, in laboratories, industry, therapeutic procedures and military circumstances. Initially, not all civilian inuries were reported in the literature because of restrictions in connection with legal proceedings,154, 192 and reports of military injuries were often restricted by secrecy. Today, laser accidents are seldom reported, as they do not contribute new medical or
The laser as a weapon
The modern battlefield is permeated with laser radiation. Laser devices may cause eye damage in the course of accidental exposure, or they may be deliberately directed against personnel. Used as weapons, visually incapacitating lasers offer many advantages over conventional weapons.26, 179 The fired energy travels at the speed of light; if a laser pulse is fired at an aircraft traveling at the speed of sound from a distance of 1 km, the aircraft will move little more than 1 mm before being hit.
Auxiliary Laser Devices
Laser devices have been used by modern armies for more than two decades87 to accomplish two main tasks: determining distance (range finding) and marking a target for delivery of laser-guided weapons (designation). Range finders emit a short pulse of energy, measure the time to detection of the pulse reflected from the target, and calculate the distance accordingly. Thousands of these devices are currently in use,136 whether hand-held or mounted on tanks or aircraft. Laser target designators
Protection
Safety standards have been developed for ocular exposure to UV, visible, and IR radiation.11, 166 The internationally accepted laser safety documents are the latest version of the American National Standards Institute standard for the safe use of lasers (ANSI Z. 136.1)11 and its European and international equivalents.12, 13 Complete protection against accidental laser injury is possible, provided that the characteristics of the instrument and its mode of employment are known. In nonmilitary
Medical management
Current medical therapy for retinal injury is mainly limited to corticosteroids at an undetermined regimen. This treatment is given with the rationale of reducing the cellular inflammatory response to injury, thus possibly minimizing its extent. It has been associated with diverse results, including complete recovery of vision.94, 200 Other anecdotal case reports describe the use of antioxidant vitamins and vasodilator drugs.29, 44, 116, 120 However, corticosteroid administration has been the
Ethics
The ethical implications of laser weapon use and development have been considered by the United Nations, the International Red Cross, government and military officials, human rights groups, and ophthalmologists.7, 9, 10, 27, 46, 81, 106, 128, 170, 178 Although it is unlikely that laser weapons can blind in the ophthalmologic or lay sense of the word, some agencies have proposed a total ban on blinding laser weapons.27, 106 Some groups have campaigned for the cancellation of “ongoing research
Conclusion
Laser devices are a common and essential part of modern medicine, industry, military, and everyday life. This leads to an increasing number of laser-related injuries. Laser radiation is mainly hazardous to the eye, because the energy focuses on the retina. Consequently, the vast majority of injuries have been ophthalmic. So far, laser eye injuries have been relatively few because of strict safety regulations.
In the future, however, many more injuries are expected, especially if laser weapons
Method of Literature Search
For the literature citations in this review, we relied mainly on articles in personal collections (M. Belkin). In addition, we searched MEDLINE, using multiple search words, including laser, retina, cornea, damage, injury, accidental, and complication. Relevant conference proceedings and government reports were hand-searched. We reviewed all articles published in the English language. Abstracts of selected articles in languages other than English were used and are noted as such in the reference
Outline
I. Physical and pathophysiologic basis of laser eye injury
A. Lasers and vulnerability of the eye to laser radiation
B. Determinants of laser-eye interaction
1. Laser-related factors
2. Eye-related factors
C. Energy thresholds for laser eye effects
1. Retina
a. Pulsed laser threshold lesions
b. Pulsed laser suprathreshold lesions
c. Continuous-wave laser threshold lesions
d. Subthreshold laser effects
2. Cornea
II. Clinical aspects of laser accidents
A. Occupational lasers
B. Ophthalmic lasers
C. Military
Acknowledgements
The authors gratefully acknowledge the considerable help of Harry Zwick, PhD and Bruce Stuck, MSc of the US Army Medical Research Detachment, Walter Reed Army Institute of Research, San Antonio, Texas, in writing this review.
The authors have no proprietary or commercial interest in any product or concept discussed in this article.
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