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2013:30 Laser pointers and eye injuries: An analysis of reported cases
Research published by the Strål Säkerhets Myndigheten (SSM - the Swedish Radiation Safety Authority)
This English-language study is a comprehensive survey of reported laser pointer injuries. The SSM is trying to correlate injuries with the laser intensity. The study was conducted because little information exists on the eye damage severity that may be expected at various laser exposure levels.
Objectives: The study investigated what dose of laser radiation, in terms of intensity and exposure time, may be associated with eye damages. The study has been limited to unwanted exposures of laser radiation from commercially available laser pointers. Of particular interest has been to search for data about functional disabilities that persist more than 6 months [e.g., permanent disabilities].
Results: The study shows that long-term vision loss can occur as a result of involuntary exposure from commercially available (strong) laser pointers at close range. The injury may occur before a normal person is able to respond by closing the eyelid, although there are only a few cases reported. Minor damage is transient within a few days. It is also likely that such a visible injury to the retina becomes functional, i.e. prevents reading skills.
The study describes the human eye, and how it can be damaged by laser pointers. Section 3-1 describes how laser damage is identified by doctors. Having a doctor identify retinal damage doesn’t always mean that vision is impaired: “Unfortunately there is a rather poor correlation between visible retinal damage and functional deficit, although the advances in SLO microperimetry have improved this correlation.”
Also, there may be “damage” not caused by lasers: “Furthermore, even healthy retinas in asymptomatic people, never exposed to laser radiation, exhibit small numbers of visible abnormalities.”
Chapter 4 is an extensive survey of reported retinal injuries from laser pointers. They found 34 cases from 1999 to 2012. (This does not include the 2013 Saudi Arabian hospital report of 14 young boys injured by high-powered blue lasers, which appeared too late for this study.) Of the 34 cases:
- 5 were deliberate exposures by the patient (they deliberately stared into the laser for more than a second or two, or numerous times)
- 5 were deliberate exposures by a doctor, on a patient whose eye was scheduled for removal due to disease
Thus, there were 24 cases in 13 years, or about 2 cases per year, of documented accidental injuries from laser pointers. In almost all cases, the laser was at close range -- less than a meter from the eye.
Section 5-3 further analyzes the 12 reported cases with the most information about exposure parameters. The exposures generally varied from 2.6 times, to about 29 times the Maximum Permissible Exposure.
The injuries were graded using the “Severity of Injury” criteria of the European Union. Most cases had severity level 2 or 3 meaning “Temporary loss of sight” or “Partial loss of sight. Permanent loss of sight (one eye)”. No case had the worst severity level 4, “Permanent loss of sight (both eyes).”
Understanding the “Exposure Dose-50” concept is essential to understanding how laser safety limits are set.
The SSM paper contains an excellent discussion in Section 5-2 about ED50, how it is derived, and many subtle considerations and uncertainties. In Section 5-3, on page 33, there is a description of how damage begins to appear at exposure levels about 10 times the MPE. “Therefore, it is also not inconceivable that the ED-50 limits have been reached” at 10 times the MPE. The authors warn that “Since the exposure data in the cited references have many uncertainties the analyses in this report must be viewed with caution.”
Laser safety limits are based on studies of the “Exposure Dose 50” or “ED50.” For visible laser light, this is the irradiance at which a given laser exposure has a 50/50 chance of causing the smallest detectable change, when aimed point-blank into the eye of a lab animal. The Maximum Permissible Exposure has been set to be about 10 times the ED50 limit; this can be considered to be a “10-times safety factor.”
The following is the authors’ conclusion:
“The easy access to commercial laser pointers has led to an increasing trend of misuse of lasers towards main targets such as pilots, drivers and law enforcement personnel. Today ́s strong laser pointers can flash blind a pilot at a distance of more than 10 km, and at shorter distances cause permanent visual dysfunction or even blindness.”
“We have analyzed 34 reported cases of laser pointer exposure and related the eye damages to existing MPE values. Among the many reports on laser pointer exposure, only a small proportion has confirmed retinal injuries. Retinal damage was described for red, green and infrared laser pointers and all occurred at very close distance to the laser, in most cases less than a meter:”
- Red lasers with ≤5 mW output power can cause a temporary and relative loss of the central vision.
• Green lasers with ≤5 mW output power can disrupt the retinal pigment epithelial layer and lead to choroidal infarction. With repeated exposures over years choroidal neovascularization can occur with associated risk of vision loss.
• Green laser with ≤7 mW output power can cause visible damage to the retinal pigment epithelium.
• Green laser with >20 mW output power can cause enlarging lesion, retinal edema and hemorrhage, if viewed for more than one second.
• Infrared radiation-A laser with wavelength between 825-880 nm and an output energy of <5mW can induce retinal edema and focal retinal detachment.
“We have identified areas where research could benefit the society. With a national database on laser pointer exposures there is a better chance to find patterns and trends on the use of laser pointers. There is a need for further research on damage mechanisms, treatment of laser damage, long-term permanent laser damage, and on the effect of visual aids and refractive errors in laser pointer retinal damage. Further, the risk of injuries or deaths secondary to laser pointer blinding requires more attention, especially from the aviation authorities. Finally, an essential area of research is the development of methods to identify functional visual deficit in the presence of structural retinal damage.”
“The laser safety limits of today are both important and meaningful in the industrial or workplace setting where the dangers are well known, as well as the methods of protection. In contrast, intentional use of laser pointers to harm others, or inappropriate use of laser pointers due to lack of knowledge about the potential harmful effects are difficult to intervene with. Two important on-going objectives for the legislative and governing bodies are information campaigns and legislation to minimize the availability of harmful laser pointers.”
From 2013:30 Laser pointers and eye injuries: An analysis of reported cases, by Stefan Löfgren, Jörgen Thaung and Cesar Lopes. Published 19 November 2013. Report number: 2013:30. ISSN: 2000-0456