Article Text

PDF

Laser pointers can cause permanent retinal injury if used inappropriately
  1. CHARLES N J McGHEE,
  2. JENNIFER P CRAIG
  1. University of Auckland Department of Ophthalmology, Private Bag 92019, Auckland, New Zealand
  2. Photobiology Unit and Department of Medical Physics, Ninewells Hospital and Medical School, Dundee, Scotland DD1 9SY
  1. HARRY MOSELEY
  1. University of Auckland Department of Ophthalmology, Private Bag 92019, Auckland, New Zealand
  2. Photobiology Unit and Department of Medical Physics, Ninewells Hospital and Medical School, Dundee, Scotland DD1 9SY
  1. Professor C N J McGhee
  1. JOHN MARSHALL
  1. Department of Ophthalmology, UMDS
  2. St Thomas's Hospital, London SE1 7EH

    Statistics from Altmetric.com

    Editor,—The authors previously published a brief report in a widely circulated ophthalmic review periodical (Eye News) on the potential risk of permanent injury from the inappropriate use of laser pens.1 The article had been prompted by two events—firstly, a flood of reported cases in the popular media of the “blinding” effects of laser pens pointed at drivers, soccer goalkeepers, and members of the general public, and, secondly, the referral to our department for clinical assessment of police and fire service personnel who had been exposed to laser pen light. Examination of the clinical cases demonstrated no permanent injury. We were also asked to review data determined for a number of laser pens that had been subjected to analysis by Edinburgh Environmental and Consumer Services Department. Many of these laser pens were mislabelled, either by exhibiting American standard classification (different from European), or simply by being inaccurately classified. Subsequently, a number of laser pens have been sent to us for examination, pending police investigations. Many of these lasers are class 3B devices according to the European laser classification, and are therefore considered potentially hazardous. None the less, we concluded that the normal blink and aversion response would prevent retinal damage from transient exposure. However, it had also been brought to our attention that the cost of these laser pens, and laser key rings, was such that they were being purchased by children. A new version of the traditional, and dangerous children's “game” of “chicken” had developed in relation to these new “toys”, the game of “chicken” being won by the child who could stare directly into the laser beam for the longest period. We concluded, “this makes lasers potentially very dangerous in the hands of children”. Fortunately, trading standards agencies throughout the UK have moved to ban sale of these laser pens and a number of legal cases are pending with regard to their sale. There have also been successful prosecutions brought against individuals who have deliberately used these laser pen devices to cause temporary dazzle and visual disturbance, without permanent retinal damage.

    We therefore were particularly interested in the recentBJO perspective by Professor John Marshall.2 In an otherwise erudite and comprehensive review we were very surprised to read his conclusions, “laser pointers, pens, or key rings if used appropriately are not an eye hazard, and even if used inappropriately will not cause permanent eye damage.” [Our italics] It has long been a physician's maxim that always andnever can rarely be applied to human biology, even if perceived risks are low. Indeed, although the majority of laser pens examined by us at the time had an output of less than 5 mW, it seemed reasonable to conclude in our article that there was thepotential for laser damage if these items were used inappropriately.

    A recent article by Luttrull and Hallisey3 is therefore of significant importance to any ophthalmologist dealing with clinical cases relating to laser pen exposure. In this reported case, a 34 year old Hispanic male was reviewed 2 days after deliberately staring into the beam of a class 3A (USA) laser pointer, held 8–10 inches from the eye, for 30–60 seconds. The laser device in question had a maximum power rating of 5 mW at a wavelength of 670 nm. Although the subject maintained 20/20 vision with a normal Amsler chart, he exhibited a focal disturbance of the retinal pigment epithelium in the left nasal macula despite resolution of his central scotoma. The right eye of this 34 year old was entirely healthy on intravenous fluorescein angiography, but the left eye demonstrated a window-type defect and hyperfluorescence in the area of retinal pigment disturbance at the macula. The authors concluded, “laser-pointing devices can cause macular injury when used inappropriately. Conformance with consumer safety recommendations should minimise potential hazards”.

    Although we agree the risks of lasting injury from laser pointing devices are remote,1 2 it cannot categorically be stated that there is no risk.2 While transient exposure is unlikely to cause long term ocular damage, this case3demonstrates that the authors' initial warnings about the theoretical risk of injuries from staring into these devices were warranted.1 The ophthalmic clinician should therefore be aware of the potential for retinal injury from gross misuse of laser pointers and these “toys” must be kept out of the hands of children and those who might use them inappropriately.

    References

    Reply

    Editor,—In writing this article I addressed five issues. Firstly, to counteract media “hype” on the “blinding potential” of laser pointers by explaining the biophysical principles involved in beam tissue interactions and, as a consequence, the ineffectual nature of such devices as retinal hazards. Secondly, I wished to address a degree of confusion generated by a misleadingly titled, well circulated, but non-peer reviewed article. Thirdly, I wished to give guidance to casualty and medical personnel first confronted with individuals who had experienced exposure to laser pointers. Fourthly, I thought it helpful to explain the differences in classification between countries housing the world's major producers and major market and the European Union. Finally, I wanted to highlight the fact that, although the derived safety criteria and system classifications varied between codes of practice, all the classifications were dependent on a common database.

    McGhee et al confused the issue of classification and potential risk in their periodical article and promulgate the confusion in their current letter. A laser pointer that goes from a 3A classification in the United States does not suddenly become more hazardous by travelling across the Atlantic. Although it moves into a 3B category within the European Union, it is still the same laser and still has the same risk profile as it had in the United States as a 3A system.

    Almost all of the UK database for retinal damage that is incorporated in the various codes of practice was derived through collaborations between my laboratory and the then Institute of Aviation Medicine, Farnborough, Hampshire. A fundamental problem implicit in all laser safety data is that empirical data only exist where laser wavelengths and time domains have importance to military applications. Throughout the world almost all of the data have been underwritten by military funding. There are two consequences which arise from such a database: the first is that we have no ED50 data for many common lasers, including helium neon and red diodes; the second is that safety authorities might err on the side of caution and, as a result, the codes of practice have huge safety margins in order to secure protection.

    McGhee et al cite a recent article as an indication that my conclusion concerning the laser safety pointers was erroneous. Far from supporting their statement, careful reading of the cited paper merely highlights one of the problems addressed in my review—namely, guilt by association. Luttrull and Hallisey were confronted by a patient whose visual acuity was 20/20. Would the fundus of the individual have been examined, and a fluorescein angiogram undertaken, unless the word “laser” had been stated? Furthermore, the individual claimed an exposure of 30–60 seconds to a device with a nominal maximum output power of 5 mW; an exposure period over this time would be associated with eye movement displacement of the retinal image and could not result in thermal damage. In a previous study we exposed stabilised animal eyes to a 5 mW HeNe laser for 5 minutes without observing retinal damage. Remember also, that in order to observe retinal damage from clinical diode laser systems 50 mW or more are required. In the cited paper, the patient claimed to have noted a red central scotoma but presumably should have seen a green afterimage. The headache reported is indicative of anxiety rather than being related to any retinal damage mechanism. The finding of a window defect on angiography is also inappropriate in that if a suprathreshold exposure had been sustained then a leak would have been apparent, not a window defect. Finally, the authors discuss the possibility that this individual may have been at high risk as a result of racial pigmentation. Again this is erroneous, because although a marginally higher risk would have been conferred by melanin for thermal insult, greater pigmentation would have lowered the risk in relation to a greater than 10 second photochemical mechanism. Given the inability of a 5 mW system to generate thermal transients of sufficient magnitude to induce retinal damage, and in the absence of an empirical biophysical study, their case does not support their conditions.

    In their final paragraph, McGhee et al agree that the risks of permanent retinal injury are remote, but they state that “there can never be zero risk”. In all safety criteria documents the aim is to reduce risk to an insignificant level. I reiterate that current US safety standards satisfy these criteria. I also reiterate that, notwithstanding the report of Luttrull and Hallisey, to date there is no evidence of irreversible retinal damage sustained from viewing laser pointers.

    References

    View Abstract

    Request permissions

    If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.