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Japan: Teen injured by LED pen "toy" held 40 seconds in his eye

NOTE: The injury described herein was NOT caused by a laser but by a light-emitting diode (LED). We are including it here because the measured power of 5 mW is similar to laser pointers, and because in mid-2013 the FDA proposed to regulate toys containing lasers. This case of an LED-caused injury may stimulate arguments on both sides. Additional discussion is in blue at the end of this story.

A December 2006 incident has come to our attention. A 15-year-old Japanese boy suffered a retinal injury and visual loss after deliberately looking into a 5 mW violet (410 nm) light emitting diode for a total of about 40 seconds. The LED was in a pen was sold as a toy called “Secret Pen”. The toy appears to consist of an LED light which can excite ink that is invisible under ordinary light but which fluoresces under ultraviolet and near-UV light. The 410 nm wavelength caused photochemical damage to the retina.

According to a 2011 paper in Retinal Cases & Brief Reports, the LED was aimed into the teen’s eye from a distance of about 1 cm. It was held there for about 20 seconds as he deliberately stared into the light. This exposure was repeated the next day. About two weeks later, decreased vision (20/50 on the Snellen scale) was noted in the right eye.
The LED emission angle was 50 degrees. The beam diameter at the 1 cm exposure distance (LED to cornea) was 9 mm. About 1.4 mW entered the boy’s pupil which had a diameter of 3.4 mm. The intensity at the fundus was 70 mW/cm². The authors concluded that “it seems very unlikely that thermal coagulation occurred.”

They then looked at the photochemical effects. The total dose was 3.16 J/cm². Because this is “close to damage threshold on rat retina” and because it took about 2 weeks for onset of vision loss, the authors concluded “retinal injury can be considered to be because of photochemical effects.”

The exposed eye’s visual acuity had been measured about 9 months before the incident at 1.0 (20/20). When presented two weeks after the incident, visual acuity was at 0.4 (20/50). Seven months later it had improved to 0.8 (20/25), and an additional year later it was 0.9 (20/22).

The authors concluded “The violet light from light-emitting diodes is a potential hazard for the retina, and thus, direct viewing into the beam should be avoided. Children, especially, should not be allowed to play with such toys without being carefully instructed about their proper use and fully supervised.”

From Obana, Akira; Brinkmann, Ralf; Gohto, Yuko and Nishimura, Kasumi. “A Case of Retinal Injury by a Violet Light-Emitting Diode”, Retinal Cases & Brief Reports, 5:223-226, 2011. The paper was presented at the 28th Annual Meeting of Japan Society for Laser and Medicine, Asahikawa, Japan, September 14, 2007, and the 61th Annual Congress of Japan Clinical Ophthalmology, Kyoto, Japan, October 12, 2007. Thanks to Leon McLin for bringing this to our attention.

Commentary from LaserPointerSafety.com

There are a number of interesting aspects to this case.

  • First, we stress the injury was caused by an LED and not a laser. However, if a violet laser were used, the outcome could be more severe since the entire laser beam would enter the pupil, unlike this case where only part of the LED’s light entered the pupil.

  • Second, this type of toy is currently being sold. A Google search for terms such as “invisible ink spy” or “secret LED writing” will turn up many such toys intended for children. It is not known how the LED characteristics of these toys compare to the “Secret Pen” in the Japanese case.

  • Third, the hazardous part of the toy was essentially a violet penlight. What made it a “toy” was the marketing to children, and selling it along with invisible ink. There was no special feature such as putting the eye to a viewfinder, or bouncing it off mirrors, or spinning it around, or putting it in a sword. It was just an LED penlight marketed to children, which emitted in the near-UV.

  • Fourth, the light was exceptionally misused. Instead of aiming at the invisible ink message, it was deliberately aimed into the boy’s eye for a total of 40 seconds, overcoming any blink reflex (which may or may not have been present for a 5 mW 410 nm light source).

As stated earlier, the FDA in mid-2013
proposed to regulate laser-containing toys. To our knowledge, there has never been an eye injury to a child from a laser-containing toy. (There have been a few injuries from laser pointer misuse by children, but we have not seen any reports of injuries from toys containing lasers.)

The case described above can be used by proponents of the FDA’s position, as well as by opponents. On one hand, a youth did sustain a well-documented, serious eye injury from a toy with a light output similar to a laser pointer (5 mW). On the other hand, the source was an LED (so FDA would not have had jurisdiction in the first place), the “toy” was basically a penlight (no special “toy” features other than marketing), and the exposure was extremely deliberate (far beyond what most children would do).