Laser pointers may damage vision

THE TRIBUNE


SCIENCE & TECHNOLOGY
Friday, August 6, 2010, Chandigarh, India


Laser pointers may damage vision
K.S. Parthasarathy



AS Dr.Timothy B L Ho, Firmley Park Hospital NHS Foundation Trust, Surrey, UK entered his house one evening, his seven year old son flashed a laser pointer on his face. The eye injury, he suffered, was not apparent immediately.
Four days later, he developed an area of partial alteration of his field of vision His son found the device, a gift from a drug company, on his father’s desk. Laser pointers which are common place now can damage vision if handled carelessly.
“My vision took several months to recover and initially I was very worried”, Dr Ho wrote in The British Medical Journal, (BMJ, 29 June 2010), when Drs Ziahosseini, Doris and Turner published in the BMJ, a laser injury case suffered by a teenager.
He bought a green diode laser pointer over the internet and shone the laser beam into his eyes while playing with it. He had no previous medical or ophthalmic problems. Tests confirmed disturbance of his retinal pigment epithelium; it took two months to improve his clearness of vision.
In yet another instance, while on the school bus, a friend attempted to determine whether a laser pointer would cause pupillary constriction (Arch Ophthalmol, Nov 1999). She made an 11 year old girl to stare at an activated laser pointer for several multi-second exposures with the right eye. The victim immediately noted decreased vision. It took many months to recover her vision; long term effects of the injury are unknown.
Retinal injuries from lasers may be caused by ablative, thermal or photochemical mechanisms. These depend on power, wavelength, exposure time and size of the pupil (BMJ, 27 May 2010). Normally, the adverse impact may be transient; they may disturb the retina and the interconnecting layers and may induce clinical conditions causing loss of sight later.
Laser pointers costing a few dollars are available in curio shops, electronic stores or office supply shops. You may buy them directly or through mail order or by placing orders with internet outlets. Children may use them as toys.
Most laser pointers used while presenting lectures operate in the visible light region of wavelengths between 600 to 670 nanometre (one-thousandth of a millionth of a metre, nm). They are low powered, battery operated, hand-held devices and are cheaper than those operating at green light of wavelength 532 nm.
The response of the eye depends on wavelength with a peak at about 550nm. It decreases as either end of the spectrum is reached. If laser pointers are compared at the wave lengths of 670 nm, 635 nm and 532 nm at the same power level, the brightness as eye perceives it will be nearly in the ratios of 1:10:30.When the laser beam is closer to the eye’s peak response, it can produce adequate visual stimulus at lower power levels.
If you want to buy a laser pointer choose only one that is labelled Class II and operates with a wavelength between 630 nm and 680 nm. Maximum output should be less than 5 milliwatts.
Before you use a laser pointer, read the caution or danger sticker carefully. Never point the laser at another person. Do not point a laser pointer at mirror-like surfaces. A reflected beam can act like a direct beam on the eye. Never look directly at the laser beam. Never view a laser beam using a binoculars or a microscope.
Lastly, you must not gift a laser pointer to a child. You may regret later. Laser pointers are not toys.
The writer is Raja Ramanna Fellow, Department of Atomic Energy