12 May 2005
Green laser pointers can cause irreversible damage to the pigment layer of the retina, say researchers in the US.
Commercially-available class 3A green laser pointers can cause visible harm to the eye's retina after exposure times as short as 60 seconds, according to ophthalmologist Dennis Robertson from Mayo Clinic in the US. (Archives of Opthalmology to be published)
Robertson performed his tests on a patient whose eye was due to be removed because of ring melanoma. He used a commercially-available class 3A green pointer with an average power of less than 5 mW.
The tests involved pointing the laser at the eye's fovea for 60 seconds, then 5 minutes on a site 5 degrees below the fovea, followed by 15 minutes on a site 5 degrees above the fovea. Color photographs of the eye were taken before and after exposure.
Twenty-four hours after exposure, Robertson found retinal damage at the fovea and the 15-minute exposure site. The retina at both sites was discolored, showing that the retina's pigment layer was damaged, although this did not cause a measurable decrease in the visual function of the patient's eye.
"People should be cautious when using green laser pointers not to point them directly at someone's eye or face," said Robertson. "This is a potential hazard to people's eye's, but it is rarely going to be a practical hazard because of the aversion reflex we have will naturally cause a person to blink or turn away."
He adds that the use of laser pointers that are more powerful than five milliwatts could damage a person's vision.
Robertson has previously published research on red laser pointers. "I tested different powers up to five milliwatts and could not create recognizable damage in the human eye with red laser pointers," he said. "We know that the retina is infinitely more sensitive to shorter wavelengths. The green lasers appear much brighter to the human eye because of the shorter wavelength and can cause damage."