Mayo Clinic ophthalmologists have found commercially available Class 3A green laser pointers can cause visible harm to the eye's retina with exposures as short as 60 seconds. The findings will be published in the May issue of Archives of Ophthalmology.
Dennis Robertson, M.D., Mayo Clinic ophthalmologist, conducted investigations with a green laser pointer directed to the retina of a patient's eye; the eye was scheduled for removal because of a malignancy. The green laser damaged the pigment layer of the retina, although it did not cause a measurable decrease in the visual function of the patient's eye. Dr. Robertson believes that longer exposures could harm vision, however. He also warns about potential damage from higher-powered green laser pointers.
"With the use of laser pointers that are more powerful than five milliwatts, there would likely be damage to the actual vision," he says. "Functional damage could occur within seconds."
Dr. Robertson does not advocate against use of green laser pointers; rather, he advocates against their misuse. "Green laser pointers are not a public health hazard at this time, but something people should be aware of," he says. "I'm raising concerns that people should be cautious when using green laser pointers not to point them at someone's eye or face. It's like how you use your knife -- carefully."
While pointing out risks of green laser pointers, he adds, "This is a potential hazard to people's eyes, but rarely is it going to be a practical hazard because the aversion reflex we have naturally will cause a person to blink or turn away from a laser light."
Green laser pointers are readily available in stores and on the Internet, according to Dr. Robertson. "Kids can buy these," he says. "They're not strictly regulated."
He adds that Class 3A green laser pointers are increasingly being used by amateur astronomers to pinpoint objects in the night sky and by the construction industry and architecture educators to point out details of structures in daylight
Dr. Robertson conducted the eye exposure test with a consenting patient two weeks before eye removal due to ring melanoma. The patient's vision was 20/20, and the macular retina appeared healthy.
Dr. Robertson exposed the patient's retina to light from a commercially available Class 3A green laser with an average power measured at less than five milliwatts: 60 seconds to the fovea, the center of acute vision; five minutes to a site 5 degrees below the fovea; and 15 minutes to a site 5 degrees above the fovea.
Dr. Robertson had color photographs taken of the eye before and after exposure to the laser.
Dr. Robertson examined the patient's eye 24 hours after laser exposure. He found retinal damage characterized by yellowish discoloration involving the pigment layer beneath the fovea and at the site of the 15-minute exposure above the fovea. Each of these sites developed a grainy texture within six days. Study of the eye tissue under a microscope also confirmed damage to the pigment layer in the laser-exposed regions.
Dr. Robertson has been interested in the effects of lights on the human eye during his career, testing operating room microscopes, lights used in the clinic, red laser pointers and now green laser pointers.
Previously, he determined red laser pointers to be quite safe. "I tested different powers up to five milliwatts and could not create recognizable damage in the human eye with the red laser pointers," he explains. "So, at least a transient exposure to red laser pointers' light is only of trivial concern."
Dr. Robertson attributes the risk differential between red and green lasers to wavelength. "We know that the retina is infinitely more sensitive to shorter wavelengths," he says. "The green lasers appear much brighter to the human eye because of the shorter wavelength and can cause damage."
Dr. Robertson says Mayo Clinic's investigations have clearly demonstrated that green laser pointers can cause irreversible damage to the pigment layer of the retina.