For years, the U.S. aviation regulatory agency, the Federal Aviation Administration, has said that exposure of air crews to "laser illumination" may cause permanent visual impairment, citing governmental studies
The new study, in the British Journal of Ophthalmology, comes as the global aviation industry battles a huge increase in the number of laser attacks on planes landing at and taking off from airports. Such attacks can disable pilots at a flight's most crucial time.
But when they're aimed from more than 100 meters away, it's impossible for laser pointers to inflict irreversible damage to the retina, said John Marshall, a professor at University College of London's Institute of Ophthalmology, who co-authored the study.
The study might make air crews feel a bit safer, Marshall told CNN. "But the real danger is the dazzle," he said.
It's called lasing. And it's a crime. Pilots targeted by these laser attacks have reported disorienting flashes, pain, spasms and spots in their vision
. The dazzle effect can trigger temporary blindness, with "catastrophic" consequences, Marshall said.
The new data add perspective to a threat that's obvious and chilling: Theoretically, anyone on the ground with a cheap hand-held laser can disable a pilot controlling an aircraft carrying hundreds of passengers.
About 1,500 lasing reports were recorded by UK aviation authorities in a recent 12-month period, the study said. In the United States, the FAA reported about 2,800 laser incidents in 2010; from January to mid-October 2015, that number had increased to over 5,300.
Pilots never more concerned
Although no aircraft accidents have been blamed on lasing, pilots have never been more concerned than they are now, says 30-year career pilot Keith Wolzinger, who flies international Boeing 777 routes about once a week.
At some airports during takeoff and landing, "some of our flight crew are always looking outside the aircraft to see if there's any laser activity," Wolzinger said. "If you get hit with a beam, the concern is, you won't be able to keep the plane on the proper path.
"I've seen lasers a dozen times, at least, although I've never been hit."
Above busy airports, where air traffic is heavy, is where lasing is especially dangerous, Wolzinger said.
Besides the relative weakness of laser beams refracted through aircraft windshields, Marshall points to the lack of medically reliable reports of permanent eye damage from such incidents.
The study mentions a case of alleged retinal damage to a pilot from a laser in 2015
. But the incident wasn't reported in a peer-reviewed medical journal, the study said. Based on the circumstances, it didn't appear that enough laser energy "entered the eye to produce irreversible damage."
Marshall said his study used previous research on how laser beams affect the human eye combined with new data that were gathered during about three years of laser field experiments at a military base.
Green lasers are worse than red
Green lasers pack more punch, the study says. Eyes are more sensitive to green lasers, which is why those are more dangerous to pilots. They "will be perceived to be far brighter," the authors wrote, "and as a consequence will result in a greater degree of dazzle."
"Maybe we should think about banning green," Wolzinger suggested.
But Marshall thinks that might be difficult. Green pointers are very popular because they're much easier to see in classroom situations, he said.
Laser pointers are getting more powerful
Although laser pointers can't inflict permanent damage to airborne pilots, there may be cause for concern in the future, Marshall said. Laser pointers have been getting more powerful and easier to buy online. In the past, they've been mostly red beams with an energy output of 1 milliwatt, he said.
But over the past eight years, lasers are shifting to mostly green with energy outputs of up to 300 milliwatts -- or even 6,000 milliwatts.
"The European Commission has mandated the European Standardisation bodies to produce a standard specifically for consumer laser products," Marshall and his co-authors wrote in an editorial. "This should allow enforcing authorities to remove unsafe products from the market. However, compliance by manufacturers will remain an issue, as will direct imports by the public purchasing unsafe laser products over the internet."
Laser pointer background checks?
In the U.S., federal penalties for lasing are stiff
. The crime carries a maximum prison sentence of 20 years and a $250,000 fine. The FAA can slap on additional civil penalties: as much as $11,000 for each violation.
Some are calling for the devices to be regulated like guns.
"Over a certain power level, they should require registration and a background check," CNN aviation analyst Les Abend wrote in a 2015 editorial
. "And being charged with a specific felony for their use is OK, but maybe a better deterrence would be to consider it as plain old attempted murder."