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UK: UPDATED - Medical report on commercial pilot injured by blue laser at 1300 feet

The journal Aerospace Medicine and Human Performance in January 2016 published a paper entitled “Blue Laser Induced Retinal Injury in a Commercial Pilot at 1300 ft”. The case report is as follows:

“An airline pilot presented to our department complaining of a blind spot in the upper left area of his visual field in the right eye (right supero-nasal scotoma) following exposure to a laser beam while performing a landing maneuver of a commercial aircraft. At around 1300 ft (396 m), a blue laser beam from the ground directly entered his right eye, with immediate flash blindness and pain. Spectral domain ocular coherence tomography highlighted a localized area of photoreceptor disruption corresponding to a well demarcated area of hypofluorescence on fundus autofluorescence, representing a focal outer retinal laser injury. Fundus examination a fortnight later revealed a clinically identifiable lesion in the pilot’s right eye commensurate with a retinal-laser burn.”

The paper said the pilot’s symptoms “fully resolved 2 wk later” and that there was no “deficit in visual function.”
The laser exposure happened at a “busy international airport within the United Kingdom.” According to the authors, “To the best of our knowledge this is the first documented case report of a likely retinal laser injury to a pilot during flight from a laser on the ground.” They believe the blue laser had a “radiant power of several watts and potentially could have led to permanent loss of central vision in the pilot’s right eye had the fovea, the area of retina responsible for high acuity vision, been involved.”

The case was first publicly announced November 23 2015 by the general secretary of the British Airline Pilots’ Association (BALPA). He said it occurred in the spring of 2015. A source told LaserPointerSafety.com that it actually occurred in the fall of 2014.

From Aerospace Medicine and Human Performance, Vol. 87, No. 1, January 2016. Full text available here for purchase. Gosling DB, O’Hagan JB, Quhill FM. Blue laser induced retinal injury in a commercial pilot at 1300 ft. Aerosp Med Hum Perform. 2016; 87(1):69–70.

UPDATED - February 3 2016: The case was reviewed by both U.S. and U.K. laser safety experts. One of these experts, who has detailed knowledge of the case and who directly reviewed the journal article’s evidence, told LaserPointerSafety.com that he “doesn’t believe it was laser-induced” and that the injury being caused by a laser “was not confirmed, despite what the journal paper says.” This expert said at least 50 watts would be needed to cause a retinal injury similar to what was detected. He said that even though high powered consumer handheld lasers in the U.K. are marketed as being up to 5 or 6 watts, they actually are only about 1 watt. This means that even if the retinal injury was caused by a laser, it could not have been a high-powered handheld laser available to consumers.

UPDATED - April 20 2016: Experts concluded that the case is suspect for a number of reasons, and that they do not believe laser targeting caused the alleged injury. This came in an April 2016 editorial written by three leading U.K. laser safety experts — including the laser safety regulator who co-authored the January 2016 medical journal report. The experts wrote: “Only one case of alleged retinal damage to a pilot resulting from laser targeting of aircraft has been reported, although not in a peer review ophthalmic journal. This case is suspect because first and foremost, the metrology and exposure geometry would suggest insufficient energy could have entered the eye to produce irreversible damage and second the fundus anomaly is in the wrong location, the wrong shape and resulted in an extremely transient reported loss of VA [visual acuity] with full recovery.”

Analysis from LaserPointerSafety.com

Note: The material below was written by LaserPointerSafety.com in January 2016, before the February and April 2016 updates listed above that cast official doubt on a laser causing the pilot’s injury.

What was the laser’s power?

Based on the data provided, it would have taken an exceptionally strong laser to even have a 50/50 chance of causing an eye injury at 1300 ft. We calculate such a laser would be well over 5 watts and possibly 30 or more watts. This is a conservative estimate. It assumes the laser and eye were not moving fast relative to each other — unlikely for a handheld laser aimed at a moving aircraft. It also assumes a relatively tight beam, and that the laser-to-aircraft distance was 1300 ft when it may well have been longer.

As of 2015, the highest power handheld visible lasers sold on the Internet are roughly 3 watts. Sometimes handheld lasers are advertised with greater powers, such as 5 or 10 watts, but the claimed power may be grossly incorrect. For example, in 2014 LaserPointerSafety.com purchased a “5 watt” handheld laser that was actually about 50 milliwatts, or 1/100th of the claimed power.

We believe one of the following scenarios is what happened:
1) The injury was a very unlucky one; the pilot just happened to experience a statistically unlikely injury that could be caused by a relatively low 3-5 watt handheld consumer laser
2) A higher powered laser in the range 5 to 30+ watts was used, possibly not handheld (e.g., an AC-powered general purpose laser). If so, this may have been a deliberate attempt to cause damage.
3) The injury, or change to the retina, was less damaging (not as serious) compared to the injuries used to determine basic laser safety concepts such as the Maximum Permissible Exposure and the Nominal Ocular Hazard distance. The doctors were able to detect subtle retinal changes that, under previous MPE/NOHD studies, might not even be perceived as injuries or damage.

Detailed analysis

The report is not clear on whether the aircraft altitude was 1300 ft, or whether the laser-to-aircraft distance was calculated to be 1300 ft. If the former, there would be an additional horizontal distance so the laser could enter the cockpit window (e.g., it did not come 1300 ft straight up through the bottom of the aircraft).

For purposes of this discussion we will be conservative and say the laser-to-aircraft distance was 1300 ft.

One of the best-known consumer handheld blue lasers is the Wicked Lasers S3 Arctic, introduced in 2010. It is called a “1-watt” laser but has an actual output around 750 milliwatts (3/4 watt). The Nominal Ocular Hazard Distance of this laser, with a 1 milliradian divergence, is 635 feet. This means that beyond 635 feet, there is a “vanishingly small” chance of laser exposure causing a minimally detectable change to the eye, under laboratory conditions when the eye and the laser are held in fixed positions relative to each other.

So a S3 Arctic could not have caused the injury at 1300 ft. This is more than twice the “safe” NOHD distance.

A more powerful laser with an output of 3.1 watts and 1 mrad divergence would have an NOHD of 1291 ft. It is possible that an exposure from a 3.1 watt laser could have caused an injury, when the eye and the laser are held in fixed positions relative to each other.

However, note that the NOHD has a built-in “reduction factor” or “safety factor”. This means that the chance of injury, if someone is at or just within the NOHD, is still very, very small.

At roughly 1/3 of the NOHD, the chance of injury increases to 50%. Specifically, at 0.316 times the NOHD, there is a 50/50 chance of a laser exposure causing a minimally detectable change to the eye, under laboratory conditions when the eye and laser are held in fixed positions relative to each other. So what we are looking for is the power of a laser that has an NOHD of 4108 ft. (This is because 1300 ft would be at the 0.316x “50/50” point.)

A laser with an output of 32 watts and 1 mrad divergence fits this. That means there is a 50/50 chance that a 32 watt/1 mrad laser exposure under laboratory conditions could have caused a minimally detectable injury to an eye that is 1300 ft. away.

If the divergence was less — a tighter beam — then the overall laser power could be lower as well. This is because a tighter beam will have greater power density at a distance than the same power spread out in a wider beam. Note however, that the higher the power output of a laser, the harder it is to make a tight beam. Adding a focusing lens on the front of the laser is not significant at long distances. So it is likely that a multi-watt relatively inexpensive consumer laser would have a beam of 1 milliradian divergence or wider.

At 8 watts and a tight 0.5 mrad divergence, there would be a 50/50 chance that a laser exposure under laboratory conditions could have caused a minimally detectable injury to an eye that is 1300 ft. away. Again, 8 watts at 0.5 mrad is exceptionally tight for a consumer laser.

Second analysis

LaserPointerSafety.com received a note from a laser safety expert who read the above.

This person wrote “Some of the more important factors are that the aircraft is obviously not stationary, and that the 1300 foot range (as a minimum) is still a very distant target. There is doubtless attenuation in the windscreen, so this even without considering the ED50, for this exposure to turn into a definite injury is highly improbable.”

The expert’s “best guess” was that the exposure was 2-3 orders of magnitude above the MPE “to hope to overcome the ameliorating factors (movement, windscreen, atmospheric effects, etc).” This means that the exposure was 100 to 1000 times above the Maximum Permissible Exposure. Recall that the MPE is the highest irradiance at which injury is unlikely. For a 1/4 second exposure that would be 2.54 milliwatts per square centimeter. So the expert’s best guess is that the actual irradiance, to cause the stated injury, would be around 254 to 2540 mW/cm².

Earlier we established that a laser with an output of 3.1 watts and 1 mrad divergence would have an NOHD of 1291. Another way of saying this is that a 3.1 watt, 1 mrad laser beam would be just at the Maximum Permissible Exposure, at the aircraft windscreen.

What this expert is now guessing is that the laser was 100 to 1000 times more powerful, or around 310 to 3100 watts. For a visible blue laser, this is exceptionally powerful. It would not be a consumer-type handheld laser.

If true — if a blue laser beam was able to cause the injury described in the paper — then it must have been a laser with special characteristics such as high power and tripod tracking, which is unlike almost all other reports of consumer laser misuse.