02 Apr 2003
The retina's damage threshold to blue laser light may be much higher than previously believed.
A recent study in the US suggests that the eye's damage threshold to short exposure of blue laser light is about 16 times higher than previously thought. The evidence was presented at the Laser Institute of America's annual International Laser Safety Conference (ILSC 2003) which recently took place in Florida, US.
Tests carried out by David Lund and Bruce Stuck at the Walter Reed Army Institute of Research in Texas, US indicate that the retinal injury threshold for exposure to 1 s of 441.6 nm light is 14 W/cm2.
In comparison, a former study conducted by the US military more than 25 years ago produced a value of just 0.91 W/cm2. Its findings were published in Nature in 1976 in a paper by Ham, Mueller and Sliney entitled "Retinal sensitivity to damage from short wavelength light".
Knowledge of the new increased damage threshold could mean a rewriting of the safety guidelines for broadband light sources.
"These new data have little immediate consequence for the laser safety guidelines. The greater impact is on the guidelines for lamps and other broadband sources," say Lund and Stuck in their ILSC paper. "The need for a large-blue light penalty for thermal exposures [an exposure of less than 10 s] no longer exists."
As to why the discrepancy between the two studies is so large, Lund and Stuck believe that it could just be of a simple calculation error. "The simplest explanation might be a misplaced decimal point," they comment.
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.
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