Effect of Loupes on Ocular Blue Light Hazard: Direct Viewing

Objectives: This study measured the effect magnification loupes have on the irradiance received by the eye from a dental curing light (LCU).

Methods: Loupes with 3.5x magnification (Design for Vision [DFV], Carl Zeiss [CZ], Quality Aspirator [QA]), and 2.5x magnification (DFV & QA) were tested over two days. The loupes were placed directly over the entrance to an integrating sphere connected to a spectrometer (USB 4000, Ocean Optics). A Sapphire Plus (Den-Mat) plasma arc LCU was fixed at a distance of 40cm pointing directly at the entrance to this integrating sphere. The spectral radiant power from this LCU was recorded 5 times both without and with each of the loupes focused at the entrance to the sphere. Using 0.02 radians as the angular subtense of the experiment, the maximum permissible cumulative blue light hazard in an eight-hour day was calculated using guidelines set by the American Conference of Industrial Hygienists (ACGIH). Weighted blue light irradiance values were compared between the brands of loupes using Fisher's PLSD, α=0.05.

Results:

The loupes increased the blue light weighted irradiance values received by the pupil by up to 8 times compared to without the loupes (p<0.05). However, since the resulting images on the retina were now 2.5x to 3.5x larger, according to the ACGIH guidelines, the maximum permissible cumulative ocular exposure to the blue light in an 8-hour day was increased to only 10 to 15s compared to that without the loupes (6 to 7s).

Conclusions: Under the extreme conditions simulating a high power PAC light shone directly at the eye from a distance of 40cm, without magnification the maximum permissible cumulative daily exposure was between 6 to 7 seconds. Through magnification loupes, the maximum cumulative daily exposure time was between 10 to 15 seconds. Further studies should be conducted on the effects of magnification loupes.