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M Rufiange, M Dumont, P Lachapelle; Effect of Light Intensity at Work on Retinal Function . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1774.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Evaluate the effect of light intensity in the working environment on the retinal function, as measured with the electroretinogram (ERG). Methods: The retinal function of 9 outdoor workers (5W: 4M; aged 23-40) was compared to that of 9 subjects working indoors in an environment without windows (3W: 6M; aged 21-43). Each participant had been working full-time (minimum 32hrs/week) in the same environment for at least 6 weeks (mean: 3.7 months). Light exposure was recorded 24hrs/day for a period of two weeks with an ambulatory monitor (Actiwatch®). ERG testings were conducted with a LKC UTAS-E-3000 system which included a Ganzfeld of 30 cm in diameter. The rate of dark adaptation was measured with flashes (average of 5) of -3.8 log cd.m-2.sec delivered every 3 minutes for a period of 30 minutes. The time required to obtain the maximal b-wave amplitude was considered as a measure of the rate of dark adaptation. After this 30-minute period of dark adaptation, scotopic ERGs were recorded using 11 intensities of blue light (-5.01 to -0.96 log cd.m-2.sec). This was followed by the photopic ERGs recorded against a white background of 30 cd.m-2 with the use of 15 intensities of white light (-0.80 to 2.84 log cd.m-2.sec). Results: Indoor workers required less time for dark adaptation than outdoor workers (p=.07). Indoor workers were also more sensitive in scotopic conditions (p<.005) but less sensitive in photopic conditions (p<.05) than outdoor workers as revealed with the intensity needed to obtain the rod and the cone b-wave Vmax. Furthermore, the entire photopic intensity-response function (photopic hill) was shifted towards the brighter flashes in the indoor group compared to the outdoor group, again showing a reduced sensitivity in the former group. Conclusion: The above results suggest that the light history of our subjects influenced their retinal sensitivity to light. It would appear that a prolonged exposure to a low light level increased the sensitivity of the rods but decreased that of the cones. We might be looking here at the manifestation of a photostasis process in humans. Animal studies on the photostasis phenomenon showed that the amount of photopigment adjusts in response to changes in the lighting environment in order to absorb a constant amount of photons per day. Funded by CIHR, FRSQ, GRENE, NSERC and Réseau-Vision.
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