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C.M. Beaulieu, S. Cote, M. Rufiange, M. Dumont, P. Lachapelle; Modulating Retinal and Circadian Sensitivies With Light History and Seasons . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5662.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We have previously shown that retinal sensitivity was highly dependent on the luminous level of our work environment. We examined if this relationship also demonstrated a seasonal effect. Methods: Eleven workers were tested during the summer (6 working indoor and 5 outdoor; mean age 29 y.) and 13 during the winter (6 indoor and 7 outdoor; mean age 30 y.). Retinal sensitivity was evaluated with the electroretinogram (ERG) using a LKC UTAS–E–3000 system. Dark adaptation was measured with series of 5 consecutive flashes of –3.41 log cd.sec.m–2 delivered every 3 minutes for a period of 30 minutes at the end of which, scotopic ERG luminance–response functions were generated (11 flashes; range:–5.01 to –0.96 log cd.sec.m–2; blue light). Photopic luminance–response functions were also obtained (15 flashes; range: –.80 to 2.84 log cd.sec.m–2; background: 30 cd.m–2). Circadian light sensitivity was evaluated with a salivary melatonin suppression test. Melatonin suppression was induced by exposure to 500 lux for 90 min, 1.5h after habitual bedtime. Results: In wintertime, indoor workers took less time (19.72 min ±2.90) to dark–adapt than outdoor workers (23.09 min ±3.27). Their scotopic Vmax was also reached at a lower intensity (–2.11 log cd.sec.m–2 ±0.19) compared to outdoor workers (–1.83 log cd.sec.m–2 ±0.23). In contrast, indoor subjects needed brighter intensities in order to reach the photopic Vmax in winter compared to outdoors (0.61 log cd.sec.m–2 ±0.18 vs 0.33 log cd.sec.m–2 ±0.11). Finally, melatonin suppression was about 30% greater in indoor workers (winter only). No such difference was noted when comparing both groups in the summer. Conclusions: For winter measurements, our results show a greater circadian and scotopic retinal sensitivity along with a lower photopic retinal sensitivity in indoor compared to outdoor workers. Since light exposure differed only in winter between the 2 groups, these results reinforce the possibility of a causal relationship between light history and the retinal and circadian light sensitivity.
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