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C. Beaulieu, M. Dumont, P. Lachapelle; Are Retinal And Circadian Sensitivities Equally Modulated By Light History? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1663.
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In a previous field study we presented results suggesting that retinal and circadian sensitivities depended upon the luminous level to which our subjects were exposed in their work environment. Our objective is to determine experimentally if there is a causal relationship between light history and retinal and circadian sensitivity.
In a controlled laboratory setting, 7 participants were exposed to a dim light (DL) environment (70 lux) and 5 participants to a bright light (BL) environment (3000 lux) 10 hours per day for 12 consecutive days. Light exposure was measured 5 days prior to the onset of experiment in the subject’s natural environment (natural light exposure: NLE) and during the entire laboratory experiment with an Actiwatch–L®. Retinal function was assessed with the electroretinogram (ERG) using a LKC UTAS–E–3000 system. Scotopic luminance–response functions were generated (11 steps; range:–5.01 to –0.96 log cd.sec.m–2; blue light) after 30 minutes of dark adaptation. Photopic luminance–response functions (15 steps; range: –.80 to 2.84 log cd.sec.m–2; background: 30 cd.m–2; white light) were obtained after 15 min of light adaptation. Circadian light sensitivity was evaluated with a salivary melatonin suppression test induced by exposing the subjects to a 500 lux background for 90 min, 1.5h after the habitual bedtime. Retinal and circadian sensitivity measures were taken before and after the experimental condition.
There was no significant group difference noted following the 12 days of exposure in the DL or BL environments. A weak correlation was found between the NLE and retinal sensitivity (scotopic: r=.202; photopic: r=.031). However, once corrected for prelaboratory illumination, the correlation between exposure to the laboratory environment and photopic ERG measures (r=.56) improves but not the scotopic one (r=–.24). Similarly, the weak correlation (r=.15) found between NLE and the melatonin suppression was enhanced (r=.55) following exposure to the laboratory environment.
Our results suggest that light history does modulate the retinal and circadian sensitivity. Again, as previously demonstrated with our field study, the photopic function appears to be the most sensitive to a change in the luminous environment. The reason for this discrepancy remains to be understood.
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