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The activity of melanopsin containing intrinsically photosensitive ganglion retinal cells (ipRGC) can be assessed by a means of pupil responses to bright blue (appr.480nm) light. Due to age related factors in the eye, particularly, structural changes of the lens, less light reaches retina. The aim of this study was to examine how age and in vivo measured lens transmission of blue light might affect pupil light responses, in particular, mediated by the ipRGC.
Consensual pupil responses were explored in 44 healthy subjects aged between 26 and 68years. A pupil response was recorded to a continuous 20s light stimulus of 660nm (red) or 470nm (blue) both at 300cd/m2 intensity (14.9 and 14.8 log photons/cm2/s, respectively). Additional recordings were performed using four 470nm stimulus intensities of 3, 30, 100 and 300cd/m2. The baseline pupil size was measured in darkness and results were adjusted for the baseline pupil and gender. The main outcome parameters were maximal and sustained pupil contraction amplitudes and the postillumination response assessed as area under the curve (AUC) over two time-windows: early (0–10s after light termination) and late (10–30s after light termination). Lens transmission was measured with an ocular fluorometer.
The sustained pupil contraction and the early poststimulus AUC correlated positively with age (p=0.02, p=0.0014, respectively) for the blue light stimulus condition only.
The maximal pupil contraction amplitude did not correlate to age either for bright blue or red light stimulus conditions.
Lens transmission decreased linearly with age (p<0.0001). The pupil response was stable or increased with decreasing transmission, though only significantly for the early poststimulus AUC to 300cd/m2 light (p=0.02).
Age did not reduce, but rather enhance pupil responses mediated by ipRGC. The age related decrease of blue light transmission led to similar results, however, the effect of age was greater on these pupil responses than that of the lens transmission. Thus there must be other age related factors such as lens scatter and/or adaptive processes influencing the ipRGC mediated pupil response enhancement observed with advancing age.