Locus coeruleus (LC) activity consists in a sustained low-frequency firing rate (tonic activity), accounting for basal pupil diameter, interspersed with event-driven higher-frequency bursts (phasic activity), accounting for event-related transient changes in pupil diameter. Pupil size measurements are used here as a non-invasive biomarker of LC activity, and to assess its evolution with age. Pupil size was measured in 72 healthy participants (34 young: age = 23.0 years ± 2.6; 38 older: age = 69.3 years ± 6.8), who underwent a 2-minute passive gaze fixation task and a fast object categorization task, where various objects embedded in semantically congruent or incongruent scenes were presented during 100ms. Data with excessive blinks or noise were removed from analysis. Cluster-based permutation testing was used to assess age-related differences in pupil phasic responses. Mean basal pupil diameter was lower in older vs. young individuals (p < 0.05). Basal pupil fluctuations, estimated by the standard deviation of the 2-minute pupil signal, were lower in the older group (p<0.001). Finally, task-evoked pupil responses involved a stronger reflexive constriction (500ms post-stimulus) followed by a weaker cognitively-driven dilation (peak at 1500ms post-stimulus) in older volunteers (p<0.05). Age-related decrease in basal pupil fluctuations and mean diameter are consistent with altered LC tonic activity. Stronger reflexive constriction in older subjects could be related with reduced inhibition exerted by the LC on the parasympathetic pupil reflex. Weaker dilation in older people also suggests reduced LC involvement in visual scene cognitive processing. Effects of scene congruence and link with long-term scene memory are currently explored.