Since the 1990s, eye-tracking researchers have investigated expert-novice differences in visual attentional processes among athletes. One such difference concerns the quiet eye (QE) phenomenon, or the time that elapses between a skilled performer's last fixation on a specific target and the subsequent initiation of a relevant motor response. Despite extensive research on QE, however, the precise attentional mechanisms underlying its effects remain unclear. Therefore, to address this issue, the present study explores the potential value of using pupillometry (the measurement of changes in pupil diameter as a function of cognitive processing) to investigate attentional effort (also known as mental effort), or the allocation of attentional resources during QE for athletes of different levels of ability. We predicted that experts would exert significantly more attentional effort (increased pupil dilation) than would their less-skilled counterparts during QE. Fifteen equestrian performers (5 expert, 5 intermediate or near-expert, and 5 novice riders) were eye-tracked while making a critical decision in a laboratory setting as they viewed a video-based show-jumping sequence. Overall, our results show that pupillometry can be used to identify skill-based differences in attentional effort during QE, F(2, 8) = 5.099, p < .05, eta(2) = 0.560). Substantial individual differences in pupil dilation were also found among participants. Furthermore, results show a significant positive correlation (r = .692, p < .05) between duration of QE and the exertion of attentional effort. Following a discussion of the theoretical significance of these findings, methodological limitations are acknowledged, and some potentially fruitful new directions for pupillometry research on QE processes are identified.