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Zusammenfassung:
Background: Photic sneezing is a widespread phenomenon characterised by sneezing in response to bright-light exposure (typically direct sunlight), affecting around 20% of the population. This photic sneeze reflex (PSR) has been documented for a long Clocks&Sleep 2023, 5 445 time, but is poorly understood. Our goals were to collect real-world data to understand the naturalistic light conditions eliciting photic sneezing, and to develop an indoor protocol to reliably induce the PSR in affected subjects using parametric stimuli, a key stepping stone for further research on this topic. Methods: This pilot study was carried out on one male adult affected by photic sneezing (n = 1). For characterisation of naturalistic light conditions eliciting photic sneezing, the subject wore an Actiwatch at torso level, measuring light levels during daytime, while light-induced sneezes were logged into a journal. To study photic sneezing in response to artificial stimuli, a bespoke setup including a multi-primary LED source and an integrating sphere was used to present a 30-second light stimulus to the subject while collecting pupillometry data with an eye-tracker. A 1 min darkness adaptation period was observed before showing the stimulus. The variables of interest were illuminance (0, 440, 1100, 4400 and 17,600 photopic lux, white light), and distance from the light source (2, 4 and 6 m). The cumulative effect of light stimuli was also assessed (over 30 min). Results: Real-world light exposure data recorded conjointly with logged photic sneeze events showed a significant increase in illuminance values around 2 min before the sneeze event, before going back down to pre-sneeze levels within 10 min after. At a sneeze event, illuminance is on average ten times bigger than the illuminance values five minutes before the sneeze event. Despite exposure to more than 150 stimuli, no sneeze could be induced in the subject using the experimental setup. A strong tickling sensation was consistently reported, which shows that sneezing was close, especially for high-illuminance settings and short sitting distances from the light source. Conclusions: Real-world light data confirmed that a sudden increase in environmental lighting conditions can induce photic sneezing. However, deeper analysis is clearly necessary, for example, on instances of illuminance increments not eliciting a photic sneeze. The experimental setup only elicited tickling sensations, but with further optimisation, it should in theory be capable of reliably inducing photic sneezes, thereby opening further mechanistic study of photic sneezing.
