Modelling the thermal effects of stimulus airflow from the Dolphin aesthesiometer on a model eye surface

Purpose: To assess the ability of the Dolphin air-pulse aesthesiometer to present multiple stimuli, which are separated temporally (in sequence) or spatially (simultaneously).

Methods: Two studies were performed to explore the cooling effects induced by double air-puff stimuli generated by a novel aesthesiometer composed of two micro-blower integrated units. The stimuli were delivered sequentially or simultaneously at the same or different spatial locations to an in vitro eye model monitored using thermography. The model eye was based on a 2-cm LED dome light mounted on a circuit board with an 8-V supply producing a baseline 32°C temperature. Single and repeated air-pulse stimuli varying in intensity, duration, inter-stimulus delay and stimulus location were presented to the model. The cooling effect produced was observed using a thermal camera and quantified using image analysis software.

Results: The instrument can deliver single stimuli, repeated single stimuli with a variable time delay or multiple stimuli either simultaneously or with a time delay between them. The thermal effects of stimuli were evaluated by measuring (relative to pre-stimulus baseline) the local temperature change and the diameter of the model eye surface region with ≥1°C reduction. Repeated stimuli at the same location produced a significantly greater effect than a single stimulus of the same intensity (larger area of cooling after the second stimulus compared to the first [|M|{SE} = 1.48 mm {0.06}, p < 0.001]). Spatially separated stimuli produced separate cooling zones, with the amount of cooling relative to stimulus intensity (rm-ANOVA, F_2,8 = 276.01, p < 0.001, $\omega$ ² = 0.96).

Conclusions: The combined use of two micro-blower units allows increased options for modification of stimulus intensity and timing of delivery that enables the production of alternative stimulus presentations and intensity compared to a single stimulus. This adaptability may enable future in vivo study of corneal sensory nerve summation.