Stimulus characteristics of a novel air-based multiple stimulus aesthesiometer

Abstract

Purpose: To (1) develop a novel air-based aesthesiometer capable of producing and applying multiple stimuli separated either by time or space; (2) identify the stimulus airflow characteristics and confirm the consistency of the novel aesthesiometer; (3) determine if the instrument can be used to investigate spatial and temporal summation in the human cornea.

Methods: (1) A novel aesthesiometer (called the Dolphin Aesthesiometer) was designed around a micro-blower (MurataTM Manufacturing Co., Japan) under software management. (2) Four studies that tested consistency and characteristics of the airflow (with and without a nozzle) were completed: (i) airflow pattern/trajectory measured using lycopodium powder, (ii) airflow surface dispersion by measuring lycopodium powder displacement; (iii) force of airflow across a range of stimulus strengths measured using a microbalance, (iv) thermal effects on the ocular surface measured using a thermal camera. (3) Two studies were performed to explore the effects of time delay and spatial separation on an in vitro eye model using thermography.

Results: (1) The instrument consists of four micro-blowers, each capable of separate or sequential stimulus delivery. Stimulus delivery under software management provided refined control of airflow rate and duration. (2) Stimulus characteristics studies: (i) airflow is coherent within the expected test distance range for the instrument, and the spread rate is constant irrespective of the stimulus strength; (ii) airflow dispersion occurs upon encountering a surface, and dispersion increases with increasing airflow rate; (iii) a consistent and small force (of the order of 10-4 N) is applied in relation to airflow; (iv) repeatable thermal effects occur in relation to the airflow, and the mode of stimulation of the Dolphin aesthesiometer is predominantly thermal in nature. Fitting a narrow diameter (1 mm) nozzle to the airflow exit of a micro-blower reduced stimulus airflow dispersion. (3) Effects of time delay and spatial separation studies: the Dolphin Aesthesiometer can deliver single stimuli, repeated single stimuli with a variable time-delay, or multiple stimuli either simultaneously or with time delay between them.

Conclusions: These studies confirm the repeatability and consistency of the novel instrument. The device is suitable for measuring corneal sensitivity. The availability of additional air-jets allows the application of multiple stimuli to facilitate corneal summation investigations. With some additional studies and calibration, this instrument will allow in vivo studies of neural signal summation in the corneal sensory nerves.