Corneal surface temperature change as the mode of stimulation of the non-contact corneal aesthesiometer

Purpose. The non-contact corneal aesthesiometer (NCCA) assesses corneal sen sitivity by using a controlled pulse of air, directed at the corneal surfac e. The purpose of this paper was to investigate whether corneal surface tem perature change was a component in the mode of stimulation. Methods. Thermo couple experiment: A simple model corneal surface was developed that was co mposed of a moistened circle of filter paper placed on a thermocouple and m ounted on a glass slide. The temperature change produced by different stimu lus pressures was measured for five different ambient temperatures. Thermal camera experiment. Using a thermal camera, the corneal surface temperature change was measured in nine young, healthy subjects after exposure to diff erent stimulus air pulses. Pulse duration was set at 0.9 s but was varied i n pressure from 0.5 to 3.5 millibars. Results. Thermocouple experiment. An immediate drop in temperature was detected by the thermocouple as soon as t he air flow was incident on the filter paper. A greater temperature change was produced by increasing the pressure of the incident air flow. A relatio nship was found and a calibration curve plotted. Thermal camera experiment. For each subject, a drop in surface temperature was detected at each stimu lus pressure. Furthermore, as the stimulus pressure increased, the induced reduction in temperature also increased. A relationship was found and a cal ibration curve plotted. Conclusion. The NCCA air-pulse stimulus was capable of producing a localized temperature change on the corneal surface. The pr incipal mode of corneal nerve stimulation, by the NCCA air pulse, was the r ate of temperature change of the corneal surface.