Pj. Murphy et al., Corneal surface temperature change as the mode of stimulation of the non-contact corneal aesthesiometer, CORNEA, 18(3), 1999, pp. 333-342
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.