Corneal surface temperature change as the mode of stimulation of the non-contact corneal aesthesiometer.
OBJECTIVE
The non-contact corneal aesthesiometer (NCCA) assesses corneal sensitivity by using a controlled pulse of air, directed at the corneal surface. The purpose of this paper was to investigate whether corneal surface temperature change was a component in the mode of stimulation.


METHODS
Thermocouple experiment: A simple model corneal surface was developed that was composed of a moistened circle of filter paper placed on a thermocouple and mounted on a glass slide. The temperature change produced by different stimulus 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 different stimulus air pulses. Pulse duration was set at 0.9 s but was varied in pressure from 0.5 to 3.5 millibars.


RESULTS
Thermocouple experiment: An immediate drop in temperature was detected by the thermocouple as soon as the air flow was incident on the filter paper. A greater temperature change was produced by increasing the pressure of the incident air flow. A relationship was found and a calibration curve plotted. Thermal camera experiment: For each subject, a drop in surface temperature was detected at each stimulus pressure. Furthermore, as the stimulus pressure increased, the induced reduction in temperature also increased. A relationship was found and a calibration curve plotted.


CONCLUSIONS
The NCCA air-pulse stimulus was capable of producing a localized temperature change on the corneal surface. The principal mode of corneal nerve stimulation, by the NCCA air pulse, was the rate of temperature change of the corneal surface.
Murphy
P J
PJ
Department of Vision Sciences, Glasgow Caledonian University, United Kingdom. pmu@gcal.ac.uk
Morgan
P B
PB
Patel
S
S
Marshall
J
J
D000388:Air; D001831:Body Temperature / Q000502:physiology*; D003315:Cornea / Q000294:innervation / Q000502:physiology*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D006801:Humans; D008953:Models, Anatomic; D009882:Ophthalmic Nerve / Q000502:physiology; D012677:Sensation / Q000502:physiology*; D013817:Thermography