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T.L. Simpson, L. Henderson; The Relationship Between Corneal Chemical Thresholds Estimated at Different Flow Rates Using a Belmonte Pneumatic Esthesiometer . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2069.
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Purpose: To examine the effects of different flow rates on corneal chemical thresholds estimated using a pneumatic esthesiometer. Methods: 20 control subjects had chemical (burning/stinging) detection thresholds (%CO2) estimated in the centre of their corneas. Stimulus temperature, flow rate and %CO2 were regulated by a computer controlled Belmonte esthesiometer and subject responses were collected by the computer using a button box. Initial mechanical thresholds were determined using a preliminary ascending method of limits and a subsequent method of constant stimuli and then chemical thresholds were estimated using an ascending method of limits. Flow rates for the delivery of the CO2 mixtures were set at 100%, 75% and 50% of the mechanical thresholds (in random order). Results: As the stimulus flow rate went down, CO2 detection threshold went up (repeated measures ANOVA p<0.0001). When the flow rates were 75% and 50% of the threshold, the CO2 thresholds were 83% and 68% of the respective chemical threshold at the maximum flow rates. Conclusions: The results illustrate the difficulty in measuring chemical thresholds with a Belmonte esthesiometer because flow rate must be selected beforehand and this selection has a direct effect on the measurement. The results also demonstrates the importance of standardizing novel techniques to make comparison between studies possible. Finally, because the thresholds are not simply related to the flow rates at which the chemical stimuli are delivered, the results point to possible interactions between the mechanical and chemical stimuli and/or interactions between the corneal chemical nociceptive channels.
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