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Varadharajan Jayakumar, Trefford L Simpson; Detectability of Belmonte pneumatic corneal chemical stimuli in asymptomatic participants.. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3953. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the detectability and response bias of asymptomatic participants for supra-threshold chemical stimuli, using signal detection theory.
The Waterloo version of modified Belmonte pneumatic esthesiometer was used in this study. Ten asymptomatic and non-contact lens wearing participants were recruited and informed consent was obtained. The mechanical thresholds were obtained first using ocular temperature medical air stimuli and then flow rate of half of the mechanical threshold was used for chemical stimuli to avoid any mechanical effect influencing participant’s response for chemical stimulation. To obtain the chemical threshold, CO2 was added to the air systematically; a fixed flow rate was used and the concentration was varied in 5% steps using the ascending method of limits procedure. The thresholds were measured twice and the average was used for measuring detectability. To keep the sensation similar across all the participants for detection, the concentration of supra-threshold stimuli was 1.5 times individual chemical threshold. 50 trials were presented with stimulus probability of 0.4 (20 signal and 30 catch trials). Between each trail, a recovery time of 25 sec was provided to the participants. The order of the presentation was randomised and trials were demarcated using computerised tones. Responses (“yes” (there was a signal) or “no” (there was no signal)) were recorded using a button box. A calibrated video camera verified the 5mm distance of the esthesiometer tip from the center of the cornea and participants were encouraged to blink during the recovery period.
The average (± SE) mechanical threshold for the group was 37.5 ± 10.2 ml/sec and chemical threshold for the group was 18.5 ± 4.7 %CO2 added. The detectability of the supra-threshold chemical stimuli was 1.16 (± 0.4) with a response bias of 2.8 (± 1.6) and criterion at 0.36 (± 0.23).
Consistent detectability and criterion/bias were obtained with stimuli scaled relative to each participant’s threshold. The criterion metric close to zero suggests a conservative strategy (as expected due to low stimulus probability) adopted by the participants. Although the experiments are much more protracted than those typically used to measure thresholds with pneumatic stimulation, participant’s responses to chemical stimulation of the cornea with pneumatic stimuli can be analysed using signal detection theory.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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