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T. Simpson, P. Situ; Nociceptive Mechanical and Chemical Stimuli Delivered Using a Belmonte Pneumatic Esthesiometer Induce Detectible Tearing. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6351.
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To determine if thresholds for the detection of tearing could be estimated psychophysically.
10 normal subjects had psychophysical thresholds at the corneal apex and approx. 2mm inside the limbus (on their corneas) to mechanical and chemical pneumatic stimuli determined using the ascending method of limits with a computerised Belmonte esthesiometer. Suprathreshold stimuli were then applied in random order (intensity, position, modality), and subjects reported the presence of the stimuli as well as whether they felt tears starting to accumulate in their eyes. "Psychometric functions" for stimulus presence and detection of tearing were fit using logistic functions, from which thresholds (50% detection) and slopes were estimated.
The tearing psychometric functions were well behaved and fit by logistic functions. In addition, there were generally strong, significant associations between stimulus detection and tearing thresholds regardless of stimulus type or position (all r at least 0.65, p<0.05). Multiple linear regression with tearing as outcome (and sensory thresholds and slope as predictors) was significant for each position and stimulus combination (R² at least 0.58, p 0.12).
Unpleasant pneumatic chemical and mechanical corneal stimuli induce tearing in a dose-response way. Subjects are able to report the presence of this tearing in ways related to stimulus intensity and also related to their detection thresholds for painful stimuli. Tearing is induced by painful stimuli delivered to both central and peripheral cornea.
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