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T.L. Simpson, D. Fonn, J. Wang, S. Hickson-Curran; Suprathreshold Scaling of Limbal Mechanical Stimuli . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3709.
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Purpose: To examine suprathreshold response to mechanical stimulation of the limbus. Methods: Thirty nine subjects rated the discomfort, using magnitude estimation (with maximum set at 100), induced by systematically administered mechanical stimuli present at the limbus. The stimuli were specific pressures applied in random order, using a Cochet-Bonnet esthesiometer (using thread lengths of 10 to 50 mm in 10mm increments) at the point in the limbal area where each subject’s threshold was 50mm. Each subject’s transducer function (pressure vs magnitude) was fit with a power function, as was the group’s mean transducer function. Results: As was anticipated based on Steven’s Power Law, the data were well described by power functions (r mean = 0.93). The mean exponent (+/- se) of the individual power functions was 0.33 +/-0.04 and the exponent of the mean power function was 0.30 +/- 0.01. A one sample t-test showed that this was statistically lower than the exponent of the power function for central cornea (t=-15.7, p=0.000) reported by Millodot (1968, J Psychonomic Soc. 12, 401-402). Conclusions: The data suggest that suprathreshold increments of mechanical limbal stimulation produces lower increments in discomfort (lower exponents) in comparison to the corneal apex. Therefore, both threshold and suprathreshold limbal stimulation is less effective compared to stimulation of the corneal apex.
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