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Emmanuel B Alabi, Varadharajan Jayakumar, Yunwei Feng, Trefford L Simpson; Pupillary Response to Corneal Mechanical Stimulation.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):582. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Ocular somatosensory-autonomic reflexes play critical roles in maintaining homeostasis of the eye. The purpose of this study was to examine the pupil reflex before and after delivery of nociceptive corneal mechanical stimuli.
Using a computerized Belmonte pneumatic esthesiometer, mechanical stimuli from levels of detection threshold to twice (2x) the threshold in 0.5x steps were delivered in random order to the central cornea of 15 healthy subjects, aged 20 - 55 years. Threshold was estimated using an ascending method of limits. Contralateral pupil imaging was performed using a modified Logitech c920 digital camera (Logitech c920; Logitech International S.A., Newark, CA) for 5 seconds before and after the stimulus. Consensual pupil sizes were then measured (average of horizontal and vertical measures) using ImageJ software (NIH, Bethesda, MD). Statistical analyses were performed using Statistica 8.0 (StatSoft Inc., Tulsa, OK) and P ≤ 0.05 was considered statistically significant. Repeated-measures ANOVA and post hoc Tukey HSD tests were used to examine the effect of intensity on pupil size.
The figures below show 8-bit processed images of the contralateral pupil before and after delivery of the painful corneal stimulus. The average pupil sizes were 5.82 ± 0.66mm (before stimulus delivery), 6.41 ± 0.63mm (at threshold), 6.62 ± 0.65mm (1.5x threshold) and 6.97mm ± 0.79 (2x threshold). Pupil sizes increased with increasing stimulus intensity (P < 0.05) and the maximum mechanical stimulus intensity induced the largest pupil sizes (all P < 0.05).
Noxious, mechanical, central, corneal stimuli evoke dose dependent sympathetic autonomic consensual pupillary dilation. This study serves as a basis for the characterization of the local stimulus-response neural circuitry relating nociceptive stimuli to autonomic responses.
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