Tear Secretion Induced by Selective Stimulation of Corneal and Conjunctival Sensory Nerve Fibers

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Purpose. To measure the increase in tear secretion evoked by selective stimulation of the different populations of sensory receptors of the cornea and conjunctiva by using moderate and intense mechanical, chemical, and cold stimuli. Methods. Six healthy subjects participated in the study. Tear secretion was measured in both eyes by the Schirmer’s test conducted under control conditions and after stimulation of the center of the cornea and the temporal conjunctiva with a gas esthesiometer. Mechanical stimulation consisted in three pulses of 3 seconds’ duration of warmed air (at 34°C on the eye surface) applied at moderate (170 mL/min) and high (260 mL/min) flow rates. Cold thermal stimulation was made with cooled air that produced a corneal temperature drop of −1°C or −4.5°C. Chemical (acidic) stimulation was performed with a jet of gas containing a mixture of 80% CO2 in air. Results. The basal volume of tear secretion increased significantly (P < 0.05, paired t-test) after stimulation of the cornea with high-flow mechanical stimuli (260 mL/min), intense cooling pulses (−4.5°C), and chemical stimulation (80% CO2). The same stimuli were ineffective when applied to the conjunctiva. Moderate mechanical (170 mL/min) and cold (−1°C) stimulation of the cornea or the conjunctiva did not change significantly the volume of tear secretion. Conclusions. Reflex tear secretion caused by corneal stimulation seems to be chiefly due to activation of corneal polymodal nociceptors, whereas selective excitation of corneal mechanonociceptors or cold receptors appears to be less effective in evoking an augmented lacrimal secretion. Conjunctival receptors stimulated at equivalent levels do not evoke an increased tear secretion.
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1 Mutch JR. The lacrimation reflex. Br J Ophthalmol. 1944;28:317–336. 2 Drummond PD. Lacrimation and cutaneous vasodilatation in the face induced by painful stimulation of the nasal ala and upper lid. J Auton Nerv Syst. 1995;51:109–116. 3 Whitwell J. Role of the sympathetic in lacrimal secretion. Br J Ophthalmol. 1961;45:439–445. 4 Ding C, Walcott B, Keyser KT. Sympathetic neural control of the mouse lacrimal gland. Invest Ophthalmol Vis Sci. 2003;44:1513–1520. 5 Dartt DA. Control of mucin production by ocular surface epithelial cells. Exp Eye Res. 2004;78:173–185. 6 Belmonte C, Gallar J, Pozo MA, Rebollo I. Excitation by irritant chemical substances of sensory afferent units in the cat’s cornea. J Physiol. 1991;437:709–725. 7 Gallar J, Pozo MA, Tuckett RP, Belmonte C. Response of sensory units with unmyelinated fibers to mechanical, thermal and chemical stimulation of the cat’s cornea. J Physiol. 1993;468:609–622. 8 Belmonte C, Gallar J. Corneal nociceptors. Belmonte C Cervero F eds. Neurobiology of Nociceptors. 1996;146–183. Oxford University Press Oxford, UK. 9 Belmonte C, Garcia-Hirschfeld J, Gallar J. Neurobiology of ocular pain. Prog Retin Eye Res. 1997;16:117–156. 10 Acosta MC, Belmonte C, Gallar J. Sensory experiences in humans and single unit activity in cats evoked by polymodal stimulation of the cornea. J Physiol. 2001;534:511–525. 11 Acosta MC, Tan EM, Belmonte C, Gallar J. Sensations evoked by selective mechanical, chemical and thermal stimulation of the conjunctiva and cornea. Invest Ophthalmol Vis Sci. 2001;42:2063–2067. 12 Belmonte C, Acosta MC, Schmelz M, Gallar J. Measurement of corneal sensitivity to mechanical and chemical stimuli with a CO2 esthesiometer. Invest Ophthalmol Vis Sci. 1999;40:513–519. 13 Schirmer O. Studien zur Physiologie and Pathologie der Träneabsonderung und Tränenabfuhr. Graefes Arch Ophthalmol. 1903;56:197–291. 14 Chen X, Gallar J, Pozo MA, Baeza M, Belmonte C. CO2 stimulation of the cornea: a comparison between human sensation and nerve activity in polymodal nociceptive afferents of the cat. Eur J Neurosci. 1995;7:1154–1163. 15 Reeh PW, Steen KH. Tissue acidosis in nociception and pain. Prog Brain Res. 1996;133:143–151. 16 Campero M, SerraJ , Ochoa JL. C-polymodal nociceptors activated by noxious low temperature in human skin. J Physiol. 1996;497:565–572. 17 Duke-Elder S, Wybar KC. The anatomy of the visual system. Syst Ophthalmol. 1961;2:540–558. 18 Boberg-Ans J. Experience in clinical examination of corneal sensitivity. Br J Ophthalmol. 1955;309:705–726. 19 Norn MS. Conjunctival sensitivity in normal eyes. Acta Ophthalmol. 1973;51:58–66. 20 Dartt DA. Regulation of mucin and fluid secretion by conjunctival epithelial cells. Prog Retin Eye Res. 2002;21:555–576. 21 Lamberts DW, Foster CS, Perry HD. Schirmer test after topical anesthesia and the tear meniscus height in normal eyes. Arch Ophthalmol. 1979;97:1082–1085. 22 Herreras JM, Perez S, Perez H, Calonge M, Pastor JC. Influence of topical anesthesia on test diagnostic of blepharitis-associated dry eye syndrome. Ocul Immunol Inflamm. 1997;5:33–41.