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Ian Meng, Stephen Barton, Andrew Twaite; Lacrimal gland removal increases primary afferent driven spontaneous blinking and produces ocular hyperalgesia in the rat. Invest. Ophthalmol. Vis. Sci. 2013;54(15):906.
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Dry eye syndrome produces ocular pain yet an animal model for assessing nociceptive responses in the dry eye condition is lacking. The aim of this study was to characterize spontaneous and evoked pain in the rat after unilateral removal of the infra- and exorbital lacrimal glands.
In male SD rats, spontaneous blinking and eye wipe behaviors elicited by hypertonic saline (2.5 and 5.0 M) was examined 2 and 8-10 weeks following unilateral removal of the infra- and exorbital lacrimal glands and in age matched controls. Furthermore, the effect of topical lidocaine (4%) on spontaneous blinking and the effect of morphine (5 mg/kg, s.c.) on spontaneous blinking and eye wipe responses was determined in dry eye and control animals.
Lacrimal gland removal resulted in an increase in spontaneous blinking in the ipsilateral eye that remained consistently elevated over an 8-week period. Lidocaine application reduced spontaneous blinking down to control levels, whereas glycerol and artificial tear solutions reduced spontaneous blinking. The time spent eye wiping was also enhanced in response to hypertonic saline (2.5 and 5.0 M) at both the 2 and 8 wk time-points. Morphine attenuated both spontaneous blinking and the response to hypertonic saline in dry eye animals.
These results indicate that dry eye produced by lacrimal gland removal produces hyperalgesia in the rat, as quantified in the eye wipe assay. In addition, spontaneous blinks in dry eye animals and their reduction by morphine and topical anesthesia, indicate the presence of persistent irritation elicited by the activation of corneal nociceptors.
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