Effects of Medetomidine, Dexmedetomidine and their combination with Acepromazine on the intraocular pressure (IOP), tear secretion and pupil diameter in dogs

Abstract

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Bilateral corneal ulceration in a cat after general anaesthesia

“…The physiological tear film is essential to protect the corneal epithelium 5,21 . In dogs and cats, general anaesthesia significantly increases the risk of corneal defects through reduction of tear production, blinking reflex and eyelid closure (lagophthalmos) 2,6,13,17,18,22–25 . Anaesthetic drugs are hypothesised to affect tear production and the tear film by interacting with the parasympathetic nervous system, 2,26 reducing blood perfusion to the lacrimal gland, altering its metabolism, and changing the composition of the tear film 27 .…”

“…The cat of the present case did not have any of these predisposing factors (young, normocephalic, sternal recumbency, no forced air, short procedure and so forth). Another relevant risk factor seems to be the drugs used for general anaesthesia, 22,23,27 while there is no knowledge on how the choice of these drugs influences the outcome. Opioid drugs have been shown to contribute to prolonged reduction of tear production in dogs, potentially impairing post‐anaesthetic healing of corneal abrasions, even though their contribution compared to other factors has not been well determined 4,25,27,32 .…”

“…5,21 In dogs and cats, general anaesthesia significantly increases the risk of corneal defects through reduction of tear production, blinking reflex and eyelid closure (lagophthalmos). 2,6,13,17,18,[22][23][24][25] Anaesthetic drugs are hypothesised to affect tear production and the tear film by interacting with the parasympathetic nervous system, 2,26 reducing blood perfusion to the lacrimal gland, altering its metabolism, and changing the composition of the tear film. 27 In humans, the application of ocular ointment during general anaesthesia to maintain the tear film reduces the incidence of corneal ulceration from above 30% to below 5%, 9,12 with similar results in dogs.…”