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Intraocular Pressure and Oculocardiac Reflex

Intraocular pressure (IOP) is normally 12 to 20 mm Hg. The eye can be considered a hollow sphere with a rigid wall; pressure rises from an increase in volume or a decrease in size.

Things that increase IOP:

• Changing eye shape by blinking (5 mm Hg) or squinting (25 mm Hg)

• Glaucoma through obstructing outflow of aqueous humor

• Ketamine by increasing blood pressure

• Succinylcholine (5–10 mm Hg) by prolonged contraction (5–10 minutes) of extraocular muscles

• Nitrous oxide if given before, during, or after placement of a gas bubble by the ophthalmologist to facilitate vitreous surgery

Things that decrease IOP:

• Volatile anesthetics by decreasing blood pressure and relaxing extraocular muscles

• Intravenous anesthetics, except for ketamine, by the same mechanism

The oculocardiac reflex consists of a trigeminal (V1) afferent and a vagal efferent.

• Triggers: Traction on extraocular muscles, pressure on eyeball, retrobulbar block, eye trauma

• Effects: Nausea, bradycardia, ventricular ectopy, ventricular fibrillation, sinus arrest

• Treatment: Stop the stimulus. Administer anticholinergic agents (atropine, glycopyrrolate). Usually the reflex self-extinguishes, but administration of local anesthetic into the rectus can performed if it does not.

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