The Oculocardiac Reflex (OCR) is a trigeminal-vagal reflex first reported by Aschner and Dagnini in 1908, hence also known as the Aschner-Dagnini Reflex. OCR is a complication that is not limited to ophthalmic surgeries, and it has been reported to occur during endoscopic surgeries of the sinoatrial node. Reports indicate that the incidence of OCR is age-related, being more common in children and decreasing with age. Individuals with systemic diseases such as cardiovascular diseases and diabetes have a higher incidence than the general population.
The incidence of OCR during strabismus and intraocular surgeries in children can be as high as 90%, while the incidence in adults is about 50%. During surgery, pressure or stimulation of the eyeball or orbit, or traction on the extraocular muscles can cause vagally mediated bradycardia or arrhythmias, which in severe cases can lead to cardiac arrest. After stimulation of the ocular tissues, the stimulus signal is transmitted via the ciliary nerve and the ophthalmic branch of the trigeminal nerve through the trigeminal ganglion to the sensory nucleus of the trigeminal nerve in the fourth ventricle, where the nerve fibers from the cortical area transmit the impulse to the vagus nerve nucleus, which then conveys the signal to the myocardial tissue, inhibiting heart rate and causing arrhythmias or even cardiac arrest.
The myocardial tissue possesses four physiological characteristics: excitability, automaticity, conductivity, and contractility, allowing it to contract regularly without central nervous system control. However, the heart is under dual control by the sympathetic and vagal nerves, with sympathetic fibers distributed throughout the atria and ventricles, while vagal fibers are primarily distributed in the sinoatrial and atrioventricular nodes. Sympathetic stimulation increases heart rate, while vagal stimulation slows down heartbeats and atrioventricular conduction. OCR is considered a typical vagal reflex.
OCR is most likely to occur during pediatric strabismus surgery. The short and small extraocular muscles are richly innervated and have their unique characteristics, making them highly sensitive. Clinical reports indicate that the internal rectus muscle is most severely affected by traction during strabismus correction surgery, followed by the lateral rectus muscle, and then the other extraocular muscles. For surgeries involving the internal rectus and superior rectus muscles, local nerve blocks at the entry point of the muscles into the globe can reduce the occurrence of ocular nerve reflexes.
OCR can also occur during fundus surgeries, orbital surgeries, and enucleation. Symptoms of OCR worsen during shallow anesthesia, hypoxia, or CO2 retention, as well as increased vagal tone. When OCR occurs, surgical stimulation should be paused, and intravenous administration of atropine generally alleviates or improves symptoms. During surgery, gentle handling should be practiced to avoid hypoxia and CO2 retention, which can help prevent OCR to some extent.
