Oculocardiac Reflex (OCR)

Definition

The Oculocardiac Reflex (OCR) is a trigeminovagal reflex that results in a sudden decrease in heart rate (bradycardia) due to mechanical stimulation of the eye or orbit. It is also called the Aschner reflex or Trigemino-Vagal reflex.

Anatomy & Pathophysiology

The OCR is a reflex arc involving both the afferent and efferent pathways:

1. Afferent Pathway (Sensory limb)

• Origin: Ophthalmic division (V1) of the Trigeminal nerve (CN V)

• Mechanoreceptors in the globe, orbit, extraocular muscles, and conjunctiva detect pressure or traction.

• Impulses travel via the long and short ciliary nerves → ciliary ganglion → ophthalmic nerve (V1) → trigeminal ganglion → sensory nucleus of the Trigeminal nerve in the pons.

2. Central Processing

• Trigeminal impulses synapse with neurons in the reticular formation of the brainstem.

• Signals are transmitted to the dorsal motor nucleus of the Vagus nerve (CN X) in the medulla.

3. Efferent Pathway (Motor limb)

• Vagal efferent fibers from the dorsal motor nucleus of CN X travel to the heart, synapsing in the cardiac ganglia.

• This leads to parasympathetic activation, causing:

• Bradycardia (most common manifestation)

• Hypotension

• Dysrhythmias (junctional rhythms, AV block, asystole in severe cases)

Triggers of OCR

• Traction or pressure on extraocular muscles, especially the medial rectus

• Direct pressure on the eyeball (e.g., during globe manipulation)

• Retrobulbar block

• Ocular trauma

• Strabismus surgery (common in pediatric anesthesia)

• Manipulation of orbital structures during craniofacial or neurosurgery

Prevention & Management

1. Prevention

• Minimize ocular manipulation (avoid excessive traction)

• Ensure adequate depth of anesthesia (light anesthesia increases reflex sensitivity)

• Use anticholinergics prophylactically (controversial but may be useful in high-risk cases, e.g., children undergoing strabismus surgery):

• Atropine: 10–20 mcg/kg IV

• Glycopyrrolate: 5–10 mcg/kg IV

2. Intraoperative Management

• Immediate cessation of stimulus (most effective intervention)

• Confirm adequate anesthetic depth

• Anticholinergic drugs if bradycardia persists:

• Atropine 10–20 mcg/kg IV (preferred)

• Glycopyrrolate 5–10 mcg/kg IV

• Chest compressions if asystole occurs

3. Desensitization Techniques

• Repeated stimulation can cause fatigue of the reflex, reducing OCR severity over time.