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Ophthalmic Anesthesia — OCR, Open Globe, Intraocular Gas, Retrobulbar
TEXTSpecialty II · 7 min read
The eye is a closed, pressurized organ with a brainstem-adjacent block field and a trigeminal-vagal reflex arc that can stop the heart. Five high-yield scenarios.
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3 min read6 sectionsOculocardiac reflex (OCR) — Aschner phenomenon
Triggered by traction on extraocular muscles (especially medial rectus during strabismus repair), pressure on the globe, retrobulbar hematoma, ocular trauma.
- sinus bradycardia
- junctional rhythm
- AV block
- asystole — within seconds of stimulus
Incidence 30-90% in pediatric strabismus surgery without prophylaxis.
- stop surgical stimulus (surgeon-stop is first-line — usually self-terminates in 20 s)
- ensure ventilation + depth of anesthesia
- glycopyrrolate
5-10 mcg/kg IV or atropine10-20 mcg/kg IV if persistent or hemodynamically significant
Reflex fatigues with repetition but recurs after a pause.
Prophylactic anticholinergic controversial in adults; reasonable in pediatric strabismus.
Open globe + full stomach — the sux debate
Classic dilemma: aspiration risk demands RSI but succinylcholine raises IOP transiently 6-12 mmHg for ~6 minutes (extraocular muscle tonic contraction + choroidal vasodilation), theoretically risking vitreous extrusion through the wound.
Modern consensus (Hagberg Difficult Airway 4e; Miller 9e Ch 50): modified RSI with rocuronium 1.0-1.2 mg/kg + cricoid pressure is the preferred approach when feasible — gives intubating conditions in 60-75 s without IOP rise, and sugammadex 16 mg/kg is available for rescue.
If sux must be used (anticipated difficult airway, no roc/sugammadex available), a defasciculating dose of nondepolarizer (rocuronium 0.06 mg/kg or vecuronium 0.01 mg/kg) 3 min prior blunts the IOP rise.
Adequate depth + opioid attenuate laryngoscopy-induced IOP spikes (which exceed sux effect).
Intraocular gas bubbles + nitrous oxide
Vitreoretinal surgeons inject SF6 (sulfur hexafluoride, intraocular half-life ~5 days), C3F8 (perfluoropropane, ~30-60 days), or air (~5-7 days) as a tamponade after retinal detachment repair or macular hole surgery.
N2O is 34× more soluble in blood than nitrogen, diffuses into the gas bubble faster than the bubble can leave bubble expansion, IOP spike to 30-50+ mmHg, central retinal artery occlusion, blindness within minutes.
- avoid N2O for 5 days post-SF6
- 30 days post-air (conservative)
- 60-90 days post-C3F8
Patients should wear a wristband.
If any doubt, skip N2O — there's no scenario where N2O is essential.
Retrobulbar + peribulbar blocks — anatomy + complications
3-5 mL local (lidocaine 2% + bupivacaine 0.75% + hyaluronidase).Blocks CN II, III, IV, VI within the cone — provides akinesia + analgesia.
- extraconal
- larger volume (6-10 mL)
- slower onset
- similar efficacy
- safer profile
Complications: globe perforation (1:1,000-10,000, higher in axial-length >26 mm myopia), retrobulbar hematoma (firm orbit, proptosis — lateral canthotomy if vision-threatening), brainstem anesthesia (intra-arterial or intradural injection along optic nerve sheath apnea, unconsciousness, contralateral pupil changes within 5-10 min; supportive care, resolves in 30-60 min), optic nerve injury, oculocardiac reflex during injection.
Sub-Tenon's block is the modern safer alternative — blunt cannula, no sharp needle, near-zero perforation risk.
IOP determinants + anesthetic management
10-21 mmHg.- aqueous humor production/drainage
- choroidal blood volume
- vitreous volume
- extraocular muscle tone
- central venous pressure
- propofol
- volatile agents (dose-dependent)
- opioids
- benzodiazepines
- nondepolarizing NMBs
- mannitol
- acetazolamide
- beta-blockers
- alpha-2 agonists
- ketamine (mild, controversial)
- sux (transient)
- coughing/bucking/Valsalva (10-40 mmHg spikes)
- laryngoscopy without adequate depth
- Trendelenburg
- hypoventilation/hypercarbia
For open-globe + glaucoma cases, smooth induction + deep extubation (or LMA exchange) + antiemetic prophylaxis are core — postoperative vomiting can blow open a fresh wound.
Oculoemetic reflex + PONV prophylaxis
Strabismus repair carries the highest PONV incidence in pediatric anesthesia (~50-80% without prophylaxis) — the oculoemetic reflex (trigeminal afferents → chemoreceptor trigger zone) plus opioid effects.
- ondansetron
0.1 mg/kg(max 4 mg) + dexamethasone0.15 mg/kg(max 8 mg) at induction - propofol-based maintenance (TIVA reduces PONV ~25%)
- minimize opioids (use ketorolac 0.5 mg/kg + acetaminophen 15 mg/kg + local infiltration by surgeon)
- avoid N2O
- adequate hydration
Adults undergoing ophthalmic surgery still have above-average PONV risk; same multimodal approach applies.
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