Regional Anaesthesia Techniques for Ocular Surgeries

Introduction

Classification of Regional Anaesthesia Techniques

A. Orbital (Intraconal/Extraconal) Blocks

1. Retrobulbar (Intraconal) Block

Needle positions for retrobulbar (intraconal) and peribulbar (extraconal) blocks - Miller's Anesthesia, 10e

• Globe placed in primary gaze (not the old "up and in" position, which increases risk of optic nerve trauma)
• A 23-27 gauge, 3 cm needle is inserted at the inferolateral orbital rim (junction of lateral one-third and medial two-thirds of the lower lid), with bevel facing the globe
• Needle advanced parallel to the orbital floor with a 10-degree upward tilt for ~15 mm past the equator of the globe
• Then redirected medially and slightly superiorly toward the apex, aiming at the optic foramen
• 2-5 mL of local anaesthetic is injected

• Rapid onset
• Excellent akinesia and analgesia
• Less volume required
• Less chemosis than peribulbar

• Retrobulbar haemorrhage (~1%) - arterial bleed causes rapid proptosis, may require lateral canthotomy
• Globe perforation - especially in axial myopia (long globe)
• Optic nerve injury / optic nerve sheath injection leading to brainstem anaesthesia (rare but catastrophic - seizures, respiratory arrest, loss of consciousness)
• Central retinal artery occlusion
• Oculocardiac reflex

2. Peribulbar (Extraconal) Block

• Two-injection technique most common:
  • Inferolateral injection: at the inferolateral orbital rim (same entry as retrobulbar but needle not redirected medially - kept parallel to orbital floor, 25 mm depth)
  • Superomedial injection: just medial to the superior orbital notch, 15-25 mm depth
• 5-10 mL per injection (larger volume needed due to extraconal placement)
• Gentle digital pressure or Honan balloon applied for 5-20 minutes to disperse the anaesthetic and reduce IOP

• Safer than retrobulbar (needle stays outside cone, away from optic nerve and vessels)
• Preferred in United States since the 1990s
• Lower risk of brainstem anaesthesia and optic nerve damage

• Slower onset (15-20 minutes)
• Larger volume needed - risk of orbital pressure rise and chemosis
• May require supplementation
• Incomplete akinesia of superior oblique (trochlear nerve outside cone)

3. Sub-Tenon's Block (Episcleral Block)

• Topical anaesthetic drops first
• A small snip is made in the inferonasal quadrant conjunctiva and Tenon's capsule (the avascular quadrant)
• A blunt curved sub-Tenon's cannula is passed posteriorly around the globe within the sub-Tenon's space
• 3-5 mL of local anaesthetic injected

• Avoids sharp needles entirely - safer
• No risk of globe perforation or optic nerve injury
• Favoured in United Kingdom and New Zealand
• Suitable for high-risk eyes (myopia, previous retinal surgery)
• Reliable anaesthesia and akinesia

• Subconjunctival haemorrhage and chemosis are common
• Requires a small incision in the conjunctiva
• Incomplete lid (orbicularis) block

B. Facial Nerve Block (for Orbicularis Oculi Akinesia)

• Injection at the lateral canthus, with needle directed superiorly and inferiorly along the orbital rim
• Blocks the terminal branches of CN VII near the orbit

• Injection over the condylar notch of the mandible (just anterior to the tragus of the ear), where the facial nerve exits the stylomastoid foramen
• Blocks the main trunk of CN VII before it branches

• Injection over the stylomastoid foramen
• More complete block but risk of dysphagia, hoarseness

C. Topical and Intracameral Anaesthesia

Local Anaesthetic Agents Used

• Mixture of lidocaine 2% + bupivacaine 0.5% is popular: fast onset (lignocaine) with prolonged duration (bupivacaine)
• Hyaluronidase (7.5-300 IU/mL) is routinely added: hydrolyses hyaluronic acid, increases tissue permeability, promotes drug spread, improves quality of block and reduces risk of extraocular muscle injury
• Epinephrine may be added to prolong block but should be avoided in glaucoma patients (risk of compromising retinal perfusion)

Complications of Regional Ocular Anaesthesia

Contraindications to Regional Ocular Blocks

• Uncooperative patient (relative)
• Bleeding diathesis (relative - especially for retrobulbar)
• Severely myopic eye (axial length >26 mm) - peribulbar or sub-Tenon's preferred
• Known allergy to local anaesthetics
• Open globe / penetrating ocular trauma (increases risk of vitreous expulsion with raised orbital pressure) - general anaesthesia preferred
• Previous retinal detachment surgery with scleral buckle

Summary Comparison

Oculocardiac Reflex (OCR) and Its Management

Definition

Reflex Arc

Stimulus (traction/pressure on globe/extraocular muscles)
        ↓
Ciliary nerves → Ciliary ganglion
        ↓
Ophthalmic division of trigeminal nerve (V1)
        ↓
Gasserian (trigeminal) ganglion → Trigeminal sensory nucleus
        ↓  [synapse]
Motor (dorsal) nucleus of the vagus nerve (in medulla)
        ↓
Vagus nerve (CN X) efferent
        ↓
Heart → Bradycardia / Arrhythmia

• Afferent limb: Trigeminal nerve (CN V1) via ciliary nerves and Gasserian ganglion
• Efferent limb: Vagus nerve (CN X)
• Central relay: Medullary cardiac inhibitory centre (nucleus of the solitary tract - dorsal vagal nucleus)

Triggers (Stimuli)

• Traction on extraocular muscles (especially medial rectus - most common trigger in strabismus surgery)
• Pressure on the globe (e.g., intraoperative manipulation, retrobulbar haemorrhage)
• Stimulation of any orbital content including periosteum
• Performance of a retrobulbar block itself
• Ocular trauma
• Direct pressure on orbital apex tissue (e.g., post-enucleation)
• Even conjunctival traction can elicit it

Clinical Manifestations

Incidence

• Reported incidence: 16-82% (wide variability depending on study population and definition)
• Higher in children (greater baseline vagal tone) - most commonly seen during paediatric strabismus surgery
• Can occur under both local and general anaesthesia

Factors that Augment the OCR

1. Hypercapnia (raised CO₂) - increases vagal tone
2. Hypoxaemia - sensitises the reflex arc
3. Shallow depth of anaesthesia - inadequate suppression of reflex
4. Opioids (fentanyl, alfentanil, remifentanil) - increase vagal tone and may contribute
5. Young age - higher baseline vagal tone in children
6. Anxiety - in awake patients
7. Rapid, forceful traction on extraocular muscles

Prevention (Prophylaxis)

1. Pharmacological Prophylaxis

• IV atropine (0.01-0.02 mg/kg) administered immediately before surgical traction - more effective than intramuscular premedication
• IV glycopyrrolate (0.01 mg/kg) - may cause less tachycardia and fewer ventricular arrhythmias than atropine
• IM anticholinergic premedication is not effective as prophylaxis (unreliable and delayed absorption)

Important caveat: Routine prophylactic anticholinergics are controversial and generally not recommended in adults because:

• Atropine itself can cause ventricular tachycardia and ventricular fibrillation
• It may cause myocardial ischaemia in patients with coronary artery disease (by increasing heart rate)
• Prophylaxis may convert a benign bradycardia into a dangerous tachyarrhythmia
• The reflex fatigues (tachyphylaxis) with repeated stimulation

2. Anaesthetic Technique

• Regional anaesthesia (retrobulbar block) can block the afferent (trigeminal) limb of the reflex - but note: the retrobulbar block itself can trigger the OCR
• Deep inhalational anaesthesia reduces the sensitivity of the reflex arc
• Ketamine induction in children has been reported to have the lowest incidence of OCR compared to propofol
• Avoiding hypercapnia and hypoxaemia (ensure adequate ventilation)
• Surgeon should apply gentle, gradual traction rather than sudden forceful pulls

Management of the OCR (When It Occurs)

Step 1: Remove the Stimulus

• Immediately notify the surgeon
• Cease surgical stimulation (release traction/pressure on globe/muscles)
• Heart rate typically returns to baseline within 20 seconds

Step 2: Assess and Correct Aggravating Factors

• Check ventilation and oxygenation - correct hypoxia and hypercapnia
• Check depth of anaesthesia - deepen if required
• These two steps alone resolve most episodes due to tachyphylaxis of the reflex arc

Step 3: Pharmacological Treatment (if bradycardia persists)

• IV atropine: 10-20 mcg/kg (or 0.6 mg in adults)
• IV glycopyrrolate: 0.1-0.2 mg in adults (10 mcg/kg in children)
• These are preferred over prophylactic use - treat only when needed

Step 4: Severe/Refractory Cases

• Infiltration of the rectus muscles with local anaesthetic (blocks the afferent limb at the source)
• IV epinephrine (adrenaline) - for severe bradycardia or asystole
• Full ACLS/CPR if cardiac arrest occurs
• Surgery should not resume until rhythm is stable and the cause is fully addressed

Tachyphylaxis

Summary Table

Oculocardiac Reflex (OCR) - Summary

• Afferent: CN V1 (ophthalmic division) via ciliary nerves → Gasserian ganglion → trigeminal sensory nucleus
• Central relay: Dorsal vagal nucleus (medulla)
• Efferent: CN X (vagus) → heart → bradycardia/arrhythmia

Management (Stepwise)

1. Release the stimulus - ask surgeon to stop; HR usually recovers in ~20 seconds
2. Correct aggravating factors - ensure adequate ventilation, oxygenation, and anaesthetic depth
3. If bradycardia persists - IV atropine 10-20 mcg/kg or IV glycopyrrolate 0.1-0.2 mg
4. Refractory cases - infiltrate rectus muscles with local anaesthetic; IV epinephrine for asystole