Retrobulbar Block

Introduction

It involves injecting local anesthetic inside the muscle cone of the orbit to block the nerves supplying the eye. Compared to peribulbar block, it provides faster onset and more profound akinesia, but with a higher risk of complications such as globe perforation and retrobulbar hemorrhage.

 

Nerve Supply to the Eye

• Optic nerve (CN II): Vision

• Oculomotor nerve (CN III): Motor control of most extraocular muscles

• Trochlear nerve (CN IV): Superior oblique muscle

• Abducens nerve (CN VI): Lateral rectus muscle

• Trigeminal nerve (CN V – Ophthalmic division): Sensory supply to the cornea and conjunctiva

Retrobulbar block aims to block CN III, CN IV, CN VI, and the ophthalmic division of CN V to achieve anesthesia and akinesia.


Technique of Retrobulbar Block

1. Patient Positioning

• The patient is positioned supine, with the head in a neutral position.

• The patient is instructed to look straight ahead to minimize globe movement.


2. Equipment Required

• Syringe: 5 mL syringe

• Needle: 23G or 25G, 38–40 mm (sharp, short-beveled needle)

• Local Anesthetic Agents:Lidocaine 2% (fast onset),Bupivacaine 0.5% (longer duration),Ropivacaine 0.75%

• Addition of Hyaluronidase (5–15 IU/mL) to enhance diffusion


3. Injection Site & Needle Insertion

• The injection is given at the inferotemporal quadrant of the orbit.

• Needle is inserted at the junction of the lateral one-third and medial two-thirds of the lower orbital rim.

• Direction of the needle: Initially perpendicular to the skin.

• Then directed posteriorly and slightly medially and superiorly to enter the muscle cone.

• Depth of insertion: 25–35 mm, avoiding excessive penetration to prevent optic nerve injury.


4. Volume of Anesthetic Injected

• 3–5 mL of local anesthetic is sufficient to achieve effective blockade.

• Smaller volume than peribulbar block due to more localized injection inside the muscle cone.


5. Confirmation of Block Success

• Akinesia (Motor Blockade): Reduced extraocular muscle movement.

• Analgesia (Sensory Blockade): Loss of pain sensation in the conjunctiva and cornea.

• Ptosis (Eyelid Drooping): Due to orbicularis oculi paralysis.

Comparison: Retrobulbar vs. Peribulbar Block

Feature

Retrobulbar Block

Peribulbar Block

Injection site

Inside the muscle cone

Outside the muscle cone

Needle depth

25–35 mm

15–25 mm

Volume of LA

3–5 mL

6–10 mL

Onset time

Fast (2–5 minutes)

Slower (5–10 minutes)

Risk of globe perforation

High

Low

Akinesia (Eye movement block)

Complete

May require supplementation

Safety

Higher risk of complications

Safer


Complications of Retrobulbar Block

Complication

Cause

Management

Globe perforation

Needle penetration into the globe, more common in high myopes

Stop injection, urgent ophthalmology evaluation

Retrobulbar hemorrhage

Injury to blood vessels in the muscle cone

Immediate orbital compression, surgery if severe

Optic nerve damage

Deep insertion, direct trauma

Visual loss may be permanent

Intravascular injection

Injection into ophthalmic artery

Immediate seizure, cardiovascular instability

Brainstem anesthesia

Spread of anesthetic via optic nerve sheath to brainstem

Respiratory depression, cardiac arrest (requires ventilation)

Oculocardiac reflex (OCR)

Stimulation of ciliary ganglion or optic nerve

Treat with atropine 0.6 mg IV


MCQs on Retrobulbar Block

1. What is the main advantage of retrobulbar block over peribulbar block?

a) Uses more local anesthetic

b) Lower risk of complications

c) Faster onset and better akinesia

d) Requires two injection sites

• Answer: (c) Faster onset and better akinesia


2. What is the correct needle insertion depth in retrobulbar block?

a) 5 mm

b) 15 mm

c) 25–35 mm

d) 50 mm

• Answer: (c) 25–35 mm


3. Which nerve is NOT blocked in retrobulbar anesthesia?

a) Optic nerve (CN II)

b) Oculomotor nerve (CN III)

c) Abducens nerve (CN VI)

d) Trigeminal nerve (CN V)

• Answer: (a) Optic nerve (CN II)


4. What is the most feared complication of retrobulbar block?

a) Oculocardiac reflex

b) Retrobulbar hemorrhage

c) Brainstem anesthesia

d) Diplopia

• Answer: (c) Brainstem anesthesia


5. In which condition is retrobulbar block contraindicated?

a) Coagulopathy

b) Previous cataract surgery

c) Hyperthyroidism

d) All of the above

• Answer: (a) Coagulopathy