Peribulbar Block

Introduction

Peribulbar block is a regional anesthetic technique used primarily for ophthalmic surgery. It involves the deposition of local anesthetic around the globe but outside the muscle cone, leading to sensory, motor, and autonomic blockade. It is an alternative to retrobulbar block, offering a safer profile with reduced risk of complications like globe perforation and retrobulbar hemorrhage.

Anatomy Relevant to Peribulbar Block

1. Bony Orbit

The orbit is a pyramidal structure composed of four walls:

• Roof – Formed by the frontal bone.

• Floor – Formed by the maxillary bone.

• Medial wall – Formed by the ethmoid and lacrimal bones.

• Lateral wall – Formed by the zygomatic and sphenoid bones.

2. Extraocular Muscles

The orbit contains six extraocular muscles, which control eye movement:

• Four rectus muscles: Superior, Inferior, Medial, and Lateral rectus.

• Two oblique muscles: Superior and Inferior oblique.

3. Nerve Supply to the Eye

The sensory and motor innervation of the eye comes from:

• Optic nerve (CN II) – Vision.

• Oculomotor nerve (CN III) – Motor supply to most extraocular muscles.

• Trochlear nerve (CN IV) – Motor supply to the superior oblique muscle.

• Abducens nerve (CN VI) – Motor supply to the lateral rectus muscle.

• Trigeminal nerve (CN V, ophthalmic division) – Sensory supply to the cornea and conjunctiva.

4. Peribulbar vs. Retrobulbar Space

• Retrobulbar space: Located inside the muscle cone, closer to the optic nerve.

• Peribulbar space: Located outside the muscle cone, providing a safer approach.

Technique of Peribulbar Block

1. Patient Positioning

• Patient is positioned supine with the head in neutral position.

• The patient is instructed to look straight ahead.

2. Equipment Required

• Syringe: 5–10 mL syringe.

• Needle: 23G or 25G, 25 mm or 40 mm needle.

• Local Anesthetic Agents:

• Lidocaine 2% (fast onset)

• Bupivacaine 0.5% (prolonged action)

• Ropivacaine 0.75%

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

3. Injection Sites

Two main approaches:

-Inferotemporal (Primary Approach)

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

• Advanced along the orbital floor without directing towards the globe.

• Depth of insertion: 25–30 mm.

-Medial Canthus Approach (Supplementary Injection)

• Needle inserted at the medial canthus perpendicular to the skin.

• Depth: 15–20 mm.

4. Volume of Anesthetic Injected

• Typically 6–10 mL of local anesthetic is used, leading to diffuse spread around the globe.

• Larger volume compared to retrobulbar block, ensuring adequate diffusion.

5. Confirmation of Block Adequacy

• Akinesia (Motor Blockade) – Assessed by reduced eye movements.

• Analgesia (Sensory Blockade) – Assessed by corneal and conjunctival anesthesia.

• Ptosis (Eyelid Drooping) – Confirms blockade of the orbicularis oculi muscle.

Advantages of Peribulbar Block

✅ Lower risk of complications compared to retrobulbar block.

✅ Larger volume of anesthetic allows better spread.

✅ Safer in patients with high myopia or coagulopathy.

✅ Better for longer procedures due to better diffusion.

Disadvantages of Peribulbar Block

❌ Slower onset (5–10 minutes) compared to retrobulbar block.

❌ Requires larger volume of anesthetic.

❌ May cause periorbital edema due to larger injection volume.

Complications of Peribulbar Block

MCQs on Peribulbar Block

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

a) Faster onset

b) Uses lower volume of anesthetic

c) Lower risk of complications

d) Provides better motor blockade

• Answer: (c) Lower risk of complications

2. The peribulbar block is injected in which space?

a) Inside the muscle cone

b) Outside the muscle cone

c) Sub-Tenon’s space

d) Retrobulbar space

• Answer: (b) Outside the muscle cone

3. Which of the following is a complication of peribulbar block?

a) Corneal abrasion

b) Pneumothorax

c) Spinal cord injury

d) Laryngospasm

• Answer: (a) Corneal abrasion

4. The most commonly used local anesthetic for peribulbar block is:

a) Halothane

b) Lidocaine

c) Nitrous oxide

d) Sevoflurane

• Answer: (b) Lidocaine

5. Which of the following conditions is a contraindication for peribulbar block?

a) High myopia

b) Coagulopathy

c) Retrobulbar hemorrhage

d) All of the above

• Answer: (d) All of the above