Peribulbar block 5 mark. Answer for anesthesia resident exam

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peribulbar block eye regional anesthesia technique

A close-up clinical photograph demonstrating a single medial peribulbar block being administered to a human eye. The image shows a syringe with a fine-gauge needle inserted perpendicular to the globe. The entry point is located approximately 5-6 mm posterior to the limbus, positioned between the insertions of the medial rectus and inferior rectus muscles. The conjunctiva and Tenon's capsule are slightly elevated at the injection site, where a small snip has been made to expose the underlying white sclera. Two gloved hands are visible: one hand stabilizes the syringe while fingers from the other hand retract the eyelids and stabilize the periorbital tissue. The iris and pupil are clearly visible, and the syringe barrel shows volume markings in milliliters. This procedural image illustrates a regional anesthesia technique used for ophthalmic surgery, emphasizing proper needle placement and tissue manipulation for safe anesthetic delivery.

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Peribulbar Block - Anesthesia Resident Exam Answer (5 Marks)

Definition

Peribulbar block (also called extraconal block) is a regional anesthetic technique for the eye where local anesthetic is deposited outside the muscle cone, around (peri) the globe (bulbar). It was first described by Davis and Mandel in 1986 as a safer alternative to retrobulbar block.

Anatomy

The four rectus muscles and their interconnecting fascial septa form a muscular cone extending from the optic foramen at the orbital apex to their insertions on the globe. In peribulbar block, the needle tip is placed extraconal - between the cone and the bony orbital wall. Cadaveric studies (Ripart et al.) have shown that extraconal injections diffuse into the intraconal space, explaining the eventual block of intraorbital structures despite extraconal placement.

Fig. 65.2 from Miller's Anesthesia 10e - Peribulbar needle enters extraconal space (shallower, parallel trajectory) vs. retrobulbar needle entering the cone

Indications

Cataract surgery (most common)
Glaucoma surgery
Corneal transplantation
Vitreoretinal surgery
Any intraocular surgery where regional anesthesia is preferred over general anesthesia

Technique

Patient position: Supine, looking straight ahead (primary gaze)

Needle: 23-25 gauge, 25 mm (max depth < 25 mm), short bevel needle

Classic Two-Injection Technique:

Inferotemporal injection - At the junction of the medial and lateral thirds (some texts: middle and lateral thirds) of the lower lid, just above the inferior orbital rim. Needle directed vertically backwards, parallel to the orbital floor, no upward angulation. Advance to < 25 mm depth. Inject 5-10 mL of local anesthetic.
Superonasal injection - At the superonasal quadrant, just below the orbital rim. Inject 2-5 mL.

Single Injection Technique:

A single inferotemporal injection of 5-10 mL suffices in many cases. After aspiration to confirm extravascular placement, slowly inject the local anesthetic.

Ocular compression (Honan balloon, 30 mmHg for 10 min, or gentle digital pressure) is applied after injection to spread the local anesthetic and reduce intraocular pressure.

Onset: Slower than retrobulbar (10-15 minutes vs. 3-5 minutes); may require supplemental injection if incomplete.

Local Anesthetic Agents

Agent	Concentration	Onset	Duration
Lignocaine (Lidocaine)	2%	Fast	Short (1-2 h)
Bupivacaine	0.5-0.75%	Slower	Long (4-8 h)
Ropivacaine	0.75-1%	Moderate	Long
Mixture	Lignocaine 2% + Bupivacaine 0.5%	Fast	Long

Additives:

Hyaluronidase 15-75 IU/mL: accelerates spread, shortens onset, reduces supplemental injection rates
Epinephrine (1:200,000): prolongs duration, reduces bleeding
Volume: Total 5-10 mL (larger than retrobulbar due to extraconal placement)

Effects of a Successful Block

Analgesia - Block of nasociliary, lacrimal, and frontal branches of ophthalmic division of CN V
Akinesia - Block of CN III, CN IV, CN VI (oculomotor, trochlear, abducens) - extraocular muscle paralysis
Reduced IOP - Due to soft tissue pressure from volume injected + Honan balloon
Chemosis (conjunctival edema) - Common due to extraconal injection, usually self-limiting

Note: Orbicularis oculi (CN VII) is OUTSIDE the cone and is NOT blocked - a separate facial nerve block (van Lint, Atkinson, or O'Brien technique) may be required to prevent lid squeezing.

Advantages over Retrobulbar Block

Feature	Peribulbar	Retrobulbar
Needle depth	< 25 mm (extraconal)	35 mm (intraconal)
Trajectory	Parallel to orbit floor	Toward orbital apex
Risk of retrobulbar hemorrhage	Lower	~1%
Risk of optic nerve injury	Lower	Higher
Risk of globe perforation	Lower	Higher (esp. myopic eyes)
Onset	Slower (10-15 min)	Faster (3-5 min)
Chemosis	More common	Less common
Volume needed	More (5-10 mL)	Less (2-5 mL)

Complications

Local:

Chemosis (most common, benign)
Subconjunctival hemorrhage
Ecchymosis/hematoma
Globe perforation (risk increased with axial length > 25 mm - high myopia)

Systemic (less common than retrobulbar):

Brainstem anesthesia - spread via optic nerve sheath into CSF causing confusion, dysphagia, apnea, cardiac arrest (postretrobulbar apnea syndrome analog)
Intravascular injection - seizures (ophthalmic artery retrograde flow to brain)
Oculocardiac reflex - bradycardia, asystole (treat with atropine, stop surgery stimulus)
Extraocular muscle damage

Contraindications

Patient refusal
Coagulopathy / anticoagulation (relative)
Axial length > 26 mm (severe myopia) - higher risk of globe perforation
Open globe injury
Local infection / cellulitis
Inability to cooperate or lie flat
Allergy to local anesthetics

Key Exam Points to Remember

First described 1986 (vs. retrobulbar which was standard before)
Needle placed OUTSIDE the cone (extraconal) - this is the defining feature
Needle depth < 25 mm and directed parallel to orbital floor (NO upward angulation toward apex)
Larger volume (5-10 mL) needed vs. retrobulbar (2-5 mL)
Hyaluronidase improves block quality
Facial nerve NOT blocked - separate van Lint/Atkinson/O'Brien block needed for lid akinesia
Main advantage: safer - reduces risk of retrobulbar hemorrhage and optic nerve injury
Main disadvantage: slower onset, more volume, higher incidence of chemosis, may need supplemental injection

Sources: Miller's Anesthesia 10e, Ch. 65; Barash Clinical Anesthesia 9e, Ch. 49; Morgan & Mikhail's Clinical Anesthesiology 7e, Ch. 36

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