By Maggie Jeffries, MD

Peribulbar blocks have similar success rates to retrobulbar blocks. Due to the absence of an intermuscular membrane to separate extra- from intraconal compartments, peribulbar injections result in a similar space for spread of local anesthetics. During a peribulbar block, local anesthetic spreads into the adipose tissue of the orbit, including the intraconal space where the nerves (motor & sensory) to be blocked are located.  Unique to peribulbar and NOT retrobulbar injections, local anesthetic spreads to the lids to block the orbicularis muscle and often obviates need for supplemental lid block.  Lid squeezing is an undesirable motor action that is not blocked by a retrobulbar injection.¹

Because peribulbar blocks are extraconal injections, there is less risk of complications such as optic nerve injury, brainstem anesthesia, and retrobulbar hemorrhage. Caution must still be taken as myopic staphyloma, which occur in highly myopic eyes (“long”, >26mm), could lead to globe perforation. As with all blocks, local anesthetic spread can be uncertain or incomplete necessitating another block to be performed.¹

Peribulbar blocks are typically performed using a 25 gauge 1” sharp or Atkinson needle. The needle is inserted at the inferotemporal corner of the eye at the junction of the lateral 1/3 and medial 2/3 of the lower orbital rim. The needle is passed posteriorly, parallel to the floor of the orbit until it is estimated to lie beyond the equator of the globe. A volume of 5–10 ml of local anesthetic is injected after negative aspiration.²

#2 Medial caruncle

#4 Insertion of needle for a peribulbar block.³

A medial canthal block is a great supplement to an infero-temporal peribulbar block when complete akinesia is desired (e.g. corneal transplant, retina).  This blocks the medial rectus muscle which is a muscle often missed with a standard peribulbar block.  A superior nasal block will also block the medial rectus and superior oblique but is a riskier block due to location in relation to orbit (risk for perforation) and vascular supply.  The medial canthus is an avascular location and lacks vital anatomic structures.

A medial canthal block is performed using a 27-gauge ½” needle.  The needle is inserted medially to the caruncle at the medial end of the lid aperture, aiming towards the nose at about a 30-degree angle. Approximately 2ml of local anesthetic is injected and you can often feel it spreading around globe with the fingers holding the lids open.  Some bleeding at the medial canthus can be expected but it is usually minimal and self-limited.  Caution should be taken as this block can induce sneezing so be prepared if patient has sharp inhale.  When using the shorter needle, ones doesn’t need to worry about needle depth.^1,4

Facial nerve blocks are more commonly needed with retrobulbar blocks as there isn’t spread through the orbital fat to the orbicularis muscle but can be used with any block.  This block is particularly useful in the setting of scleral buckle retina procedure where lid manipulation often triggers patient discomfort.  A facial nerve block is also great for patients who squint against the lid speculum.  The Van Lindt facial nerve block is the most common performed in ophthalmology and involves injecting local anesthetic at the crossing between a vertical line 1 cm lateral of the outer orbital rim and a horizontal line 1 cm below the inferior orbital rim.⁶ An additional benefit of the use of a facial nerve block is that the facial nerve innervates the conjunctiva and thus blocking this nerve provides additional conjunctival anesthesia.⁷

Summary:

Peribulbar and medial canthal blocks, when used separately or together, can be just as effective retrobulbar blocks. They can provide complete akinesia and analgesia when performed properly and, with the addition of a facial nerve block, can provide additional akinesia and analgesia of the eyelid. The facial nerve block will also provide some sensory block of the conjunctiva.

References

1. Ripart J, Mehrige K, Della Rocca, R. Local & Regional Anesthesia for Eye Surgery. NYSORA https://www.nysora.com/local-regional-anesthesia-for-eye-surgery
2. Lopatka CW, Magnante DO, Sharvelle DJ, Kowalski PV. Ophthalmic blocks at the medial canthus. Anesthesiology 2001;95:1533.
3. Ripart J, Lefrant JY, Vivien B,  Charavel P, Fabbro-Peray P. Ophthalmic Regional Anesthesia: Medial Canthus Episcleral (Sub-Tenon) Anesthesia Is More Efficient than Peribulbar Anesthesia: A Double-blind Randomized Study. Anesthesiology 2000; 92: 1278-1285.
4. Hustead RF, Hamilton RC, Loken RG. Periocular local anesthesia: medial orbital as an alternative to superior nasal injection. J Cataract Refract Surg 1994 Mar; 20(2):197-201.
5. Anker R, Kaur N. Regional anaesthesia for ophthalmic surgery. BJA Education 2017 July; 17(7): 221–227.
6. Schimek F, Fahle M. Techniques of facial nerve block. British Journal of Ophthalmology 1995;79:166-173.
7. Ruskell GL. Innervation of the conjunctiva. Trans Ophthalmol Soc UK 1985; 104(pt 4): 390-5.