Ophthalmic Regional Anesthesia

Indications

There are no specific indications for regional anesthesia during ophthalmic procedures.  This procedure exists simply as an alternative to general or local anesthesia (LA).  The choice of anesthesia should be individualized based on the patient, the procedure, and the needs of the surgeon.

Contraindications

Age less than 15 years old

Procedure lasting more than 90 minutes

Uncontrolled cough, tremor or convulsive disorder

Disorientation or mental impairment

Excessive anxiety or claustrophobia

Bleeding or coagulation disorder

Perforated globe

Goals

Analgesia

Akinesia

Control of intraocular pressure

Avoidance or obtundation of the oculocardiac reflex

Medications

The most commonly used LA agents are a 1:1 mixture of 2% Lidocaine with 0.5% or 0.75% Bupivicaine.

The addition of Epinephrine or Hyaluronidase is provider dependent.

Anatomy

Extraocular Muscles of the Eye—Six sets of muscles that control movements of the eyeball.  They are the superior and inferior rectus, which move the eye up and down; the medial and lateral rectus, which move the eye to either side; and the superior and inferior oblique, which move the eye upward and outward and downward and outward.

Other Skeletal Muscles of the Eye—Orbicularis oculi muscle which is attached to the deep surface of the skin and is responsible for eyelid closure, including automatic and reflex blinking action.

Goal

For the LA to be delivered to the ciliary ganglion and the nerves of the eye to provide adequate blockade.

For additional eye anatomy, please refer to:  http://www.pitt.edu/~anat/

Types of Regional Techniques for Eye Surgery

Peribulbar (Pericone Block):  LA is deposited around the eye, but not within the rectus muscle cone.

Retrobulbar (Intracone Block):  LA is deposited behind the eye within the rectus muscle cone itself.

Peribulbar Block

A peribulbar block involves injections above and below the orbit, with LA deposited in, behind, beneath, and above the orbicularis oculi muscle, and behind the globe.  Of note, the LA does not enter the confines of the cone of the rectus muscle.  Therefore, the potential for intraocular injection is decreased because the anesthetic is deposited outside the muscle cone.  The risk for intraconal hemorrhage and direct optic nerve injury is also decreased.

Technique—Neutral Gaze Position

The patient is asked to look at a point in the distance with the pupil in a central position.

Enter the skin at point B with a 25-27 gauge 2.5cm needle.

The needle is kept perfectly vertical and penetrates approximately 1.5cm deep through the skin.

The position of the skin penetration at point B is well inferior to the orbital brim.

The needle is then walked over the orbital brim.

The needle is pushed over the brim by the left thumb of the operator. 

Inject 1 mL of LA here to block the orbicularis oculi muscle, but…

ALWAYS ASPIRATE BEFORE INJECTING!

Next, advance the needle into the inferolateral peribulbar space anterior to the equator of the globe and inject 2 ml of LA.  Finally, advance the needle past the equator but still outside of the cone and inject 4 ml of LA. 

Next, withdraw the needle while simultaneously injecting a small amount of local anesthetic subcutaneously.

After the needle is withdrawn and the skin is anesthetized, pressure is applied to the skin against the maxillary bone. 

The index finger maintains pressure on the area where the first injection was given, while the second peribulbar injection is being administered.

The medial peribulbar space is entered through the caruncle just lateral to the medial canthus. 

The needle is advanced as it remains vertical and parallel to the laminal paparisa.  Stay close to the bone, and inject 2 mL of LA here.

Finally, a third injection can be given superior and lateral to point C above the globe.

Remove the needle and apply light pressure to the orbit and its contents.

Retrobulbar Block

The retrobulbar block is aimed at blocking the ciliary ganglion, ciliary nerves, and cranial nerves II, III, and VI.  This is accomplished by delivering the LA into the muscle cone itself.  However, cranial nerve IV is not affected, as it is located outside of the muscle cone.

Technique

Ask the patient to look straight ahead.  By looking upward or inward the needle path may approach the optic nerve, ophthalmic artery, and vein.

Using a 25-27 gauge 20-35 mm needle, enter the skin at the same point as the first peribulbar injection (Point B).

Advance slowly. 

The needle is “walked” over the brim of the orbit and is advanced directly posteriorly.  When the tip of the needle reaches the equator of the eye, it is directed upward and medially so that the tip of the needle lies directly posterior to the pupil.

The needle should only penetrate retrobulbar fat and intermuscular septum.  If resistance is felt, the needle may be in muscle, optic nerve, or the wall of the eye and it should be withdrawn and redirected.

First, administer a very small test dose of LA.  If the needle is in the eye, the patient will experience severe pain.

Next, inject 4 ml of LA.  During the injection, the upper eyelid will start to sag and the eye will bulge forward.  It is important to note bulging of the upper eyelid and not the lower eyelid.  Lower eyelid bulging signals injection into the inferior peribulbar space. 

Withdraw the needle and apply pressure against the maxillary bone. 

Assessment of Block Efficacy

Signs of a successful block include:

No eye movement or minimal eye movement in any direction

Analgesia

Temporary vision impairment

Ptosis

Complications

Oculocardiac Reflex (involving cranial nerves V and X)—Manifested by bradycardia, junctional rhythm, or even asystole.  May occur secondary to traction on the eye and ocular muscles.

Hypoxia, hypercarbia, and light anesthesia  potentiates this reflex and should be avoided.

Atropine or glycopyrrolate can be used to treat this reflex.

Inadvertent Brain Stem Anesthesia—Injection into the CSF can occur during the block due to perforation of the meningeal sheaths that surround the optic nerve.

The patient may experience disorientation, amaurosis fugax (transient episodic blindness), aphasia, hemiplegia, unconsciousness, convulsions, and respiratory or cardiac arrest.

Central retinal artery occlusion

Puncture of the posterior globe

Penetration of the optic nerve

Allergic reactions

Hemorrhage

References

Questions