July 17, 2001

Peribulbar versus retrobulbar anesthesia for ophthalmic surgery: An anatomical comparison of extraconal and intraconal injections

Ripart J, Lefrant JY, de La Coussaye JE, Prat-Pradal D, Vivien B, Eledjam JJ. Anesthesiology 94:56-62, 2001

Commentary by Kathryn McGoldrick, M.D.

Retrobulbar anesthesia (RBA), a regional ophthalmic anesthetic technique, has been used for decades and consists of injecting a small volume (3-4 ml) of local anesthetic into the muscle cone of the eye. Owing to the occurrence of a wide range of complications associated with RBA, anesthesiologists and ophthalmologists began to turn to peribulbar anesthesia (PBA), which consists of introducing a needle into the extraconal space, as a theoretically safer form of regional ocular anesthesia. PBA was formally described in 1986 [1-4] and is based on the "tissue compartment principle." The latter refers to the phenomenon wherein a needle is inserted into a compartment and the local anesthetic injected spreads by virtue of its pressure and volume throughout the compartment. With PBA a relatively large volume (8-12 ml) of local anesthetic is injected into the extraconal space; to provide adequate analgesia and akinesis of the globe, the extraconal local anesthetic must spread to the intraconal space.

The investigators clearly demonstrated in this well-designed study that there was no evidence of the existence of an intermuscular septum separating the intraconal and extraconal spaces. Rather, they confirmed that intraconal and extraconal spaces largely communicate and they appear to be part of a common spreading space, the corpus adiposum of the orbit.

I am extremely uncomfortable, however, with the authors’ recommendation that RBA be replaced with PBA because both types of anesthesia can cause problems that are potentially vision-threatening or life threatening. Serious complications associated with retrobulbar block include, for example, retrobulbar hemorrhage; direct intravascular injection that can produce virtually instantaneous seizures if injected intra-arterially; stimulation of the oculocardiac reflex; eyeball perforation and intraocular injection; central retinal artery occlusion; and penetration of the optic nerve. An initially insidious but potentially fatal complication may also develop when accidental access to cerebrospinal fluid occurs during performance of RBA owing to perforation of the meningeal sheath that surrounds the optic nerve. This can result in the gradual onset of unconsciousness, apnea, and cardiovascular collapse. Granted, when PBA is properly performed, the muscle cone is not entered and, therefore, injury to the optic nerve should theoretically be prevented and the likelihood of central spread of local anesthetic should be greatly minimized. Ocular perforation, however, has been reported after PBA, as have peribulbar hemorrhage and ecchymoses. Additionally, some surgeons object to increased forward pressure on the eyeball consequent to the larger volume of local anesthetic deposited in the orbit compared with retrobulbar block. The risk for inadvertent injury to a rectus muscle remains significant for both RBA and PBA.

Although PBA should theoretically lead to a lower risk of complications than RBA, there are no comparative studies to confirm that complications occur less frequently with PBA than RBA. It is essential to appreciate that both are essentially "blind" (excuse the pun!) techniques wherein, absent ultrasound or other guidance, the operator cannot see the tip of the needle and, hence, of necessity is unable to be absolutely certain of its location. Given these limitations of PBA and RBA it is not surprising that, for appropriate types of surgery and appropriate patients, ophthalmologists are relying on less invasive and less risky types of anesthesia techniques such as topical analgesia or a parabulbar method of sub-Tenon’s infusion of anesthetic via a flexible, curved cannula.

References

1. Davis DB, Mandel MR. Posterior peribulbar anesthesia: An alternative to retrobulbar anesthesia. J Cataract Refract Surg 1986;12:182-4.
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2. Davis DB, Mandel MR. Efficacy and complication rate of 16,224 consecutive peribulbar blocks: A prospective multicenter study. J Cataract Refract Surg 1994;20:327-37.
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3. Bloomberg LB. Administration of periocular anesthesia. J Cataract Refract Surg 1986;12:677-9.
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4. Bloomberg LB. Anterior periocular anaesthesia: Five years experience. J Cataract Refract Surg 1991;17:508-11.
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Peribulbar versus retrobulbar anesthesia for ophthalmic surgery: An anatomical comparison of extraconal and intraconal injections

Ripart J, Lefrant JY, de La Coussaye JE, Prat-Pradal D, Vivien B, Eledjam JJ. Anesthesiology 94:56-62, 2001

BACKGROUND: Peribulbar and retrobulbar anesthesia have long been opposed on the basis of the existence of an intermuscular membrane, which is supposed to separate the intraconal from the extraconal spaces in a water-tight fashion. A local anesthetic injected outside the cone should spread through this septum to reach the nerves to be blocked. The existence of this septum is questioned. The aim of this study was to compare the spread of a colored latex dye injected intraconally or extraconally to simulate both retrobulbar and peribulbar anesthesia.

METHODS: The authors used 10 heads from human cadavers. For each head, one eye was injected intraconally, and the other eye was injected extraconally. The heads were then frozen and sectioned into thin slices following various planes. They were then photographed and observed.

RESULTS: There was no evidence of the existence of an intermuscular septum separating the intraconal and extraconal spaces. Those two spaces appeared to be part of a common spreading space, the corpus adiposum of the orbit.

CONCLUSIONS: These results are in accord with the fact that clinical studies were not able to clearly demonstrate that retrobulbar anesthesia is more efficient than peribulbar anesthesia. On the basis of a similar clinical efficacy of the two techniques as a result of similar spreading of the local anesthetic injected, and a potentially higher risk of introducing the needle into the muscular cone, the authors recommend replacing retrobulbar anesthesia with peribulbar anesthesia.