Correspondence  |   October 2004
Is It in the Episcleral Space or in the Medial Canthal Extraconal Space?
Author Notes
  • Hauser-Ross Eye Institute, Sycamore, Illinois.
Article Information
Correspondence   |   October 2004
Is It in the Episcleral Space or in the Medial Canthal Extraconal Space?
Anesthesiology 10 2004, Vol.101, 1045. doi:
Anesthesiology 10 2004, Vol.101, 1045. doi:
To the Editor:—
I was interested to see the article by Nouvellon et al.  1 describing their results using the episcleral block technique that was described by Dr. Jacques Ripart. This is an excellent article, but I have a few comments.
In my opinion, the block was not in the episcleral space in the majority of these patients. The authors report that the median depth of needle insertion was 15 mm, with the needle having been inserted posterior to the caruncle. The average eye is approximately 23.5 mm in axial length, which tells us that the tip of the needle was well beyond the equator of the eye (in the frontal plane) in more than half of the patients. With the needle inserted this deeply, I believe that it is anatomically impossible for the needle tip to have remained in the episcleral space. The injections were made into the medial canthal fat-filled space, not into the episcleral space. When the needle depth was only 5–10 mm, it is quite probable that the tip was in the episcleral space. The median volume of anesthetic injected provides further proof of my thesis. When 10 ml anesthetic is injected into the episcleral space, significant and noticeable chemosis occurs 100% of the time, but the authors describe chemosis in only 6 of 2,031 patients.
I am especially worried about the range of needle depth insertion. The deepest reported insertion depth was 35 mm. In my opinion,2 a needle longer than 25 mm should never be inserted into this part of the orbit. Even the 25-mm needle should not be inserted to its complete depth, the shoulder of the needle not being allowed to go beyond the plane of the iris. The reason for this is that the optic canal lies directly at the rear of the medial wall of the orbit. A needle placed aggressively along this wall can reach the optic canal in many patients, resulting in damage to the optic nerve, ophthalmic artery, or both.
Finally, because the majority of injections were made into the medial canthal fat-filled space (in my opinion), why not use a safer route to that space? Hustead et al.  3 described a much safer technique, in which the needle is inserted into the little tunnel that lies between the caruncle and the medial canthus and is advanced parallel and very close to the medial wall. With this technique, there is much less chance of endangering the globe or the medial rectus muscle, and the technique is easy to learn and easy to teach.
Hauser-Ross Eye Institute, Sycamore, Illinois.
Nouvellon E, L’Hermite J, Chaumeron A, Mahamat A, Mainemer M, Charavel P, Mahiou P, Dupeyron G, Bassoul B, Dareau S, Eledjam J-J, Ripart J: Ophthalmic regional anesthesia: Medial canthus episcleral (sub-Tenon) single injection block. Anesthesiology 2004; 100:370–4Nouvellon, E L’Hermite, J Chaumeron, A Mahamat, A Mainemer, M Charavel, P Mahiou, P Dupeyron, G Bassoul, B Dareau, S Eledjam, J-J Ripart, J
Kumar CM, Fanning GL: Orbital regional anaesthesia, Ophthalmic Anaesthesia. Edited by Dodds C, Kumar C, Fanning G. Lisse, Swets & Zeitlinger, 2002, pp 77–8Kumar, CM Fanning, GL Orbital regional anaesthesia,Dodds C, Kumar C, Fanning G Lisse Swets & Zeitlinger
Hustead RF, Hamilton RC, Loken RG: Periocular local anesthesia: Medial orbital as an alternative to superior nasal injection. J Cataract Refract Surg 1994; 20:197–201Hustead, RF Hamilton, RC Loken, RG