Correspondence  |   October 2004
Is It in the Episcleral Space or in the Medial Canthal Extraconal Space?
Author Affiliations & Notes
  • Emmanuel Nouvellon, M.D.
  • * Hôpital Caremeau, Nîmes, France.
Article Information
Correspondence   |   October 2004
Is It in the Episcleral Space or in the Medial Canthal Extraconal Space?
Anesthesiology 10 2004, Vol.101, 1045-1046. doi:
Anesthesiology 10 2004, Vol.101, 1045-1046. doi:
In Reply:—
We thank Dr. Fanning for his interest in our work and for his pertinent comments. We would like to give some responses.
We assume the block we described actually corresponds to a sub-Tenon (episcleral) injection. As we stated in our first article,1 when we began using this technique, we were convinced that it was another peribulbar approach, similar to the technique of Hustead et al.  2 However, after intensive anatomical work,3,4 we found that the space of injection was really a sub-Tenon (episcleral) injection rather than a peribulbar (extraconal) or a retrobulbar (intraconal) approach.5,6 These anatomical statements are reinforced by the better clinical efficacy of our technique as compared with the peribulbar approach,7 which confirms the well-established efficacy of the other approaches of sub-Tenon anesthesia.8,9 
Regarding the depth of needle insertion, we agree that it is hazardous to insert a needle into the posterior part of the apex. We advocate not going beyond 15–20 mm to ensure that the needle tip is actually in the sub-Tenon space. In our study, the median depth of needle injection was 15 mm, roughly measured because we used a nongraduated needle. At this depth, we assumed that the injection was in the episcleral space. In our study, the maximum depth of insertion was 35 mm, which is obviously too deep. These blocks (n = 4) were performed at the beginning of the study (all occurred in the first 50 cases).
Sub-Tenon injection frequently produces chemosis. Because the fascial sheath of the eyeball fuses anteriorly with the bulbar conjunctiva, episcleral injection results in subconjunctival infiltration. The occurrence of chemosis is quasi-mandatory in all high-volume sub-Tenon injections, regardless of the route used (needle or blunt canula).9 After injection, we applied an ocular compression using a Honan balloon, which resulted in resorption of the chemosis. In our study, we reported only incidents including persistent chemosis hindering the surgical procedure, not all chemosis observed immediately at the end of injection.
Although it is useful, it is impossible to assume that the technique described by Hustead et al.  2 is safer than ours. First, there is a lack of sufficiently powered comparative studies to demonstrate the superiority of one of these techniques in terms of safety. Because of the low incidence of complications such as globe perforation, thousands of patients should be included in such comparative studies. Second, in our technique, we insert the needle tangentially to the sclera, which should prevent perforation. In case of uncontrolled wrong direction of the needle, a point of insertion of the needle located at a greater distance from the globe may result in contact at a 90° angle between the needle and the sclera and may theoretically lead to a perforation more easily than our technique does. Therefore, the main risk factor for perforation is the lack of experience of the physician who performs the block, more than the technique itself.
In conclusion, we are aware that all the techniques requiring a needle insertion into the orbit—including ours—are associated with their own hazards for cataract surgery. If no akinesia is requested, we think that the safest technique is topical anesthesia. If a good akinesia technique is required, sub-Tenon block, regardless of the technique, might be considered because of its efficacy. An effective block may prevent additional injections are thus decrease puncture hazards. Finally, for eye blocks to be efficient and safe, we emphasize the need for anesthesiologists to properly learn and practice them.
* Hôpital Caremeau, Nîmes, France.
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