A new technique for delivering sub-Tenon's anaesthesia in ophthalmic surgery

Sub-Tenon's local anaesthesia has become an accepted technique for anterior and posterior segment eye surgery.^1–5 It is a safe, quick, and effective method of local anaesthesia. However, it requires a certain amount of skill for dissection into the sub-Tenon's space. This dissection can lead to bleeding and chemosis.

We describe a modification of the current technique of sub-Tenon's anaesthesia which aims to simplify the method of local anaesthetic delivery, avoid bleeding, and chemosis while maintaining effective anaesthesia.

Case report

Fifty consecutive patients undergoing anterior segment surgery scheduled for local anaesthesia were recruited for this study.

For this procedure, a 22 gauge Venflon standard intravenous cannula was used. The conjunctiva was anaesthetised with topical amethocaine 1%. A Barraquet speculum was inserted. The conjunctiva was grasped 5 mm from the limbus using toothed forceps. Under direct visualisation the tip of a 22 gauge Venflon was used to introduce the plastic cannula under the conjunctiva and Tenon's fascia (keeping the needle tip visible at all times) (Fig 1A). The plastic cannula was advanced over the needle, which was drawn back and removed (Fig 1B). Four millilitres of lignocaine 2% with 30 international units (IU)/ml of hyalase was then injected through the plastic cannula (Fig 1C).

Figure 1.

New technique for delivering sub-Tenon's anaesthesia injection.

All 50 patients had anterior segment surgery. Forty six were cataract operations with posterior chamber lens implant, and four were phacotrabeculectomies. None experienced excessive discomfort on delivery of the block. All local anaesthetic blocks were performed by one operator and no complication which prevented surgery occurred. No patient who was scheduled for local anaesthesia was considered unsuitable for this technique.

All patients had effective anaesthesia and akinesia for the surgical procedure. None complained of pain. Top up of anaesthesia was not required in any case. Twenty eight patients had complete or partial ptosis.

Subconjunctival haemorrhage extending more than one quadrant occurred in one patient, but this did not interfere with surgery. None had chemosis.

Comment

Sub-Tenon's local anaesthesia is a well established technique for ophthalmic surgery. Although the Venflon cannula does have a sharp needle, it is used simply as an introducer to place the blunt plastic cannula in the correct tissue plane. The needle tip is kept under direct visualisation at all times. Thus there is minimal risk of ocular perforation with this technique.

Venflon cannulas are used for intravenous delivery of drugs and fluid so are readily available, inexpensive, and disposable. Sub-Tenon's cannulas in current use are specialised cannulas and therefore more costly than intravenous cannulas.

We describe a modification of the current technique of sub-Tenon's anaesthesia which simplifies the method using an intravenous cannula. We predict that this method is easier to learn and that it maintains the efficacy of this type of anaesthesia without compromising safety.