Deep topical fornix nerve block versus peribulbar block in one-step adjustable-suture horizontal strabismus surgery

E. S. Aziz*,1 and M. Rageh2

1Department of Anaesthesia, Faculty of Medicine, Cairo University, 35A Abou El Feda Street, Zamalek, Cairo, Egypt. 2Department of Ophthalmology, Research Institute of Ophthalmology, Cairo, Egypt*Corresponding author

Accepted for publication: 29 August, 2001


    Abstract
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
Background. We compared the efficacy of deep topical fornix nerve block anaesthesia (DTFNBA), which does not paralyse the extraocular muscles, with peribulbar block in patients undergoing one-step adjustable-suture horizontal strabismus surgery. Patients with a vertical, oblique squint were excluded from the study.

Methods. We studied 100 patients, allocated randomly to two groups. Group 1 (n=50) received peribulbar block with 5 ml of 1:1 mixture of 0.5% plain bupivacaine and 2% lignocaine supplemented with hyaluronidase 300 i.u. ml–1. Group 2 (n=50) received DTFNBA with placement of a sponge soaked in 0.5% bupivacaine deep into the conjunctival fornices for 15 min. No sedation was given to either group. Analgesia was assessed by direct questioning of patients during the procedure. A three-point scoring system was used (no pain =0, discomfort =1, pain =2). If the pain score was 1, the patient was asked to look in the opposite direction to decrease the tension on the periosteal attachment of the muscle to relieve discomfort. If the pain score was 2 at any stage of the operation, general anaesthesia was given.

Results. In Group 2, significantly more patients (15) experienced discomfort than in Group 1 (no patients) (P<0.05), but general anaesthesia was not needed.

Conclusions. DTFNBA is a useful technique for intraoperative adjustable-suture strabismus surgery. It does not alter muscle tone, thus allowing the surgeon to adjust the muscle sutures intraoperatively, and reducing the incidence of under- or over-correction of the squint in the immediate postoperative period.

Br J Anaesth 2002; 88: 129–32

Keywords: anaesthetic techniques, regional, topical; surgery, ophthalmic; enzymes, hyaluronidase


    Introduction
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
In this study, we compared deep topical fornix nerve block anaesthesia (DTFNBA) as described by Rosenthal,1 with peribulbar nerve block in patients undergoing one-step adjustable-suture strabismus surgery. Using adjustable sutures during strabismus surgery allows the ophthalmic surgeon to prevent over- or under-correction of the squint in the postoperative period.2 Adjustable sutures can be attached to one or more ocular muscles. If the alignment is not satisfactory at the end of surgery, one or more of the muscles can be moved to a new position to produce the optimal alignment. This suture adjustment is usually performed within 24 h of the initial surgery.

The popularity of the adjustable-suture technique was the stimulus for introducing the use of topical anaesthesia in strabismus surgery.3 Unlike general anaesthesia and regional block techniques in eye surgery, DTFNBA avoids prolonged recovery of the eye muscles from motor block and allows suture adjustment at the time of surgery (rather than within the next 24 h), in what we call one-step adjustable-suture strabismus surgery. When adjustable sutures are used intraoperatively in co- operative fully alert patients who have received DTFNBA, the patient can move their eyes freely. Thus, the alignment of the eyes can be fully assessed at the time of surgery instead of postoperatively, as in the standard technique.


    Methods and results
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
One hundred patients scheduled for elective adjustable horizontal strabismus surgery were enrolled in the study after we had obtained approval from the institutional ethics committee and patient consent. We estimated our sample size on the basis of the method described by Lerman.4 A sample size of 45 can detect a 20% difference between each group; this will give an alpha value of 0.05 with a power of 80%. With a fall-out rate of approximately 10%, we decided to increase the number of patients in each group to 50. All patients had been assessed as suitable for a regional block technique and were not premedicated. Patients were allocated randomly to one of two groups (closed-envelope method): Group 1 (n=50) received peribulbar block. Group 2 (n=50) received DTFNBA. The axial length (the distance from the cornea to the retina) is usually measured using the axial length scanner. If the axial length is 26 mm or longer, the globe is elongated. Patients with an elongated globe were omitted from the study because of an increased risk of globe perforation if peribulbar block is used.5 Patients with a vertical, oblique squint (which is less common) were also excluded because access to the muscles surgically is more difficult. Children and uncooperative patients were excluded from the study.

Before the block, a peripheral vein was cannulated, and heart rate and oxygen saturation were monitored; arterial pressure was monitored non-invasively. In both groups, the conjunctival fornices were first anaesthesized with local anaesthetic drops (0.4% oxybuprocaine).

All peribulbar blocks were performed by the same person by single inferotemporal injection of 5 ml of a 1:1 mixture of 0.5% plain bupivacaine and 2% plain lidocaine supplemented with hyaluronidase, 300 i.u. ml–1, using a 5 ml syringe and a 25 gauge, 25 mm long disposable needle.6 7 With the gaze fixed straight ahead in the primary position, the injection site was identified at the junction of the lateral one-third and medial two-thirds of the inferior orbital rim. The direction of the needle was slightly medial and cephalad. The local anaesthetic was injected slowly over a period of 1 min. To ensure complete paralysis of the eye before starting surgery, another medial injection of 3 ml of the same local anaesthetic mixture was given transconjunctivally with a 30 gauge, 25 mm needle on the medial side of the caruncle, at the extreme medial side of the palpebral fissure.

DTFNBA was performed using two 2x3 mm sponges cut from the tip of a MicrospongeTM (regular tip) (Alcon® surgical), soaked with 0.5% bupivacaine, applied deep into the conjunctival fornices.1 8 The sponges were removed after 15 min. The surface anaesthetic effect was tested by grasping the limbus with Castroviejo 0.12 tissue forceps.

A simple pain scoring system was used for both groups: no pain=0, discomfort=1, pain=2. Scoring was performed at several stages of the operation: conjunctival incision, muscle hooking, muscle suture, muscle cutting, scleral suture, and conjunctival suture. If the pain score was 1, the patient was asked to look in the opposite direction to decrease the tension on the periosteal attachment of the muscle and relieve the discomfort. If the pain score was 2 at any stage of the operation, general anaesthesia was given.

In Group 2 (DTFNBA), following correction of the muscle, the patient was asked to sit up and sterile spectacles were applied. Spectacles were sterilized by soaking then in Alkanol for 7 min (100 g Alkanol contains 70.5 g isopropanol, 0.05 g chlorhexidine digluconate and 30% hydrogen peroxide solution). The amount of optical correction induced was observed. If the correction was unsatisfactory, the tuck or recession on the muscle was changed until the correction was satisfactory. The final knots were tied and the conjunctiva secured. A combined antibiotic–steroid ointment was applied, and the eyes left uncovered.

Parametric data were analysed using Student’s t-test; non-parametric data were compared using the Mann–Whitney test. A P value of <0.05 was considered statistically significant.

There was no significant difference between the patient characteristics of the two groups (Table 1).


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Table 1 Patient characteristics in the two groups. There were no significant differences between groups
 
In Group 1, the pain score was 0 at all stages while operating on the medial and lateral recti. In Group 2, the pain score was 0 at all stages while operating on the lateral recti. When operating on the medial recti, 15 patients experienced discomfort during muscle hooking (P<0.05), which disappeared on asking the patient to abduct their eyes when slight backward pressure on the globe (retropulsion) was applied. These procedures relax the muscle and decrease the tension on the periosteal insertion of the muscle. No patient in either group experienced pain at any other stage of the operation. The number of patients in each group with each pain score at the various stages of surgery on the medial recti is shown in Table 2.


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Table 2 Number of patients with each pain score at various stages of the operation on the medial rectus. Differences between groups were tested using the Mann–Whitney test (*P<0.05)
 

    Comment
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
In order to improve the success rate of surgical correction of strabismus in young and adult patients, different techniques using adjustable sutures have been described.2 These suture adjustments are usually performed within 24 h of the initial surgery. Although readjusting the sutures in this way helps to improve the success rate of strabismus surgery, it may have disadvantages. Tissue oedema around or within the muscle to be adjusted may make the procedure difficult. In addition, the patient may be reluctant to undergo another procedure, and there may be operative complications such as suture slippage and suture breakage, all of which require return to the operating room for full exploration.9 Even after full adjustment, a residual over- or under-correction may still be present and necessitate another surgical procedure. We therefore decided to perform one-step adjustable-suture strabismus surgery under DTFNBA to improve the overall success rate in young and adult patients and to avoid the disadvantages of readjusting the sutures within 24 h of surgery.

Although most ophthalmic surgeons believe that pain in squint surgery results from pulling on a muscle, studies have proved that this is not altogether true. Pain also results from the retraction of an extraocular muscle causing traction on the pain-sensitive periosteum at the muscle origin.10 In group 2 (DTFNBA), we found that hooking a horizontal extraocular muscle (i.e. lateral or medial rectus) is much less painful if the patient is asked to look in the opposite direction to the hooked muscle. This causes relaxation of the muscle to be hooked so that traction on the periosteum is less, with less discomfort. In all our patients, hooking of the lateral rectus muscle was simple and painless, whereas hooking of the medial rectus muscle resulted in discomfort in 15 patients. The line of pull of the medial rectus is straighter than that of the lateral rectus because the arc of contact of the lateral rectus with the globe is greater. In addition, there is an attachment between the medial rectus sheath and the pain-sensitive meninges around the optic nerve, but there is no such attachment in the lateral rectus. The absence of fascial attachments between the medial rectus and other muscles also results in a more direct pull on the periosteum. Slight backward pressure on the globe (retropulsion) with active abduction of the eye while hooking the medial rectus relieves the discomfort.

This study proved that one-step adjustable-suture strabismus surgery under DTFNBA is an effective alternative when patients are properly selected. Because it does not interfere with muscle tone, DTFNBA produces a more accurate result than retrobulbar, peribulbar or sub-Tenon’s anaesthesia. Further studies are required to test the usefulness of this technique for vertical, oblique strabismus and to correct diplopia, as these patients were not included in the present study.

We conclude that, when using the appropriate selection criteria and techniques, one-step adjustable-suture strabismus surgery using DTFNBA is an effective alternative to peribulbar block for most young patients requiring strabismus surgery. The technique avoids the disadvantages of other types of local and general anaesthesia.


    References
 Top
 Abstract
 Introduction
 Methods and results
 Comment
 References
 
1 Rosenthal KJ. Deep topical fornix nerve block anaesthesia. J Cataract Refract Surg 1995; 21: 499–503[ISI][Medline]

2 Pratt-Johnson JA. Adjustable-suture strabismus surgery: a review of 255 consecutive cases. Can J Ophthalmol 1985; 20: 105–9[ISI][Medline]

3 Diamond GR. Topical anaesthesia for strabismus surgery. J Pediatr Ophthalmol Strabismus 1989; 26: 86–90[Medline]

4 Lerman J. Study design in clinical research: sample size estimation and power analysis statistics. Can J Anaesth 1996; 43: 184–91[Abstract]

5 Ducker JS, Belmon JB, Benson WE, et al. Inadvertent globe perforation during retrobulbar and peribulbar anaesthesia: patient characteristics, surgical management and visual outcome. Ophthalmology 1991; 98: 519–26[ISI][Medline]

6 Apel A, Woodward R. Single injection peribulbar local anaesthesia. Aust N Z J Ophthalmol 1991; 19: 149–53[ISI][Medline]

7 Aziz ES. Peribulbar block using a single inferotemporal injection technique with high dose hyaluronidase. Egypt J Anaesth 1997; 31: 85–90

8 Aziz ES, Samra A. Prospective evaluation of deep topical fornix nerve block versus peribulbar nerve block in patients undergoing cataract surgery using phaceoemulsification. Br J Anaesth 2000; 85: 314–6[Abstract/Free Full Text]

9 Kraft SP, Jacobson ME. Adjustable suture techniques in strabismus surgery. Ophthalmol Clin North Am 1992; 5: 93–103

10 Lavrich JB, Neslon LB. Local anaesthesia for strabismus surgery. Ophthalmol Clin North Am 1992; 5: 131–41





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