There are chances of scleral perforation in the high risk situations such as thin sclera and restricted field of the operation, and in those cases, we can choose the modified suspension-recession technique or hang-back recession [20
]. Several reports on hang-back recession in strabismus patients have shown that this technique is as effective as the conventional recession method [21
]. However, [Capo et al. 23
] reported somewhat different results, stating that the hang-back recession group had a significantly greater failure rate compared to the conventional recession group. They found that late over-corrections occurred more frequently in the hang-back recession group one year after surgery, and this is presumed to be a result of posterior displacement of the rectus muscle. [Wright 24
] also described over-correction in small recessions, which resulted from central sag of hanging muscles.
Animal studies have shown the movement of hanging muscles both horizontally and vertically before being reattached in hang-back recession, with most of them exhibiting anterior displacement [5
]. Several explanations have supported the pathogenesis of anterior displacement, including hemorrhage at the time of operation and direct forward growth of muscle fibers [5
]. [Ohtsuki et al. 8
] suggested that hang-back recession produces more connective fibrous tissue around the new insertion site compared to conventional recession and that this fibrous tissue might aid the muscle in growing forward.
In our study, the muscle moved, on the average, 0.16
mm backward in the control group and 0.31
mm backward in the fibrin glue group. At a glance, it can be seen that more displacement occurred in the fibrin glue group. However, it is reasonable to analyze both anterior and posterior displacement separately because both anterior and posterior displacements occurred in both groups. The results showed that anterior displacement occurred more frequently in the control group (5 of 16 eyes vs. 1 of 16 eyes), and so did posterior displacement (8 of 16 eyes vs. 6 of 16 eyes). Whatever the amount of recession is increased, especially in recession posterior to the equator, risk of anterior displacement would be increased. On the other hand, in low recession procedures, for example 4
mm recession, as in this study, risk of posterior displacement would be increased. And, only 3 eyes showed exact reattachment among 16 eyes with hang-back suture alone. The recessed muscle in the fibrin glue group, on the other hand, reattached with much more stability at the new insertion site (9 of 16 eyes), and the stability was statistically greater compared with the control group (p
0.028). The recessed rectus muscle in the control group seemed to be movable in both forward and backward direction. Although explanations on such movements are not suggested in this study, the instability of hang-back technique alone might allow more room for unwanted under- or over-correction. Although posterior displacement may not be omitted because of sagging of posterior traction force of the recessed muscle, Fibrin glue creates an adhesive bed that prevent from anterior displacement. Thus, Fibrin glue may be helpful in stabilizing the new insertion in hang-back recession as expected.
It is, of course, quite another matter for fibrin glue to be used safely without sutures in strabismus surgery. [Tonelli et al. 18
] reported on the instability of the sutureless Faden operation with fibrin glue, and [Spiere et al. 16
] also showed that fibrin glue was not strong enough to overcome the contractive strength of the muscle in small amount of recessions. We did not measure horizontal displacement, however, the horizontal displacement would not be seen in small recession like 4
mm recession in the present study.
This combined surgical technique has several disadvantages. It takes a little more operation time for applying fibrin glue, costs more, and eliminates the possibility of performing adjustable suture surgery.
No significant complications were found in either group. Fibrin glue did not cause anticipated chemical problems; rather, it aided hemostasis, as shown in Figure . Whether this technique can be applied to human eyes, however, is a different matter. The composition of the extraocular muscles differs in rabbit eyes, as do eyeball movements and the severity of the postoperative inflammatory reaction [7
]. Cost-effectiveness also has to be considered in clinical application.