Measured recession or retroplacement of the lateral rectus is the procedure of choice for weakening this muscle in exodeviations. In certain instances, a marginal myotomy is a satisfactory and even desirable procedure for weakening the lateral rectus muscle, but this procedure should be reserved for specific cases (see Chapter 10). A modified recession procedure is accomplished by the hang-back technique.
A minimum lateral rectus recession is 4 mm. Less recession should not be undertaken if surgery to weaken the lateral rectus is justified. The maximum measured lateral rectus recession had been 7 mm in adults and 6 mm in children. However, most surgeon now perform 8 mm and even up to 10 mm or even larger recessions of the lateral rectus without crippling the muscle's effect (Figure 5).
A Minimum lateral rectus recession, 4.0 mm
B ‘Maximum’ lateral rectus recession, 8.0 mm
Large recessions of the lateral rectus may be performed in certain cases without severely restricting motility because the muscle continues to act through attachments to the intermuscular membrane. The lever arm is reduced, but abducting power remains. The extent to which the intermuscular membrane is severed from the muscle border can influence the degree of weakening accomplished by a given lateral rectus recession (Figure 6). As with the medial rectus, an extreme example is the case of a slipped or lost muscle that has had extensive freeing of the muscle borders from intermuscular membrane. In these cases little, if any, abduction is present postoperatively. On the other hand, free tenotomy, which is always performed with minimal dissection of the adjacent intermuscular membrane, in most cases leaves the patient with some abduction. Free tenotomy is infrequently done. It is often unpredictable and can be crippling. However, in some cases of large angle exotropia in a previously operated patient who may have mechanical restrictions, free tenotomy or one guarded by an adjustable suture may be done. This may also be considered a type of hang-loose procedure with more posterior globe-suture attachment. In extreme cases where lateral rectus function needs to be eliminated, the lateral rectus is detached and reattached to the lateral orbital periostium.
Lateral rectus recession with minimal intermuscular membrane dissection
When attempting to engage the lateral rectus with a muscle hook, care should be taken to avoid inadvertently including all or part of the inferior oblique muscle at its insertion (Figure 7). This complication can be avoided by making the initial sweep of the hook from above. If the hook is passed upward from below, it must not be thrust too deeply into the orbit. Inclusion of the inferior oblique in lateral rectus recession will, if undetected, lead to unpredictable surgical results accompanied by restrictions in motility. This has been called the inferior oblique inclusion syndrome.
Care should be exercised to avoid unintended inclusion of the inferior oblique when hooking the lateral rectus
When the lateral rectus is detached from the globe, the muscle should be lifted and the undersurface and the inferior border of the lateral rectus should be freed from the inferior oblique muscle (Figure 8).
It is good practice to lift the lateral rectus to confirm that the inferior oblique is not attached to the lateral rectus or included in the suture. The relationship of the lateral rectus and inferior oblique makes it unlikely that the lateral rectus will be ‘lost.’