Faden operation (posterior fixation sutures).

Abstract

The ocular rotational power which a rectus muscle exerts is a product of the muscle's force and the length of the lever arm between the muscle's tangential point of contact with the globe and the centre of rotation of the eye. A recession operation weakens a rectus muscle because the distance between the muscle's origin at the orbital apex and its insertion into the surface of the globe is decreased, so that the muscle becomes slack. Provided that the recession does not exceed the conventional maximum (Table I), the length of the lever arm is not reduced. Even when the eye moves into the field of action of the recessed muscle, the length of the rotational lever arm remains unchanged as the tangential point of muscle action is still on the surface of the globe. If the muscle is over- recessed, not only does it become very slack but the effective lever arm is reduced in length and mechanical restriction of movement ensues. The weakening effect of a conventional recession operation is therefore approximately the same in all directions of gaze in which the muscle is active (Figs. 1 and 2). Table I Maximum recession possible without limiting ocular motility.