The tendons of the recti muscles are inserted into the globe at the following distances from the corneo-sclerotic junction: internal, 5 mm.; inferior, 6 mm.; external, 7 mm.; superior, 8 mm. Each muscle is held in place by expansions on either side of the tendon as well as by the tendinous insertions. Division of these expansions allows a greater retraction of the muscle and is, therefore, to be undertaken when a considerable degree of squint has to be overcome. On the other hand, there will be a danger that the muscle may not regain a proper attachment to the globe if division be too freely performed, and a squint in the opposite direction may result; proptosis also may be caused thereby. It is, therefore, better to combine tenotomy with advancement in high degrees of squint over twenty degrees convergent and in all cases of constant divergence. This is usually better than performing a tenotomy in the other eye, as there still remains the muscle of the other eye in reserve to tenotomize if necessary, if the advancement be insufficient to correct the squint. Further, it is much easier to rectify a muscular error by accurate tenotomy than by advancement. Division of the tendon of the internal rectus only, without its expansion, will usually rectify cases of latent convergent strabismus with a deviation of about 12° prism (Maddox test). Cases of latent divergent strabismus of about 8° prism (Maddox test) require complete division of the tendon of the external rectus, and, in some cases, of the expansion as well. Tenotomy of the superior rectus for hyperphoria should only be undertaken in bad cases; that is to say, of over 12° prism, any lateral deviation being first corrected, as occasionally the correction of the lateral deviation, especially when this is due to the faulty insertion of a muscle, will sometimes correct the hyperphoria present.
Partial tenotomies are performed by some surgeons for the correction of latent muscular errors, but the experience of most in this country is that little benefit is gained unless the tendon be completely divided. Tendon-lengthening by various methods has been performed, but has not come into general use.
After all operations upon the ocular muscles both eyes should be occluded to keep the eyes at rest whilst the muscle is gaining its fresh attachment to the globe; this usually takes about seven days, after which time both eyes should be uncovered, and if there is a tendency to convergence atropine should be used. Glasses correcting any error of refraction should be worn.
TENOTOMY
Tenotomy may be performed by (1) the open, or (2) the subconjunctival method.
Instruments. Speculum, straight blunt-pointed scissors, strabismus hook, needle and silk, needle-holder.
Operation. The operation is performed under adrenalin and cocaine.
1. By the open method. The surgeon stands on the right side facing the patient when dividing the right external or the left internal rectus, but at the head of the table when dividing the right internal or the left external rectus.
