EFFECT OF ANTAGONIST WEAKENING ON DEVELOPED TENSION IN CAT EXTRAOCULAR-MUSCLE

Purpose. In a previous study, the authors found that recession of an e xtraocular muscle resulted in atrophy of both the recessed muscle and its antagonist. To determine if atrophy, caused by weakening of an ext raocular muscle, results in changes in developed tension in the antago nist, the authors studied force development of the cat lateral rectus muscle after adductor weakening. Methods. Tenotomy of the left inferio r, medial, and superior rectus muscles was performed in 18 cats. At 3, 6, and 12 weeks after surgery, the right (control) and left lateral r ectus muscles were exposed through a lateral orbitotomy and were attac hed to isometric force transducers. Length-tension curves were obtaine d by direct muscle stimulation using bipolar contact electrodes at 0.1 Hz and 50% suprathreshold stimulus intensity. In addition, peak tetan ic tension was measured at the optimal resting tension using a 5-secon d stimulus train at 200 Hz. Pooled data from the operative and control muscles at each postoperative interval were compared. Results. Three weeks after adductor weakening, a 28% decrease in maximal single-twitc h tension was seen in the left lateral rectus muscle when compared wit h controls. This difference disappeared at 6 weeks. No statistically s ignificant changes in peak tetanic tension occurred at any time interv al after surgery.Conclusions. Adductor weakening results in a transien t decrease in single-twitch tension in the antagonist lateral rectus m uscle in the cat.