SUMMARY
The effect of the proparacaine hydrochloride 0.5% on the horizontal rectus muscles force was studied in fifteen strabismus patients during one-stage adjustable suture strabismus surgery. The muscles were grasped with a modified Green's strabismus hook and both maximal and minimal (rest) isometric force values were registered on a digital dynamometer attached on the surgical microscope before and after one and two drops of topical anesthetic. One drop of anesthetic did not change the maximal isometric force, while two drops reduced significantly both maximal (Fcalc 4.03*; Fcrit 3.34; Tukey's test: after two drops < initial) and minimal (Fcalc 38.20*; Fcrit 3.34; Tukey 's test: after two drops < initial and after one drop) isometric forces, the last more severely. Although it was not necessary to change the surgical technique neither were surgical results unexpected after one and two drops of topical anesthetic, it is safer to instill only one drop of the anesthetic if it is really necessary and do not too close to the alignment time to prevent an undesired surgical result.