[Motor blockade by retrobulbar anesthesia. Phenomenology and mechanism of action]. / Motorische Blockade durch Retrobulbäranästhesie. Phänomenologie und Mechanismen.

ABSTRACT

UNLABELLED The aim of this study was to analyze quantitatively the phenomenology and mechanisms of motor blockade induced by retrobulbar anesthesia (RETRO). PATIENTS AND METHODS: Prior to cataract surgery, 34 patients received RETRO using the intraconal technique of Atkinson. Four milliliters of mepivacaine 2% (Scandicain), prilocaine 2% (Xylonest) or lidocaine 2% (Xylocain) were injected in randomized order. Prior to injection, as well as 5, 30, 90, 120, 180, 300 and 420 min after injection, the following variables were determined deviation of the eye from the primary position (Krimsky test), horizontal and vertical ocular motility (Kestenbaum limbustest), and rotatory ocular motility (presence of in- or excycloductions). RESULTS: The directions in which the eye deviated after RETRO were abduction and depression. The maximum deviations amounted to 7-8 degrees abduction and 3-4.5 degrees depression and were observed 30 min after injection. Horizontal and vertical ocular motility was nearly completely and symmetrically reduced 30 min after RETRO. There were no significant differences between the three local anesthetics used. DISCUSSION: The present findings may be interpreted as temporary palsy of N.III and N.VI during RETRO (symmetrical blockade of horizontal and vertical recti eye muscles) with unaffected function of N.IV and superior oblique muscle (maintained incycloduction ability; hypotropia and exotropia). An additional possible mechanism to account for the observed downward deviation is that the eye assumes its physiological divergent resting position during RETRO.