Influence of extraocular muscle co-contracture on globe length.

From the Smith-Kettlewell Institute of Visual Sciences, Pacific Medical Center. This investigation was supported by Research Career Program Award No. K3 NB-14,094 from the National Institute of Neurological Diseases and Blindness; Public Health Service Program Project Research Grant No. NB-06038, and General Research Support Grant No. S SOI FR-0S566. bearing surface was fashioned from a 1-mm-wide steel rod. One end formed a slotted hoop which was placed around the optic nerve, in contact with the posterior pole of the globe. The rod was bent so that it passed under the muscle cone, around the globe, and ended in front of, but not in contact with, the cornea (fig. 1) . This arrangement exhibited a longitudinal stiffness of 500 g/mm. Freedom of movement was verified by manual pressure backward on the rod. A silk thread joined the rod to a cantilever spring connected to a Grass strain gauge displacement transducer. A suture was placed in the cornea at the anterior pole of the globe and connected to a second Grass transducer. Steel piano wire cantilever springs, 70 mm long and 0.3 mm wide were attached to the strain gauges to allow movement to be recorded with a spring constant of 10 mg per mm on an Offner chart recorder. In this way the total globe retraction produced by intravenous injection of succinylcholine could be