Isometric Force Development in Human Horizontal Eye Muscle, Attached to or Detached from the Globe

Abstract

Abstract: : Purpose: To compare force development in single, horizontal human eye muscle, first when the muscle was still attached and later when it was detached from the globe. Methods: Eleven horizontal muscles of 8 patients were examined during surgery under topical anesthesia for concomitant strabismus. None of the muscles had been operated before. Isometric muscle tension was recorded with a strain gauge system. A silk suture (5-0) was applied to the tendon of the muscle and the suture was tied around the strain gauge probe. An initial tension of 10 g was applied with the muscle relaxed. The testing was done first when the muscle was still attached to the globe and then after the tendon had been cut.The subject made saccadic eye movements with the non-recorded eye by fixating LEDs in the center and at 10, 20 and 30 degrees horizontally to each side. In the tension signals, peak tension (Fp), steady tension (Fs), the ratio Fp/Fs, and the maximal velocity of tension change (Fv) were measured. Statistical analysis was done with MANOVA. Results: The values of Fp, Fs, Fp/Fs and Fv at different amplitudes of the saccadic eye movements were compared in the attached and the detached muscle. There were no consistent statistical differences between the values obtained in the two conditions. Conclusions: The muscle force development, measured at the tendon, was the same in muscles attached to the globe and in muscles free from the globe. This implies that muscle tension can be properly recorded in muscles still attached to the globe, which increases the possibilities to study contractile properties of various eye muscles in procedures of ophthalmic surgery performed under topical anesthesia.

Keywords: extraocular muscles: development • eye movements: recording techniques • strabismus