Presentations

Selected conference presentations and local publications

Injection Treatment of Strabismus

Extraocular Muscle Forces

Use and fabrication of the MFT/M-2.11 Muscle Force Transducer for NHP extraocular muscle.

Objectives: Motoneuron activity during symmetric convergence (in which only vergence-related neural components respond) predicts horizontal rectus co-contraction (Mays & Porter, 1984; Gamlin et al, 1989; Zhou & King, 1998). Paradoxically, muscle force measurements during both symmetric convergence, and in the aligned eye during asymmetric convergence (the later being methodologically cleaner because the instrumented eye does not change position), fail to show force increases or co-contraction (Miller et al, 2002). We have now demonstrated the complete "missing EOM force paradox" by simultaneously recording horizontal rectus motoneuron activity and muscle force during asymmetric convergence. Methods: Vergence-related medial rectus motoneurons were identified and recorded extracellularly in rhesus monkeys in the usual way. Medial rectus muscle forces were recorded with chronically-implanted muscle force transducers (MFTs; Miller et al, 1992). Results & Conclusions: In asymmetric convergence, medial rectus motoneurons having high vergence gains increased activity as the ipsilateral medial rectus muscle in the aligned eye decreased force. It is unlikely that ipsilateral motoneurons with strong conjugate components offset changes in activity of vergence cells, because of the similarity of symmetric & asymmetric muscle force findings. Studies of lateral rectus motoneurons and conjugate-vergence interactions are ongoing. The simple notion of an oculomotor "final common path" must be replaced by more realistic models of motoneuron recruitment, muscle fiber interaction, and extraocular mechanics.

Extraocular Biomechanics & Modeling

Jampolskys group has opposed the notion of EOM pulleys (see also McClung, Allman, Dimitrova & Goldberg, 2006) that has evolved over the past 20 years based on broad evidence of many types (see review in Miller 2007a, below), including recently, the compelling findings of Ghasia & Angelaki (2005) and Klier & Angelaki (2006), which Lee et al misrepresent and dismiss. Here, they use unproven, artifact-vulnerable, poorly specified methodology, where suitable broadly accepted methodology exists, and report only selected data. In interpreting their results, Lee et al selectively apply their arguments to an obsolete non-pulley model and a straw-man pulley model, the later having trochlea-like, localized, rigid pulleys, never proposed elsewhere. Even with these biases, Lee et al cannot explain their data without assuming the existence of distributed, elastic, musculo-orbital, origin-determining EOM pulleys.

Orbit is a unique software tool that provides easy access to a sophisticated biomechanical model, able to simulate classical strabismus syndromes and data from individual cases, clarifying diagnostic and treatment possibilities in well-defined physiologic terms. This manual introduces both the biomechanical method of strabismus analysis and the use of Orbit, which is available in an emulation environment that runs under OSX on modern Intel Macs.

Extraocular Tissue Architecture

From the MethLab

Quantitative histology of extraocular muscles (EOMs) conventionally uses sampling to avoid having to count, or worse measure, the many thousands of fibers in each crossectional slice. Unfortunately, this tissue is highly inhomogeneous, and unbiased sampling difficult. We've developed a practical method to segment essentially all the muscle fibers in hundreds of stained EOM slices and calculate their individual areas, excluding voids, connective tissues, blood vessels, and nerves.

Orbit is a unique software tool that provides easy access to a sophisticated biomechanical model, able to simulate classical strabismus syndromes and data from individual cases, clarifying diagnostic and treatment possibilities in well-defined physiologic terms. This manual introduces both the biomechanical method of strabismus analysis and the use of Orbit, which is now available in an emulation environment that runs under OSX on modern Intel Macs.

Other Presentations