Is Divergence Active? An Electromyographic Study

Tamler, Edward; Jampolsky, Arthur

doi:10.1016/0002-9394(67)90243-7

Cited by 29 publications

(4 citation statements)

References 6 publications

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“…Further, if the higher LR abducting forces were balanced by higher MR adducting forces, overall horizontal rectus co-contraction would result. Some electromyograph (EMG) studies suggest that there is co-contraction in convergence (Tamler and Jampolsky 1967;Tamler et al 1958), whereas others do not (Breinin 1957), presumably because of variability of motor unit sampling, small sample sizes, and instability of EMG electrode placement. An alternative to MR co-contraction is for cyclovertical eye muscles to provide adducting forces to balance the excess LR force predicted in convergence.…”

Section: Introductionmentioning

confidence: 99%

Missing Lateral Rectus Force and Absence of Medial Rectus Co-Contraction in Ocular Convergence

Miller

Bockisch

Pavlovski

2002

Journal of Neurophysiology

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For a given position of the eye in the orbit, most abducens motoneurons (LRMNs) fire at higher rates in converged gaze than when convergence is relaxed, implying that lateral rectus (LR) muscle force will be higher for a given eye position in convergence. If medial rectus (MR) muscle force balances LR force, it too would be higher in convergence, that is, LRMN recording studies predict horizontal rectus co-contraction in convergence. Three trained rhesus monkeys with binocular eye coils and custom muscle force transducers (MFTs) on LR and MR of one eye alternately fixated near (approximately 7 cm) and far (200 cm) targets with vergence movements of 20-30 degrees. Tonic muscle forces were also measured during conjugate fixation of far targets over a 30 x 30 degrees field. MFT characteristics and effects on oculomotility were assessed. Contrary to predictions, we found small (<1 g) decreases in both LR and MR forces in convergence, for those gaze positions that were used in the brain stem recording studies. This missing LR force paradox (higher LRMN firing rates in convergence but lower LR forces) suggests that motoneurons or muscle fibers contribute differently to oculorotary forces in converged and unconverged states, violating the final common path hypothesis. The absence of MR co-contraction is consistent with, and supports, the missing LR force finding. Resolution of the missing LR force paradox might involve nonlinear interactions among muscle fibers, mechanical specialization of muscle fibers and other articulations of the peripheral oculomotor apparatus, or extranuclear contributions to muscle innervation.

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Section: Introductionmentioning

confidence: 99%

Missing Lateral Rectus Force and Absence of Medial Rectus Co-Contraction in Ocular Convergence

Miller

Bockisch

Pavlovski

2002

Journal of Neurophysiology

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“…Tamler and Jampolsky (1967) demonstrated active divergence by recording increased electromyographic activity in the lateral rectus muscles on divergence movements. Tamler and Jampolsky (1967) demonstrated active divergence by recording increased electromyographic activity in the lateral rectus muscles on divergence movements.…”

Section: Aetiologymentioning

confidence: 96%

Heterophoria and Anomalies of Convergence and Accommodation

2013

Diagnosis and Management of Ocular Motility Disorders

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“…The presence of a mid-brain centre of convergence has been questioned by Warwick (1956) and others have stressed the importance of the cerebral cortex in convergence and divergence. Westheher, (1971), Hoyt and Daroff (1971), Tamler and Jampolsky (1967) considered divergence to be an active function and Jampolsky (1970) considered divergence paralysis to be due to bilateral paralysis of the lateral recti. The relative weakness of divergence in distance eso deviation supports divergence as an active function as does the ex0 movement seen on focussing for a distance in some patients.…”

Section: Commentmentioning

confidence: 99%

Distance ESO Deviation—A Basic Deviation or Paralysis of Divergence

Gillies¹

1974

Aust N Z J Ophthal

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Summary A Group of one hundred patients is described with the condition of distance eso deviation or convergent squint which is present for distance viewing together with an exo deviation for near viewing and in‐between distance and near there is a neutral point or crossing distance where there is no deviation. The crossing distance determines the distance at which an exo deviation will be present. Accommodation increases the degree of eso deviation and shortens the crossing distance, especially in younger patients, but does not have much effect in presbyopic patients. Distance eso deviation occurs at all ages and varies in degree from a small phoria to an obvious tropia. It is a cause of diplopia in elderly patients, and may be the underlying cause of convergent squint in young patients. It is distinct from the rare condition of divergence paresis.

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Is Divergence Active? An Electromyographic Study

Cited by 29 publications

References 6 publications

Missing Lateral Rectus Force and Absence of Medial Rectus Co-Contraction in Ocular Convergence

Missing Lateral Rectus Force and Absence of Medial Rectus Co-Contraction in Ocular Convergence

Heterophoria and Anomalies of Convergence and Accommodation

Distance ESO Deviation—A Basic Deviation or Paralysis of Divergence

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