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V. E. Das; Response Properties of Cells in the Supraoculomotor Area in Non-Human Primates With Strabismus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2997.
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Non-human primates reared with daily alternating monocular occlusion for the first four months of life develop large horizontal strabismus, A/V patterns and Dissociated Vertical Deviation (DVD). The purpose of this study was to investigate whether neuronal activity within the supraoculomotor area (SOA -cells that are monosynaptically connected to medial rectus motoneurons and respond to changes in vergence angle or accommodation) of juvenile strabismic monkeys was correlated with the angle of misalignment and therefore helps to define the state of strabismus in these animals.
We recorded single-cell neural activity from tonic SOA neurons in two rhesus monkeys with exotropia as they performed fixation and eye movement tasks during monocular viewing and at two different viewing distances. Binocular eye movements were acquired using the search coil method. Data analysis included correlating neural firing rates with strabismus angle with either eye viewing, at near (30cm) and far (61cm) viewing distances and during cross-axis eye movements that lead to appearance of A/V patterns and DVD.
The SOA was identified based on anatomical location (~2mm dorsolateral to the oculomotor nucleus) and functional criteria (responds to changes in vergence angle but not conjugate eye position). At either viewing distance, horizontal strabismus angle was different depending on eye of fixation and the activity of tonic SOA cells varied in correlation with the angle of strabismus. Small change in strabismus angle due to change in viewing distance was also reflected in SOA cell activity. Though activity of SOA cells was clearly correlated with horizontal strabismus angle, there was no modulation of activity with either conjugate eye position as tested during horizontal smooth-pursuit or with horizontal cross-axis movements that lead to A/V patterns as tested during vertical smooth-pursuit. Comparison of SOA population activity in these strabismic animals and normal monkeys (described in the literature) suggests that both vergence thresholds(misalignment threshold in the case of the strabismic animals) and vergence position sensitivities (misalignment sensitivity for strabismic animals) are different in the strabismic animals compared to the normals.
Our data suggests that activity within the SOA cells is important in determining the state of horizontal strabismus possibly by altering vergence tone in extraocular muscle. The lack of correlated SOA activity with horizontal cross-axis movements suggest that circuits mediating horizontal strabismus angle and those that mediate A/V patterns are likely different.
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