May 2006
Volume 47, Issue 13
ARVO Annual Meeting Abstract  |   May 2006
Horizontal Rectus Muscle Anatomy in Naturally and Artificially Strabismic Monkeys
Author Affiliations & Notes
  • A. Narasimhan
    UCLA, Los Angeles, CA
    Biomedical Engineering,
  • L. Tychsen
    Washington University, Washington D.C., DC
  • V. Poukens
    UCLA, Los Angeles, CA
    Jules Stein Eye Institute,
  • J.L. Demer
    UCLA, Los Angeles, CA
    Jules Stein Eye Institute,,
  • Footnotes
    Commercial Relationships  A. Narasimhan, None; L. Tychsen, None; V. Poukens, None; J.L. Demer, None.
  • Footnotes
    Support  U.S. Public Health Service, NEI: grant EY–08313 and core grant EY–00331
Investigative Ophthalmology & Visual Science May 2006, Vol.47, 5068. doi:
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      A. Narasimhan, L. Tychsen, V. Poukens, J.L. Demer; Horizontal Rectus Muscle Anatomy in Naturally and Artificially Strabismic Monkeys . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5068.

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      © ARVO (1962-2015); The Authors (2016-present)

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Purpose: : Structural abnormalities of extraocular muscles (EOMs) or their pulleys are associated with some forms of human strabismus. We investigated whether such abnormalities are associated with artificial or naturally occurring horizontal strabismus in monkeys.

Methods: : Binocular alignment and grating acuities were determined in 10 monkeys representing various species using magnetic search coil recording and behavioral observations. Four animals were orthotropic, 2 had naturally occurring "A" pattern esotropia, 2 had concomitant and one "V" pattern esotropia induced by lid suturing in infancy, and one had "A" pattern exotropia induced by prism wear. After euthanasia, 16 orbits were examined by high resolution magnetic resonance imaging (MRI) technique in the coronal plane. The paths and sizes of horizontal rectus EOMs were analyzed quantitatively in a standardized coordinate system. The whole orbits were then serially sectioned in the coronal plane, stained for connective tissues, and microscopically examined.

Results: : Quantitative analysis of MRI revealed no significant differences in horizontal rectus EOM sizes or paths among the orthotropic, naturally, or artificially strabismic monkeys. Histological examination demonstrated no differences in EOM size, structure, or innervation among the three groups, and no differences in connective tissues in the pulley system. The accessory lateral rectus (ALR) EOM was bilateral in specimens where it was present, but small, inconsistently located, and sparsely innervated and always in a site with little mechanical advantage for ocular rotation. Any significant connective tissue sleeve suggestive of a pulley did not surround the ALR. Characteristics of the ALR were found to be uncorrelated with strabismus.

Conclusions: : Structural abnormalities of horizontal rectus EOMs and associated pulleys are unrelated to natural or artificial horizontal strabismus in monkeys. The ALR is unlikely to contribute to horizontal strabismus in primates. However, these findings do not exclude a possible role of pulley abnormalities in disorders such as cyclovertical strabismus.

Grant Support: : Supported by U.S. Public Health Service, NEI: grant EY–08313 and core grant EY–00331.

Commercial Relationship: : None.

Keywords: amblyopia 

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