Neuro-Ophthalmology Japan
Online ISSN : 2188-2002
Print ISSN : 0289-7024
ISSN-L : 0289-7024
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Key Points of Eye Movement Disorders
Yasuo Suzuki
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2021 Volume 38 Issue 2 Pages 124-132

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Abstract

 The following is a summary of points for the gentle and easy evaluation of abnormal eye movements.

 Point 1: Understand the five categories of normal eye movement.

 Eye movements are classified into four types of conjugate eye movements(saccades, pursuit, vestibulo-ocular reflex, and optokinetic nystagmus)and one type of disconjugate eye movement. The motor commands and control signals for the different types of eye movements are generated by different neural circuits in the oculomotor center.

 Point 2: The oculomotor periphery consists of the nuclei of cranial nerves III, IV, and VI, and their axons and extra ocular muscles. It does not distinguish oculomotor signals for different types of eye movements and is named the final common pathway. The orbital soft tissue has viscoelasticity, and the eye position is maintained by sustained contraction of the extra ocular muscles, which antagonizes the elastic resistance of the orbit.

 In mammals, extra ocular muscle planes are roughly coincided with semicircular canal planes.

 Point 3: By understanding the mechanism of the oculomotor center and evaluating eye movement disorders by type and direction, it is possible to make a localized diagnosis.

 Point 4: Convergence signals of disconjugate eye movements project directly from the mesencephalic reticular formation to the bilateral medial rectus subnuclei without passing through the abducens internuclear neuron. Therefore, diplopia caused by disorder in the disconjugate eye movement center does not show horizontal eye position or fixation eye dependence.

 Point 5: Subjective head-free eye movements are gaze movements and involve eye-in head movements and head-in-space movements. Therefore, it is not uncommon for patients with diplopia or nystagmus to achieve a compensatory head position when looking forward.

 In the case of thyroid-associated ophthalmoplegia, a patient with vertical diplopia may have a natural chin-up position when looking upward.

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© 2021 The Japanese Neuro-Ophthalmology Society
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