Questions and Answers
What is the primary action of the Inferior Rectus muscle when the eye is in the primary position?
Which muscle is responsible for intorsion in addition to elevation in the primary position?
Which muscle inserts furthest from the limbus in the primary position?
Which cranial nerve innervates the Lateral Rectus muscle?
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Which of the following muscles does NOT arise from the annulus of Zinn?
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What is the primary action of the inferior oblique muscle in primary position?
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Which cranial nerve innervates the inferior oblique muscle?
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What is the angle between the inferior oblique muscle and the visual axis of the eye in the primary position?
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What is one of the secondary actions of the inferior oblique muscle?
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Which muscle is responsible for intorsion during its primary action?
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Study Notes
Anatomy of Extraocular Muscles (EOM)
- The eye has six (or seven) EOM, which are divided into:
- Four Rectus Muscles: Medial, Superior, Inferior, Lateral
- Two Oblique Muscles: Superior Oblique, Inferior Oblique
- One Levator Muscle: Levator Superioris
- All rectus muscles arise from the Annulus of Zinn, a common tendinous ring around the optic canal.
Medial Rectus Muscle
- Originates from the Annulus of Zinn.
- Attaches 5.5 mm from the limbus.
- Innervated by the inferior division of the Oculomotor nerve (CN III).
- Primarily adducts the eye in the primary position.
- Prone to injury during ethmoid sinus surgery.
Lateral Rectus Muscle
- Arises from the Annulus of Zinn.
- Inserts 6.9 mm from the limbus.
- Innervated by the Abducent nerve (CN VI).
- Functions primarily as an abductor in the primary position.
Superior Rectus Muscle
- Arises from the Annulus of Zinn and inserts 7.7 mm from the limbus.
- Innervated by the superior division of the Oculomotor nerve (CN III).
- Primary action is elevation, with secondary actions of intorsion and adduction.
Inferior Rectus Muscle
- Originates from the Annulus of Zinn, inserting 6.5 mm from the limbus.
- Innervated by the inferior division of the Oculomotor nerve (CN III).
- Responsible for depression, with secondary actions of extorsion and adduction.
Superior Oblique Muscle
- Originates from the orbital apex above the Annulus of Zinn.
- Passes through the trochlea, making an angle of 51° with the visual axis.
- Innervated by the Trochlear nerve (CN IV).
- Primary action is intorsion, with secondary actions of depression and abduction of the eye.
Inferior Oblique Muscle
- Arises from the maxillary bone, posterior to the orbital rim.
- Inserts under the Lateral Rectus muscle.
- Innervated by the inferior division of the Oculomotor nerve (CN III).
- Primary action is extorsion, with secondary actions of elevation and abduction.
Other Concepts in EOM Physiology
- Hering’s Law of Equal Innervation: Equal innervation to corresponding muscles of both eyes for coordinated movements.
- Binocular Single Vision (BSV): Ability to fuse images from both eyes and perceive depth.
- Strabismus: Condition characterized by misalignment of the eyes.
Terms and Prefixes Related to Eye Movement
- Eso: Convergence (nasal rotation)
- Exo: Divergence (temporal rotation)
- Hyper: Superior rotation
- Hypo: Inferior rotation
- Incyclo: Sup pole rotated nasally
- Excyclo: Sup pole rotated temporally
Types of Eye Deviations
- Esotropia: Eye deviates inward towards the nose.
- Exotropia: Eye deviates outward.
- Hypertropia: Eye positioned higher than the other.
Measurement Techniques for Eye Deviation
- Ductions: Movement of one eye while the other is covered.
- Versions: Movements of both eyes in the same direction.
- Corneal Light Reflex (Hirshberg Test): Method to assess eye alignment.
- Krimsky Test: Uses prisms to achieve symmetrical corneal light reflections.
Tests for Eye Movement and Strabismus
- Cover Test: Detects heterotropia and heterophoria.
- Titmus Test: Assesses stere acuity.
- Worth 4-Dots Test: Evaluates fusion and suppression.
Clinical Significance
- Measurement of deviations in terms of prism diopters and angles important for diagnosis and management of strabismus.
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Description
This quiz explores the anatomy and basic physiology of the extraocular muscles (EOM) in the human eye. It covers the six muscles involved in eye movement including the four rectus muscles and the two oblique muscles. Test your knowledge of these crucial components of visual function.
