Course Content
MASTERING OCULAR ANATOMY: ADVANCED
Deepen your understanding of ocular anatomy as you delve further into the complex structures and functions of the eye. This lesson covers the eye's main parts and regions while developing your understanding of the principles of refraction and accommodation. You will also learn about the six extraocular muscles and gain valuable insight into how the eye moves.
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Overview of the Visual System
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Refraction and Accommodation
00:00
Anatomy of the Retina
00:00
Extraocular Muscles and Eye Movements
00:00
Key Takeaways
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Knowledge Check
MASTERING OCULAR ANATOMY: ADVANCED
About Lesson

Extraocular Muscles and Eye Movements

Chapter 4 of 5

There are 6 extraocular muscles organized in 3 pairs. One pair controls horizontal movements, one pair controls vertical movements, and one pair controls rotational movements. The extraocular muscles are the six extrinsic muscles of the human eye. They are six extraocular muscles arranged in three pairs, responsible for horizontal and vertical gaze and torsional or rotational movements.

How Are the Extraocular Muscles Controlled?

Eye movements are under central nervous system control. The third, fourth, and sixth cranial nerves are responsible for eye movements.

  • The third cranial nerve (oculomotor nerve -): controls all extraocular muscles except for the superior oblique muscle controlled by the trochlear nerve (IV), and the lateral rectus muscle controlled by the abducens nerve (VI)
  • The fourth cranial nerve (trochlear nerve): controls the superior oblique muscle, consequently the ability of the eye to look down and inwards
  • The sixth cranial nerve (abducens nerve) controls the lateral rectus muscle and, consequently, the ability to move each eye outwards

Understanding Eye Movement

Eye movements can be affected by either a muscle mechanical limitation or an input problem from cranial nerve anomalies such as paralysis or partial paralysis. In more complex cases, the ability of the eyes to move together is typically affected from a vascular accident to a very specific area of the brain.

  • Conjugate movement (the eyes move in the same direction) is typical when shifting gaze right or left
  • Disjunctive (opposite directions) is convergence of the two eyes on a near object. Disjunction can be performed voluntarily, but is usually triggered by the nearness of the target object

The Movement of the Eye May Be Affected by Damage to the Cranial Nerves

  • If the eyes are not capable of moving in a coordinate fashion, this can result in double vision that may or not be constant and may only be apparent in one gaze direction
  • Unilateral damage to the third nerve will typically result in an eye that is down, looking outwards, with or without ptosis, and potentially associated with mydriasis (pupil dilation)
  • Damage to the trochlear nerve (IV) can also affect the two most anterior external eye structures. This can lead to diplopia. In certain gaze directions, the eye may be adducted. The result will be an eye which can not move downwards properly (especially downwards when in an inward position). This is due to impairment in the superior oblique muscle
  • Damage to the sixth nerve and/or the lateral rectus can also lead to double vision. A sixth nerve palsy patient typically presents with one eye turned inward
  • If the anomaly is present from birth (congenital) and the eyes cannot function well together and cannot align on a target, the brain will typically choose one eye to align on the target, and the other eye will be deviated, not aligned on the target, and therefore ignored by the brain. If, during the first 7-8 years of life, an eye is not “used” by the brain, the neural connection between the eye and the brain will not develop correctly, leading to a “lazy” eye, also known as amblyopic. Amblyopia can happen for two main reasons: because an eye is deviated (strabismic amblyopia) or because an eye has a clear image and the other does not (refractive amblyopia)
  • Ophthalmoparesis is weakness or paralysis of one or more extraocular muscles
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Medial Rectus

The medial rectus muscle inserts at the anterior (front) and medial (toward the nose side) portion of the eye. The muscle’s origin is behind the eye on the common ring tendon. The primary function of the medial rectus muscle is to adduct (move inside or toward the nose) the eye, and it has no secondary function.

Superior Oblique

The superior oblique muscle possesses unique characteristics. It inserts on the superior, lateral (ear- side), and posterior (back) of the eye. The anatomical origin is behind the eye on the lesser wing of the sphenoid bone, but the superior oblique muscle acts like a pully and loops back through a connective tissue sling called the trochlea. Even though the superior oblique muscle is positioned above the eye, its unique use of the trochlea gives it a primary function to intort the eye, with secondary functions of depression and abduction.

Inferior Oblique

The inferior oblique muscle is also unique and inserts on the inferior, posterior, and lateral portions of the eye. Its origin is on the medial (middle) maxillary bone. The primary function of the inferior oblique muscle is extorsion, and the secondary functions are elevation and abduction.

Inferior Rectus

The inferior rectus inserts at the anterior (front) portion of the eye, and its origin is behind the eye on the common ring tendon. Its primary function is to depress the eye, and it has a mild secondary function of adduction and extorsion.

Superior Rectus

The superior rectus muscle inserts at the anterior (front) portion of the eye. The muscles’s origin is located behind the eye on the common ring tendon. The primary function of the superior rectus muscle is to elevate the eye. It has a mild secondary function of adduction and intorsion.

Lateral Rectus

The lateral rectus muscle inserts at the anterior (front) and lateral (toward the temporal side) portion of the eye. The muscle’s origin is behind the eye on the greater wing of the sphenoid bone and the common ring tendon. The primary function of the lateral rectus muscle is to abduct (move outside) the eye, and it has no secondary function.