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Related Concept Videos

Muscles of the Eye01:20

Muscles of the Eye

The muscles of the eye are sophisticated structures that control eye movement and focus, allowing for the precise and rapid adjustments necessary for vision. The human eye is controlled by ten muscles — six extraocular muscles, three intraocular muscles, and one primary eyelid retractor muscle.
Extraocular Muscles
The six extraocular muscles surround the eyeball and control its movements. They are responsible for a wide range of eye motions, including looking up, down, left, right, and rotating...
Accessory Structures of the Eye01:17

Accessory Structures of the Eye

Optical perception, or vision, is an extraordinary sense dependent on converting light signals received via the ocular organs. These organs, known as eyes, are securely positioned within the bony cavities of the skull, called orbits. The orbits serve a dual purpose: a protective shield for the ocular globes and a stable attachment point for the soft ocular tissues. The eye's external protective mechanisms include the eyelids, which are edged with lashes that act as a barrier against foreign...
Fascicle Arrangement in Skeletal Muscles01:25

Fascicle Arrangement in Skeletal Muscles

Fascicles are bundles of muscle fibers in a skeletal muscle. Muscle fascicle arrangement is directly associated with the power and range of motion of various muscles. The configuration of these fascicles can vary, leading to different functional outcomes.
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Muscles for Facial Expressions01:14

Muscles for Facial Expressions

The craniofacial muscles are a collection of approximately 20 thin skeletal muscles situated beneath the skin of the face and scalp. These muscles, primarily responsible for the vast array of human facial expressions, originate from the bones or fibrous structures of the skull and extend outwards to connect with the skin. While most skeletal muscles in the body are enveloped in thick fascia, facial muscles generally have a more delicate fascial covering, with the buccinator muscle being a...
Cranial Nerves: Types Part I01:14

Cranial Nerves: Types Part I

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Muscle Coordination and Action

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Agonists
Agonist muscles, often called prime movers, are the primary muscles responsible for producing a specific movement.

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Related Experiment Video

Updated: Jun 6, 2026

Assessing Binocular Central Visual Field and Binocular Eye Movements in a Dichoptic Viewing Condition
07:45

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Published on: July 21, 2020

Incomitant strabismus: does extraocular muscle form denote function?

Burton J Kushner1

  • 1Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, 53705, USA. bkushner@wisc.edu

Archives of Ophthalmology (Chicago, Ill. : 1960)
|December 15, 2010
PubMed
Summary
This summary is machine-generated.

Extraocular muscle overaction or underaction may not stem from anatomical changes. Altered neural input or fiber type shifts in normal-sized muscles can explain clinical observations in strabismus.

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Area of Science:

  • Ophthalmology
  • Neuroscience
  • Muscle Physiology

Background:

  • Traditional understanding links extraocular muscle (EOM) dysfunction to atrophy/hypoplasia (underacting) or enlargement (overacting).
  • Clinical observations, including "overacting" inferior obliques and normal EOM diameters in superior oblique palsy, challenge this paradigm.
  • Existing models fail to consistently explain diverse EOM behaviors observed in clinical practice.

Purpose of the Study:

  • To reconcile inconsistencies between EOM size and function observed in clinical practice.
  • To propose alternative mechanisms for EOM contractile activity beyond anatomical changes.
  • To investigate the role of neural input and muscle remodeling in EOM dysfunction.

Main Methods:

  • Review of clinical observations and existing literature on EOM function and structure.
  • Theoretical analysis of neural input modulation and muscle fiber type shifts.
  • Exploration of vergence adaptation as a potential mechanism for EOM remodeling.

Main Results:

  • Identified discrepancies between EOM size and observed clinical function (e.g., overacting muscles with normal diameters).
  • Proposed that altered neural input to anatomically normal EOMs can cause apparent under- or overaction.
  • Suggested that shifts in muscle fiber type and distribution within normal-sized EOMs can alter contractile activity.

Conclusions:

  • EOM contractile activity is not solely determined by muscle size or anatomical pathology.
  • Changes in neural stimulation and muscle remodeling (fiber type shifts) are plausible explanations for observed EOM dysfunction.
  • These revised concepts can reconcile previously inconsistent clinical findings in ophthalmology.