Differences Between Clinically-Relevant Eye Movements and Anatomical Functions of Eye Muscles

Introduction

Confusion exists between the cardinal positions of gaze and the anatomical functions of eye muscles.
A previous video discussed eye movements and cranial nerves, which may have contributed to this confusion.

Cardinal positions of gaze are specific directions in which a person is asked to look to test various eye muscles.
Key Points:
- They do not correspond directly to the anatomical actions of the eye muscles.
- Exception: Horizontal rectus muscles align with their anatomical function.

Superior Oblique:
- Primary Action: In torsion
- Secondary Action: Depression
- Tertiary Action: Abduction
- Resulting Movement: Down and out
Inferior Oblique:
- Primary Action: Extortion
- Secondary Action: Elevation
- Tertiary Action: Abduction
- Resulting Movement: Up and out
Inferior Rectus:
- Primary Action: Depression
- Secondary Action: Extortion
- Tertiary Action: Adduction
- Resulting Movement: Down and in
Superior Rectus:
- Primary Action: Elevation
- Secondary Action: In torsion
- Tertiary Action: Adduction
- Resulting Movement: Up and in

To isolate and test eye muscles, change the visual access.
Diagnostic Gaze Positions:
- Oblique Muscles:
  - Move toward the side to deduce the muscle action (e.g., looking medially tests superior oblique).
- Recti Muscles:
  - Move laterally to deduce their action (e.g., looking laterally tests medial/lateral rectus).

Example: Weakness of the Superior Oblique Muscle
- Affected individuals struggle to look down and in, such as toward the tip of their nose.
- They may tilt their head to the opposite side of the affected muscle to minimize the impact of the weakness (known as ocular torticollis).

Understanding the difference between clinical testing and anatomical actions is crucial for accurate diagnosis and treatment of eye muscle issues.