Ductions, Versions, and Vergences Flashcards
What are ductions
The movements of ONE eye
Ductions can be explained by
Rotations around one or more axes
Fick’s axes (3)
X axis (horizontal, transverse)
- Divides eye into anterior and posterior halves
- Supraductions and infraductions
Y axis (sagittal, visual)
- Divides eye into medial and lateral parts
- Incycloduction (intorsion) and excycloduction (extorsion)
Z axis (vertical) -Adduction and abduction
If the course of the muscle is parallel to an axis…
Then no rotation around that axis can occur
If the course of the muscle is perpendicular to an axis…
Then the only rotation for that muscle is around that axis
Actions from primary gaze of the medial rectus
Perpendicular to the Z/vertical axis. So it is able to adduct the eye.
Actions from primary gaze of the lateral rectus
Perpendicular to the Z/vertical axis. So it is able to abduct the eye.
Actions from the primary gaze of the superior rectus
- Supraduct
- intortion
- adduction
Actions from the primary gaze of the inferior rectus
- Infraduct
- extortion
- adduction
Actions from the primary gaze of the superior oblique
- Intorsion
- Infraduct
- abduction
Actions from the primary gaze of the inferior oblique
- Extortion
- Supraduct
- abduction
Cardinal position of gaze
6 Positions of gaze isolates each EOM
Clinically useful to determine if each EOM is functioning properly.
If exactly 23 degrees from the primary position,
The superior and inferior rectus are perpendicular to the horizontal axis and will supra duct (SR) and infra duct (IR) the eye
If exactly 51-55 degrees from primary position
The superior oblique will infraduct and the inferior oblique will supraduct
Agonist/antagonist pairs
Lateral rectus/medial rectus
superior rectus/inferior rectus
superior oblique/inferior oblique
When an agonist contracts (Stimulated), its antagonist
relaxes (inhibited)
Synergist
A muscle that works in concert with another muscle to generate movement.
Versions
Movement of both eyes in the same direction
Dextroversion
Both eyes move to the right
Dextroelevation
Both eyes move up and to the right
Dextrodepression
both eyes move down and to the right
Levoversion
Both eyes move to the right
Levoelevation
Both eyes move up and to the left
Levodepression
Both eyes move down and to the left
Elevation
Both eyes move up
Depression
Both eyes move down
Hering’s law of equal innervation
Pair of muscles receives equal and simultaneous excitatory or inhibitory signals (versions)
Vergences
Movement of both eyes in opposite directions
What occurs during convergence
Each eye is adducted to fixate at near target
What occurs during divergence
Each eye is abducted to fixate at distance target
