The Laws Flashcards
What is Sherrington’s Law?
The law of reciprocal innervation– when a muscle contracts, its direct antagonist relaxes to an equal extent; allows for smooth movement; neural excitation=neural inhibition
How many eyes does Sherrington’s Law affect?
one eye
Name the antagonistic EOM pairs:
lateral and medial rectus; superior and inferior rectus; superior and inferior oblique
What is Hering’s Law?
The synergistic EOMs receive equal and simultaneous innervation; contract of one occurs with equal and simultaneous contraction of the contralateral agonist
How many eyes does Hering’s law involved?
two eyes
What are the EOM agonist/yoked muscles?
RIO=LSR RSR=LIO RLR=LMR RIR=LSO RSO=LIR RMR=LLR
Which is more likely: overaction or underaction?
Underaction- more likely for a muscle to be too weak
What are some possible reasons for diplopia?
EOMs, nerves, neuromuscular junction, brain
What is the forced duction test and what is it testing?
This tests muscle movement/restriction; a positive test is if the eye resists moving upon the pressure of forceps; a negative test is when the eye can move with forceps, most likely a problem with the nerve or junction
The eyes are ___ moving
constantly
Does it matter which way we go first for ductions and versions?
No, this is translational movement in two directions and it is commutative, can go either way
Does it matter which way we go first with 3D rotation?
Yes, 3D motion is not commutative, objects attain a new orientation relative to the previous one
What are Fick’s Axes
X: horizontal aka pitch
Y: line of sight aka roll
Z: vertical aka yaw
How are clinical axes different than Ficks?
Y and Z are switched aka Z is line of sight
What is translation?
Movement in 3 dimensions; end position can be described by 3 Cartesian coordinates, the center of the eye is the reference; translation is flat movement in Euclidean space; a single translation never results in returning to the original position
What is rotation?
Movement in 3D; end position can NOT be described by 3 coordinates, space is curved; you will eventually make it back to the orientation in which you began
Who made the first mechanical model of the eye and its muscles?
Ruete
What did Ruete and Donders find in 1840?
They studied the movement of eyes by tracking a red cross and mapping the green afterimage; away from the center, the after image did not match the grid because the eye rotates in curved space
What is Donder’s law?
The torsional position of the eye “12 o’clock position” is always the same for a given direction of gaze regardless of how the eye got there; the same rotation each time
What does Donder’s law not mean?
It does not mean the eye always has the same 12 o’clock position; it does not say what the resultant torsional angle is for an eye movement, just that its always the same one
