The Laws

Question 1

What is Sherrington’s Law?

Answer 1

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

Question 2

How many eyes does Sherrington’s Law affect?

Answer 2

one eye

Question 3

Name the antagonistic EOM pairs:

Answer 3

lateral and medial rectus; superior and inferior rectus; superior and inferior oblique

Question 4

What is Hering’s Law?

Answer 4

The synergistic EOMs receive equal and simultaneous innervation; contract of one occurs with equal and simultaneous contraction of the contralateral agonist

Question 5

How many eyes does Hering’s law involved?

Answer 5

two eyes

Question 6

What are the EOM agonist/yoked muscles?

Answer 6

RIO=LSR
RSR=LIO
RLR=LMR
RIR=LSO
RSO=LIR
RMR=LLR

Question 7

Which is more likely: overaction or underaction?

Answer 7

Underaction- more likely for a muscle to be too weak

Question 8

What are some possible reasons for diplopia?

Answer 8

EOMs, nerves, neuromuscular junction, brain

Question 9

What is the forced duction test and what is it testing?

Answer 9

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

Question 10

The eyes are ___ moving

Answer 10

constantly

Question 11

Does it matter which way we go first for ductions and versions?

Answer 11

No, this is translational movement in two directions and it is commutative, can go either way

Question 12

Does it matter which way we go first with 3D rotation?

Answer 12

Yes, 3D motion is not commutative, objects attain a new orientation relative to the previous one

Question 13

What are Fick’s Axes

Answer 13

X: horizontal aka pitch
Y: line of sight aka roll
Z: vertical aka yaw

Question 14

How are clinical axes different than Ficks?

Answer 14

Y and Z are switched aka Z is line of sight

Question 15

What is translation?

Answer 15

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

Question 16

What is rotation?

Answer 16

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

Question 17

Who made the first mechanical model of the eye and its muscles?

Answer 17

Ruete

Question 18

What did Ruete and Donders find in 1840?

Answer 18

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

Question 19

What is Donder’s law?

Answer 19

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

Question 20

What does Donder’s law not mean?

Answer 20

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