VF - Eye Movements 2 - Mechanics - Week 5

Question 1

Define Donder’s law.

Answer 1

Torsional positions of an eye is determined by horizontal and vertical eye positions. They arent free to have any torsional position.

Question 2

Define Listing’s law.

Answer 2

Any eye position can be reached from primary position by a single rotation of the eye around an axis lying in a plane perpendicular to the visual axis when in primary position. This plane is called Listing’s plane.

Question 3

Define the basis for pulleys in the eye.

Answer 3

The EOMs are separable into orbital and global layers.

Orbital layers insert onto the connective tissue structures.

Question 4

Why do pulleys matter, and what do they do?

Answer 4

They change the functional origins of the EOMs.
Without them, muscle bellies would change and be at an angle to a given eye meridian, thus changing how it moves the eye.
Pulleys prevent this, and allow uniform eye movement.
They constrain the muscles, and reduce the degrees of freedom of motion in the EOMs.

Question 5

Describe what the orbital and global layers of EOMs do.

Answer 5

Orbital - position the pulleys.

Global layer - moves the eye.

Question 6

Do orbital and global layers differ histologically?

Answer 6

Yes.

Question 7

Is Listing’s law violated? Explain why.

Answer 7

Vestibular responses violate Listing’s Law at least some of the time. The need to accommodate all possible head postures leads to this. There may still be some constraints, however, as head tilt has been shown to induce pulley assembly counterrotation.

Question 8

Link Listing’s law to refractive correction. How can this be avoided?

Answer 8

Correcting an astigmatic eye at tertiary gaze. The eye rotates on an axis, but the eyeglasses remain stationary.
Bi-aspheric lens may be a solution.