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Ocular Motility > Listing's Law > Flashcards

Listing's Law Flashcards

1
Q

Who was the ophthalmologist who first mentioned Listing’s Law in a textbook?

Who verified the law using careful measurements and afterimages?

A

Ruete

Helmholtz

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2
Q

Did Listing bae the law purely on geometrical aesthetic without formal measurements?

A

Yes. Later verified by Helmholtz.

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3
Q

Listing’s plane

A

Equator. Separates anterior and posterior halves.

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4
Q

What is false torsion

A

A phenomenon of mismatch of curved space and a flat plane. (between the visual and spatial axes)

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5
Q

When can false torsion get worse?

A

When you aren’t grounded by gravity. Ex: on an airplane.

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6
Q

“Eye’s point of view”

A

The literal line of stimulated photoreceptors on the retina.

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7
Q

Donder’s

A

The farther away from primary gaze (eccentricity), the more tilt will be seen.

In other words, the amount of tilt in a tertiary position depends on the eccentricity of the position.

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8
Q

Eccentricity

A

How far away your eyes are from primary gaze.

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9
Q

We are normally pretty good at compensating for the mismatch. Our brains learn this as a part of normal development as long as there is normal visual experience. When can it mess up?

A

Insults during development (drugs, birth injuries, genetic disorders)
Degenerative conditions (various disease processes or tumors)
-Acquired or traumatic brain injury

^^ To fix, VT or neurorehab.

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10
Q

Which axises are assumed to be fixed in the skull?

A

Vertical (Z) and horizontal (X)

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11
Q

Big picture.
Danders law told us what?
Listings law told us what?

How does listings law implies donders law?

A

Donders told us there was ONE orientation at 12 o clock.
Listings told us what the orientation actually is

For any gaze orientation, there is only one unique eye orientation.

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12
Q

Listings law in Helmholtz coordinates formula

A

T = -HV/2

T= torsional angle of rotation in radians
H= horizontal angle of rotation in radians
V= vertical angle of ration in radians

**Must convert values to radians if given in degrees to plug into the formula.
Once you find the value of T in radians, convert back to degrees. If it is positive, then it tells you CW. If negative, CCW.

Positive is defined as clockwise, right, and up from the SUBJECTS point of view.

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13
Q

Positive is defined as what? From who’s perspective?

A

Positive is defined as clockwise, right, and up from the SUBJECTS point of view.

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14
Q

How to convert from radians to degrees

A

180 degrees= pi radian

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15
Q

By definition, listings law talks about (1 or 2) eye(s) in which gaze?

A

Talks about a single eye in primary gaze.

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16
Q

If eye does not start in primary gaze, the plane is considered the ____ plane

A

Velocity plane.

Listings plane is one specific velocity plane.

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17
Q

For any eye position, there is an associated velocity plane. What is the velocity plane called in primary gaze?

A

Called listings plane. Listings plane is a specific velocity plane.
Orthogonal to the line of sight

18
Q

The orientation of the velocity plane depends on what/?

A

The initial eye position.

19
Q

If the eye starts at any point other than primary gaze, how do you determine where the velocity plane is?

A

The velocity plane is rotated in the same direction as gaze by 1/2 alpha where alpha = the angle away from primary gaze at which you began.

in other words

The corresponding velocity plane for any eye position other than primary gaze is rotated half as far as the line of sight. This is the half angle rule.

20
Q

Listings half angle rule (saccades and smooth pursuit)e

A

The corresponding velocity plane for any eye position other than primary gaze is rotated half as far as the line of sight in the same direction. This is the half angle rule.

Velocity plane= (1/2)(alpha)

21
Q

When converged, the velocity plane is rotated ____

A

Temporally. Roughly 1/4 of the vergence angle.

22
Q

What is the binocular extension of listings law (vergence) ?

A

During convergence, the orientation of each eye is determined by rotation about axes that lie in a plane. This plane is rotated temporally and symmetrically in each eye and a quarter as much as the vergence angle

(1/4)(alpha)

23
Q

Both eyes open? and eyes converge? Which way will the plane rotate?

A

The plane with diverge.

24
Q

Listings law is not constant. When is listings law obeyed?

A

It is obeyed when the patient is not moving such as during fixations, saccades, and pursuits. Head is fixed.

Listings law is violated during VOR (head movement) and sleep.

25
Q

What is half-listings law?

A

A strategy used for VOR. Compromise between optimal retinal image stabilization and max motor efficiency (compliance with listing’s).

26
Q

IDEAL VOR requires rotation around the head’s axis, independent of gaze direction. Stabilities ENTIRE retinal image. Actual measurements show this doesn’t happen. Why?

A

This is when the head is moving.

Eyes rotate 70-75% accuracy compared to head movements.

During head movements, velocity plane tilts in the same direction, but only 1/4 to 1/3 as much as the gaze line. This is where we get the 75% value.

Ex: Left to right head roll gives counter-roll with gain of approx 70%.

27
Q

VOR

A

Vestibulo-ocular reflex.

28
Q

Which 4 things work together to create the rotational positions taken by our eyes?

A

Neural commands driving fixation, saccades, and pursuits constrain the eye to obey listing’s law.

Muscles may be arraigned in such a way as to simplify the brain’s work.

The superior colliculus and cerebellum are both involved.

29
Q

All EOMs except the ___ has a pulley. What does it have instead?

A

All EOM’s except the SO have a pulley. The SO has the trochlea instead, which does the same job. Doesn’t need another one.

30
Q

The FUNCTIONAL origin of the individual EOM is at it’s:

A

Pulley

31
Q

Hypothesis:

Contraction of the orbital layer of recti muscles can occur where?

A

At any location. This creates a pulley that directs the muscle path, causing the global layer to contract from this point.

32
Q

What is the effect of having a pulley if the pulley is equally distant away from the center as the insertion is from the center?

A

You get a change in muscle axis that is half the eye’s motion.

33
Q

What is the effect of having a pulley that is further away from the center than the insertion is away from the center?

A

The angle of change will be smaller. Basically, if closer the pulley sits to the center of rotation than the insertion, the angle of change will be larger.

34
Q

What are the main 2 functional significances of maintaining listings law?

A
  1. Optimization of visual information processing (VIP). Your perceptual ability is easiest when listing’s law is obeyed. Brain doesn’t have to think as hard. allowed for optimization of image flow across the retina, simplifying neural processing of visual info. If listings law is violated, the image flow gets very off everything you move eyes. Neurologically difficult to process.
  2. Optimization strategy for motor efficiency. Allows muscles to have the easiest possible job moving the eye around. All gaze shifts toward and away from primary gaze are made along the shortest curved path possible through space. This is true. This can reduce muscle workload and keep eyes closer to primary gaze, slowing quick responses.
35
Q

Who came up with the idea that the significance of listing’s law was to optimize VIP? What is the problem with this idea?

A

Hering. He thought that Listing’s allowed for optimization of image flow across the retina, simplifying neural processing of visual info. If listings law is violated, the image flow gets very off everything you move eyes. Neurologically difficult to process.

Problem. Only eye rotation relative to the head follows listings. Head movement makes eye rotation violate listings, making the neurological processing very complex.

36
Q

Who came up with the idea that the significance of listing’s law was to optimize the strategy for motor efficiency?

A

Fick and Wundt. They believed listings enhanced motor efficiency by minimizing rotational eccentricity.

All gaze shifts toward and away from primary gaze are made along the shortest curved path possible through space. This is true. This can reduce muscle workload and keep eyes closer to primary gaze, slowing quick responses.

37
Q

What is the idea that balanced motor efficiency and image stabilization?

A

VOR. Giving stabilization at a small portion- the fovea- not the entire retina would allow for both. This is true. We do not stabilize the image across the entire retina EVER.

38
Q

Binocular extension of listings.

A

A compromised strategy between motor efficiency and stereoscopic search. Instead of searching the entire retina, brain searches small zones for matching features. This is more efficient for brain.

Much easier time conceptually understanding what is in your environment.
Brain does not search every pixel or point, but rather looks for matching features, then locks in.

39
Q

Is listings law adaptive?

A

YES. It can change over time.

Demonstrated with changing vergence demand as you are converging and diverging all the time. Pretty big change of where images fall on retina.

May minimize cyclodisparity- simplifies neural processing. Listings law makes it possible to accept small amounts of cyclodisparity and still fuse the images.

40
Q

What did studying patients with paralytic strabismus demonstrate about listings law?

A

Acute (recent) peripheral palsy caused by damage to CN 6: Listings law violated in damaged eye.

Chronic peripheral palsy caused by damage to CN 6: Both damaged and non damaged eye obeyed listings law. Suggests that the neural circuitry underlying listings law is adaptive, probably by adjusting the innervations to the remaining EOM.

Palsy caused by brain stem lesion: Abnormal ocular torsion in both eyes, regardless of duration or severity of the palsy. Suggests that neural adaptive mechanisms underlying listings law cannot adapt after certain brainstem lesions.

41
Q

2 hypotheses about neural control?

A

Older, not supported: Pre motor neurons encode 3D angular velocity. Like mom (brain) telling 16 year old (eye) where to turn, how to steer, where to end up, how hard to push on the pedal.

Supported: Kinematically appropriate eye movements could be generated from the ocular motor plant itself. Pre motor neurons encode eye orientation, rather than angular velocity. Computer model proves this for saccades (head still) but not VOR (head moving) yet.
Ex: Mom telling kid where they need to end up and letting the kid figure it out- telling them to take the fastest route possible.

Ocular Motility (8 decks)

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