Listing's Law Flashcards
Whomst was Listing?
A german mathematician (1808 to 1882)– created laws of ocular rotations based on geometrical aesthetics
Who was Ruete?
Ophthalmologist that first mentioned Listing’s Law in his textbook on ophthalmology
Who was Helmholtz?
He verified Listing’s Law using careful measurements of afterimages
What is Listing’s plane?
A plane that passes through the equator of the globe, perpendicular to the fixation line/line of sight in the primary position
What is the ocular equator?
A circumference of the eye specifying the locus of points equidistant from the anterior and posterior poles of the globe
What is false torsion?
The mismatch between the visual and spatial axes aka eye coordinates and space coordinates (perceived as tilt that gets worse farther from the center)
What is the implication of tilt on Donders?
The amount of tilt in a tertiary position depends on the eccentricity of the position
What happens when the brain does not adjust for false torsion?
Vertigo; congenital or degenerative
Why does false torsion occur?
Because rotation occurs along a curved path aka space is curved– points can not be projected onto a flat grid
Why do we care about false torsion?
Our brain can make mistakes, we can’t use lines to determine the torsional position of the eye; we need a coordinated system for a common frame of reference
What are the planes in an upright posture?
median plane is vertical and transverse plane is horizontal
What are eye-fixed coordinates?
L/R around vertical is yaw
U/D around horizontal is pitch
CW/CCW around visual axis is roll
*eye fixed systems are defined by the order of their rotations
Describe Fick’s Axes
Axes that specify eye positions in terms of rotation around x, y, and z axis
Which of Fick’s axes is fixed in the skull?
The vertical axis Z
Which axes are reversed in FIck’s?
Y and Z
What Fick’s axis is abduction and adduction around? (first rotation)
Z axis aka L and R
What Fick’s axis is torsion and rotation around?
Y axis (visual axis) aka CW and CCW
What Fick’s axis is elevation and depression around?
X axis aka transverse axis
True or False: Fick and Helmholtz use the same axes?
True
Which of Helmholtz’s axes is assumed to be fixed in the skill?
X (horizontal)
What is the first rotation for Helmholtz?
X axis aka elevation and depression
What is Listing’s law?
The eye assumes only those orientations that can be reached by a single rotation around an axis in Listing’s Plane
What is Listing’s plane perpendicular to?
The line of sight
True or False: Listing’s Law implies Donder’s Law
True (for any one gaze orientation there is only one unique eye orientation)
What is the equation for Listing’s Law
T=-HV/2
T=torsional angle of rotation in radians
H=horizontal angle of rotation in radians
V=vertical angle of rotation in radians
What Listing/Helmholtz coordinates are positive?
Up, right, clockwise – from the Subject’s point of view
What does the formula of Listing’s Law calculate?
It quantifies the torsional angle for each gaze direction– torsion that differs from the calculation is said to violate Listing’s Law
What is Listing’s Half-Angle Rule? And when do you use it?
Plane is tilted in the same direction as the line of sight by HALF AS MUCH; Used when the eye doesn’t start in primary position
What is another name for Listing’s Plane (like when not in primary gaze)?
The velocity plane
What is the half-angle rule in words?
For any position other than PRIMARY position, the corresponding velocity plane is rotated half as far as the line of sight
When does Listing’s Law not apply?
Binocularly or not looking at optical infinity
What is the binocular extension of Listing’s Law?
When converged, velocity plane is rotated TEMPORALLY roughly 1/4 of the vergence angle
When is Listing’s Law not obeyed?
During VOR aka head movement and during sleep
What eye position strategy is used for VOR?
Half Listing’s Law which is not the 1/2 angle rule; it is a compromise between optimal retinal image stabilization and max motor efficiency (compliance with Listing’s)
Half Listing’s Law for VOR
During head rotation, velocity plane tilts in the same direction, but only 1/4 to 1/3 as much as the gaze line; L/R head roll gives counter-roll with gain of approx. 0.7
What is involved in obeying Listing’s Law?
Neural commands, muscles, superior colliculus and cerebellum
What two parts make up recti muscles?
global and orbital parts
Where is the functional origin of the individual EOM?
It’s muscle pulley
Which EOM does not have a pulley?
Superior oblique
True or False: Orbital and global parts of the muscle separate at the end as we age?
True
How do muscle pulleys work in general?
Contraction of the orbital layer can occur at any location, creates a pulley that directs the muscle path, the global layer contracts effectively from this point, force is redirected such that Listing’s is obeyed
What happens if the pulley is equally as far from the center or the eye as the insertion is?
The pulley results in a alpha/2 change in vector force
What happens if contraction is farther distance from center than the center is to the insertion?
The pulley results in alpha/3.5 change in vector force
Why bother maintaining Listing’s Law during rotation?
Optimization of visual information processing aka perceptual ability is easiest when Listing’s Law
Why do different systems implement Listing’s Law differently?
Optimization strategy for motor efficiency aka easy job for muscles moving the eye around
What is VOR?
balance between motor efficiency and image stabilization, giving stabilization at small portion– the fovea (not the entire retina)
Why is the binocular extension of Listing’s helpful?
It’s a compromise strategy between motor efficiency and stereoscopic search– instead of searching the entire retina, brain searches small zones for matching features making stereo matching more efficient
Is Listing’s Law adaptive?
Yes, readily adjusts to new conditions// demonstrated with changing vergence demand– may minimize cyclodisparity which simplifies neural processing
What group of patients demonstrate that Listing’s is adaptive?
Paralytic strabismus patients
What are the three groups of unilateral CN VI palsy?
acute peripheral from presumed ischemic lesion, chronic peripheral palsy from ischemic lesion, and central fascicular lesion from injury to brainstem
What happened with the acute peripheral palsy patient?
listing’s law was violated in paretic eye– new injury and lack of O2
What happened with the chronic peripheral palsy patient?
Both paretic and non-paretic eyes obeyed Listing’s law even tho LR was weak– this shows that neural circuitry of listings law is adaptive with enough time– probably by adjusting innervations to the remaining EOM
What happened with the central fascicular palsy patient?
demonstrated abnormal ocular torsion (Listings violated) in both eyes– suggests neural adaptive mechanism cannot adapt to certain brainstem lesions
What’s the old, unsupported hypothesis of ocular motor control?
Pre-motor neurons encode 3D angular velocity which is then transformed into a 3D eye position signal by a neural integrator via nonlinear computations AKA there are detailed instructions to follow
What is the alternative hypothesis for ocular motor control?
Kinematically-appropriate eye movements could be generated from the ocular motor plant itself, with mobile pulleys that shift with gaze direction, pre-motor neurons could encode eye orientation rather than angular velocity aka laisez faire just get there
Is the alternative hypothesis supported by a computer model?
Yes, it works for saccades but not VOR
