Torsion means rotation about line of sight,torsion is directly related to the rotation of image dat v perceive of the surounding level
Laws of ocular motility 2
OCULAR MOTILITY LAWS
Sherrington’s law, Before stating all these law it is
necessary to define positions of the eye.
PRIMARY – Primary position assumed by the eye when one
is looking straight ahead with body and head erect.
SECONDARY- Adducted, Abducted, elevated or depressed
position of the globe termed as secondary .
TERTIARY- The oblique positions of the eye are termed as
Donder’s law :
During fixation, saccades and smooth pursuit the eye rotates
freely in horizontal and vertical dimensions but torsion is
constrained. This restriction on ocular torsion is described by
donder’s law and listing’s law.
Donder’s law : donders described this theory, by stating that
each position of line of sight belongs to the definite
orientation of vertical and horizontal retinal meridian relative
to the coordinate of the space.
Orientation is always same irrespective where the eye comes
from and depends upon the amount of elevation or
depression and lateral rotation of the globe.
The orientation of retinal meridian pertaining to the
particular position of the globe is achieved irrespective of
the path the eye has taken to reach that position, after
returning to the initial position the retinal meridian is
oriented exactly as it was before the movement was
initiated, this is known as , Donder’s Law.
Listing ‘s law states that each movement of the eye from
the primary position to any other position involves a
rotation around a single axis lying in the equatorial plane
,also called as listing’s plane.
This plane was defined earlier as being fixed in the orbit
and passing center of rotation of the eye and its equator,
when the eye is primary position
Any position of the eye can described by specifying the
orientation of the axis of rotation in listing’s plane and
magnitude of rotation from primary position
Listing’s law implies that all eye movements from primary
position are true to the meridians and occurs without torsion
with respect to the primary position.
This law is obviously true for movements around horizontal
and vertical axes in the equatorial plane.
Listing’s law holds during fixation, saccades, smooth pursuit
but not during sleep .
Agonist,Antagonist,synergists and yoke
Agonist muscles : muscle that cause specific eye
Antagonist muscles : a movements in the direction
opposite produced by agonist is caused by its
Synergists muscles :Two muscles moving an eye
in the same direction are synergists.
Yoke muscles :Muscles that cause the two eyes
move in same direction are known as yoke muscles
Isolated innervations to an extraocular muscle of the eye do
not occur nor can the muscles from the one eye alone
innervated , to perform an eye movements impulses are always
Whenever an impulse for the performance of eye movements
sent out, corresponding muscles of each eye receives equal
innervations to contract or relax, this the basic law of equal
innervations proposed by Hering.
E.g during levoversion the right medial rectus and left lateral
rectus receives equal and simultaneous flow of innervations.
similarly during convergence right and left medial rectus
muscles receives equal and simultaneous flow of innervations.
When the head is tilted to the left,the muscles
group controlling excycloduction of the right eye
and incycloduction of left eye receive equal and
simultaneous flow of innervations
Sherrington’s law of reciprocal innervation
This law states that during ocular motility an increased flow
of innervation to the contracting agonist muscle is
accompanied by a decreased flow of innervation to the
relaxing antagonist muscle.
During levoversion,an increased innervational flow to the
right medial rectus and left lateral rectus, accompanied by
decreased flow of innervation to right lateral rectus and left
But in certain pathological condition ,co-contraction of
antagonistic muscles instead of relaxation antagonist muscle
occurs. For e.g Duane’s retraction syndrome, limits the
amount of movement achievable