Laws of ocular motility 2

laws of ocular motility

1. FUNDAMENTAL OCULAR MOTILITY LAWS

2. OCULAR MOTILITY LAWS Donder’s law Listing’s law Hering’s law 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 tertiary position.

3. 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.

4. \ 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.

5. LISTING’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

6. 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 .

7. Agonist,Antagonist,synergists and yoke muscles Agonist muscles : muscle that cause specific eye movements. Antagonist muscles : a movements in the direction opposite produced by agonist is caused by its antagonists. 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

8. HERING’S LAW 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 integrated. 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.

9. 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

10. Clinical application of Herings’law

11. 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 medial rectus 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

12. Clinical application of Sherrington's law