Motor physiology of the eye

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Information about Motor physiology of the eye

Published on June 16, 2016

Author: DrTukezbanHuseynova

Source: slideshare.net

1. Motor physiology of extraocular muscles. Tukezban Huseynova, MD Specialist in Strabismus and Refractive Cornea, Briz-L Eye Clinic, Baku, Azerbaijan Tukezban@gmail.com

2. Introduction  A common coordinate system for translation and rotation of the eye.

3. Basic Kinematics

4. Center of Rotation In primary position the center of rotation is located about13.5 mm (in myopes, 14.5 mm) behind the apex of the cornea on the line of sight, which places it 1.3 mm behind the equatorial plane.

5. Definitions of Terms and Action of Individual Muscles Cardinal movements of the eye. Duction movements - The rotations of the single eye are termed. Adduction - Rotations around the vertical axis (horizontal excursions of the globe), movement nasalward . Abduction - Rotations around the vertical axis, movement templeward. Elevation or sursumduction - Rotations around the horizontal axis (vertical excursions of the globe), movement upward. Depression or deorsumduction - Rotations around the horizontal axis movement downward.

6. Definitions of Terms and Action of Individual Muscles  Ductions. Secondary positions, right eye. A, Adduction. B, Abduction. C, Sursumduction (elevation). D, Deorsumduction (depression).

7. Definitions of Terms and Action of Individual Muscles Cycloductions - Rotations around the anteroposterior axis of the globe, known as, rotate the upper pole of the cornea templeward (excycloduction) or nasalward (incycloduction). Ductions. Secondary positions, right eye. A, Adduction. B, Abduction. C, Sursumduction (elevation). D, Deorsumduction (depression).

8. Definitions of Terms and Action of Individual Muscles Positions of the globe Primary position is assumed by the eye when one is lookin straight ahead with body and head erect. Secondary positions is the adducted, abducted, elevated, or depressed positions of the globe. Tertiary positions is the oblique positions of the eye.

9. Definitions of Terms and Action of Individual Muscles  Some tertiary positions, right eye. A, Gaze up and right. B, Gaze up and left. C, Gazedown and right. D, Gaze down and left.

10. Definitions of Terms and Action of Individual Muscles Terms related to the mechanism of muscles. Tangential point is a point at which the center of the muscle or of its tendon first touches the globe. The arc of contact is the arc formed between the tangential point and the center of the insertion of the muscle on the sclera. The muscle plane is determined by the tangent to the globe at the tangential point and the center of rotation.

11. Definitions of Terms and Action of Individual Muscles  Schematic presentation of muscle plane, medial rectus, axis of rotation, tangential point, and arc of contact.

12. Definitions of Terms and Action of Individual Muscles Muscle Primary Secondary Tertiary Medial rectus Adduction — — Lateral rectus Abduction — — Inferior rectus Depression Excycloduction Adduction Superior rectus Elevation Incycloduction Adduction Inferior oblique Excycloduction Elevation Abduction Superior oblique Incycloduction Depression Abduction Action of the Extraocular Muscles from the Primary Position.

13. The Fundamental Laws of Ocular Motility.

14. Donder’s Law Donders34 expressed this theory in 1848 by stating that to each position of the line of sight belongs a definite orientation of the horizontal and vertical retinal meridians relative to the coordinates of space.

15. Listing’s Law.  Listing suggested 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 Listing’s plane.  Listing’s law implies that all eye movements from the primary position are true to the meridians and occur without ‘‘torsion’’ or cyclorotation with respect to the primary position.

16.  Bowl with inscribed meridians and movable disk carrying a cross to produce afterimage to show that eye movements from primary position are true to meridians.

17. Sherrington’s Law of Reciprocal Innervation.  Considered as the mover producing that movement, the muscle is called an agonist.  A movement in the direction opposite that produced by the agonist is caused by its antagonist.  Two muscles moving an eye in the same direction are synergists.  Synergistic muscles in the two eyes—muscles that cause the two eyes to move in the same direction —are known as yoke muscles.

18. Sherrington’s Law of Reciprocal Innervation.  Whenever an agonist receives an impulse to contract, an equivalent inhibitory impulse is sent to its antagonist, which relaxes and actually lengthens. This is Sherrington’s law of reciprocal innervation.  Sherrington’s law applies to all striated muscles of the body and is not limited to the extraocular muscles.

19. Sherrington’s law of reciprocal innervation. A, On levoversion, increased contraction (+) of the RMR and left lateral rectus LLR is accompanied by decreased tonus (0) of the antagonistic RLR and LMR muscles B, Increased activity of both medial rectus muscles and decreased tonus of both lateral rectus muscles during convergence. C, Contraction and relaxation of opposing muscle groups on dextrocycloversion when the head is tilted to the left shoulder. RSO,; RSR,; LSO,; LSR,; RIO,; RIR,; LLO,; LIR..

20. Hering’s Law of Equal Innervation.  Herington Law of equal innervation states that during any conjugate eye movement, equal and simultaneous innervation flows to the yoke muscles  In the case of a paretic squint, the amount of innervation to both eyes is symmetrical, and always determined by the fixating eye, so that the angle of deviation will vary according to which eye is used for fixation.

21. Hering’s law of equal innervation. A, During levoversion the right medial rectus and the left lateral rectus muscles receive an equal and simultaneous flow of innervation. B, During convergence the right and left medial rectus muscles receive equal and simultaneous innervation. C, When the head is tilted to the left, the musclegroups controlling excycloduction of the right eye and incycloductionof the left eye receive equal and simultaneous innervation. However, inclination of the head is only partially compensated for by wheel rotations of the eyes.

22. Survey of Ocular Movements and Their Characteristics.

23. Terminology of Ocular Movements Uniocular movements. - All uniocular rotations are termed ductions. - Prism vergences should never be called ductions. Binocular movements. - Synchronous simultaneous movements of the two eyes in the same direction are called versions. - Synchronous simultaneous movements of the two eyes in opposite directions are called vergences. - Versions are fast and vergences are slow eye movements.

24. Monocular Movements Binocular Movements (ductions) Versions Vergences Adduction Dextroversion Convergence Abduction Levoversion Divergence Sursumduction Sursumversion Right sursumvergence* Deorsumduction Deorsumversion Right deorsumvergence† Incycloduction Dextrocycloversion Incyclovergence Excycloduction Levocycloversion Excyclovergence Terminology of Ocular Movements

25. Versions  To enlarge the field of view and to bring the object of attention onto the fovea.  Versions are either voluntary or involuntary.  They are voluntary if the subject moves the eyes of his or her own volition.  They can be horizontal, vertical and oblique versions.

26. Versions  Naturally occurring cycloversions are postural reflexes.  They arise from stimuli in the neck muscles and the inner ear.  When the head is lifted, the eyes go down; when the head is lowered, the eyes go up.  This is the oculocephalic reflex - doll’s head phenomenon, oculovestibular reflex,Puppenkopfphanomen.

27. A, Levoversion with the head turned to the right. B, Dextroversion with the head turned to the left. C, Depression of the eyes with the chin elevated. D, Elevation of the eyes with the chin depressed.

28. Vergences  The vergences fulfill the second of the two tasks assigned to the motor system of the eyes.  They are movements of the two eyes in opposite directions,they are also known as disjunctive movements.  Vergence movements serve not only to bring the eyes into proper alignment but also to maintain this alignment.  These movements are performed also in the interest of single binocular vision.  Divergence movements are not an active function but simply the return of the globes to a more parallel position by elastic forces when convergence impulses were relaxed.

29. Coordination of Eye Movements  Separate systems exist to control each different subtyppe of eye movement: saccades, smooth pursuit, and vergence.  May be nuclear or supranuclear.  May be reflexive or voluntary.  Separate systems exist to govern vertical and horizontal eye movements.

30. Targeting Eye Movements. 1. Saccades: Quick, darting conjugate movements which direct the to eye to a new target. 2. Smooth pursuit: A slower conjugate movement which allows for tracking of a moving object, or of a stationary object while we are moving. 3. Convergence: A dysconjugate movement of both eyes toward the midline to allow for focusing on a near object by adjusting the angle between the eyes.

31. How the Extraocular Muscles Work  Underaction of the extraocular muscles can be readily explained due to reduced rotation of the globe.  Observation of clinical strabismus suggests that only cases of excess innervation such as occurs in the yoke muscle of a paretic muscle can legitimately be called overaction.

32. Testing for Muscle Weakness and Restriction.

33. Clinical evaluation of strabismus with restricted motility Underaction. A. Fixing with the sound eye (primary deviation) - a right esotropia is observed. B. Levoversion is essentially normal. C. Dextroversion shows limitation of abduction in the right eye. D. Fixing with the paretic eye and/or mechanically restricted right eye produces a larger secondary deviation.

34. Clinical evaluation of strabismus with restricted motility Overaction. .

35. Passive duction testing of the oblique muscles A. The eye is grasped at the 2 o’clock and 10 o’clock position (right eye from above) in preparation. B. The eye is pushed back into the orbit and is guided from nasal to temporal. As it goes over the normal superior oblique tendon, the eye ‘pops’ up. C. With a lax or loose tendon the cornea disappears and remains hidden behind the upper lid as the eye is rotated. D. The relative path of the globe as it passes over a normal tendon. E. A lax superior oblique tendon allows the globe to be pushed backward into the orbit. The superior oblique traction test.

36. Passive duction testing of the oblique muscles A .The right eye is grasped at the limbus. B. The eye is rotated nasally and ‘pushed back’ in the orbit. C1. The eye is brought temporally -- the surgeon ‘feels’ for the ‘pop up’ of the inferior oblique which is still present. C2. If no ‘pop’ is felt, the inferior oblique has been effectively weakened. D. The eye normally recedes in abduction regardless of the state of the inferior oblique. The inferior oblique traction test viewed from above the patient’s head.

37. Thank You.

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