1

 X-axis a transverse axis passing through the center of the eye at the equator  Y-axis a sagital axis passing through the pupil  Z-axis a vertical axis 2

 Voluntary vertical rotations of the eye occur about X axis  Voluntary horizontal rotations of the eye occur about Z axis  Involuntary torsional rotations of the eye occur about Y axis 3

 The center of rotation and includes the X and Z axes  The Y axis is perpendicular to this plane 4

 Primary position : straight ahead  Secondary positions : straight up,straight down, right,left  Tertiary positions : up & right, up & left, down & right, down & left 5

 The point of effective or physiologic insertion is the tangential point where the muscle first contacts the globe  The action of the eye muscle : a vector of force that acts at this tangential point to rotate the eye  The length of muscle actually in contact with the globe 6

7

8

9

10

11

12

 Adduction:movement of the eye nasally  Abduction:movement of the eye temporally  Elevation (supraduction): upward rotation  Depression (infraduction): downward rotation  Intorsion (incycloduction):nasal rotation of the superior portion of the vertical corneal meridian  Extorsion(excycloduction):temporal rotation of the superior portion of the vertical corneal meridian 13

 Agonist: the primary muscle moving the eye in a given direction  Synergist: the muscle in the same eye as the agonist that acts with the agonist to produce a given movement  Antagonist: the muscle in the same eye as the agonist that acts in the direction opposite to that of the agonist 14

 Increased innervational and contraction of a given muscle are accompanied by a reciprocal decrease in innervation and contraction of its antagonist 15

 Version: eye movements conjugate and the eyes move in the same direction  Vergence: eye movements disconjugate and the eyes move in opposite directions 16

 Dextroversion : movement of both eyes to the patient’s right  Levoversion : movement of both eyes to the patient’s left  Elevation : upward rotation of both eyes  Depression : downward ratation of both eyes  Dextrocycloversion : both eyes rotate so that the superior portion of the vertical corneal meridian moves to the patient’s right  Levocycloversion : movement of both eyes so that the superior portion of the vertical corneal meridian rotates to the patient’s left 17

 Two muscles (one in each eye ) that are the prime movers of their respective eyes in a given position of gaze 18

 The six positions of gaze in which one muscle of each eye is the prime mover are known as the cardinal positions of gaze 19

20

 Equal and simultaneous innervation flows to yoke muscles concerned with the desired direction of gaze  Important clinical implications especially when dealing with a paralytic or restrictive strabismus 21

 Primary deviation: the amount of misalignment when the normal eye is fixating  Secondary deviation: the amount of misalignment when the paretic or restrictive eye is fixating  The secondary deviation is larger than the primary deviation 22

 Convergence: movement of both eyes nasally relative to a given position  Divergence: movement of both eyes temporally relative to a given position  Vertical vergence: less frequently encountered,can also occur; one eye moves upward and the other downward 23

 Incyclovergence : a rotation of both eyes so that the superior portion of each vertical corneal meridian rotates the toward the median plane  Excyclovergence : a rotation of both eyes so that the superior portion of each vertical meridian rotates away from the median plane 24

 Tonic convergence :the constant innervational tone to the extraocular muscles when a person is awake and alert  Accommodative convergence of the visual axes : part of the synkinetic near reflex  Voluntary convergence : a conscious application of the near synkinesis 25

26