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OCULAR MOTILITY DISORDERS
DR. MANALI HAZARIKA SINGH
Visual axis [line of vision]- Passes from the fovea, through the nodal point of the eye to the point of fixation. Anatomical axis- It is a line passing from the posterior pole through the centre of the cornea.
Angle kappa- Angle subtended by the visual and anatomical axes (5˚).+ve – fovea temporal to the centrenasal corneal reflex
-Lateral & medial walls of orbit are at an angle of 450 to each other -Orbital axis forms an angle of 230 with both lateral & medial walls
-In primary position of gaze, visual axis forms an angle of 230 degrees with orbital axis -Actions of EOM depend upon position of globe at the time of muscle contraction
Anatomy of the extraocular muscles
-4 recti & 2 obliques
-The recti have a common tendinous origin called the annulus of Zinn, at the orbital apex
InsertionsMedial rectus [MR] – 5.5 mm behind nasal limbus
Lateral rectus [LR]- 6.9 mm behind temporal limbus
Superior rectus [SR]- 7.7 mm behind superior limbusInferior rectus [IR]- 6.5 mm behind inferior limbus
Superior oblique [SO]- -Originates from body of sphenoid, superomedial to optic foramen & runs forwards through trochlea
-Inserts in the posterior upper temporal quadrant of the globe
Inferior oblique [IO] – -Originates from lower & inner orbital walls near lacrimal fossa
-Inserts in the posterior lower temporal quadrant of the globe
Nerve supply – MR, SR, IR and IO - 3rd, SO - 4th LR 6th cranial nerves
Actions of Extraocular muscles
Rotation of the eye around a centre of rotation
3 types of rotations possible
1.The globe rotates left or right on the vertical axis
2.The globe moves up or down on the horizontal
axis
3.Torsional movements occur around the anteroposterior axis- Intorsion and extorsion
Superior rectus –
Primary action – ElevationSecondary - Adduction & Intorsion
Globe abducted 230 - Visual & orbital axes coincide & SR acts only as an elevator
Globe adducted 670 degrees - Angle between visual & orbital axes is 900 - SR acts only as an intortor
Inferior rectus –
Primary – Depression
Secondary - Adduction & Extorsion
Globe is abducted 23 degrees - IR acts only as a depressor
Globe adducted 67 degrees - IR acts only as an extortor
Medial rectus - Adducts the globe
Lateral rectus – Abducts the globe
Superior oblique –
Primary – Intorsion
Secondary - Depression Abduction
Globe adducted 510 –
Visual axis coincides with line of pull of muscle - SO acts only as depressor
Eye abducted 390 –
Visual axis & SO make an angle of 900 degrees - SO acts only as an intortor
Inferior oblique – Primary- Extorsion
Secondary – Elevation Abduction
Muscle Primary Action
Subsidiary Actions
Lateral rectus Abduction None
Medial rectus Adduction None
Superior rectus Elevation Adduction, Intorsion
Inferior rectus Depression Adduction, Extorsion
Superior oblique Intorsion Depression, Abduction
Inferior oblique Extorsion Elevation, Abduction
Ocular movements
Field of action – Direction of gaze in which the muscle exerts its greatest contraction force as an agonist
eg. LR in abduction MR in adduction
Ductions – Monocular eye movements
Adduction, abduction, elevation, depression, intorsion & extorsion
Versions- Binocular, simultaneous, conjugate movements [in the same direction]
Vergences - Binocular, simultaneous movement of two eyes in opposite directions
Movements - Convergence & divergence
Ocular movements
Positions of gaze- 6 cardinal and 9 diagnostic
Dextroversion Primary position
RE LE
Laevoversion
Dextroelevation
Laevoelevation Elevation
Depression Dextrodepression
Laevodepression
Agonists – Primary muscle, moving the eye in a given directioneg. LR in abduction
Antagonists –
Muscles of the same eye that move the eye in opposite directionseg. RLR to RMR
Synergists –
Muscles of the same eye that move the eye in the same direction eg. RSR & RIO in elevation of right eye
Yoke muscles – Pairs of muscles, one in each eye, that produce conjugate ocular movements eg. Yoke muscle of RLR is LMR for right gaze
Contralateral antagonists- A pair of muscles [one from each eye], having opposite actioneg. RLR & LLR, RMR & LMR
Laws of ocular motility
Sherrington law of reciprocal innervation-
This states that during ocular motility, increased innervation to a contracting extraocular muscle is accompanied by a reciprocal decrease in innervation to its antagonist
Applies for both ductions and versions
For example, during adduction, when MR contracts, LR automatically relaxes
Laws of ocular motility
Herring law of equal innervation-
This states that during movement of both eyes in the same direction, equal and simultaneous innervation flows to a pair of yoke muscles
For example, RLR & LMR receive equal innervation for right gaze
Binocular single vision [BSV]-Perception of a single image
Synaptophore – To assess BSV
Grade I- Simultaneous perceptionAbility to see 2 dissimilar objects simultaneously Grade II- Fusion. Ability to superimpose 2 incomplete but similar images to form one complete imageGrade III- StereopsisAbility for depth perception.
Corresponding points-
Areas on each retina that share same subjective visual direction
Eg. the foveae
Points on nasal retina have corresponding points on temporal retina of the other eye
Strabismus
Normally, the visual axes of two eyes remain parallel to each other in all directions of gaze, except when they converge for near vision
Strabismus or squint may be defined as a
misalignment of the visual axes of the two eyes,
that is, it is a condition in which the visual axes of
the two eyes are not directed simultaneously to
the same fixation point
HISTORY
AGE OF ONSET SYMPTOMS VARIABILITY GENERAL HEALTH BIRTH HISTORY FAMILY HISTORY PREV. OCULAR HISTORY
VISUAL ACUITY CYCLOPLEGIC REFRACTION & FUNDUS HP, EOM DETAILS OF DEVIATION TESTS FOR BINOCULARITY FORCED DUCTION TEST (IF MOVTS ARE
RESTRICTED)
DIRECTION – EXO,ESO,HYPER,HYPO,INCYCLO,EXCYCLO
FREQ- LATENT,MANIFEST,INTERMITTENT MAGNITUDE- FOR DISTANCE & NEAR ,
WITH/WO GLASSES COMITANCY –COMITANT/INCOMITANT LATERALITY-UNI,ALTERNATING ACCOMODATIVE CONVERGENCE/ACCOMO-
LOW/N/HIGH
Cover test: tropia Uncover test:
phoria Alternate cover
test: tropia + phoria
WORTH 4-DOT TEST
TESTS FOR STEREOPSIS