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