extra ocular movements

Extra Ocular Movements

(aka)…and you thought hyperopia was

bad…

WHAT ARE WE GOING TO DO T’DAY?

• Some (very, very little) Basics– Extra Ocular Muscles– Innervation

• Control of movements

• Movements– Terminology– Actions– Testing

BASICS

The Extra Ocular Muscles

The Extra Ocular Muscles -Origin


LR

IR

SR

MR

SO

IO

Annulus

TROCHLEA


LR

IR

SR

MR

SO

IO

TROCHLEA


LR

SRSO

IOIR


IR

SR

MR

SO

IO

TROCHLEA


LR MR

SR

IR

IO

SO


SO

SR LRMR

IO


LR

IR

SR

MR

SO

IO


SR

LR

MR


23°SRIR

51°SOIO

OPTICAL AXIS

THE EXTRA OCULAR MUSCLES

• Superior & Inferior Recti make an angle of 23° with the eye ball

• Superior & Inferior Obliques make an angle of 51° with the eye ball

• Angular attachment allows for actions in multiple directions

INNVERVATION

LR6 SO4 O3

SOME RULES

RULES #1• BOTH EYES MUST MOVE TOGETHER

• MUSCLES IN BOTH EYES ARE THUS PAIRED

• PARIED MUSCLES (YOKE MUSCLES) HELP MOVE THE EYE IN A GIVEN DIRECTION.

• THEY BOTH THUS GET SIMILAR STIMULATORY SIGNALS FROM THE BRAIN (HERRINGS LAW)

RULES #2• MUSCLES IN ONE EYE HAVE AN AGONIST-

ANTAGONIST RELATIONSHIP

• THE HORIZONTAL RECTII FORM ONE SET

• THE VERTICAL RECTII/ OBLIQUES FOR THE OTHER SET

• WHEN ONE MUSCLE IN THE SET CONTRACT THE OTHER MUST RELAX (SHERRINGTON’S LAW)

RULES #3

• MUSCLE ACTIONS & TESTING ARE DIFFERENT!

CONTROL OF MOVEMENTS

WHY?

• Eyes; you have to see

• Eyes must ‘fix’ on an object for you to see clearly

• Two Step process– Find what you want to see (Voluntary fixation)– Keep your eyes ‘glued’ to it (Involuntary fixation)

STEP 1: Find what you want to see STEP 2: Keep your eyes fixed on it

SUPRA NUCLEAR: CONTROL MEHANISM

CONTROL MECHANISMS• INVOLUNTARY– Tremors (Help keep image refreshed)– Drifts (Help keep image refreshed)– Flicks (Help eyes move so that image fall on fovea

again)

• VOLUNTARY– Pursuits (Slow movements to ‘track’ objects)– Saccades (Fast movements to ‘jump’ to objects)

INVOLUNTARY MOVEMENTS

DASHED = TREMORS/ DRIFTSSOLID = FLICKS

VOLUNTARY MOVEMENTS

• PURSUITS– To ‘follow’ objects– What we usually test

• SACCADES– To ‘rapidly’ shift gaze to an object of interest

THE SUPERIOR COLLICULI

• Jack of all trades

• Help in involuntary tracking

• Help in voluntary tracking

• Even if the visual cortex is kaput, these help turn the head in direction of ‘interest’

NUCLEAR LEVEL CONTROL

Co-ordinate eye movements -Between eyes* -Eyes and ears -Eyes and neck

Mostly via Superior colliculus*

VOLUNTARY MOVEMENTSPursuitsSaccades

EXTRAOCULAR MOVEMENTS

Y

X

Z

ROTATIONAL MOVEMENTS

PURSUITS(also applies to saccades, but we’ll deal with those a little later)

TERMINOLOGY• DUCTIONS– Examining movement of one eye – Remember it is not possible to move one eye

alone!

• VERSIONS– Movements of both eyes in the same direction

• VERGENCE– Movements of both eyes in opposite direction

PURSUITS: DUCTIONS

TERMINOLOGY: DUCTIONS

TORSIONAL MOVEMENTS

Rotation around ‘Y”

axis

INTORSIONInward rotationSuperior Rectus & Oblique

EXTORSIONOutward rotationInferior Rectus & Oblique

HELP KEEP YOUR WORLD STRAIGHT!

PRACTICE!

PURSUITS: VERSIONS

TERMINOLOGY: VERSIONS

INFRA VERSION

DEX

TRO

VER

SIO

N LEVO VERSIO

NSUPRA VERSION

One eye follows the other

Agonist Pairs in both eyes

These are called ‘Yoke’ muscles

Both get equal impulses

HERING’S LAW

TERMINOLOGY: VERSIONS

INFRA VERSION

DEX

TRO

VER

SIO

N LEVO VERSIO

NSUPRA VERSION

The antagonist muscles to yokes…

… are inhibited…

…to allow for optimal actions…

…of yoke muscles

SHERRINGTON’S LAW

TORSIONAL MOVEMENTS

• TORSIONAL MOVEMENTS CAN ALSO BE DEFINED FOR BOTH EYES

• INWARD ROTAION: INCYCLOVERSION

• OUTWAR ROTATION: EXCYCLOVERSION

PURSUITS: VERGENCE

TERMINOLOGY: VERGENCE

THE NUT CRACKER

• Its all good knowing Versions & Ductions

• But they DO NOT tell us anything about integrity of muscle function

• As clinicians it is more important to know about muscle functions

http://forums.studentdoctor.net/archive/index.php/t-109725.html

MUSCLE ACTIONS

• ACTIONS ARE DETERMINED BY POSITION OF EYE BALL– Primary Position: Straight ahead– Secondary Positions: Left, Right, Up, Down– Tertiary positions: Oblique

• MUSCLES, THUS, HAVE COMPLEX ACTIONS

MUSCLE ACTIONS

EYES STRAIGHT EYES U/D/L/R EYES OBLIQUE

MUSCLE ACTIONS

• MUSCLES, THUS, HAVE COMPLEX ACTIONS

MUSCLE ACTIONS

• THANK FULLY WE OPHTHALMOLOGISTS ARE MASTERS OF SIMPLFICATIONS

→

MUSCLE TESTINGWe want to know: Is the muscle Working?

MUSCLE TESTING• An amazing over-simplification

• Makes life easy

• One muscle = Moves eye in one position only

• Six muscles = Six position = Cardinal positions

MUSCLE TESTING: CARDINAL POSITIONS

DEXTRO-CYCLO Whaa….??

• To make things even simpler

• Refer to eye positions with reference to where they are in relation to the straight gaze

MUSCLE TESTING: CARDINAL POSITIONS

OUT IN

DOWN & OUT DOWN & IN

UP & OUT UP & IN

EYE MOVEMENTS

RT: SR LT: IO

RT: IO LT: SR

RT: MR LT: LR

RT: SO LT: IR

RT: IR LT: SO

RT: LR LT: MR

THESE ARE YOKE PAIRS (ACTING IN PAIRS)

UP RT

RT

UP LT

LT

DWN LTUP RT

THE RECTUS- OBLIQUE INTRIGUE

• Superior & Inferior Rectii elevate and depress an abducted eye respectively

• Inferior & Superior Oblique elevate and depress an adducted eye respectively


• To Remember this:• Minimize Angle between:– Eyeball & muscle

• The position of the eye ball– Determines muscle action


1. Minimize Angle 23°

1: RECTII MUSCLES

2. EYE ABDUCTS

3. RECTII THEN ELEVATE OR

DEPRESS


1. Minimize Angle

2: OBLIQUE MUSCLES

2. EYE ADDUCTS

3. OBLIQUES THEN ELEVATE OR

DEPRESS

51°


• Superior & Inferior Rectii elevate and depress an abducted eye respectively

• Inferior & Superior Oblique elevate and depress an adducted eye respectively

• The eye DOES NOT have to be turned exactly 23° or 51°. Maximal abducted or adducted gaze would do

EYE MOVEMENTS

RT: SR LT: IO

RT: IO LT: SR

RT: MR LT: LR

RT: SO LT: IR

RT: IR LT: SO

RT: LR LT: MR

UP RT

RT

UP LT

LT

DWN LTUP RT

MUSCLE TESTING• Wait… What about up & down gaze

• As well as Straight ahead??

• These movements involve more than one muscle

• Cardinal Positions + – Straight ahead (all muscles)– Up (Superior Rectus + Inferior Oblique)– Down (Inferior Rectus + Superior Oblique)

• = 9 Diagnostic Positions of gaze

9 DIAGNOSTIC POSITIONS OF GAZE

SIX CARDINAL POSITIONS + STRAIGHT + UP + DOWN= 9 DIAGNOSTIC POSITIONS

ALL MUSCLES

SR + IO (BE)

IR + SO (BE)

RT: SR LT: IO

RT: LR LT:MR

RT: IR LT: SO

RT: IO LT: SR

RT: MR LT: LR

RT: SO LT: IR

CLINICAL SKILL

RT: LR LT:MR

RT: SR LT: IO

RT: IR LT: SO

SR + IO (BE)

IR + SO (BE)

RT: IO LT: SR

RT: SO LT:IR

MAKE A BROAD 3 LIMBED “H”, OBSERVING THE EYE AS IT MOVES

RT: MR LT: LR

LIMB 1 LIMB 2(Not very useful as can’t isolate one

muscle dysfunction)

LIMB 3

CLINICAL SKILL

• IT does not matter how the triple limb “H” is formed as long as all directions are tested!

EOM SKILL: PURSUITS IN PAIRS

SACCADES

SACCADES

• All of what we have done

• Only faster!

EOM SKILL: SACCADES IN PAIRS

UTILZING SACCADES & PURSUITS• PURSUITS

– Continuously follow a moving object with eyes– Like the pen in the video above– A ball rolling along the ground– A pretty figure walking by– Watching videos

• SACCADES– Switch gaze to a point of interest rapidly, really rapidly. – Like the pen and hand in the video above– A cricket ball being bowled or hit– Objects that pass by you as you drive– Reading (changing lines)– Observing paintings

WHAT HAPPENS WHEN A MUSCLE FAILS TO FUNCTION?

EOM PALSY

• The eye fails to move in the direction of muscle function

• The visual axis are misaligned (‘PARALYTIC-SQUINT’)– Eye turned in (adducted) = Internal squint (ESO-TROPIA)– Eye turned out (abducted) = External squint (EXO-TROPIA)

EOM PALSY• The patient experiences diplopia

• If the patient in an adult the diplopia is intractable (i.e. will not go away)– Patients adopt a compensatory head posture to get over

the diplopia • To minimize misalignment of axis

– OR they simply close their eye

• If the patient is a child (< 9 years) the visual cortex will ‘adapt’ by suppressing the blurrier of the two images to negate diplopia

OR– They adopt a compensatory head posture to get over the

diplopia

INTERNAL SQUINT

MINIMIZE MIS-ALIGMENT OF EYES

TURN HEAD SO THAT THE RIGHT EYE MOVES OUT

JUST LIKE LOOKING TO THE RIGHT

VISUAL AXIS ARE ‘RE-ALIGNED’

OTHER WAYS OF GETTING A SQUINTFAULT IN EITHER OF THESE MECHANISMS

CAN CAUSE CHILDHOOD SQUINTEYE MOVEMENTS NORMALCALLED ‘NON-PARALYTIC SQUINTS’

extra ocular movements

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