Strabismus: An Introduction

Professor K N Jha, MS

Email: kirtinath.jha@gmail.com

Movements of the eyeballs

• Y-axis: anteroposterior axis, coincident with

line of sight

• Z-axis: Vertical axis

• X-axis: horizontal axis

Movements of the eyes

X-axis : Elevation/depression

Y-axis : Intorsion /extortion

Z-axis : Adduction /abduction

EXTRAOCULAR MUSCLES

Extraocular muscles

• The four recti

• The two oblique

• Origin and insertion

• The nerve supply of the muscles

Extraocular muscles

• Agonist

• Antagonists

• Synergists e.g. SR/IO

• Yolk muscles :synergistic muscles in two eyes

Cardinal movements

• Adduction

• Abduction

• Elevation

• Depression

Relationship of Vertical Muscles

Actions of the EOM

EOM Primary action Secondary Tertiary

MR Adduction - -

LR Abduction - -

IR Depression Excycloduction Adduction

SR Elevation Incycloduction Adduction

IO Excycloduction

Elevation Abduction

SO Incycloduction

Depression Abduction

Positions of the eyes

• Primary

• Secondary

• Tertiary

Positions of gaze

RSR LIO

LSR RIO

RLR LMR

LLR RMR

RIR LIO

LIR RSO

Movements of the Eye balls

• Ductions: All uniocular rotations

• Versions: Simultaneous synchronous movements

of the two eyes in the same direction

• Vergence: Simultaneous synchronous movements

of the two eyes in the opposite directions .

Hering’s law of equal innervation

• Whenever an impulse for the performance of an

eye movement is sent out ,corresponding

muscles of the each eye receive equal innervation

to contract or relax.

• Practical implication of Hering’s law

Sherrington law of reciprocal innervation

Sherrington 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.

Nervous control of ocular movements

• III,IV,VI cranial nerves

• Voluntary ocular movements

• Involuntary reflexes

Control of ocular movements

• Saccades

• Smooth pursuit

• Vergence

• Fixation

• Vestibulo-ocular reflex

• Optokinetic movements

Binocular vision

Corresponding retinal points

• Retinal elements of the two eyes that share

common visual direction.viz, fovea

• Disparate points

Fixation

• Fixation means seemingly steady maintenance

of image of an object of attention on the

fovea.

• Monocular /binocular fixation

Binocular fixation

• If the two visual axes intersect at fixation point

this is called the state of binocular fixation.

• All the object points that simultaneously

stimulate two fovea have a common visual

direction.

Grades of Binocular vision

• SMP: simultaneous macular perception

• Fusion: Unification of visual excitation from

Corresponding retinal images into single visual

image.

• Stereopsis: Relative ordering of visual image in

depth.

Normal ocular alignment

• Normal ocular alignment

• Ocular misalignment (strabismus/Squint)

Deviations of the eyes

• Properties and characteristics:

comitant/incomitant, latent/ manifest

• Direction: Eso/Exo

• Origin : Supranuclear/ Infranuclear/ Myogenic

• Temporal behaviour: Constant/Intermittent

• Additional features: Amblyopia/suppression/ eccentric

fixation

Points to remember

• Grades of binocular vision

• EOM: origin , insertion , nerve supply, and actions

• Cardinal movements and cardinal positions of

gaze

• Movements of the eye balls

• Hering’s and Sherrington’s laws