extra ocular motility @farhana.islam
TRANSCRIPT
There are 2 types of muscles ~4 Recti muscles ~Superior rectus (SR) ~Inferior rectus (IR) ~Medial rectus (MR) ~Lateral rectus (LR)2 Oblique muscles ~Superior oblique (SO) ~Inferior oblique (IO)
6 muscles . . .
Recti muscles
Origin Insertion Nerve supply
SR Superior part of common tendinous ring of zinn
sclera through the tendon about 7.7mm posterior to limbus.
3rd nerve(oculomotor )
IR inferior part of common tendinous ring of zinn.
sclera through the tendon about 6.5mm posterior to limbus.
3rd nerve (oculomotor )
LR Lateral part of common tendinous ring of zinn.
sclera through the tendon about 6.9 mm posterior to limbus.
6th nerve (abducent)
MR Medial part of common tendinous ring of zinn.
sclera through the tendon about 5.5mm posterior to limbus.
3rd nerve (oculomotor )
Oblique muscles
Origin Insertion Nerve supply
SO At the apex of the orbitFrom body of sphenoidAbove & medial to the optic foramenBy a narrow tendon.
Behind the equator in the sclera
4th nerve (trochlear nerve)
Oblique muscles
ORIGIN INSERTION
NERVE SUPPLY
IO Arises by a rounded tendonFrom a shallow depressionOn the orbital plate of maxillaJust lateral to the orifice of the naso lacrimal duct.
Behind the equator ,in the lower & outer part of sclera,in temporal side, by a short tendon.
3rd nerve(oculomotor nerve)
MR:Medial muscular branch of ophthalmic artery+Lacrimal artery
IR & IO :Medial muscular branch of ophthalmic artery + Infra orbital artery
LR,SR,SO: Lateral muscular branch
BLOOD SUPPLY…
MUSCLES PRIMARY SECONDARY TERTIARY
SR Elevation Intorsion Adduction
IR Depression Extortion Adduction
LR Abduction
MR Adduction
SO Intorsion Depression Abduction
IO Extorsion Elevation Abduction
ACTIONS . . .
Fick’s axis Z
Fick’s law : 3 axes are perpendicular to each other & intersect at the centre of rotation.
A hypothetical point around which the eyeball performs rotatory movements
centre of
rotation
Centre of rotation
Describes 3 axes- 1) X (horizontal) axis. 2)Y (antero-posterior)axis. 3)Z (vertical) axis.
Fick’s law
1)Duction: the movement of one eye
Abduction Adduction Supraduction or elevation Infraduction or depression Incycloduction or intorsion Excycloduction or extorsion
Ocular movements…
2)Version: the movement of two eyes in the same direction
1)Dextroversion 2)Levoversion 3)Supraversion 4)Infraversion 5)Dextroelevation 6)Dextrodepression 7)Levoelevation 8)Levodepression 9)Dextrocycloversion 10)Levocycloversion
Cont…
Terminology of Ocular Motility
Agonist Any particular EOM producing a
specific ocular movement.e.g for abduction LR in right eye.
Synergist Two muscles moving an eye in the
same direction E.g– SR / IO - Synergist for
elevation movement
Antagonist The muscles having opposite
action in the same eye Example – medial and lateral
rectus
Cont…
•Yoke muscle (Contralateral synergists)a pair of muscle one in each eye which contract simultaneously during version movement
• Pairs for six cardinal positions of gaze • Dextroversion – RLR- LMR• Levoversion – LLR- RMR• Dextroelevation – RSR-LIO• Levoelevation – LSR- RIO• Dextrodepression – RIR-LSO• Levodepression –LIR-RSO
Cont…
• Contralateral Antagonista pair of muscles, one in each eye having opposite action eg. RLR & LLR.
Cont..
Hering’s Law An equal and simultaneous innervation flows
from brain to a pair of muscle of both eyes which contracts simultaneously in different binocular movements.
Laws of EOM Movements
Clinical Significance:1.Secondary deviation > > Primary deviation2.Inhibition palsy of the contralateral antagonist
Sherrington’s Law During eye movement an increased flow of
innervations to the contracting agonist muscle is accompanied by an equal and simultaneous decreased flow of innervations to the relaxing antagonist muscle
Cont…
1.During dextroversion, an increased flow to the right LR & left MR is accompanied by a decreased flow to the right MR & left LR muscles.
2.
Example:
Donder's Law For each tertiary position, there is one
and only one orientation of the vertical and horizontal meridians of retina.
There is no rotation around the antero-posterior (Y) axis. (no torsion or twist occur).
The eye reaches all tertiary position without movement around the Y axis.
The eye always returns to the same orientation from which it started.
Anatomy & Physiology of Eye by A.K.Khurana
Binocular vision & Ocular motility by Gunter K.Von Noorden
Internet
References…