1. EXTRAOCULAR MUSCLES Dr.Lhacha Wangdi (Resident), Department of Ophthalmology JDWNRH 2. Learning objectives 1. Physiology of ocular movement 2. Anatomy of extra ocular muscles (EOM) 3. Clinical correlates 3. Outline 1. Gross anatomy of EOM 2. Physiology of extra ocular movement 3. Perimuscular connective tissue 4. Microscopic anatomy of EOM 5. Law of ocular movements 4. Introduction Extraocular muscle (EOM) plays vital role in visual system 1. Provides static adjustment of binucular alignment necessary to enable BSV and steropsis 2. Precise dynamic movements to acquire and maintain visual targets Fibers of EOMs are mesodermal in origin and Perimuscular Connective tissues are neural crest in origin 5. Extraocular muscles 7 extraocular muscles 1. Lateral rectus 2. Medial rectus 3. Superior rectus 4. Inferior rectus Levator Pelpebrae Superioris Two oblique musclesFour Rectus muscles 5.Superior oblique 6.Inferiro Oblique 6. Muscle cone The rectus muscle forms the muscle cone within the orbit with apex at their origin and base at their penetration of tenons capsule. Each muscle is surrounded by fibrous capsule which are attached by thin continuous membrane called intermuscular septum Intermuscular septum divides orbital fat pad into extraconal fat and intraconal fat which help to maintain cushioning effects. Intermuscular septum fuses with tenon 3mm from the limbus Fibrous capsule Intermuscular septum Intraconal fat Extraconal fat Muscle cone 7. The fascia bulbi The tenon capsule/fascia bulbi is an envelope of elastic fibrous connective tissue Form protective covering and the site of attachment of EOM Tenon capsule fuses with optic nerve sheath posteriorly and anteriorly with intermascular septum, 3 mm posterior to the limbus. EOM penetrates the tenon capsule 10 mm posterior to their insertion Tenons are divided into anterior and posterior parts Tenon capsule 10mm 8. Muscle pulley As the EOM penetrates the tenon capsule the connective tissue forms the sleeves around the muscles creating muscle pulleys. Discrete rings of dense collagen tissue encircling EOM & are about 2mm length Pulley redirects the muscle and acts as functional origin it also prevents displacement of muscle during movement Because of pulley mechanism muscle are inflect at the insertion forming angle with the orbital axis. muscle pulley Pulley Angle 9. Rectus origin- Annulus of zinn Annulus of Zinn is a fibrous ring in the orbital apex It is attached to the lesser and greater wing of spenoid bone and spans over superior orbital fissue It gives attachment to all rectus muscle Annulus of zinn is also an important landwark through which many important structure passes Optic nerve Ophthalmc artery Ocular motor nerve Nasociliary branch of CN VI Abducent nerve Trochlear nerve Lacrimal nerve Frontal branches of CN VI Superiror ophthalmic vein 10. Principle of ocular movement Because of pear shape Medial and lateral wall of an orbit are at the angle of 45 each other Orbital axis therefore forms 23 with both medial and lateral wall When the eye in in primary position the visual axis forms 23 of angle with the orbital axis Action of muscle depends on muscle plane in relation to optical axis 45 23 23 11. Fick model of EOM Eye movement occurs through the central of rotation Listing plane is an imaginary coronal plane passing through the centre of rotation of globe Globe rotates on X and Y axis of Fick which intersect with in the listing plane Globe rotates right and left(adduction/abduction)on the vertical axis of Z Moves up and down(elevation/depression)on horizontal X axis Torsional movement(intorsion/extorsion)occurs on Y axis 12. Medial Rectus Originates from the medial part of annulus of zinn It is 10.3 mm wide, 40.8 mm long with 3.7 mm tendon extension at insertion Inserts in horizontal meridian 5.5mm from the limbus 5.5 mm Medial rectus 13. Lateral rectus Originates from the lateral part of annulus of zinn spanning the superior orbital fissure It is 40.6 mm in length, 9.2 mm wide with 8 mm long tendon at insertion It inserts to the eye globe laterally in horizontal meridian 6.9mm from the limbus. 6.9mmLateral rectus 14. Horizontal muscle- MR action Insertion point of horizontal muscle are straight and vertical. In primary position the muscle plane of horizontal recti (line from origin to insertion) coincides with visual axis Horizontal recti are therefore are purely horizontal movers on vertical Z axis and have only primary actions. Medial rectus- adduction Lateral rectus- abduction visual axis Muscle plane of MR Insertion point MR with pulley 15. Inferior rectus Originates from the inferior part of annulus of zinn It is 40 mm in length, 9.8mm wide and has 5.5 mm tendon extension at insertion In is inserted inferiorly to eye globe in vertical meridian 6.5 mm from the limbus 6.5mm Inferior rectus 16. Inferior rectus- action IR is inserted in laterally oblique position 6.5mm behind the inferior limbus In primary position, muscle plane forms 23 angle with visual axis Primary action is depression Due to its laterally oblique insertion with angle of 23acting inferiorly 2nd actions are adduction and extrosion Clinical correlates-When globe is abducted 23 it is purely depressor- optimal position for testing the function of IR 23 Visual axis Muscle plane 17. Superior rectus Originates from the superior part of annulus of zinn It is 41.8mm long, 10.6mm wide with 5.8mm tendon extension at insertion Inserts to the eye lobe superiorly in vertical meridian 7.7mm from the limbus 7.7 mm Superior rectus 18. Superior rectus- action SR is inserted in medially oblique position 7.7mm above the superior limbus In primary position muscle plane form 23 angle with visual axis Primary action is elevation Due to its medially oblique insertion with 23angle, 2nd action are adduction and intorsion Clinical correlates-When eye is abducted 23 it act only as elevator- optimal position for testing the function of SR 23 19. Superior oblique Originates from the body of sphenoid bone, above and medial to the optic foramen It is 40mm long, 10.8 wide and has 20mm tendonous extension(longest) It passes through the trochlea (cartilaginous pulley ) at the superonasal orbital rim, hook back from trochlea under the superior rectus inserting posterior to the center of rotation. trochlea Superior oblique 20. Superior oblique- actions Due to pulley effect of trochlea SO is inserted in medial oblique position in superior posterior temporal quadrant of globe In primary position the muscle plane of SO forms 51 angle with the visual axis. The primary action is intorsion 2nd actions are- depression and abduction When the globe is adducted 51visual axis coincides with the line of pull of muscle- acts as pure depressor therefore optimal position for testing SO function Visual axis Muscle plane of SO 51 21. Inferior oblique Originates from a shallow depression of orbital plate of maxillary bone at the anteromedial cornerof orbital floor near the lacrimal fossa It is 37mm long, 9.6mm long and has no tendon It extends posterior to the inferior rectus, laterally and superiorly to insert at posterior inferior temporal quadrant of eye globe behind the medial rectus Inferior oblique 22. Inferior oblique IO passes backward and laterally to insert in lateral oblique position in temporal lower quadrant of globe In primary position muscle plane of IO forms 51 angle with visual axis primary action is extorsion (out and up) 2nd actions are- elevation and abduction When the eye is adducted 51- it acts purely as elevator therefore this position is optimal for testing the function of IO muscle. Visual axis Muscle plane of IO 51 Inferior oblique 23. SPIRAL OF TILLAUX Insertion of rectus muscle forms an imaginary spiral ring around the limbus . MR nearest and SR furthest from the limbus 5.5 mm 6.5mm 6.9mm 7.7mm MR SR LR IR Clinical correlates; 1. Important landmark during strabimus surgery 2. Sclera is thinnest at the insertion of rectus (0.3mm)-common site for perforation during severe blunt trauma to the globe 24. Blood supply EOM are supplied by the branches of ophthalmic artery. 1. Muscular branches 2. Lacrimal braches As the ophthalmic artery enter the muscle cone through the optic canal it braches to Lateral and Medial muscular branches Medial muscular branch Lateral muscular branch 25. Muscular artery course along with CN111 to enter rectus muscle at the junction of posterior and middle one third. Lateral muscular branches- a. lateral rectus b. sup rectus c. LPS d. SO Medial muscular branches- a. medial rectus b. inferior rectus c. IO Lacrimal branch-LR and SR 26. Anterior ciliary artery (ACA) 7 in no. Branches of muscular arteries Along tendons of muscles and pierce sclera 4 mm from the limbus and enter eyeball Join the LPCA to form the major arterial circle of iris. Supplies -- Cilliary body and iris. ACA runs in pair in each rectus muscle except LR which has only one ACA Muscular branch LR with single ACA Clinical correlates: interruption of ACA during surgery involving more than two rectus muscle can result in anterior segment ischemia! 27. Venous drainage of EOM The venous drainage of the extraocular muscles is via the superior and inferior orbital veins to ophthalmic veins Anterior ciliary vein Cavernous sinus Inferior ophthalmic vein Superior ophthalmic vein Superior orbital vein inferior orbital vein Clinical correlates: Secondary Perimuscular infection following EOM trauma can spread infection to cavernous sinus . Cavernous vascular disease can present as opthalmoplegia and proptosis 28. Nerve supply of EOM Three cranial nerves 3. Trochlear nerve2. Abducent nerve1. Oculomotor nerve Superior obliqueLateral rectus 1. Superior rectus 2. Medial rectus 3. Inferior rectos 4. Inferior oblique 5. Levator pelpebrae 29. Innervation ctn Rectus muscle are innervated from the intraconal surface of muscle belly at junction of middle and posterior third of muscle. SO is innervated by trochlear nerve via the extracornal route above the annulus of zinn 30. Structure of EOM Each EOM consist of 2 layers 1. Orbital layer which located superficially near the orbital wall 2. Globar layer which is located more deeper Fibers of Global layer become contiguous with tendon to insert on the globe ; orbital layer is inserted on muscle pulley 31. Microanatomy of EOM EOM are striated muscles with bundles of muscle fibers(functional units) which is made up of actin and myocin filaments Compared to skeletal muscle(SM)EOM fibers are small and numerous with abundant nucleus which are highly innervated- ratio of nerve to muscle fiber of 1:3-1:5 compared 1: 50-1:125 of SM EOM has more contractile units This accounts for very precise and rapid movement of eye by EOM 32. EOM Fibers Two type 2.Multiply innervated fibers (MIFs)1.Singly innervated fibers(SIFs) Large diameter Arranged irregularly Abundant mitochondria Multiply innervated Many branches 1 nerve as en grappe Mostly found in orbital layer of EOM Allows fatigue resistant smooth ocular movement Small diameter Regularly arranged Fewer mitochondria Singly innervated 1 nerve, 1 branch as en plaque Mostly found in globular layer of EOM Allows rapid, saccadic and precise movements 33. Law of ocular motility Agonist-antogonist- pair of muscle of same eye that move in opposite direction e.g- LR and MR Synergist- pair of same eye muscle that move in same direction e.g- SR and IO- elevation Yoke muscle- contralateral pair of muscle that move in same direction- e.g left SO and right IR-levoelevation Sherrington law-reciprocal innervation- increased innervation to one EOM is accompanied by reciprocal decreased innervation to antagonist- agonist/antagonist action eg. LR & MR Hering law- equal innervation to EOM during conjugate eye movement- yoke muscles. 34. Ocular movements Ocular movement occurs around the axis of Fick 3 basic ocular movements 1.Ductions 2.Version- monocular movement around the axis of Fick Binocular, simultaneous, conjugate movements- (in same direction) Binocular, simultaneous, disjugate /disjunctive movement-in opposite direction 3.Vergences- 1.Convergence 2.divergence 35. Ductions Are tested by occluding one eye and asking the patient to follow target in each direction of gaze Ductions consist of following- 1.adduction-MR 4.depression- 2.abduction-LR 6.Extorsion (IO) 3.Elevation (SR) 5.Intorsion (SO) OD 36. version Tested with both eye open and asking patient to follow a target in each direction of gaze. Following are the various gaze of versions-9 cardinal gaze 3.Dextroelevation (ODSR+OSIO) 2.Destroversion ODLR+OSMR) 5.Laevoversion (OSLR+ODMR) 6.Laevoelevation (OSSR+ODIO) 7.Laevodrepression (OSIR+ODSO)9.drepression 8.elevation 1.Primary position 4.Dextrodrepression (ODIR+OSSO) 37. 37 38. References J.J Kanski clinical ophthalmology- 7th edition Yanof and Duker ophthalmology-4th edition AAO- section 4 & section 6 Stallards surgical method Oxford textbook of ophthalmology Dauns clinical ophthalmology Internet sources