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Anatomy of extraocular muscles and ocular motility

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anatomy of extraocular muscles

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Anatomy of extraocular muscles and ocular motility

  1. 1. Dr.k.vanya
  2. 2. Bony orbit  Angle of the medial and lateral walls of the orbit is 45° so the optical axis forms approimately 23 °with both medial &lateral walls.  The medial walls of the 2 orbits are parallel to each other.
  3. 3. Extraocularmusles(EOM):-6  Four recti:-  Superior rectus  Inferior rectus  Medial rectus  Lateral rectus
  4. 4.  Two oblique muscles:-  Superior oblique  Inferior oblique  In addition levator palpebrae superioris also present &it inserts into upper eye lid for elevating palpebral fissure.  The 4 rectii arises from fibrous ring (annulus of zinn)around optic foramen.
  5. 5.  Vertical recti(sup.&inf. Rectus ) run in line with orbital axis & are inserted infront of equator.  They form an angle of 23° with visual axis.
  6. 6. Superior rectus  Arises from upper part of annulus o zinn.  Below the attachment of levator M.  Continuous with attachment of med.,&lat. Recti  Pierces tenon’s capsule &it is inserted into sclera 7.7 mm from superior limbus.  Length 48 mm;width 9mm.  N.supply:-sup.divison of oculomotor N.  B.supply:-lat. Muscular branch of ophthalmic A.
  7. 7. Inferior rectus  Shortest of all recti  Arises from lower part of optic foramen.  Attached to sclera at 6.5 mm from inferior limbus  Lies b/w globe and inf.oblique.  Also attached to fascial sheath of lower lid.  Length 40mm;width 9mm  N.supply:-branch of inf divison of oculomotor N.  B.supply:-medial muscular branch of ophthalmic A.
  8. 8. Medial rectus  Largest ocular M& stronger than lateral rectus.  Arise from medial & inferior sides of optic foramen  Passing along medial wall of orbit ;inserts 5.5mm from nasal limbus.  Length 40mm;thicker than other EOM.  N.supply:-inf.divison of oculomotor N.  B.supply:-medial muscular branch of ophthalmic A. 
  9. 9. Lateral rectus  Arises from annular tendon.  Pierces tenon’s capsule &inserts in sclera at 6.9 mm from temporal limbus.  Length 48mm;2/3 of cross sectional area of MR.  N.supply:-Abducent N enters lR on its ocular aspect,just post.to its mid point.
  10. 10. Spiral of tillaux  Imaginary line joining the insertions of the 4 recti and is an important anatomical landmark when performing surgery.  The insertions are located progressively further away from the limbus in a spiral pattern.  the medial rectus insertion is closest .  Superior rectus is farthest.
  11. 11.  Obliques are inserted behind equator & form an angle of 51° with visual axis.
  12. 12. Superior oblique  Longest& thinnest EOM.  Arises from common origin at the apex of orbit; superomedial to optic foramen.  Runs forward to trochlea(cartilaginous ring at upper&inner angles of orbit)  After threading through this it becomes tendinous  It changes its direction completely and runs over the globe under SR to attach above & lat, to posterior pole.
  13. 13.  Ant.fibres of S.O tendon-intorsion  Post.fibres of S.O tendon-extorsion  N.supply:-Trochlear N(4) after dividing into 2-3 branches enters muscle superiorly.  B.supply:-superior muscular branch of ophthalmic A.
  14. 14. Inferior oblique  Only EOM not arising from apex of orbit  It arises anteriorly from lower & inner orbital walls near lacrimal fossa.  Running below inf.rectus& attaches below&lat. to post.pole of globe.  N.supply:-Inf.divison of oculomotor N.  B.supply:-Infraorbital &medial muscular branches of ophtalmic A.
  15. 15. Action of extraocular muscles  Rotation around centre of rotation  Centre of rotation lies 12/13 mm behind cornea.  3 types of rotation: 1. Rotation around fick vertical axis Z—side to side 2. “ “ fick horizontal axis X– up&down 3. “ “ fick antero posterior axis– torsion
  16. 16. Uniocular movements  Ductions – only one eye is open,the other covered/closed tested by asking the pt. to follow a target in each direction of gaze.  Types of ductions:- 1. Adduction 2. Abduction 3. Supraduction 4. Infraduction 5. Incycloduction 6. excycloduction
  17. 17. Binocular movements  Versions:-both eyes open,attempting to fixate a target &moving in same direction.  Binocular ,simultaneous,conjugate movements in same direction.  Abduction of one eye accompanied by adduction of other eye is called conjugate movements.
  18. 18. Types of versions:-  Dextroversion&laevo version  Elevation&depression  Dextro elevation&dextro depression  Laevo elevation& laevo depression
  19. 19.  Torsional movements/righting reflexes:-  When you tilt head to maintain upright image.  Vergences:- binocular,simultaneous,disjugate/disjunctive movements (opp.direction)  Convergence– simultaneous adduction  Divergence– outward movement from convergent position
  20. 20. Types of convergence  Reflex ----tonic  ----proximal  ----fusional  ----accommodative  voluntary
  21. 21. Actions of EOM ACTION PRIMARY SECONDARY TERTIARY MR ADDUCTION ------ --------- LR ABDUCTION ------ --------- SR ELEVATION INTORSION ADDUCTION IR DEPRESSION EXTORSION ADDUCTION SO INTORSION DEPRESSION ABDUCTION IO EXTORSION ELEVATION ABDUCTION
  22. 22.  Both obliques have same tertiary action because inserted behind the center of rotation,  pull post. pole of globe medially  when they contract ant.portion of eye so it causes abduction
  23. 23.  Both recti have same tertiary action bcz they inserted anterior to centre of rotation  pull ant.portion of globe medially so it causes adduction
  24. 24.  Synergists:-ref.to muscles having same primary action in same eye.  Ex:-sup.rectus & inf.oblique----elevators  inf.rectus&sup.oblique-----depressors  Antagonists:-having opp.action in same eye  Ex:-sup.&inf. Recti  sup.&inf.oblique
  25. 25.  Yoke muscle(contralateral synergists):-  Ref. to pair of muscles (one from each eye) which contract simultaneously during version movements.  Ex :-in dextroversion RLR &LMR  Contralateral antagonist:-pair of muscle (one from each eye)having an opposite action.  Ex:-in dextroversion RLR & LLR
  26. 26. Diagnostic positions of gaze:-9 1 Primary position of gaze:-assumed by eyes when fixating a distant object with head erect. 6 cardinal positions :- to test 12 EOM in their main field of action
  27. 27. 1. Dextroversion 2. Laevo version 3. Dextro elevation 4. Leavo elevation 5. Dextro depression 6. Laevo depression  +2 Elevation  Depression
  28. 28. Laws of ocular motility 1. Hering’s law of equal innervation:- during any conjugate movement equal & simultaneous innervation flows to yoke muscles
  29. 29. 2. Sherrington law of reciprocal innervation :-  inc.innervation to an EOM is accompanied by reciprocal dec. in innervation to its antagonist.  Ex:-RMR & RLR
  30. 30. Supranuclear control of ocular movements:- 1. Saccadic system 2. Smooth pursuit system 3. Vergence system 4. Vestibular system 5. Optokinetic system 6. Position maintenance system
  31. 31.  Saccadic system:- saccades are sudden,jerky,conjugate,movements as the gaze shifts from one object to other.  voluntary(normal)  invoiuntary(peripheral,auditory,visual stimuli)
  32. 32.  Smooth pursuit eye movements:-  Tracking movements of eye as they follow moving object  Voluntary movements  When the velocity of moving object inc. replaced by small saccades(“catchup saccades”)
  33. 33.  Vergence movement:  Allow focussing an object which moves away from/towards observer.  Very slow disjugate movements
  34. 34.  Vestibular eye movement:-  Effective in compensating for effects of head movements in disturbing visual fixation  Through vestibular system
  35. 35.  Optokinetic system:-  a movement following the moving scene , succeeded by rapid saccade in opp.direction  Position maintenance system:-  Helps to maintain specific gaze by rapid micro movements called “flicks” & slow micro movements called “drifts”.
  36. 36. Bibilography  Adler’s physiology of eye -11th edition  Wolff’s anatomy of eye -8th edition  Parson’s disease of eye-21st edition  Jack.j.kanski brad bowlingclinical ophthalmology - 7th edition  A.k.Khurana comprehensive ophthalmology - 5th edition

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