EOM and it's clinical applied aspects in ophthalmology

Presentation on EOM

1. ANATOMY AND FUNCTIONS OF EXTRAOCULAR MUSCLES PRESENTER- DR NIKITA SAH MODERATOR- DR VATSALYA MAAM

2. INTRODUCTION 7 extraocular muscles

3. STRUCTURE OF EOM Voluntary and striated Ratio of nerve fibres to muscle fibre is high EOMs exhibit a 2 layer organisation: Outer orbital layer- Inner global layer

4. ORBITAL AND FASCIAL RELATIONSHIPS Within the orbit, a complex musculofibroelastic structure suspends the globe, supports the EOM and compartmentalizes the fat pads. The intense fibrous connections can be illustrated clinically by the consequences of tissue entrapment in blowout fractures, fibrosis of delicate fibrous septa after retrobulbar haemorrhage.

5. Adipose tissue-

6. Muscle cone Muscle capsule- Each rectus muscle has a surrounding fascial capsule that extends with the muscle from its origin to its insertion. Tenon capsule- Posteriorly - optic nerve sheath Anteriorly - intermuscular septum 3mm from the limbus

7. The pulley system- The rectus muscles are surrounded by fibroelastic pulleys that maintain the position of the EOMs relative to the orbit. They stabilize the muscle path, preventing sideslipping or movement perpendicular to the muscle axis.

8. SUPERIOR OBLIQUE Superior oblique is the longest and thinnest eye muscle. Origin – Orbital apex , above the Annulus of Zinn Insertion – supero medial wall of the orbit, becomes tendinous before passing through the trochlea , inserts posterior to the equator in the superotemporal quadrant.

9. INFERIOR OBLIQUE Origin: Periosteum of the maxillary bone Insertion- inferior to the inferior rectus and inserting under the lateral rectus muscle in the postero lateral portion of the globe close to the macula

10. VERTICAL RECTI The vertical recti run in line with the orbital axis and are inserted infront of the equator. They form an angle of 23º with the visual axis

11. SUPERIOR RECTUS Origin- Upper part of Annulus of Zinn Insertion- 7.7mm behind the limbus INF ERIOR RECTUS Origin- Lower part of Annulus of Zinn Insertion- 6.5 mm behind the limbus

12. HORIZONTAL RECTI In primary position, the horizontal recti are purely horizontal movers MEDIAL RECTUS Origin- Annulus of Zinn Insertion- 5.5mm behind nasal limbus LATERAL RECTUS Origin- Annulus of Zinn Insertion- 6.9mm behind temporal limbus

13. LEVATOR PALPEBRAE SUPERIORIS Origin- Orbital apex from the lesser wing of the sphenoid Insertion- It becomes an aponeurosis in the region of superior fornix and has both cutaneous and a tarsal insertion.

14. SPIRAL OF TILLAUX It is an imaginary line joining the insertions of the 4 recti muscles.

15. BLOOD SUPPLY

16. Lateral rectus - LACRIMAL ARTERY. Inferior oblique and Inferior rectus INFRA ORBITAL ARTERY. The muscular branches give rise to the anterior ciliary arteries accompanying the rectus muscle. These pass to the episclera of the globe and supply anterior segment.

17. VENOUS SYSTEM Parallels the arterial system, emptying into the superior and inferior orbital veins. Vortex veins (4 or more) are located posterior to the equator. 2 of them are consistent: just posterior to the IO muscle and SO tendon.

18. NERVE SUPPLY 1. OCCULOMOTOR SUPERIOR DIVISION- LPS, SR INFERIOR DIVISION- MR, IR, IO and ciliary ganglion 2. TROCHLEAR- contralateral SO 3. ABDUCENS- ipsilateral LR

19. ANATOMICAL CONSIDERATIONS FOR OPHTHALMIC PROCEDURES Nerves to the rectus muscle and superior oblique enter the muscle approx one-third of the distance from the origin.

20. Cranial nerve IV is outside the muscle cone, but could be reached by a retrobulbar needle and injured by inj of LA The nerves supplying the inferior oblique muscle enters the lateral portion of the muscle.

21. During surgery of IO muscle, careful inspection of infero -lateral quadrant should be done. Integrity of muscle capsules should be maintained during surgery. The intermuscular septum can be used as a point of reference in locating a muscle during surgery.

22. The inferior rectus is distinctly bound to the lower eyelid by the fascial extension from its sheath. Recession Resection Sclera is thinnest just posterior to the 4 rectus muscle insertions. Thus scleral perforation is always a risk during eye muscle surgery

23. Simultaneous surgery on 3 rectus muscles may induce ant segment ischaemia . Avoid penetration of Tenon capsule 10mm or more posterior to the limbus – restrictive adhesion

24. OCULAR MOVEMENTS 1. DUCTIONS- Monocular movt around the axis of Fick . Tested by occluding the fellow eye and asking the patient to follow a target in each direction of gaze 2. VERSIONS- Binocular, simultaneous, conjugate movements.

25. FIELD OF ACTION The gaze position in which the effect of EOM is most readily observed. Not the same in vertical muscles. For eg . IO (abductor and elevator)- Adduction

26. PRIMARY, SEONDARY AND TERTIARY ACTIONS The LR and MR have primary actions of abduction and adduction respectively. The SR and IR have primary actions of elevation and depression, and due to their oblique insertion on the globe of 23º , they also have secondary action of extorsion and intorsion and tertiary action of adduction.

27. The primary action of obliques is extorsion and intorsion , due to their oblique insertion of 51º, their secondary action are elevation and depression, tertiary action is abduction.

28. ACTIONS OF EOM

29. The superior muscles are intortors ; inferior muscles, extortors . The vertical rectus are adductors; oblique muscle, abductors.