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STRABISMUS BY DR. AMER ISMAIL ABU IMARA JORDANIAN BOARD OF OPHTHALMOLOGY I.C.O.

STRABISMUS BY DR. AMER ISMAIL ABU IMARA JORDANIAN BOARD OF OPHTHALMOLOGY I.C.O. PALESTINIAN BOARD IN OPHTHALMOLOGY. بسم الله الرحمن الرحيم علم فن تخيل قرار متابعة ” لا يوجد علم دون تعب ... ودراسة مستمرة ... و متابعة حثيثة ”

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STRABISMUS BY DR. AMER ISMAIL ABU IMARA JORDANIAN BOARD OF OPHTHALMOLOGY I.C.O.

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  1. STRABISMUS BY DR. AMER ISMAIL ABU IMARA JORDANIAN BOARD OF OPHTHALMOLOGY I.C.O. PALESTINIAN BOARD IN OPHTHALMOLOGY

  2. بسم الله الرحمن الرحيم • علم • فن • تخيل • قرار • متابعة ” لا يوجد علم دون تعب ... ودراسة مستمرة ... و متابعة حثيثة ” قال رسول الله صلى الله عليه و سلم : ( ان الله يحب اذا عمل احدكم عملا ان يتقنه ) .

  3. DEFENITIONS • VISUAL AXIS (line of vision ) : passes from the fovea through the nodal point of the eye to the point of fixation ( object of regard ) . In normal binocular single vision (BSV) the two visual axes intersect at the point of fixation , with the images from the two eyes being aligned by the fusion reflex and combined by binocular responsive

  4. cells in the visual cortex to give BSV . ORTHOPHORIA Implies perfect ocular alignment in the absence of any stimulus for fusion which is uncommon. HETEROPHORIA ( PHORIA ) Implies a tendency of the eyes to deviate when fusion is blocked (latent squint ). Slight phoria is present in most normal individuals and is overcome by the fusion reflex.

  5. It can be either esophoria or exophoria . When fusion is insufficient to control the imbalance the phoria is described as decompensating and is often associated with symptoms of binocular discomfort or double vision ( diplopia ). HETEROTROPIA It implies a manifest deviation in which the visual axes do not intersect at the the point of fixation .

  6. The images from the two eyes are misaligned so that either double vision is present or more commonly in children , the image from the deviating eye is suppressed at cortical level . Why squint in childhood ? 1- failure of the normal development of binocular fusion mechanisms. 2- oculomotor imbalance secondary to differences in refraction of the two eyes

  7. Why squint in adult ? 1- failure of fusion , for example secondary to poor vision in one eye . 2- weakness of muscles . 3- restriction of muscles . 4- damage to nerve supply .

  8. Horizontal deviation ( latent or manifest ) is the most common form of strabismus . • A vertical deviation almost invariably reflects abnormal ocular motility . • Upward displacement of one eye relative to the other is termed hypertropia and a controlled upward imbalance a hyperphoria . • Downward displacement is termed a hypotropia and controlled imbalance a hypophoria .

  9. ANATOMICAL AXIS Is a line passing from the posterior pole through the center of the cornea . Because the fovea is usually slightly temporal to the anatomical center of the posterior pole of the eye , the visual axis does not usually correspond to the anatomical axis of the eye .

  10. ANGLE KAPPA Is the angle subtended by the visual and the anatomical axes and is usually about 5 degrees . The angle is positive when the fovea is temporal to the center of the posterior pole resulting in a nasal displacement of the corneal reflex and negative when the converse applies .

  11. A large angle kappa may give the appearance of a squint when none is present ( pseudo- squint ) and is seen most commonly as a pseudo- exotropia following displacement of the macula in ROP where the angle may significantly exceed + 5 degrees .

  12. ANATOMY OF EXTRAOCULAR MUSCLES The lateral and medial orbital walls are at angle of 45 degrees with each other. The orbital axis therefore forms an angle of 22.5 degrees with both the lateral and medial walls . ~ 23 degrees

  13. When the eye is looking straight a head at a fixed point on the horizon with the head erect ( primary position of gaze ), the visual axis forms an angle of 23 deg. With the orbital axis . The action of the extraocular muscles depend on the position of the globe at the time of muscle contraction .

  14. Primary action : of a muscle is it’s major effect when the eye is in the primary position . Subsidiary actions : are the additional effect which depend on the position of the eye . Listing plane : is an imaginary coronal plane passing through the center of rotation of the globe .the globe rotates on the X and Z axes of Fick, which intersect in Listing plane .

  15. The globe rotates left and right on the vertical Z axis . • The globe moves up and down on the horizontal X axis . • Torsional movements ( wheel rotation ) on the Y ( sagittal) axis which traverses the globe from front to back ( similar to the anatomical axis of the eye . • Intorsion occurs when the superior limbus rotates nasally and extorsion on temporal rotation .

  16. HORIZONTAL RECTUS MUSCLES When the eye is in the primary position , the horizontal recti are purely horizontal movers on the vertical Z axis and have only primary actions . MEDIAL RECTUS : originates at the annulus of Zinn at the orbital apex and inserts 5.5 mm behind the nasal limbus . it’s sole primary action is adduction . LATERAL RECTUS : originates at the annulus of Zinn and inserts 6.9 mm

  17. Behind the temporal limbus .it’s sole primary action is abduction . VERTICAL RECTUS MUSCLES The vertical recti run in line with the orbital axis and are inserted in front of the equator . They therefore form an angle of 23 deg. With the visual axis .

  18. SUPERIOR RECTUS : originates from the upper part of the annulus of Zinn and inserts 7.7mm behind the superior limbus. The primary action is elevation , secondary actions are adduction and intorsion . when the globe is abducted 23 deg. The visual and orbital axes coincide . In this position it has no subsidiary actions and can only act as elevator .

  19. This is therefore the optimal position of the globe for testing the function of thesuperior rectus muscle . If the globe was adducted 67 deg. , the angle between the visual axis and orbital axis would be 90 deg. In this position the superior rectus could only act as intorter .

  20. INFERIOR RECTUS : originates at the lower part of the annulus of Zinn and inserts 6.5 mm behind the inferior limbus . The primary action is depression , secondary actions are adduction and extorsion . When the globe is abducted 23 deg. The inferior rectus acts purely as a depressor. As for superior rectus , this is the optimalposition of the globe for testing the function of the inferior rectus muscle .

  21. If the globe was adducted 67 deg. The inferior rectus could only act as an extortor . SPIRAL OF TILLAUX The spiral is an imaginary line joining the insertions of the four recti and is an important anatomical land mark when performing surgery . The insertions get further away from the

  22. Limbus and make a spiral pattern . Med.rectus 5.5 mm Inf.rectus 6.5 mm Lat. Rectus 6.9mm Superior rectus 7.7 mm

  23. OBLIQUE MUSCLES The obliques are inserted behind the equator and form an angle of 51 deg with the visual axis .

  24. SUPERIOR OBLIQUE Originates superomedial to the optic foramen. It passes forward through the trochlea at the angle between the superior and medial walls and is then reflected backwards and laterally to insert in the posterior upper temporal quadrant of the globe .

  25. The primary action of the superior oblique is intorsion , secondary actions are depression and abduction . The anterior fibers of the superior oblique tendon are primarily responsible for intorsion and the posterior fibers for depression , allowing separate surgical manipulation of these two actions .

  26. When the globe is adducted 51 deg. The visual axis coincide with the line of pull of the muscle . In this position it can only act as a depressor . This is therefore , the best position of the globe for testing the action of the superior oblique muscle. Thus , although the superior oblique has an abducting action in primary position , the main effect of the superior oblique weakness is seen as failure of depression in adduction .

  27. When the eye is abducted 39 deg. The visual axis and the superior oblique make an angle of 90 deg. With each other . In this position the superior oblique can only cause intorsion .

  28. INFERIOR OBLIQUE Originates from a small depression just behind the orbital rim lateral to the lacrimal sac . It passes backward and laterally to insert in the posterior lower temporal quadrant of the globe , close to the macula . The primary action is extorsion , secondary actions are elevation and abduction .

  29. When the globe is adducted 51 deg. , the inferior oblique acts only as an elevator . When the eye is abducted 39 deg. , it’s main action is extorsion .

  30. MUSCLE PULLEYS The four rectus muscles pass through condensations of connective tissue and smooth muscle just posterior to the equator . These condensations act as pulleys and minimize upward and downward movements of the of the bellies of the medial and lateral rectus muscles during up-gaze and down-gaze … and horizontal movements of the superior rectus and inferior rectus bellies in

  31. Left and right gaze . Pulleys are the effective origins Of the rectus muscles and play an important role in the coordination of eye movements by reducing the effect of horizontal movements on vertical muscle actions and vice versa . Displacement of the pulleys can be one cause of abnormalities of eye movements such as V and A patterns .

  32. NERVE SUPPLY LATERAL RECTUS :is supplied by the 6th cranial nerve . ( abducent nerve – abducting muscle ). SUPERIOR OBLIQUE : is supplied by the fourth cranial nerve . ( trochlear nerve – muscle associated with the trochlea ) . OTHER MUSCLES : together with the levator muscle of the upper lid and the ciliary and

  33. Sphincter pupillae muscles are supplied by the 3rd ( oculomotor ) nerve .

  34. OCULAR MOVEMENTS DUCTIONS Ductions are monocular movements around the axes of Fick . They consist of adduction , abduction , elevation , depression , intorsion and extorsion . They are tested by occluding the fellow eye and asking the patient to follow a target in each direction of gaze . Torsional ductions are mainly observed in association with other abnormal eye movements .

  35. VERSIONS Versions are binocular, simultaneous , conjugate movements ( in the same direction ) . Dextroversion and laevoversion ( gaze right , gaze left ) , elevation ( up-gaze ) and depression ( down-gaze ). These four movements bring the globe into the secondary positions of gaze by rotation around either a vertical Z or a horizontal X axis of Fick .

  36. Dextroelevation and dextrodepression ( gaze up and right , gaze down and right ) and laevoelevation and laevodepression ( gaze up and left and gaze down and left ). These four oblique movements bring the eyes into the tertiary positions of gaze by rotation around oblique axes lying in Listing plane , equivalent to simultaneous movement about both horizontal and vertical axes .

  37. Torsional movements to maintain upright images occur on tilting of the head . These are known as the righting reflexes . On head tilt to the right the superior limbi of the two eye rotate to the left , causing intorsion of the right globe and extorsion of the left .

  38. VERGENCES Vergences are binocular , simultaneous , disjugate or disjunctive movements ( in opposite directions . Convergence is simultaneous adduction ( inward turning ) , divergence is outwards movement from a convergent position. Convergence may be voluntary or reflex .

  39. Reflex convergence has four components : • Tonic convergence : which implies inherent innervational tone to the medial recti , when the patient is awake . • Proximal convergence : is induced by psychological awareness of a near object. • Fusional convergence : is an optomotor reflex , which maintains BSV by insuring that similar images are projected onto corresponding retinal areas of each eye .

  40. It is initiated by bitemporal retinal image disparity . • Accommodative convergence : is induced by the act of accommodation as part of the synkinetic - near reflex . Each dioptre of accommodation is accompanied by a constant increment in accommodative convergence , giving the accommodative convergence by accommodation ( AC/A ) ratio .

  41. This is the amount of convergence in prism dioptres per dioptre change in accommodation . The normal value is 3-5 prism dioptre . this means that one dioptre of accommodation is associated with 3-5 prism dioptres of accommodative convergence . It will be shown later that abnormalities of the AC/A ratio play an important role in the aetiology of strabismus .

  42. These changes in accommodation , convergence and pupil size , which occur in response to a change in the distance of viewing are known as the near triad and occur in response to both image blur and temporal image disparity .

  43. POSITIONS OF GAZE SIXCARDINAL :positions of gaze are those in which one muscle in each eye has moved the eye into that position as follows : • Dextroversion ( right lateral rectus and left medial rectus ). • Laevoversion ( left lateral rectus and right medial rectus ). - Dextroelevation ( right superior rectus and left inferior oblique ).

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