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The extraocular muscles and ocular movements

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The extraocular muscles and ocular movements

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The extraocular muscles and ocular movements

  1. 1. THE EXTRA OCULAR MUSCLES AND OCULAR MOVEMENTS
  2. 2. There are Fourteen Extraocular Muscles, Six Inserted in to each globe which are responsible for movement of the eyes, and one inserted in to each upper eyelid, responsible for raising it. These muscles are : 1. Rectus Muscles Horizontal recti Lateral rectus (LR) Medial Recus(MR) Vertical Recti Superior Rectus(SR) Inferior Rectus(IR) 2. Oblique Muscles Superior Oblique (SO) Inferior Oblique (IO) 3. Lid elavator muscles Levator Palpebrae Superioris (LPS) ANATOMY the xtraocular muscles Consist of stiped muscle fibers . The recti muscles and the superior oblique originate from tendinous ring, the annulus of zinn, which surrounds the optic foramen at the apex of each orbit. The levator muscles has its origin just above the annulus of the zinn. The inferior oblique arises from the orbital floor, just behind the orbital margin and close to the angle formed, fanning out to form a cone like shap-e ( the muscle cone).
  3. 3. In front of the globe. The superior oblique passes forward betweeen the medial and superior recti until it reaches the trochlea or pulley, a ring of cartilage situated just inside the orbital margin in the angle formed by the roof and medial wall. The muscles passes through the pulley and is reflected obliquely backwards , passing under the superior rectus muscles, to be inserted in to the posterior superior temporal quadrant of the globe. The inferior oblique passes obliquely backwards, running running approximately parallel with the superior oblique, passing between the inferior rectus and the globe to be inserted in to the posterior inferior temporal quadrant. The levator muscles passes forward above the superior rectus , just below the orbital roof, and is inserted in to the skin of the upper eyelid. NERVE SUPPLY The extraocular muscles are supplied by the cranial nerves as follows: the sixth nerve supplies the lateral rectus, the fourth nerve supplies the superior oblique and the third nerve supplies the medial rectus, inferior rectus and inferior oblique via its inferior division. The superior division of the third nerve supplies the superior rectus and the levator muscle. The inferior division also carries the nerve supply to the sphincter muscle in the iris, which constructs the the pupil an dto the ciliary muscle, which control accomodation.
  4. 4. •Elevation in adduction •Adduction •Depression in adduction ACTIONS OF THE EXTRAOCULAR MUSCLES Movement of the globe is brought about by contraction of the extraocular muscles. Each muscle has a main action, which increases, in one position of gaze . When the eyes look ahead, they are in the primary position. They are maintained in that position by simultaneous contraction of the rectus and oblique muscles. As the eyes move away from the primary position, one or more muscles increase their contraction and others relax to allow movement to take place. The diagnostic position for the right eye shown in fig 1 & fig 2. elevation depression •Elavation in abducn •Abduction •Depresssion in abduction Primary position •Elevation in abduction •Abduction •Depression in abduction Fig 1 position of a gaze of the right eye as seen by the examiner T N
  5. 5. •Superior rectus •Lateral rectus •Inferior rectus Primary position •Inferior oblique •Medial rectus •Isuperior oblique Superior rectus Inferior rectus T N Fig 2 – the main extra ocular muscles (of right eye) which act in the diagnostic position of gaze, as seen by the examiner T -Temporal N- Nasal Actions of the extraocular muscles Horizontal recti muscles Lateral Rectus Abduction (outward movement) Medial rectus Abduction (inward movent)
  6. 6. Muscle Primary Position Adducted Position Abducted Position Superior rectus Inferior rectus Superior oblique Inferior oblique Primarily an elevator also intorter and adductor Primarily a depressor also extorter and adductor Primarily intorter also depressor and abductor Primarily intorter also elevator and abductor Weaker elevator better intorter Weaker depressor better extorter Mainly depressor weaker intorter Better elevator Better elevator weaker intorter Better depressor weaker extorter Better intorter Better extorter
  7. 7. Secondary actions of extraocular muscles the lateral rectus and the medial rectus have only one action but the vertically acting muscles have additional secondary action. There are 1. Abductipon or adduction, suplimenting the actions of the lateral and medial rectus. 2. Wheel rotation nasally or tempoprally, assessed from the 12’o clock position on the linbus. Wheel rotation nasally is termed intorsion, wheel rotation temporally is termed extorsion. each muscles secondary actions increase when the eye is turned away from the position of main action. For eg: the main action of the superior rectus increases when the eye is abducted, its secondary actions increase when the eye is adducted. As in table below. OCULAR MOVEMENT the purpose of ocular movement is to place the image of the object of interest on the fovea of each eye, so that the best possible vision is obtained an binocular single vision(BSV) can be maintained in all positions of gaze. This requires that the two eyes move simultaneously, at the same speed and in exacly the same direction. Muscles are paired to achieve movements in the same direction. Paired muscles are termed synergists or yolk muscles.
  8. 8. LAWS GOVERNING OCULAR MOVEMENTS 1. Hering’s laws of equal innervation,which states that an increase in innervation always goes equally to synegistic muscles. Using the above example, when the right lateral rectus contracts to move the eyes to the right, an equal amount of innervation goes to the left medial rectus to bring about coordinated movements. 2. sherrington’s law of reciprocal innervation, which states that an increase in innervation never takes place simultaneously in antagonistic muscles. The antagonist of the right lateral rectus is the medial rectus, which has a directly opposed action. The right lateral rectus cannot contract unless the antagonistic medial rectus relaxes. Relaxation of the antagonistic muscles allows smooth movents to the place . synergistic muscles can be in opposite eyes, termed contralateral synergistic or in the same eye, termed ipsilaterar synergists. An eg of contralateral synergists is the right superior rectus and the left inferior oblique, which work as a pair to bring about movement up and to the right. An eg. Of ipsi lateral synergists is the right superior rectus and the right inferior oblique, which act together to move the eye directly up. Contralateral synergists muscles are shown in the diagnostic position of gaze (fig 3).
  9. 9. R E RI O LS R RM R LLR RS O LIR RSR LIO RL R LM R RIR LSO T N L E LS R RI O LLR RM R LIR RSO LIO RSR LM R RL R LSO RIO T Fig 3 contralateral synergists muscles in the diagnostic positions of gaze.
  10. 10. Ipsilateral synergist are both elevating muscles on looking up, both depressing muscles on looking down likewise the levator and superior rectus are synergists. When the superior rectus contracts to elevate the eye,the levator contracts to r5aise the upper eyelid.When the eye looks down,both the superior rectus and the levator relax and the eye lid follows the downward movement of the eye. Ipsilateral antagonists are muscles in the same eye with directly opposed main actions.In the right eye these are the lateral and medial rectus, the superior and inferior recti and the superior and inferior oblique. VERSIONS a version is a conjugate all parallell eye movement in which both eyes move in the same direction. Versions are describe as dextroversions, both eye move to the right, laevoversion, both eye eyes move to the left, dextroellevation, both eyes move up end to the right, dextrodepression, both eyes move down and to the right laevoversion and levodepression are use to describe the movement up and to the left and down and to the left respectively. DUCTIONS a ductionn is a movement of one eye, abduction being outward movement, adduction inward movent. Supraduction and infraduction apply to upward and downward movement respectively, but these later terms are rarely used.
  11. 11. VERGENCES A vergence is a disjugate or non parallel eye movement in which the eyes moves in oposite direction. These movements are neccesssary to maintain foveal fixation and BSV as objects approach or recede from the eye. They comprise : 1. convergence, brought about by contrction of both medical rectus muscles. 2. Divegent , brought about by contraction of both lateral rectus muscles small amounts of vertical and torsional vergences are also possible and are used to control vertical or torsional squint. EXAMINATION OF OCULAR MOVEMENTS versions are tested routinely by asking the patient to follow a moving target, controlled by the examiner, in to the diagnostic positions of the gaze, observing the extent of movement of each eye . Horizontal movements are always tested first ,followed by vertical movements. precausions 1. A cover test first should be first performed. The result can help in the assessment of occular movement. A vertical squint suggest that there may be a defective vertical movement. A manifest squint influences the method of resting as described below
  12. 12. 2. The patients head must be kept straight. It may be necessary to hold it, especially when testing a child. 3. The target must be easy to see and small enough to ensure accurate fixation on it. A small torch is ideal, but must not be too bright. 4. The target should be held about 40cm from the patient’s eyes and should be kept at level when testing horizontal versions. 5. Both eyes must be visible to the examiner.It may be necessary to raise the eyelids slightly to see the eyes as they look down,but the eyelid position must be observed before doing this,because abnormal lid movements are sometimes seen and must be noted. 6. The target should be moved smoothly at a moderate speed,not too fast for the patient to follow it.It must be moved to the limits of gaze,otherwise small defects of movement can be missed. 7. If movement in one eye appears limited,the other eye should be covered and ductions tested,comparing the amount of movement.This can sometimes happen with a manifest squint.If for example,there is a large right exotropia,the right eye will remain divergent when the fixing left ete watches the target into the left –hand field,so that that the right medial rectus appears limited. This should be checked with the left eye covered,when it may be found that adduction is full.Ductions must always be checked when there is an underaction noted in any position of gaze on versions(compering the movement with both eyes open and with both eyes open and with the normal eye covered.
  13. 13. REAULT if both eyes move equally and smoothly in all directions of gaze, ocular movemen tis full. Abnormal ocular movements comprise. 1. underaction, seen when the eyes are directed into one or more positions of gaze. For example, if the right lateral rectus underacts or is prevented from acting mvement of the right eye will stop as the target is movedfurther to the right, but the left eye will continue to followthe target to the limit of gaze. 2. Overasction, which is usually the result of underaction in the other eye . According to Hering’s law , more innervation is send to, for example, th eright lateral rectus in an effort to improve defective movement: th esame innervation goes to the normal left medial rectus, which does not need it,causing it to make an excessive movement. This is best seen by coveringthe left eye (in the same example) to make the defective eye fix. As that eye fixes, th eye behind the cover can be observed, making the overaction more obvious. Underaction may be marked or slight.detection of slight underation is easier f the movement of the suspect ete is compared with the same movement in the normal eye. For eg:, abduction of each eye can be compared by making the patient look at the target held well to the right , then at target held well to the left. An alternate cover test is useful in detecting abnormalities of ocular movement and should performed in all cases, holding the fixation target in each diagnostic position of gaze inturn while the cover test is performed,
  14. 14. position of main action of the defective muscles. This is particularly useful in suspected superior oblique palsy, which is sometimes obscured by the shape of the palpebral fissure on looking down and in. Recording the results underaction and overaction can be described in relation to the position of gaze in which they are seen: - Underaction of the RE on laevodepression, with overaction of the LE. -Alternatively they can be described in relation tto the muscles involved: -- underaction of the right superior oblique with overaction with the left inferior rectus. -An indication of the amount of limitation of movement should be given, classed as slight, moderate, marked or no movement.this classification become easier with experience. This is usually graded from one to four overaction indicated by (+) sign and underaction indicated by (-) sign. -Deficits of ocular movement can be recorded diagramatically as shown in this eg (fig 4 &5)
  15. 15. RE RSR RLR RSR RMR RIO RSO LE LI O LMR LSO LSR LLR LIR Fig 4 field of actions of muscles
  16. 16. Recording overaction and underatcion RE LE Fig 5 (++)overaction –underaction it is important to record any other abnormalities seen when testing ocular movement. These sighns can help in the diagnisis. They include nystagmus, which may be preesnt in certain position gaze, retraction the globe in which the eye ball is seen to move back into the orbit into one or more position sof gaze, any changes in the palperal fissure (narrowin gor widening) an dan increase in the horizontal angle in of squint on looking up or orlookking down.this is quit a common findings in defects of vertical eye movement. +++ _ ++

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