EOMs PDF

The EOM are the tracking mechanism that allow for: foveal fixation, binocular fusion, and target tracking Fick’s Axes X-axis: nasal to temporal ○ Supraduction and infraduction Y-axis: anterior to posterior ○ Intorsion and extortion Z-axis: superior to inferior ○ Adduction and abduction These axes in...

The EOM are the tracking mechanism that allow for: foveal fixation, binocular fusion, and target tracking Fick’s Axes X-axis: nasal to temporal ○ Supraduction and infraduction Y-axis: anterior to posterior ○ Intorsion and extortion Z-axis: superior to inferior ○ Adduction and abduction These axes intersect at the center of rotation A fixed point is defined as being located 13.5 mm behind the cornea Versions: eye movements are paired meaning both eyes do the same coordinated movement in the same direction; conjugated eye movements Yoked muscles: two muscles that work at the same time and towards the same direction ○ Example: RMR and LLR are yoke muscles Dextroversion/Levoversion Supraversion/Infraversion Vergences: eye movement in the opposite direction simultaneously; are disjunctive eye movements Non-yoked motions ○ Convergence/Divergence ○ Incyclovergence (intorsion)/ Excyclovergence (extorsion) Cyclorotation: torsion-cyclorotations Rotation about the Y-axis ○ Y-axis runs horizontally, from anterior to posterior These are described with respect to a point at 12 o’clock on the superior limbus ○ Interior (incyclorotation) rotation nasally ○ Extorsion (excyclorotation) rotation temporally Patient can counteract motion with a head tilt (up to 7-9 degrees) Muscles: antagonist vs agonist muscles Agonist muscles are prime movers Antagonist perform the opposite movement of the agonist (example: Medial Rectus and Lateral rectus) Hering’s Law of Equal Innervation Equal and simultaneous innervation from the oculogyric centers to the yoke muscles, causing simultaneous contraction for binocular movements Example: head tilt to the right ○ Right eye muscle group that intort and left eye muscle group that extort receive equal and simultaneous stimulation On Right head tilt: OD needs to turn inward (incyclotorsion) and OS needs to turn outwards (excyclotorsion) Muscles responsible: RSR, RSO, LIO, and LIR Sherrington’s Law of Reciprocal Innervation Increased contraction of the agonist muscle is associated with diminished contractile activity of its antagonist muscle Right gaze: increased contraction of the RLR and LMR accompanied by antagonistic RMR and LLR Convergence: increased activity of RMR and LRM with associated decreased activity of the LLR and RLR Head tilt to the right: ○ Muscle group for incyclotorsion of the OD and the excyclotorsion of the OS contract, ○ While muscle for excyclotorsion of the OD and incyclotorsion of the OS must relax Innervation: (nerve & muscle) Oculomotor nerve - MR, SR, IR, IO, levator, iris sphincter Inferior division - MR, IR, IO Superior division - SR CN 4 (Trochlear) - SO CN 6 (Abducens) - LR Vascular supply: (muscle & vascular supply) Medial & Inferior rectus, Inferior oblique - Inferior muscular artery branch of the ophthalmic artery Lateral & superior rectus, Superior oblique - Superior (lateral) muscular branch of ophthalmic artery Medial rectus: ADDuction Largest and strongest of the ocular muscles Lateral rectus: ABDuction Superior Rectus: Primary: elevation Secondary: intortion Tertiary: ADDuction Inferior Rectus: Primary: depression Secondary: Extortion Tertiary: ADDuction Superior oblique: longest and thinnest muscle Primary: intortion Secondary: depression Tertiary: ABDuction Inferior oblique: Primary: extortion Secondary: elevation Tertiary: ABDuction When in ADDuction: the SO and IO become the main elevators and depressors Only IO elevates Only SO depress When in ABDuction: the SR and IR are in charge of elevation and depression Only SR elevate Only IR depress Vertical muscles: SR and IR lie in a plane ~23 degrees relative to the visual axis in the primary position This gives rise to secondary and tertiary actions Secondary action of vertical rectus muscles is torsion Tertiary action of both IR and SR muscles is adduction When in abduction, the SR and IR are in charge of elevation and depression Oblique muscles: superior and inferior oblique muscles are the primary muscles for torsion As the direction of pull for both muscles form a 51 degree angle (relative to the visual axis in the primary position) Secondary action is a vertical movement Tertiary action is abduction When in ADDuction, the obliques are in charge of elevation and depression SR and IR lie in a plane of ~23 degrees in primary gaze When the OD is turned outward (ABDucted) ~23 degrees, the SR acts as a pure elevator and the IR acts a pure depressor So: when the eye is fully ABDucted, it can only be elevated by the SR and depressed by the IR The SO and IO lie in a plane that makes an angle of ~51 degrees from primary gaze When the eye is turned inward (ADDucted), ~51 degrees the IO acts as a pure elevator and the SO acts as a pure depressor So: when the eye is fully ADDucted, it can only be elevated by the IO and depressed by the SO Any limitation of movement when looking inward ~51 degrees and the downward would be due to the SO (in and down) or the IO (in and up) So: when the eye is ADDucted, it can only be elevated by the IO and depressed by the SO Broad H Test: gaze can be directed about 30-40 degrees in each direction to be able to detect any movement limitation Motility test of the horizontal and vertical acting muscles Interpreted in terms of field of action of the 6 EOMs The field of action refers to the field in which a certain muscle has greatest action Fields of action of the 4 vertically acting muscles are based on the muscle planes of each muscle Used to assess the patient’s ability to perform conjugate eye movements ○ Identify deviations that could result from strabismus, EOM dysfunction or palsy Conjugate movement: saccades or pursuits Pursuits: keep the image in the fovea ○ Used for tracking, slower movements ○ Reading ○ Mediated by the parieto-occipital junction (area 19) with a velocity of degrees/sec Saccades: fast movements ○ When reading jumping from one sentence to the next ○ Mediated by the frontal lobe (area 8) ○ Used to follow objects faster than 45 degrees/sec up to 400 degrees/sec Recording: SAFE or FESA (Smooth, Accurate, Full, and Extensive) OD, OS Describe any problem such as nystagmus, jerky movement, reported diplopia, restriction, lagging, non-comitancy, or head movements Identify the direction of gaze that result in diplopia or discomfort and the eye that is affected Examples: ○ SAFE OD, OS, OU ○ EOM: Diplopia at Right gaze OD lagging/undershoot ○ EOM: SAFE, OD pain in left gaze ○ Expected: SAFE OD/OS/OU No pain or diplopia Endpoint nystagmus if target is take to the extreme limits NSUCO Saccades Test for voluntary saccadic movement by having the patient look from one target to the next when instructed Hold two different colored targets at 40 cm from the patient and separated by 20 cm Observe: accuracy, ability, head movements and body movements MSUCO Pursuits Also evaluated with Broad H One target is held at 40 cm from the patient Patient is instructed to watch the target as it is moved Move the target into 2 clockwise circles (~20 cm diameter), 2 counterclockwise and one sweep across midline Observe accuracy, ability, head movement and body movement Isolated 3rd Cranial Nerve Palsy Symptoms: ○ Diplopia with both eyes open, disappears closing one eye ○ Droopy eyelid, with or without pain Signs: ○ Binocular horizontal diplopia ○ Limitation on ocular movement ○ Ptosis ○ May have pupillary involvement ○ Exotropia and/or hypotropia (depending on which division is affected) Etiology: aneurysm (PCA), microvascular disease (DM, HTN), tumor, trauma, congenital, uncal herniation, cavernous sinus mass Aneurysms If experiencing some or all of the following symptoms, regardless of age, patient should undergo immediate and careful medical evaluation ○ Localized HA (thunderclap) ○ Dilated pupils ○ Blurred or double vision ○ ○ ○ Pain above and behind the eye Weakness and/or numbness Difficulty speaking Isolated 4th Cranial Nerve Palsy Symptoms: ○ Double vision with both eyes open, disappears closing one eye ○ Patient might be asymptomatic, may have trouble reading Signs: ○ Binocular vertical diplopia (above one another) ○ Deficient inferior movement when looking down and in ○ Hypertropia increases when looking toward the direction of the uninvolved eye or tilting the head towards the ipsilateral shoulder Patient might have a compensatory head tilt to the contralateral shoulder Involved eye is higher when patient looks straight ahead Hypertropia increases when looking in the direction of the uninvolved eye or tilting towards ipsilateral shoulder Head tilt towards the contralateral shoulder to eliminate diplopia Causes: ○ Vasculopathic: DM and HTN are common ○ Tumor: 4th CN has a long course through the cranial vault, anything affecting along the course may cause a palsy ○ Congenital: common in children Be careful since they compensate with head tilts ○ Trauma: 4th CN long and skinny course, anything along it may cause a palsy ○ Others: idiopathic, demyelinating disease, aneurysms Isolated 6th Cranial Nerve Palsy Symptoms: ○ Double vision with both eyes open, worse at distance than near ○ More pronounced in the direction of the paretic lateral rectus Signs: ○ One eye is unable to turn outward (abduction, temporally) ○ Etiology: ○ Vasculopathy: increased ICP, Multiple Sclerosis, Cavernous sinus mass ○ In children: benign post viral, pontine glioma, trauma Brown Syndrome Harold W. Brown described the syndrome Difficulty looking up and in due to a mechanical cause around the superior oblique ○ Due to shortening or tightening of the anterior superior oblique tendon Eyes point out in a straight gaze (divergence in upgaze) Widening of the eyelids in the affected eye in adduction Head tilts backwards (compensatory chin elevation to avoid double vision) Near normal elevation in abduction