EOMs Flashcards
Which types of eye movements (ductions, versions, vergences) are monocular, and which are binocular?
monocular - ductions
binocular - versions (conjugate) and vergences (disjunctive)
Dextroversion means?
right gaze (both eyes look right)
Levoversion means?
left gaze (both eyes look left)
Supravergence means?
one eye looks up, the other doesn’t move
Infravergence means?
one eye looks down, the other doesn’t move
What does tertiary position of gaze mean?
the eyes are rotated around both vertical and horizontal axes (looking both up/down and left/right)
What is the origin of the rectus muscles?
SR: Common tendinous ring + ON sheath
MR: CTR + ON sheath
LR: CTR + spina recta lateralis (on the greater wing of sphenoid bone)
IR: CTR only
What is the spiral of Tillaux
insertions of the rectus muscles on the sclera, the MR insertion is closest to the limbus, then IR, LR and furthest is the SR insertion
What is the largest and thickest EOM?
Medial rectus due to so much converging
How many degrees is the SR insertion compared to the sagittal axis?
23 degrees (roughly half of the 45-degree orbit) IR is similar, parallel to SR
What are the actions of the SR?
primary - elevation
secondary - adduction, intorsion
What are the actions of the IR?
primary - depression
secondary - adduction, extorsion
What is the longest and thinnest EOM?
Superior oblique
What is the origin of the SO muscle?
anatomic origin is the lesser wing of the sphenoid bone, medial to the optic canal, and then the trochlea is considered the physiological origin
What angle does the SO muscle make with the sagittal axis?
55 degrees
What are the actions of the SO muscle?
primary - intorsion
secondary - depression, abduction
Which is the shortest EOM?
Inferior oblique muscle
What is the origin of the IO muscle?
on maxillary bone, posterior to the inferior medial rim
What angle does the IO muscle make with the sagittal axis?
51 degrees
What are the actions of the IO muscle?
primary - extorsion
secondary - elevation, abduction
What is Sherrington’s Law of Reciprocal Innervation?
contraction of a muscle is accompanied by a simultaneous and proportional relaxation of the antagonist
What is Hering’s Law of Equal Innervation?
the innervation to the muscles of the two eyes is equal and simultaneous, thus the movements of the two eyes are normally symmetric (binocular movements)
What is the origin of the levator palpebrae superioris (LPS)?
the lesser wing of the sphenoid, anterior/superior to the optic canal (muscle sheath blends with the sheath of SR)
What are frontal eye fields and where are they located in the brain?
Frontal eye fields are located in the frontal cortex and are involved in voluntary and reflex movements, etc., it communicates with EOMs via the paramedian pontine reticular formation (PPRF)
Where in the brain does visual processing occur?
striate cortex located in the occipital cortex
Which of the superior vs inferior colliculus receives visual inputs from the LGN?
superior colliculus
What eye movements does the PPRF primarily coordinate?
coordination of eye movements, particularly horizontal movements
What is the medial longitudinal fasciculus (MLF)?
coordinates eye movements, connecting CNVIII, CNIII, CNIV, and CNVI, also receiving input from the cerebellum and/or superior colliculus.
the rostral interstitial nucleus of the MLF (riMLF) is primarily in the midbrain
How does a lesion in the MLF present?
affected eye can’t adduct in horizontal gaze, but convergence is generally still intact
T/F: the riMLF is the location of the vertical gaze center?
True
What is the vestibulo-ocular reflex?
connections between vestibular nucleus and EOM nuclei through the MLF to coordinate eye movements in response to head movements, allowing eyes to remain fixed on a target even when the head is moving
Which eye muscle is the only one to have a single nucleus and not a pair?
LPS
Which is the only cranial nerve to exit the midbrain/pons posteriorly?
CNIV - trochlear
The fibers to which EOMs decussate and supply contralateral eye to their nuclei?
SR and SO
Which cranial nerve damage is most likely to be involved with increased ICP?
CNVI - abducens
Which cranial nerve damage is most likely to be involved in trauma?
CNIV - trochlear
What are saccades vs. pursuits?
saccades - rapid eye movements, FEF and superior colliculus (contralateral)
pursuits - smooth tracking movements, parietal lobe (ipsilateral)
which EOMs originate from the CTR and optic nerve sheath?
SR and MR (pain on eye movement with nerve swelling)
what are some qualities that EOMs have that are unique from other skeletal muscle in the body?
blood supply is denser in EOMs, nerve supply is denser and more finely tuned, EOM movements are faster and more fatigue resistant
which EOM inserts onto the sclera closest to the limbus and which is farthest?
MR is closest, 5.5mm from limbus
SR is furthest, 7.7mm from limbus
(LR is 6.9mm and IR is 6.5mm from limbus)
what is the only EOM that does not originate on the CTR?
IO - originates on the maxilla
what connections ensure that the eyelid is raised when the eye is in upgaze?
the sheath covering the SR is connected to the sheath of the LPS and the connective tissue of the superior conjunctival fornix, all causes the eye to lift the lid when the eye is in upgaze
ligament of Lockwood
IR sheath combines with IO sheath to form the suspensory ligament of Lockwood, attaches to the inferior tarsal plate and extends from the zygomatic bone to the lacrimal bone to provide support for the globe
how do the EOMs get their blood supply?
blood is supplied mainly by the muscular branch of the ophthalmic artery, superior lateral branch supplies the SR, LR, and SO, and the inferior medial branch supplies the MR, IR, and IO.
The lacrimal, supraorbital, and infraorbital arteries provide a minor blood supply to the EOMs also
how are the EOMs innervated?
superior division of CNIII - SR
inferior division of CNIII - IR, IO, MR
CNVI - LR
CNIV - SO
Velocity and latency of saccade
1000 deg/s velocity
200ms latency
Velocity and latency of pursuits
50 degrees/sec, 125ms latency
What does an INO present as?
Cannot adduct same side as lesion, and has horizontal nystagmus on the contralateral eye/gaze
What is OKN?
Optokinetic nystagmus, following a moving object while head stays still
“TONS of movement” in 3month old is normal presence of T -> N OKN movement ability only (cannot do N->T yet)
VOR vs. OKR?
VOR keeps image on fovea when head is moving (eyes moving opposite to head movement), still happens when eyes are closed. 300 deg/sec velocity and 15msec latency.
Becomes OKR (optokinetic reflex) if head is moving for greater than 30 seconds in duration
Donder’s Law
Orientation of the eye for a particular gaze is always the same, regardless of where the eye was initially positioned before moving to that gaze
Listing Law
Eye moves around the Listing’s plane/axes
(Y is forward and backwards, X is side to side, and Z is up to down)
What is the Troxler effect and how do eye movements fix this?
Fading of peripheral images when fixating on a central object, involuntary eye movements prevents this by moving and using new cells
Micro saccades
Correct microdrifts and micro tremors (2-10 deg.sec, 6arcmin amp)
Micro tremors
Unintentional due to neural noise, (65-75Hz, 10arcmin amp)
Microdrifts
Unintentional, due to neural noise, like micro tremors but larger and slower (1arcmin/sec, 6arcmin amp)))
Testing for VOR/vestibular dysfunction:
“ROC”
1. Rotational
2. Oculocephalic
3. Caloric testing
Rotational testing for vestibular system
Rotate patient in chair 20s, eyes normally have a slow conjugate movement in direction of rotation, then a fast movement in opposite direction
Oculocephalic testing for vestibular system
“Dolls eyes”, eyes should move opposite to head movement when fixating a distant object and turning head side-to-side
Caloric testing for vestibular system
COWS is the normal response (look at fast phase)
Cold water - fast movement to opposite side
Warm water - fast movement to same side
Same as “caloric nystagmus”
What conditions would have a positive forced duction test?
Orbital fracture with trapped muscle, TED, Browns, myositis, Duanes
What abnormal deviation conditions would have a negative forced duction test?
CN3,4,6 palsies, ischemia, tumour
What germ cell layer do the EOMs derive from and in what order?
Mesoderm
CN3 muscles, then LR, then SO
Which EOMs have blood supply from both ICA and ECA arteries?
IR and IO
Vergence eye movements are driven by?
Retinal disparity (to maintain motor fusion)
In what ways are EOMs different from other skeletal muscles in the body?
- Blood supply is denser in EOMs
- Nerve supply is denser and more finely tuned
- EOM movements are faster and more fatigue resistant due to a unique combination of white (fast) and red (slow but sustaining) muscle fibres
What can happen to the EOMs during TED?
EOM restrictions! Not palsy. So if you see an Eso deviation its not because of LR palsy it is because of MR restriction.
Most common: IMSLO
How does IOI (idiopathic orbital inflammation) look different from TED?
TED has just EOMs swelling/restricting, IOI has EOMs and tendons all swelling.
What are the common causes of an INO?
young patient - MS
older patient - stroke
the primary action for obliques is
torsion
superiors always __________ and inferiors always ________
S - intort and I - extort
obliques always ________ and S/I recti always ___________
obliques aBduct, recti adduct
