Eye movements

what are the 4 different types of eye movements?

saccades, smooth pursuit, vergence, and vestibule-ocular

define: saccades

rapid, ballistic movements that abruptly change the point of fixation, voluntary and reflexive

define: smooth pursuit

much slower tracking movements of the eyes designed to keep a moving stimulus on the fovea

voluntary and reflexive

define: vergence

conjugate eye movements, the two eyes move in the same direction

define: vestibule-ocular

stabilize the eyes relative to the external world, reflexive and compensate for head movements, prevents visual images from slipping on the surface of the retina as head position

what do eye movements do in humans?

high acuity vision restricted to the fovea, scanning, smooth pursuit, and stabilized images on the retina

define: optical axis

imaginary line perpendicular to the cornea that intersects the center of the entrance of the pupil

define: orbital axis

the orbital axis bisects the orbit and diverges 23 degrees from the visual axis

what is the position of the eye when people are awake? what about asleep/anesthetized?

awake: optical axis

asleep/anthestizied: orbital axis

why do we care about the 2 different axes of the eyeball?

the superior rectus, inferior rectus and the oblique muscles can have more than one action depending on the horizontal position of the eyeball at the start of the movement, this influences how eye movements are tested

what are the 4 conjugate movements?

vergence, convergence, divergence and torsional

define: divergence and torsional movements

divergence: occurs while maintaining fixation on an object away from the eyes

torsional: eyes move around the AP axis to counteract head movement in maintaining fixation on an object

what is disconjugate?

both eyes move in the same direction with different amplitude and frequency. Lesions to specific regions of the brain and cranial nerves can cause this

what muscles are innervated by CN 3

superior, medial and inferior rectus, and inferior oblique

what muscles are innervated by CN 4?

superior oblique

what muscles are innervated by CN 6?

lateral rectus

what muscles do elevation of the eye?

superior rectus and inferior oblique

inferior oblique: pulls the eye up and out

superior rectus: pulls the eye up and in

what muscles do depression?

superior oblique: pulls the eye down and out

inferior rectus pulls the eye down and in

what are the primary and secondary functions of the torsional movements?

primary: superior and inferior oblique muscles

secondary: superior and inferior rectus muscles

look at chart with eye muscles and actions and make sure you understand

what does damage to oculomotor nerve look like?

paralysis of muscles, down and out, ptosis, pupillary dilation and loss of accommodation

what does damage to the trochlear nerve look like?

at rest, extortion of the right eye. Vertical diplopia, not usually visible to examiner, not usually visible to examiner, patient may state they have diplopia when walking down stairs

what does damage to abducens nerve look like?

patient is unable to abduct the right eye on the right conjugate gaze, may present with horizontal diplopia

look at clinical testing of extra-ocular muscles

what is a major cortical and subcortical structures involved in eye movements?

frontal eye fields

what are the major sites in the cortex that generate eye movement?

frontal eye fields (saccades) and parietal lobe (smooth pursuit)

what is important in the midbrain?

vertical gaze center

what is important in the pons?

horizontal gaze center

what are horizontal eye movements generated by (think CN)?

what does the medial longitudinal fasiculus connect?

CN 6 and 3,

connects: oculomotor, trochlear, abducens, and vestibular nuclei

what do the MLF connections allow for? what would a lesion result in?

allow for conjugate gaze, lesions result in intraneuclear ophthalmoplegia

what is the function of the paramedian pontine reticular formation?

generates ipsilateral horizontal eye movemetns

where are the 2 main nuclei in the vertical gaze centers?

rostral interstitial nucleus and interstitial nucleus of cajal

what is the purpose of the interstitial nucleus of cajal?

maintains up gaze

what is the cause of vertical gaze lesions and what are some signs?

cause: compression of tectal plate, pinealoma, hydrocephalus

signs: upward gaze palsy, and light-near dissociation

what do vestibule-ocular movements do?

stabilize gaze relative to the outside world, compensate for head movements, respond to internal stimulus form the vestibular system

what do the optokinetic eye movements do?

stabilize gaze relative to the outside world, respond to external stimulus from visual system

what occurs to the rates of firing when turning to the right for example?

turn head to right there is an increase firing and a decrease on the left side

what are some fun facts about the vestibule-ocular reflex?

mediated by brainstem circuits, very fast reflex, faster than voluntary pursuit, VOR is normally suppressed in an awake person unless awake person is told to maintain fixation on an object as head is turned

what are optokinetic movements sensitive to? what do they rely on cues?

sensitive to slow movements of large areas of the visual field,

relies on cues indicating motion of the visual field

how do you test optokinetic movements?

eyes automatically tract stripes until eyes reach the limit of their excursion

what is the difference between vestibule-ocular and optokinetic movements?

vesibulo-ocular: response to quicker movements of the head detected by the vestibular system

optokinetic movements: in response to slower movements of the visual field detected by the visual system

what is the difference between physiological and pathological nystagmus?

physiological: slow component for tracking an object while head is moved and fast component when resetting eye position

pathological: occurs with unilateral damage to vestibular system resulting in an difference in R vs. L firing rates in the absence of head movement

where are the frontal eye fields located?

premotor cortex and adjacent cortices and frontal pursuit center

where are the parietal pursuit centers?

parietal lobe and lateral inter parietal area

what are the 2 sites for generate saccades?

cortex: frontal eye field

brainstem: superior colliculus

what are the frontal eye fields for and what does stimulation induce?

FEF: is volitional center for saccadic eye movements

FEF: stimulation induces saccadic eye movements to the contralateral side

what does damage to FEF present with?

eyes look toward the side of lesion (gaze preference)

what does damage to PPRF look like?

eyes look away from side of lesion

where are saccades and pursuit movements generated from?

saccades: generated in the FEF and superior colliculus

pursuit movements: generated in parietal lobe and areas the also generate saccades

look at lesions affecting lateral gaze