Eye Movements & Disorders

Question 1

Which axes do the eyes move in?

Answer 1

Vertical for LR (abduction/adduction)
Horizontal for UD (elevation/depression)
Sagittarius for torsional action

Question 2

Explain the visual axis and plane of muscle action

Answer 2

VA: line joining fixation point and fovea

Plane: line of muscle action

Question 3

Why do actions change with gaze position?

Answer 3

visual axis/muscle plane relationship changes with gaze

Question 4

Which 2 laws explain why eyes move conjugately?

Answer 4

Hering’s: (equal innervation for coordination of muscle pairs for BE) so LMR/RLR work together to look right

Sherringtons: coordination of muscle pairs in one eye, agonist muscle contracts inhibiting direct antagonist muscle

Question 5

Explain duction

Answer 5

examines any limitations

Question 6

Explain the 2 types of gaze shifting

Answer 6

Saccades: fast eye movements bringing objects of interest onto fovea

Vergence: eyes move in equal/opposite directions (near to distant)

Question 7

What are the 4 types of gaze holding?

Answer 7

Vestibular: holds retinal image steady on fovea during brief head rotation
Optokinetic: holds retinal image steady during sustained head rotation
Smooth Pursuit: holds image of small, moving target on fovea
Fixation: holds eye in primary position (object detail)

Question 8

Explain neural control of eye movements involving brain stem nuclei

Answer 8

Frontal/Parietal higher cortical areas command eye movement - send input to brain stem:

oculomotor (III) nuclei
abducens (VI)
trochlear (IV)

excitatory burst neurones (vertical/horizontal movements) controlled via omnipresent neurones send signals to III nuclei for muscles

Question 9

Explain a saccade and how they’re tracked

Answer 9

Frontal fields (frontal cortex ~ Brodmann Area 8) send commands to superior colliculus/cerebellum/parietal cortex which send signals to brain stem nuclei

can be (in)voluntary; redirects eye so image on fovea

quantitative eye trackers for clinical oculomotor disorders

Question 10

State some saccade characteristics and the velocity-amplitude relationship

Answer 10

Latency/Amplitude/Duration/Peak Velocity

higher amplitude (bigger saccade) ~ increased peak velocity also known as the main sequence

Question 11

What disorders involve saccades?

Answer 11

Slow saccade: FEF/Parietal lesions, muscle weakness, burst cell abnormalities, delayed latency

Inaccurate saccades: Hyper/hypometrias

Parkinson’s: saccade slows down not on main sequence

Question 12

Explain smooth pursuit and how it’s clinically tested

Answer 12

eye movements match small target speed maintaining image on fovea

movement quality judged by gain (peak vel.) and phase (temporal sync between eyes/target)

tests with motility:
slow pursuit (interspersed with saccades)
pursuit affected by MT/FEF/cerebellum lesions

Question 13

Explain vergence and it’s disorders

Answer 13

disconjugate eye movements in equal/opposite directions stimulated by retinal disparity/blur

Convergence insufficiency in young adults/presbyopes

Parkinson’s/progressive supranuclear palsy

brainstem lesions

Question 14

Explain neural control of the vestibular system

Answer 14

fluid-containing semicircular canals disrupted by head movements send signals to vestibular nuclei (oculomotor in brain stem)

Question 15

Explain the vestibulo-ocular reflex and its associated disorders

Answer 15

VOR stabilises gaze allowing clear vision during brief head movements

unsteady gaze requires corrective saccade at end to bring target onto fovea

vestibular disease (central/peripheral) due to tumours-stroke/infection/trauma

vertigo, nystagmus, dizziness

Question 16

Explain the optokinetic system and how its tested

Answer 16

assists VO system keeping retinal image steady - mediated by vision during sustained head movements

test with moving stripes

Question 17

Explain fixation, 3 components and its disorders

Answer 17

fixation keeps eyes aligned on target under movement (high f tremors, drifts and microsaccades) - prevents image fading for optimal vision/perception processing

Involuntary saccadic fixation instability or Nystagmus

Brain tumours, MS etc.

Question 18

Explain voluntary and end point nystagmus

Answer 18

Voluntary: series of back to back saccades in V/H planes (5-8% pop.)

Endpoint: light jittery movement on gaze extremities (>40 deg.) usually brief (low amp./freq.)

Question 19

How does congenital nystagmus differ from acquired?

Answer 19

Congenital: benign in first months (children) can be idiopathic (no apparent vis. issues), sensory impaired (albinism, cataract, ON hypoplasia) which manifest latent nystagmus (strabismus)

Acquired: indicates tumour/systemic condition, associated with nausea, vertigo, movement disorders