Types, role and neural control of eye movements Flashcards
Why do we have eye movements?
To achieve clear and stable vision.
What are the two principal types of eye movements?
Steady images on the retina: Vestibulo-ocular, optokinetic, smooth pursuit.
Change line of sight: Saccades, vergences.
What is the primary function of holding an image on the fovea?
Achieve best visual acuity (VA) and avoid oscillopsia.
What is the vestibulo-ocular reflex’s function?
Holds images steady during brief head rotations.
What is the optokinetic response?
Holds images steady during sustained head rotation.
What is the role of smooth pursuit?
Keeps a moving target on the fovea.
What is the function of saccades?
Brings objects of interest onto the fovea.
What is vergence?
Moves eyes in opposite directions for single-object focus.
What does fixation achieve?
Holds images steady on the fovea for clear vision.
What tools assess fixation?
Visuscope and 4 dioptre prism.
What is oscillopsia?
Perception of motion due to unstable fixation.
Define saccades.
Fast, conjugate eye movements to bring objects into focus on the fovea.
What is saccadic suppression?
Prevents blur during saccadic movements.
What is the average latency of a saccade?
~200ms.
What is the peak velocity range for saccades?
400–700 degrees/second.
What is the saccadic main sequence?
Larger saccades have higher peak velocities.
What maintains a new eye position after a saccade?
The step, providing tonic innervation.
What generates a saccade pulse?
Excitatory burst neurons in the brainstem.
Where are horizontal saccades controlled?
Paramedian Pontine Reticular Formation (PPRF).
What part of the brain controls vertical saccades?
Rostral interstitial nucleus of the Medial Longitudinal Fasciculus (riMLF).
What is smooth pursuit?
Slow tracking movement to maintain objects on the fovea.
What stimuli initiate smooth pursuit?
Movement of an object off the fovea.
What is the latency of smooth pursuit?
80–120ms.
What part of the brain processes moving stimuli?
Middle temporal visual area (MT).
What happens in smooth pursuit with unilateral lesions?
Ipsilateral defect.
What is the main driver of vergence movements?
Retinal image disparity and blur.
What is the latency of disparity-driven vergence?
160ms
What controls convergence movements?
Mesencephalic reticular formation and subnuclei at the MR level.
What is convergence insufficiency?
Difficulty sustaining convergence, causing diplopia.
What is spasm of near reflex?
Overactivation causing variable esotropia and blurred vision.
What does the VOR stabilize?
Gaze during brief head movements.
What is the latency of VOR?
<15ms.
What generates eye movements in VOR?
Hair cells in semicircular canals.
What are the VOR abnormalities?
Disequilibrium, vertigo, oscillopsia.
What is caloric stimulation?
Tests VOR using warm or cold water in the ear.
What is the optokinetic response?
Combines smooth pursuit and saccades for stable vision during sustained movement.
What is optokinetic after-nystagmus?
Continued eye movement after stimulus stops.
What does the optokinetic drum test?
Full-field stimulus response.
What is vestibular nystagmus?
Eye movement caused by vestibular system abnormalities.
What is the quick phase of nystagmus?
Fast, repositioning movement during head rotation.
What is post-rotational nystagmus?
Nystagmus after head movement stops.
How is vestibular nystagmus differentiated?
Present only in the dark (no visual stimuli).
What controls horizontal saccades?
Contralateral frontal eye fields (FEF) and parietal cortex.
What happens with a PPRF lesion?
Ipsilateral gaze palsy.
What is the role of the superior colliculus?
Involved in initiating and directing saccades.
What is the role of the cerebellum in eye movements?
Adaptive control and accuracy.
How are saccades clinically assessed?
By observing speed, accuracy, and latency.
What does an eye tracker measure?
Velocity and peak saccadic movements.
What are common smooth pursuit abnormalities?
Initiation defects, low gain, or asymmetry.
What is the swinging baby test?
Observes nystagmus and ductions during head rotation.
