Eye Movements Flashcards
HORIZONTAL SACCADE pathway
- initiated in the frontal eye field (FEF) located in the frontal lobe (see pg. 95)
- neuronal connection from FeF to superior colliculus in the midbrain
- neuronal connection from superior colliculus to contra-lateral PPRF (paramedian pontine reticular formation)
- excitation of right FEF initiates leftward saccade and vica versa
What is the troxler effect and phenomena
(Troxler effect
an unchanging stimulus held completely stationary in field in view away from foveal fixation can fade and disappear - caused by neural adaptation, the ignoring persistent, unchanging stimuli stare at the black cross
Troxler’s phenomenon
very small ‘drift’ movements of the eye and therefore retina at regular intervals prevents neural adaptation and the aforementioned Troxler effect
Types of nystagmus
–> gaze-evoked nystagmus - commonest type, no nystagmus in primary position, nystagmus becomes apparent on ocular movement - can be caused by cerebellar & brainstem lesions, medications (anti-epilepsy, sedatives)
–> fixation nystagmus - nystagmus in primary position - can be caused by poor vision from a young age, multiple sclerosis, diffuse neurological abnormalities
-> vestibular nystagmus - vestibular pathway pathology - commonly acute labyrinthitis - Alexander’s law applies to vestibular nystagmus = the nystagmus is exacerbated by gazing in the direction of nystagmus beat
-> congential nystagmus can be caused by significantly reduced acuity including congenital cataract, coloboma involving the optic disc, often familial, but often there is no cause found even after investigation
Define florens law
Stimulation of the semicircular canals leads to nystagmus in the plane of the canal
Sacade controlled by
Frontal lobe
900° per second
Damage to FEF = CONTRALATERAL effect
smooth pursuit controlled by
Occipitoparietal lobe
100° per second
Damage to occupat = ipsilateral effect
