Visual system and neurology Flashcards
Recall the 4 landmarks of the neuronal pathway connecting the eye and the brain
CNII
Optic chiasm
Optic tract
Genticulate tract
Describe the decussation of afferent fibres originating in the eye
Half of fibres decussate at midline of optic chiasm, predominately those that originate from nasal retina
Where where the retinal ganglion cells synapse with 4th order sensory neurons
Lateral genticulate nucleus
Where is the lateral genticulate nucleus situated?
Thalamus
Recall the afferent neuronal visual pathway from the lateral genticulate nucleus to the brain
LGN
Optic radiation
Primary visual (striate) cortex
Extra-striate cortex
Name the 1st, 2nd and 3rd order neurones in the afferent visual neuronal pathway
1st = photoreceptors 2nd = bipolar cells 3rd = retinal ganglion cells
What is the key feature in distinguising between lesions anterior to and posterior to the optic chiasm?
Anterior = affects one eye only, posterior = affecting both eyes
What is the result of a lesion posterior to the optic chiasm
Bilateral contralateral homonymous henianopia
What is the result of a lesion at the optic chiasm?
Bitemporal hemianopia
Where is the primary visual cortex situated?
Calcarine sulcus
Describe the projection of the visual field onto the primary visual cortex
Superior visual field projects ABOVE Calcarine fissure, right hemifield from both eyes projects to left side of PVC and vice versa
Recall the neuronal systems mediating accommodation of the eye
Dark to light: PNS CNIII
Light to dark: SNS innervating radial muscle
Which muscle is responsible for controlling the radius of the pupillary aperture?
Iris circular muscle
Recall the afferent pathway of neurons involved in the pupillary reflex
RGCs
Pretectal nucleus
BILATERAL Edinger-Westphal
Recall the efferent pathway of neurons involved in the pupillary reflex
Edinger-Westphal
Ciliary ganglion –> short posterior ciliary nerve
How is a consensual response to light brought about?
Afferent signals transmitted to bilateral edinger-westphal nuclei, so efferents initiated in both eyes
What is duction?
Movement in one eye
What is version?
Movement of both eyes in same direction
What is vergeance?
Movement of both eyes in different directions
What are the 2 different speeds of eye movement?
Saccade
Smooth pursuit
Which eye movement speed can be voluntary?
Saccade
What drives the “smooth pursuit” speed of eye movement?
Moving object
Name the reflex that is commonly used to test visual acuity in pre-verbal children?
Optokinetic nystagmus reflex
