Eye And Vision Flashcards
What is the visual pathway?
Retina- optic nerve- optic chiasm- optic tracts- LGN- optic radiations- primary visual cortex (occipital lobe)
Where does the optic nerve exit the globe?
Optic canal
Which fibres cross at the optic chiasm?
Nasal fibres
Where is the LGN situated?
Near the thalamus
Where do the optic radiations travel?
Upper division: direct route through the parietal lobe
Lower division: anteriorly through meyers loop and then posteriorly through the temporal lobe to the visual cortex
Where is the visual cortex?
Either side of the calcarine sulcus in the occipital lobe
What percentage of the optic tract terminates at the LGN?
90%
Where does the medial route of the optic tract terminate?
Superior colliculus- visual association pathways and automatic scanning
Pretectal nucleus- light reflex
Superchiasmatic nucleus of hypothalamus- photoperiod regulation
What is the pupillary reflex?
Afferent: retinal ganglion cells to the pretectal nucleus
2 efferent (one for each side): from pretectal nuclei to iris sphincter muscles via the edinger westphal nucleus and ciliary ganglions
What is a consensual reflex?
Pupillary reflex in response to light entering the contralateral eye
What is RAPD?
Relative afferent pupillary defect
Only the afferent limb of light reflex is affected- efferent is normal
Light shone in affected eye will cause dilation
What are the causes of RAPD?
Multiple sclerosis
Ischaemic optic neuropathy
Glaucoma
Optic nerve compression
Ischaemia (rvo, retinal artery occlusion)
Retinal detachment
Do media opacities cause RAPD?
No!
What is the accommodation reflex?
Afferent: from retinal ganglion cells to visual cortex via the LGN and eventually to the frontal eye field
FEF sends fibres to both motor and edinger westphal nuclei
Efferent: motor nuclei increase output to medial recti to cause bilateral adduction
Edinger-westphal nucleus sends preganglionic parasympathetic fibres which synapse at the ciliary ganglion.
Postganglionic PS fibres innervate ciliary muscles and sphincter pupillae leading to increased lens thickness