Lecture 5-Retina And Central Visual Pathways Flashcards
What do bipolar cells synapse with?
Axons of ganglia which converge to form the optic nerve
What does the retinal pigment epithelium prevent?
Excessive refraction by absorbing light as it has melanin
What are horizontal cells?
Cells for lateral vision, they prevent receptors next to the point of strongest stimulation from sending signals
What is amaurosis fugax?
“Black curtain falling over vision” is indicative of occlusion of central retinal artery
Which fibres form the optic chiasm?
Nasal fibres
Where does the optic tract run to?
Lateral geniculate nucleus
Where do the superior radiations run through?
Parietal lobe
Where do the inferior radiations run through?
Temporal lobe
Which fibres are responsible for temporal field of vision?
Nasal fibres
Which fibres are responsible for nasal field of vision?
Temporal fibres
What causes monocular blindness?
Lesion of the optic nerve eg optic nerve glioma or retinoblastoma in children, optic sheath meningiomas in adults
What causes bitemporal hemianopia?
Lesion at the optic chiasm
What causes left homonomous hemianopia?
Lesion of right optic tract, affecting right temporal and left nasal fibres (stroke common)
What causes right homonomous hemianopia?
Lesion of left optic tract
Describe the blood supply of the occipital lobe
-Posterior cerebral artery -Middle cerebral artery -> occipital pole
Why is there macular sparing in a stroke affecting the posterior cerebral artery?
Middle cerebral artery isn’t damaged and this supplies the occipital pole which represents the macula therefore macular function is spared
In the light reflex, where does the afferent optic nerve synapse?
In the pretectal area
What are the three Cs of the accommodation reflex?
Convergence (medial rectus)
pupillary Constriction
Convexity of the lens
Why is the fovea represented as a thin nerve fibre layer on an optical coherence tomogram (OCT)?
Fewer cells for light to pass through -> high definition
What is the medial longitudinal fasciculus?
Tract which connects all extra-ocular muscle nuclei
How does the medial longitudinal fasciculus aid in gaze fixation?
MLF receives input from vestibular apparatus and this informs eye muscles about the position of the head in order to be able to fixate gaze
How does multiple sclerosis affect the MLF?
Demyelinates white matter (MLF tract) so conduction is slowed down and coordination is impaired
