4. Retina And Central Visual Pathways Flashcards
What are the layers of the retina?
Pigmented layer
Photoreceptor cells
Horizontal cells
Bipolar cells
What is the role of the pigmented layer?
Acts as main site of absorption of light
Helps anchor photoreceptor cells
What is the role of photoreceptor cells?
Rods - Black and white
Cones - colour, high detail
What is the role of horizontal cells?
Lateral inhibition - help narrow down signals that are being sent
What is the role of bipolar cells?
Connect photoreceptor cells to axons of ganglion cells to optic nerve
Describe the visual pathway from the eyes
- Optic nerve leaves each eye from superior and inferior temporal fibres and superior and inferior nasal fibres
- They then join at the optic chasm, nasal fibres decussate, temporal fibres remain ipsilateral
- Optic tracts formed, from optic chasm to lateral geniculate nucleus
- Optic radiations formed, from lateral geniculate nucleus to primary visual cortex (occipital lobe)
What are the 2 routes to get to the primary visual cortex?
Superior optic radiations - through parietal lobe (continuation of superior quadrant fibres)
Inferior optic radiations - through temporal lobe (continuation of inferior quadrant fibres)
What do visual fields relate to?
Peripheral vision
What is responsible for our temporal field of vision?
Nasal retinal fibres
What is responsible for our nasal field of vision?
Temporal retinal fibres
What happens if there is an optic nerve lesion?
Monocular blindness
Both nasal and temporal visual fields are lost on ipsilateral side
What happens if there is an optic chiasm lesion in the centre?
Bitemporal hemianopia
Both temporal visual fields are lost
What can cause optic chiasm lesion?
Pituitary tumour
What is homonomous hemianopia?
Lesion in optic tract
Ipsilateral nasal visual field and contralateral temporal visual field are lost
What is responsible for our inferior quadrant field of vision?
Superior radiations
What is responsible for our superior quadrant field of vision?
Inferior radiations
What is a homonomous inferior quadrantanopia?
Lesion of superior optic radiation (parietal lobe)
- Loss of inferior nasal visual field on ipsilateral side
- Loss of inferior temporal visual field on contralateral side
What is homonomous superior quadrantanopia?
Lesion of inferior optic radiation (temporal lobe)
- loss of superior nasal visual field on ipsilateral side
- loss of superior temporal visual field on contralateral side
What are the 3 aspects of the accommodation reflex?
Convergence (medial rectus)
Pupillary constriction (constrictor pupillae)
Convexity of the lens to increase refractive power (ciliary muscle)
Why does he accommodation reflex follow the visual pathway via the lateral geniculate nucleus to the visual cortex?
Cerebral cortex must be involved because it is relating to image analysis
