The Retina And Central Visual Pathways Flashcards
Which area has the highest intensity of cells in the retina?
The macula densa
What are the 3 layers of the wall of the eye?
Choroid
Pigmented layer
Neural layer
What pigment is found within the pigmented layer?
Melanin- absorbs light rays, prevents them from bouncing around within the eye
What are the different cells in the retina and how do they connect to each other from outside to in?
The outermost cells in the retina are the rods and cones. Rods detect light levels and cones detect coloured light.
These cells then connect to bipolar cells and then these connect to ganglion cells which feed into the optic nerve.
What is the role of horizontal and amacrine cells?
They act as gates to modulate the passage of impulses from photoreceptors to ganglion cells.
What is amaurosis fugax?
It is like a curtain over the vision as a result of vascular occlusion.
Which visual field do temporal fibres recieve?
The nasal field
Which fibres decussate at the optic chiasm?
Nasal fibres
Where is the lateral geniculate nucleus found?
Within the thalamus
Which fibres run in the superior radiation?
Fibres picking up the inferior field of vision
Where does the superior radiation run?
Through the parietal lobe
A compression of the optic chiasm will cause which visual defect?
Bitemporal hemianopia
A lesion in the right superior radiation will cause which visual defect?
Left inferior quadrantonopia
What kind of nerve lesion will cause monocular blindness?
What kinds of things can cause this?
Lesion in optic nerve
Can be caused by optic nerve glioma or retinoblastoma, optic sheath meningiomas
Left homonomous hemianopia will be caused by?
A lesion of the right optic tract
Why does macular sparing occur when the lesion is in the visual cortex?
The visual cortex is located in the occipital lobe which has a dual blood supply. Part from the posterior cerebral artery and the rest from the middle cerebral artery which supplies the occipital pole.
In a stroke affecting the posterior cerebral artery most of the occipital lobe will be lost, although the part of the visual cortex supplying the macula will be retained, because it is supplied by the middle cerebral artery.
How does the pupillary light reflex occur?
Light hits the retina and is converted to signals travelling down the optic nerve. This synapses with an interneurone in the pretectal area of the midbrain and then this synapses with the oculomotor nerve fibres in the edinger westphal nucleus.
This causes contraction of the sphincter pupillae muscle causing the pupil to constrict.
Both oculomotor nerves are stimulated causing consensual light reflex also.
What are the 3 C’s of the accomodation reflex?
Convergence
Constriction (of pupil)
Convexity of lens to increase
How does the accomodation reflex occur?
Sensory information travels down the optic nerve and ends up at visual cortex. Visual cortex determines that close image is too blurry so sends signal to pretectal area. This synapses with oculomotor nerve causing contraction of ciliary muscle, medial rectus/ (inhibition of )lateral rectus and sphincter pupillae.
