13 Visual pathway

Question 1

Describe the three neuron chain of the visual pathway.

Answer 1

1o is bipolar cell.
2o is ganglion cell that forms optic nerve going to lateral geniculate nucleus of the thalamus.
3o is the optic radiation form the LGN to the cortex.

Question 2

Why does an increase in CSF pressure cause blurred vision?

Answer 2

CSF pressure spreads to meningeal coverings of the optic nerve. Swelling causes compression of the central retinal vein causing papilloedema.

Question 3

Describe the retinopic mapping of the visual cortex.

Answer 3

Left visual field goes to right cerebral hemisphere.
Upper vision goes to lower bank of calcarine sulcus.
Centre of vision goes to occipital pole.

Question 4

What is a probable cause of heteronymous hemianopia?

Answer 4

Pituitary tumour.

Question 5

What is a probable cause of bilateral central scotomas?

Answer 5

Head injury from a backwards fall.

Question 6

Describe the pathway controlling the pupillary light reflex.

Answer 6

10% of optic neurones go to pre-tectal area. Interneurons bilaterally serve the Edinger-Westphal Nuclei. Occulomotor nerve from EWN to ciliary ganglion. Postganglionic nerve to sphincter pupillae.

Question 7

Which nerves are damaged in:
Reduced pupillary constriction.
Absent pupillary constriction.

Answer 7

Reduced: optic nerve.
Absent: occulomotor.

Question 8

What are the three components of the accommodation reflex?

Answer 8

Accommodation - ciliary muscles.
Pupils constrict - sphincter pupillae.
Oculair convergence - medial rectus.