5. The Retina and Central Visual Pathways

Question 1

What are the 10 layers of the retina?

Answer 1

Inner limiting membrane, nerve fibre layer, ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, external limiting membrane, layer of rods and cones, retinal pigmental epithelium.

Question 2

What does the retinal pigmented layer contain?

Answer 2

Melanin.

Question 3

What are the roles of the retinal pigmented layer?

Answer 3

Melanin absorbs some light, and it acts as an anchor for photoreceptors.

Question 4

What are the two clinical conditions linked with the roles of the retinal pigmented layer?

Answer 4

In albinism - less melanin so light not absorbed and too bright. If the retina is detached, then you have floaters.

Question 5

What are the roles of rod and cone cells?

Answer 5

Rods - black and white vision, helpful in the dark. Cones - colour and increased acuity.

Question 6

Where is the highest concentration of cone cells and therefore the place of highest acuity?

Answer 6

Fovea centralis.

Question 7

Why is there a blind spot in vision?

Answer 7

No photoreceptors are at the optic disc.

Question 8

How can raised intracranial pressure be picked up on via fundoscopy?

Answer 8

Papilloedema of the optic disc.

Question 9

What can fundoscopies pick up?

Answer 9

Retinopathies, vascular occlusions, macula health, optic disc health.

Question 10

Which visual fibres run ipsilaterally and which decussate?

Answer 10

Temporal fibres run ipsilaterally, nasal fibres decussate.

Question 11

Where do the optic tracts run to?

Answer 11

Lateral geniculate nucleus.

Question 12

Which fibres contribute to the temporal field of vision?

Answer 12

Nasal fibres.

Question 13

Which fibres contribute to the nasal field of vision?

Answer 13

Temporal fibres.

Question 14

How are visual field defects named?

Answer 14

According to the are of visual loss.

Question 15

What (unilateral/bilateral) are signs of visual field defects at the following points: before optic chiasm, at optic chiasm, after optic chiasm?

Answer 15

Before - unilateral and ipsilateral.
At - bilateral.
After - bilateral and contralateral.

Question 16

What causes monocular blindness?

Answer 16

Lesion of the optic nerve.

Question 17

What can cause a lesion of the optic nerve?

Answer 17

Optic nerve glioma or retinoblastoma (children), optic sheath meningiomas (middle aged).

Question 18

What is bitemporal hemianopia?

Answer 18

Tunnel vision, loss of temporal fields of vision.

Question 19

What causes bitemporal hemianopia?

Answer 19

Lesion at the optic chiasm that affects both nasal fibres.

Question 20

What can cause a lesion at the optic chiasm?

Answer 20

Pituitary gland pathology or anterior communicating artery aneurysm.

Question 21

What is left homonomous hemianopia?

Answer 21

Loss of the temporal field of vision of the left eye and nasal field of vision of the right eye.

Question 22

What causes left homonomous hemianopia?

Answer 22

Lesion of the right optic tract that affects right temporal and left nasal fibres.

Question 23

What can cause a lesion of the right optic tract?

Answer 23

Vascular causes (stroke) most likely, or neoplasia/trauma.

Question 24

What is contralateral lower quadrantic anopsia?

Answer 24

Loss of inferior nasal field of vision on ipsilateral eye, and loss of inferior temporal field of vision on contralateral eye.

Question 25

What causes contralateral lower quadrantic anopsia?

Answer 25

Lesion of the superior optic radiation.

Question 26

What is contralateral upper quadrantic anopsia?

Answer 26

Loss of superior nasal field of vision on ipsilateral eye, and loss of superior temporal field of vision on contralateral eye.

Question 27

What causes contralateral upper quadrantic anopsia?

Answer 27

Lesion of the inferior optic radiation.

Question 28

Why does a stroke of the posterior cerebral artery lead to macular sparing?

Answer 28

Occipital lobe has dual blood supply from posterior cerebral and middle cerebral artery. Most of the occipital lobe will be lost but the middle cerebral artery supplies the occipital pole which represents the macula so function is spared.

Question 29

Describe the pathway of the light reflex.

Answer 29

Light stimulates the afferent nerve in the pathway, CN II. This synapses in the pretectal area and gives rise to neurones supplying the Edinger Westphal nuclei bilaterally. Both CN III are stimulated to cause direct and consensual pupillary constriction via parasympathetic fibres.

Question 30

What are the three aspects of the accommodation reflex?

Answer 30

Convergence, pupillary constriction, convexity of lens.

Question 31

Why must the cerebral cortex be involved in the accommodation reflex?

Answer 31

The pathway is related to imaging analysis.

Question 32

Describe the pathway of the accommodation reflex.

Answer 32

Light detected by retina, synapses in lateral geniculate nucleus, goes off to visual cortex for processing, information passed to midbrain then to Edinger-Westphal and oculomotor nuclei to activate both. The ciliary ganglion and sphincter pupillae cause pupil constriction and lens thickening and the medial recti contract for convergence.