Session 4 - Lecture 1: The Retina and Central Visual Pathways

Question 1

Name the layers of the eye from deep to superficial and name the specific cells found within the retinal layers.

Answer 1

Axons of ganglion cells to optic nerve –> ganglion cells –> amacrine cell –> bipolar cells –> horizontal cells –> cone and rod cells –> pigmented layer –> choroid –> sclera.

Question 2

What is the name of the structure through which the central vein and artery and optic nerve pass through at the back of the eye?

Answer 2

Optic disc.

Question 3

What layers and cells make up the retina?

Answer 3

Axons of ganglion cells to optic nerve –> ganglion cells –> amacrine cell –> bipolar cells –> horizontal cells –> cone and rod cells –> pigmented layer.

Question 4

What structure is seen to be visibly altered by performing a fundoscopy with vascular occlusion?

Answer 4

Branch of central retinal artery or vein

Question 5

What structure is seen to be visibly altered by performing a fundoscopy with degeneration?

Answer 5

Macula.

Question 6

What structure is seen to be visibly altered by performing a fundoscopy with papilloedema?

Answer 6

Optic disc.

Question 7

A dark spot is visible on a fundoscopy with lighter edges surrounding it, name these two structures.

Answer 7

Darker spot = fovea.

Lighter edges around dark spot = macula.

Question 8

Describe the function of the fovea.

Answer 8

Located in the center of the macula lutea of the retina, the fovea is responsible for sharp central vision, which is necessary in humans for activities where visual detail is of primary importance, such as reading. The fovea provides the clearest vision of all. Only in the fovea are the layers of the retina spread aside to let light fall directly on the cones, the cells that give the sharpest image.

Question 9

Describe the function of the macula.

Answer 9

Also called macula lutea, a yellow-pigmented area on the central retina, containing color-sensitive rods and the central point of sharpest vision.

Question 10

What sections can the visual pathway be split up into in terms of the optic nerve.

Answer 10

Left eye = circle split vertically, left portion = temporal fibre, right portion = nasal fibre.
Right eye = circle split vertically, left portion = nasal fibre, right portion = temporal fibre.
Both eyes can be split further to superior and inferior to make up four quadrants i.e. superior temporal, etc.

Question 11

What happens to the nasal and temporal fibres as they reach the optic chiasm?

Answer 11

Nasal fibres decussate and temporal fibres remain ipsilateral.

Question 12

After the fibres pass the optic chiasm, what structure do they reach within the optic tract and what fibres are contained within this structure?

Answer 12

Optic chiasm –> lateral geniculate nucleus

LGN contains temporal fibres from the ipsilateral side and nasal fibres from the contralateral side.

Question 13

What structures connect the LGN to the primary visual cortex, state their location and what specific fibres they contain?

Answer 13

Optic radiations:
Superior optic radiations = parietal lobe - contain continuations of superior temporal and nasal fibres aka Baum’s loop.
Inferior optic radiations = temporal lobe - contain continuations of inferior temporal and nasal fibres aka Meyer’s loop.

Question 14

Fill in the gaps in the following sentence:
Visual fields relate to _______ vision, these fields overlap to form our _______ vision which is good for ______ perception.

Answer 14

Visual fields relate to peripheral vision, these fields overlap to form our binocular vision which is good for depth perception.

Question 15

Which fibres are responsible for our temporal field of vision?

Answer 15

Nasal fibres.

Question 16

Which fibres are responsible for our nasal field of vision?

Answer 16

Temporal fibres.

Question 17

Describe the presentation and lesion location of monocular blindness.

Answer 17

CN II lesion, temporal and nasal fibres on the IPSILATERAL side are affected as the lesion occurs before optic chiasm. Therefore the nasal and temporal visual fields are lost on the ipsilateral side.

Question 18

Describe the presentation and lesion location of bitemporal hemianopia.

Answer 18

Lesion of the optic chiasm, nasal fibres on both side are affected, therefore both TEMPORAL VISUAL FIELDS are lost.

Question 19

Describe the presentation and lesion location of homonomous hemianopia.

Answer 19

Lesion of the optic tract i.e. between the optic chias and LGN.
Ipsilateral temporal fibres and contralateral nasal fibres affected, therefore ipsilateral nasal and contralateral temporal visual field are lost.

Question 20

What is the general term given to visual field defects that involve the optic radiations?

Answer 20

Quadrantanopias.

Question 21

Describe the presentation and lesion location of a homonomous inferior quadrantanopia.

Answer 21

Lesion of right superior optic radiation for example (parietal lobe).
Superior temporal fibre on ipsilateral side affected = loss of inferior nasal visual field.
Superior nasal fibre on contralateral side affected = loss of inferior temporal visual field.

Question 22

Describe the presentation and lesion location of a homonomous superior quadrantanopia.

Answer 22

Lesion of the right inferior optic radiation for example (temporal lobe).
Inferior temporal fibre on ipsilateral side affected = loss of superior nasal visual field.
Inferior nasal fibre on contralateral side is affected = loss of superior temporal visual field.

Question 23

What presentation would a patient exhibit if they had a superior and inferior radiation lesion, and give a common example of how this could happen?

Answer 23

Homonomous hemianopia = ipsilateral superior and inferior temporal fibres
Contralateral superior and inferior nasal fibres
So contralateral temporal and ipsilateral nasal visual fields affected. This can commonly occur with a stroke.

Question 24

Describe the vascular basis of macular sparing.

Answer 24

Occipital lobe has dual blood supply = posterior cerebral artery and middle cerebral artery. In a stroke affecting posterior cerebral artery, most of occipital lobe will be lost, however, the middle cerebral artery supplies the occipital pole which represent the macula and therefore macular function i.e. central vision, will be spared.

Question 25

Describe the pathway of the light reflex.

Answer 25

Optic nerve —> synapses in pretectal area —> gives rise to neurones supplying edinger-Westphal nucleus of occulomotor nerve —> ciliary ganglion —> eye sphincter.

Question 26

Describe the accommodation reflex.

Answer 26

Required for near vision and involves three aspects:
- Convergence ( medial rectus).
- Pupillary constriction (constrictor pupillae).
- Convexity of lens to increase refractive power (ciliary muscle).
Cerebral cortex involved as this process involves image analysis, therefore the reflex follows the visual pathway via the LGN to the visual cortex.