L5 - Visual Pathway

Question 1

3 layers of the eye

Answer 1

Sclera
Uvea - pigmented vascular layer
Retina - neural layer

Question 2

Sclera

Answer 2

Tough and fibrous

Continuous with the dural sheath of the optic nerve

Question 3

Uvea

Answer 3

Choroid

Ciliary body and iris

Question 4

Retinal layers

Answer 4

Retinal pigment epithelium:

• absorbs light therefore prevents light from bouncing around in the eyeball causing flare
• anchor photoreceptors - converts light into action potential

Neural layer:

Photoreceptors

Bipolar cells:

• first order sensory neurones that receive input from photoreceptors
• connect photoreceptors to axons of ganglion cells

Ganglion cells:

• receives input from bipolar cells
• axons of the ganglion cells form the optic nerve

Question 5

Horizontal cells

Answer 5

Connect bipolar cells which assists with enhancing edges via lateral inhibition

Question 6

Amaurosis fugax

Answer 6

• Occlusion symptoms occurs of the central retinal artery (branch of the ophthalmic artery)
• curtain coming down obscuring vision
• symptom of stroke

Question 7

How to visualise retinal layers

Answer 7

Optical coherence tomography (OCT)

Question 8

Blind spot

Answer 8

Optic disc

Question 9

What can fundoscopy detect?

Answer 9

• Retinopathies - due to hypertension or diabetes
• Vascular occlusion - amourosis fugax
• macular degeneration
• optic disc - papilloedema

Question 10

Fovea

Answer 10

Small distance between the nerve fibre layer and the retinal pigment layer therefore high acuity vision

Question 11

Nasal and temporal fibres at the optic chiasm

Answer 11

Nasal fibres decussate

Temporal fibres remain ipsilateral

Question 12

Lateral geniculate nucleus

Answer 12

Receive optic tracts

Question 13

Superior optic radiations

Answer 13

• continuation of the nasal and temporal superior quadrant fibres
• Baum’s loop
• Travel via parietal lobe
• run to the primary visual cortex

Question 14

Inferior optic radiations

Answer 14

• continuations of the inferior nasal and temporal quadrant fibres
• Meyer’s loop
• travel via the temporal lobe
• run to the primary visual cortex

Question 15

Visual field

Answer 15

Area that is visible by each eye

Question 16

Binocular vision

Answer 16

• Area of visual field overlap between both eyes

- Allows depth perception

Question 17

Temporal visual field

Answer 17

Temporal visual field detected by the nasal retinal fibres

As light travels in straight lines

Question 18

How are visual field defects named

Answer 18

By the area of visual field loss

Question 19

Optic nerve lesion

Answer 19

• both temporal and nasal fibres on the ipsilateral side are affected as has not decussated
• therefore both the nasal and temporal visual fields affected
• monocular blindness

Question 20

Optic chiasm lesion

Answer 20

• left and right nasal optic fibres are affected
• therefore temporal visual field loss in both eyes
• bitemporal hemianopia
• commonly caused by pituitary tumours and aneurysms that can compress the chiasm

Question 21

Left optic tract lesion

Answer 21

• left temporal fibres (ipsilateral) and right nasal fibres (contralateral) affected
• therefore left nasal visual field and right temporal visual field affected
• homonomous hemianopia

-

Question 22

Superior radiations

Answer 22

Inferior quadrant visual field detected by the superior optic radiations

• project into parietal lobe

Question 23

Quadrantanopias - right superior optic radiation

Answer 23

• Lesion affecting the superior right temporal fibre and superior left nasal fibre
• Therefore the inferior right nasal visual field (ipsilateral) and inferior left temporal visual field (contralateral) is affected
• Homonomous inferior quadrantanopia

Question 24

Lesion of the right inferior optic radiation (temporal lobe)

Answer 24

• lesion of the right inferior temporal fibre (ipsilateral) and left inferior nasal fibre (contralateral)
• therefore the right superior nasal visual field affected and left superior temporal visual field affected
• homonomous superior quadrantanopia

Question 25

Lesion in right superior and inferior radiations

Answer 25

• due to e.g. stroke affecting the parietal and temporal lobe
• superior and inferior right temporal fibres affected and superior and inferior left nasal fibres affected
• therefore superior and inferior right nasal visual field affected and superior and inferior left temporal visual field affected
• homonomous hemianopia

Question 26

Macular sparing

Answer 26

Occipital lobe has a dual blood supply:

• posterior cerebral artery
• middle cerebral artery (occipital pole)

In a stroke affecting the posterior cerebral artery most of the occipital lobe will be lost but the middle cerebral artery supplies the occipital pole which represents the macula

Therefore macula vision i.e. central vision will be spared

Question 27

Pupillary light reflex

Answer 27

1. Light stimulates the afferent optic nerve
2. It gives off a branch that synapses in the pretectal area onto the interneurone
3. The interneurone travels to the brain stem which supplies the Edinger Westphal nucleus
4. The preganglionic fibres run with the occulomotor nerve and synapses in the ciliary body.
5. Postganglionic fibres run with the trigeminal nerve to the constrictor pupillae and ciliary muscle
6. Both occulomotor nerves are stimulated to cause direct and consensual pupillary constriction.

Question 28

Accommodation reflex

Answer 28

• light from near objects refract more exceeding the limit of the lens

Therefore the accommodation reflex causes:

• convergence
• pupillary constriction
• lens becomes more convex - increases refractive power via the ciliary muscle

1. Reflex follows the lateral geniculate nucleus to the visual cortex for image analysis
2. Fibres sent from the primary visual cortex to the midbrain to the EDW nucleus and occulomotor nerve
3. Stimulation causes parasympathetic pupil constriction and ciliary muscle contraction for lens thickening and medial rectus contraction to adduct eye inwards towards the midline