Visual System

Question 1

List the order of layers that impulses travel through in the Retina

Answer 1

Superficial to Deep

• Pigmented epithelia layer
• Neural layer
• Bipolar cell layer
• Ganglion cell layer
• Nerve fibre layer/ Optic nerve

Question 2

What are the Bipolar cells?

How are they connected? What do these do and how?

Answer 2

1st order neurones that receive input from photoreceptors

By horizontal cells that assist in enhancing edges through a process called Lateral Inhibition

Question 3

The Ganglion cells receive input from the Bipolar cells.

What do their axons form?

Answer 3

The optic nerve/ nerve fibre layer

Question 4

How does direction of light travel differ to that of impulse travel in the eye?

Answer 4

Light travels deep to superficially

Impulses travel superficially to deep

Question 5

How does Lateral Inhibition work?

Answer 5

Inhibition of the photoreceptors to the left and right of the ones that are most in-line with the image being seen

Question 6

On a fundosocopy, where does the macula appear in relation to the optic disc?

Answer 6

Sits lateral to the optic disc

Question 7

What can occlusion of the central retinal artery cause?

Answer 7

Amaurosis Fugax- Sudden visual loss

Question 8

Name a specialist technique that can be used to visualise the layers of the retina

Answer 8

Optical Coherence Tomography (OCT)

Question 9

What is the medial retina referred to as?

Light from which field is detected here?

Answer 9

Medial retina= Nasal retina

Detects light from Temporal/ Lateral field

Question 10

What is the lateral retina referred to as?

Light from which field is detected here?

Answer 10

Lateral retina= Temporal retina

Detects light from Nasal/ medial field

Question 11

Describe the pathway of the Retina fibres to the Lateral Geniculate Nucleus

Answer 11

Via Optic tracts;

• Nasal fibres decussate at the Optic Chiasm to project to the contralateral Lateral Geniculate Nucleus
• Temporal fibres project to the Ipsilateral Lateral Geniculate Nucleus

Question 12

Describe the pathway of the Retina Fibres from the Lateral Geniculate Nucleus to the Primary Visual Cortex

Answer 12

• Fibre from the Superior Retina (Inferior field) run through the Superior Optic Radiation through the Parietal Lobe
• Fibres from the Inferior Retina (Superior field) run though the Inferior Optic Radiation through the Temporal Lobe

Question 13

List the fibres running though the Superior Optic Radiation in the Left and Right hemisphere

Answer 13

Left Superior Optic Radiation;

• Fibres from Superior Temporal region of Left Retina
• Fibres from Superior Nasal region of Right Retina

Right Superior Optic Radiation;

• Fibres from Superior Temporal region of Right Retina
• Fibres from Superior Nasal region of Left Retina

Question 14

List the fibres running though the Inferior Optic Radiation in the Left and Right hemisphere

Answer 14

Left Inferior Optic Radiation;

• Fibres from Inferior Temporal region of Left Retina
• Fibres from Inferior Nasal region of Right Retina

Right Inferior Optic Radiation;

• Fibres from Inferior Temporal region of Right Retina
• Fibres from Inferior Nasal region of Left Retina

Question 15

What is Baum’s Loop?

Answer 15

The Superior Optic Radiations

Question 16

What is Meyer’s Loop?

Answer 16

The Inferior Optic radiations

Question 17

What is our Binocular vision?

Why are they useful?

Answer 17

The overlap of visual fields of each eye

Good for depth perception

Question 18

Are visual field defects according to area of visual loss OR site of lesion?

Answer 18

Area of visual loss

Question 19

What is a Scotoma?

Answer 19

A localised retina defect-> small patch of visual loss

Question 20

Which site in the Visual pathway is affected in Monocular Blindness?

How does this present?

Answer 20

• Optic nerve

- Ipsilateral loss of Visual and Temporal visual fields

Question 21

Which site in the Visual pathway is affected in Bitemporal Hemianopia/ Tunnel vision?

How does this present?

Answer 21

• Optic Chiasm
• Loss of Peripheral vision in both eyes

(Nasal fibres affected so Temporal visual fields lost)

Question 22

Suggest 2 non-optic causes of Bitemporal Hemianopia

Explain how?

Answer 22

• Pituitary adenoma
• Aneurysm of Anterior Communicating Artery

Cause compression of the Optic Chiasm

Question 23

Which site in the Visual pathway is affected in Contralateral Homonymous Hemianopia?

How does this present?

Answer 23

• Optic tract OR Lateral Geniculate Nucleus

- Loss of Contralateral Temporal and Ipsilateral Nasal visual fields

Question 24

Which Optic nerve/ LGN is affected in a Left Homonymous Hemianopia

Answer 24

Right

Question 25

Which site in the Visual pathway is affected in Contralateral Homonymous Inferior Quadrantanopia? Which fibres are affected? How does this present?

Answer 25

- Superior Optic radiation Affected fibres are; - Ipsilateral Superior Temporal fibres - Contralateral Superior Nasal fibres - Loss of Ipsilateral Inferior Nasal and Contralateral Inferior Temporal visual fields

Question 26

How would a Right Homonymous Inferior Quadrantanopia present?

Answer 26

Left Superior Optic radiation affected so affected fibres are; - Left Superior Temporal fibre - Right Superior Nasal fibre So loss of; - Left Inferior Nasal field - Right Inferior Temporal field

Question 27

What do you get if both Superior and Inferior Optic radiations are affected on one side?

Answer 27

Contralateral Homonymous Hemianopia

Question 28

List 3 sites that can be affected to cause Contralateral Homonymous Hemianopia

Answer 28

- Optic tract - Lateral Geniculate Nucleus - Superior and Inferior Optic Radiations on same side

Question 29

Compare the outcomes of; - Non vascular damage to Occipital lobe - Occlusion of Posterior Cerebral artery Explain the difference in outcome

Answer 29

Non vascular occipital lobe damage; - Contralateral Homonymous Hemianopia without Macular sparing PCA Occlusion; - Contralateral Homonymous Hemianopia with Macular sparing - Area of visual cortex that supplies the macula receives blood from Deep branch of the MCA (so a PCA occlusion has no effect)

Question 30

Regarding the Pupillary light reflex, identify the; - Afferent arm - Processing centres - Efferent arm

Answer 30

Afferent: Optic nerve Processing centres: Pretectal nucleus, which projects to Edinger Westphal nuclei bilaterally Efferent: CN III

Question 31

Is the Consensual or Direct pupillary light reflex mediated by the bilateral projections from the Pretectal nucleus

Answer 31

Consensual

Question 32

What are the 3 effects of the Accommodation reflex?

Answer 32

‘3 Cs’ - Pupillary constriction - Convergence of eyes (Medial Rectus) - Convexity of Lens to increase refraction (Ciliary muscle)

Question 33

How do we know the Cerebral Cortex is involved in the Accommodation reflex?

Answer 33

Image interpretation occurs

Question 34

The Afferent arm of the Accommodation reflex is the Optic nerve. Describe the Processing centre component

Answer 34

- Reflex follows visual pathway via the Lateral Geniculate Nucleus to reach the Visual Cortex for interpretation - Once image is processed, fibres project to CN III nuclei and Edinger Westphal nuclei

Question 35

In the Accommodation reflex, what do fibres projecting from the following do? - CN III nuclei - Edinger Westphal nuclei

Answer 35

From CN III nuclei; - Cause pupillary constriction From EW nuclei; - Cause convergence of eyes (medial rectus stimulation) - Cause lens thickening (ciliary muscle simulation)

Question 36

What is the Medial Longitudinal Fasciculus? Suggest a disease that affects it, causing interference with conjugate eye movements

Answer 36

A set of fibres connecting the Oculomotor, Trochlear, Abducens and Vestibulocochlear nuclei Multiple Sclerosis