4.1: The Eye And Vision

Question 1

What are the three layers on the eye?

Answer 1

Sclera
Choroid
Retina

Question 2

Which layer is affected in albinism?

Answer 2

The pigmented layer contains no melanin

Question 3

What is the fovea of the eye?

Answer 3

The small pit in the centre of the macula that is responsible for sharp vision as it has the highest concentration of cone photoreceptor cells

Question 4

Why is the optic disc known as the blind spot?

Answer 4

As this is where the optic nerve enters the retina, and it contains no photoreceptor cells

Question 5

What are the photoreceptor cells and what are their functions?

Answer 5

Rods and cones
Rods are involved in picking up low levels of light for black and white vision
Cones are good for coloured vision in bright light and higher acuity vision

Question 6

How can the retina be investigated?

Answer 6

Optical coherence tomography, OCT

Question 7

Do the temporal fibres of the eye run ipsilateral or contralateral?

Answer 7

Ipsilateral

Question 8

Do the nasal fibres of the eye run ipsilateral or contralateral?

Answer 8

Contralateral

As they dessucate at the optic chiasm

Question 9

Which fibres of the eye dessucate at the optic chiasm?

Answer 9

The nasal fibres

Question 10

Are temporal fibres responsible for our temporal field of vision?

Answer 10

No
Temporal fibres are responsible for our nasal field of vision
Nasal fibres are responsible for our temporal field of vision

Question 11

What are the optic radiations?

Answer 11

Parts of the fibres that split into superior and inferior parts and run to the primary visual cortex

Question 12

What would a lesion of the right optic nerve causes?

Answer 12

Monocular blindness
Loss of vision through the right eye
So vision would only be through the left eye

Question 13

When will tunnel vision be seen?

Answer 13

Aka bitemporal hemianopia

Due to a lesion at the optic chiasm
Loss of both temporal fields of vision, so both nasal fibres are affect (temporal fibres spared)

Question 14

What is a common cause of a lesion at the optic chiasm?

Answer 14

Overgrowth of the pituitary gland

Question 15

What would a lesion at the right optic tract cause?

Answer 15

Left homonomous hemianopia
Affects right temporal and left nasal fibres
So affects right nasal field and left temporal field

Question 16

What happens in a right homonomous hemianopia?

Answer 16

Lesion at the left optic tract

Affect left temporal and right nasal fibres

Question 17

A lesion where would cause a quadrantopia?

Answer 17

A lesion in only one optic radiation (would affect only the respective superior or inferior portion of the visual field)

Question 18

A left superior quadrantopia would mean a lesion has occurred where?

Answer 18

In the right inferior optic radiation

Question 19

A right inferior quadrantopia would mean a lesion has occurred where?

Answer 19

In the left superior optic radiation

Question 20

What is macula sparing?

Answer 20

When macula function (central vision) is spared in a stroke affecting the posterior cerebral artery due to the dual blood supply of the occipital lobe
The middle cerebral artery would still be present to supply the occipital pole which represents the macula

Question 21

What are the afferent and efferent nerves involved in the pupillary light reflex?

Answer 21

Afferent: CN II, optic nerve
Efferent: CN III, oculomotor nerve

Question 22

What happens in the pupillary light reflex?

Answer 22

Light shine in one eye and is detected by the retina
Signal sent via afferent optic nerve
Synapses to the pretectal nucleus
Which gives rise to neurones supplying the Edinger Westphal nucleus bilaterally
Sends signal to constrict the pupil down both of the oculomotor nerves parasympathetics, via the sphincter pupillae muscles

Light -> optic nerve -> lateral geniculate nucleus -> pretectal area -> Edinger Westphal nucleus -> oculomotor nerve -> ciliary ganglion

Question 23

What’s the accommodation reflex?

Answer 23

When the eyes focus from a distant object to a near object, three reactions take place:

1. Constriction of pupils via sphincter pupillae
2. Contraction of ciliary muscles to thicken the lens
3. Convergence of both eyes via medial rectus muscles

Question 24

What is amaurosis fugax?

Answer 24

Transient blindness “like a curtain coming down over vision”
Due to blockage of the retinal artery causing hypoxia of the retina
Vision returns within a few hours
Could preclude a stroke

Question 25

What is Meyer’s loop?

Answer 25

The inferior optic radiation