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Clinical Neuroscience > Session 4: The Retina and Central Visual Pathways > Flashcards

Session 4: The Retina and Central Visual Pathways Flashcards

1
Q

Three layers of the eye.

A

Sclera

Uvea

Retina

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2
Q

What is the sclera continous with?

A

The dural sheath of the optic nerve

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3
Q

Contents of the uvea.

A

Choroid

Ciliary body

Iris

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4
Q

Neural layer of the retina - superficial to deep:

A

Retinal pigment epithelium

Photoreceptor cells

Bipolar cells

Ganglion cell layer

Nerve fibre layer

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5
Q

Function of the retinal pigment epithelium.

A

Prevents light from bouncing around in the eyeball causing a glare.

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6
Q

What are the bipolar cells?

A

First order neurones receiving input from photoreceptors.

These bipolar cells are connect by horizontal cells which assist with enhancing edges through a process called lateral inhibition.

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7
Q

Purpose of the ganglion cell layer.

A

Receives input from bipolar cells and axons of ganglion cells form the nerve fibre layer.

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8
Q

Give example of conditions fundoscopy can pick up.

A

Hypertensie retinopathy

Diabetic retinopathy

Macular degeneration

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9
Q

What is amaurosis fugax?

A

Sudden visual loss due to occlusion of the cenral retinal artery.

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10
Q

What is the medial retina called?

A

The nasal retina

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11
Q

What is the lateral retina called?

A

Temporal retina.

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12
Q

Light coming from the temporal field is detected by:

A

The nasal retina

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13
Q

Light coming from the nasal field is detected by:

A

The temporal retina

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14
Q

Explain the route of the light stimulus once it has become the optic nerve.

A

Optic nerve will run to the optic chiasm and will then form optic tracts.

Ganglion cell axons project to a part of the tahalmus called the lateral geniculate nucleus. This is via the optic tract.

The lateral geniculate nucleus projects to the visual cortex through the optic radiations.

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15
Q

What are the superior optic radiations?

A

Ganglion cells from the superior retina - inferior field.

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16
Q

What do the superior optic radiations run through?

A

The parietal lobe

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17
Q

What are the inferior optic radiations?

A

Ganglion cells from the inferior retina - superior field.

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18
Q

What do the inferior optic radiations run through?

A

Temporal lobe

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19
Q

What is monocular blindness?

A

Complete visual field loss of one eye

20
Q

What is scotoma?

A

A localised defect in the retina that can cause a small patch of visual loss.

21
Q

Explain the route of the temporal fibres through the optic chiasm.

A

They will travel from the optic nerve to the optic tract on their ipsilateral side.

22
Q

Explain the route of the nasal fibres through the optic chiasm.

A

They will decussate and then travel to the optic tract contralaterally.

23
Q

What is monocular blindness?

A

Complete visual field loss in one eye.

24
Q

What is bitemporal hemianopia?

A

Visual loss of the temporal fields.

25
Q

What is contralateral homonymous hemianopia?

A

Visual loss of one temporal field and one nasal field.

26
Q

What is contralateral superior quadrantopia?

A

Visual field loss of one of the superior temporal field quadrants and one of the superior nasal field quadrants.

27
Q

What is contralateral inferior quadrantopia?

A

Visual field loss of one of the inferior temporal field quadrants and one of the inferior nasal field quadrants.

28
Q

What is contralateral homonymous hemianopia with macula sparing?

A

Similar to contralateral homonymous hemianopia but macula is spared.

One nasal field and one temporal field is lost but the whole field of the macula remains intact.

29
Q

What will a lesion here cause?

A

Optic nerve leading to monocular vision loss of the ipsilateral eye (left)

30
Q

What will a lesion here cause?

A

Optic chiasm

Bitemporal hemianopia

31
Q

What will a lesion here cause?

A

Optic tract

Contralateral homonymous hemianopia meaning visual loss of the temporal field on the right eye and the nasal field on the left eye.

32
Q

What will a lesion here cause?

A

Inferior (temporal) optical radiations

Contralateral homonomous superior quadrantopia meaning visual field loss of upper temporal quadrant of right eye and upper nasal quadrant of left eye.

33
Q

What will a lesion here cause?

A

Superior optical radiation

Contralateral homonomous inferior quadrantopia meaning visual field loss of lower temporal quadrant of the right eye and the lower nasal quadrant of the left eye.

34
Q

What will a lesion here cause?

A

Contralateral homonymous hemianopia

Visual field loss of temporal field of right eye and nasal field of left eye.

35
Q

How might contralateral homonymous hemianopia with macula sparing occur?

A

The primary visual cortex is supplied by the posterior cerebral artery.

However the macula is supplied by a branch of the middle cerebral artery.

This means that in the case of an occlusion of the posterior cerebral artery there will still be macula sparing.

36
Q

How might both superior and inferior optic radiations be affected?

A

Stroke

37
Q

What does optical coherence tomography do?

A

A specialist technique that can be used to visualise the layers of the retina.

38
Q

Afferent and efferent of light reflex.

A

Afferent = optic nerve

Efferent = oculomotor nerve

39
Q

Explain the light reflex.

A

Light shone in one eye and afferent signal goes via optic nerve into the pretectal nucleus. Then goes bilateral to both Edinger westphal nuclei and carried on oculomotor nerve to ciliary body and constrictor sphincter pupillae.

This causes constriction of both pupils.

40
Q

Explain the accommodation reflex.

A

When the eye is unable to refract the light effectively anymore because the object is too close.

This causes convergence of the eyes via medial rectus.

Pupillary constriction via constrictor pupillae.

Fattens the lens via the contraction of ciliary muscle causing laxity of the suspensory ligaments.

The cerebral cortex must be involved.

The reflex follows the visual pathway via the lateral geniculate nucleus.

41
Q

Action of horizontal cells.

A

Help narrow down the light signal that is being sent by lateral inhibition.

This means that it detects the signal from the area of light impulse. The horizontal cells will inhibit any adjacent (lateral) photoreceptors that are not under the stimulus of the light.

42
Q

Why is the primary visual cortex involved in the accommodation reflex?

A

Because it is relating to image analysis

43
Q

Explain the accommodation reflex.

A

An object close by where refraction isn’t possible anymore there will be convergence, constriction and fattening of the lens.

Information is sent via optic nerve -> optic chiasm -> optic tract and then ultimately to primary visual cortex.

It will then communicate with the Edinger-Westphal nuclei (similarly to the light reflex) and cause impulse of the parasympathetic fibres of the CN III to cause constriction of pupils as well as contraction of the ciliary muscles which cause the suspensory ligaments to go lax -> fattening of the lens.

44
Q
A
45
Q

Where do the inferior optic radiations travel in the brain?

A

In the temporal lobe or specifically in Meyer’s loop.

Clinical Neuroscience (22 decks)

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