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Neuroscience > Vision > Flashcards

Vision Flashcards

1
Q

What are the cranial nerves involved?

A 
3rd= oculomotor
4th= trochlear
6th= abducens
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2
Q

What are the three broad aspects of vision?

A
  • Visual field
  • Visual acuity
  • Colour vision
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3
Q

What is the visual field?

A

‘Field of view’= essentially optical definition

‘True VF’= spatial array of visual sensation available to subject

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4
Q

Describe the normal human visual field

A 
-From vertical meridian
= 60* nasally
= 100* temporally (lateral)
-From horizontal meridian
= 60* above
= 75* below
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5
Q

What colour objects have a narrower visual field?

A

Red (compared to white)

smaller radius

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6
Q

What is visual acuity?

A
  • A measure of the clarity of vision

- Spatial resolution

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7
Q

What is colour vision?

A

Different frequencies of EMR are perceived as different colours

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8
Q

What are the components of the visual pathway?

A
  • Retina
  • Optic nerve
  • Optic chiasm
  • Optic tract
  • Lateral geniculate nucleus
  • Optic radiation
  • Visual cortex
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9
Q

What is the retina?

A

-Layers of neuronal cells
=only neurones that are directly light sensitive are photoreceptor cells
-Connected by synapses

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10
Q

What are the types of photoreceptor cells in the retina?

A

Rods
Cones
Photosensitive ganglion cell

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11
Q

What are the layers of the retina?

A
  • Nerve fiber layer
  • Ganglion cell
  • Inner plexiform
  • Inner nuclear
  • Outer plexiform
  • Outer nuclear
  • External limiting membrane
  • Rods and cones
  • Pigmented epithelium
  • Lamina vitrea
  • Choroid
  • Sclera
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12
Q

What happens when light hits the retina?

A

Light stimulates rods and cones

  • Signal to other cells that go to surface of retina (ganglion)
  • Axons to optic nerve
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13
Q

Describe rods

A

Function mainly in dim light
Black and white vision
-120 million

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14
Q

Describe cones

A 
Function in bright light
Perception of colour
=L-cones Red 564 nm
=M-cones Green 533 nm
=S-cones Blue 437 nm
-6-7 million
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15
Q

What are photosensitive ganglion cells important for?

A

Reflexive responses to light

Constriction of pupil

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16
Q

Describe the pathway from retina to nerve

A
  • Signals from rods and cones
  • Processed by other retinal neurones
  • Axons of the retinal ganglia cells form the optic nerve
17
Q

What are the special areas on the retina?

A
  • Macula= yellow oval spot near retina centre, specialised for high acuity vision (6mm) (13* degrees of central field)
  • Fovea= a pit in the macula centre, the area of greatest VA and best colour vision- many cones (1.5 mm) (3* of central field)
18
Q

Describe the fovea

A

Occupies 0.01% of VF
3* of visual angle
10% of optic nerve axons

19
Q

How are rods and cones distributed?

A

Rods= periphery
Cones= fovea
None in blind spot

20
Q

How can visual acuity be affected?

A

Light is impaired in transmission through eye
Disease of cornea and lens
Refractive (optical) problems
Developmental anomalies/ changes in elasticity in lens in age

21
Q

Which VA problems are correctable?

A

Refractive errors correctable with glasses/ lens

Neurological VA problems (difficulty in neural structures) not correctable

22
Q

What are visual fields based on?

A

Angle of view
Enlarge with distance
Depend on object size (small= small field) and colour

23
Q

What are blind spots?

A

Temporal field side of fixation
Optic nerve head/ disc has no light sensitive cells
Displaced from point of fixation
Not noticed in normality

24
Q

Describe blind spot in disease

A
  • BS reflects optic nerve
  • BS size reflects optic nerve size
  • Enlarged= papilledema, optic neuritis
25
Q

How does visual information cross in the visual pathway?

A

Light from right visual space goes to both left and right eyes
Right visual space light enters right eye and hits nasal retina, enters left eye and hits temporal retina
So nasal retinal half has to cross at optic chiasm

26
Q

Describe how the chiasm is involved in the visual pathway

A 
Pre-chiasm= all data from one eye
Chiasm= half the data crosses (from nasal retina)
Post-chiasm= all left visual space data on right, all right visual space data on left
27
Q

What are the types of visual field defects?

A
  • Major visual field defects (loss of substantial segment of visual field)
  • Constriction of peripheral field
  • Enlarged blind spots
  • Scotomata (holes in visual field)
28
Q

What are the classifications of major visual field defects?

A
  • Pre-chiasmal (trauma, removal of one eye, optic nerve)= uni-ocular loss
  • Chiasmal (bitemporal hemianopia so affects temporal half of field, problems with pituitary gland like tumour)
  • Post-chiasmal (homonymous hemianopia, so left hemisphere loss of right visual space so left nasal field and right temporal)
29
Q

What are quadrantopias?

A
  • Lesion to optic radiation where fibers fan and spread out

- Upper quadrant= superior

30
Q

What are other major visual field defects?

A

Altitudinal VFDs= upper half of visual field loss

31
Q

What are the colour vision defects?

A

Congenital or acquired (optic neuritis)

32
Q

What are the extraocular muscles?

A
  • Superior, inferior, lateral and medial rectus

- Superior (down) and inferior (up) oblique

33
Q

What does the third cranial nerve innervate?

A

All the recti but lateral rectus
Innervates inferior oblique
Opens eye lid and parasympathetic pupil (diameter)

34
Q

What does the 4th cranial nerve innervate?

A

Superior oblique

35
Q

What does the 6th cranial nerve innervate?

A

Abducts eye via Lateral rectus

36
Q

What are the movements caused by the recti muscles?

A 
Straight
Superior= up
Inferior= down
Medial= in
Lateral= out
37
Q

What are the movements caused by the oblique muscles?

A 
Superior= down
Inferior= up
38
Q

What are ocular palsies?

A

Eye takes on abnormal position because of unopposed action of remaining intact muscles

39
Q

What is diplopia?

A

Results from failure to align eyes (two eyes)

  • Double vision may mean blurred vision
  • Did it resolve if you closed/ covered one eye

Neuroscience (33 decks)

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