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neuro lectures > the eye and visual system > Flashcards

the eye and visual system Flashcards

1
Q

how many layers does the eye have

A

3

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2
Q

why do we need 2 eyes (2)

A
  • to see in 3D (stereopsis)
  • widens our visual field
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3
Q

what are the 3 layers

A

outer
middle
inner

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4
Q

what is the outer layer made of

A

sclera and cornea

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5
Q

what is the middle layer made of

A

uvea/ choroid

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6
Q

what is the inner layer made of

A

retina

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7
Q

describe sclera structure

A

cross linked collagen fibres - makes it white
tough fibrous outer coat

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8
Q

describe cornea

A

transparent
also made of collagen but the fibres are laid out in parallel
must have a smooth spherical surface

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9
Q

what is the limbis

A

the area where sclera and cornea meet.
this is where most stem cells of the cornea are

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10
Q

functions of sclera

A
  • gives protection to eyeball since its made from a tough layer of collagen
  • maintains shape of eyeball
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11
Q

what does the sclera serve as an insertion point for

A

the external muscles of the eye

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12
Q

what is the sclera a continuation of

A

dura mater and cornea

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13
Q

what does choroid do

A

blood supply and nutrition to retina

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14
Q

what is middle layer made of

A

iris
ciliary body
choroid

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15
Q

what is the iris

A

coloured part at front of the eye
contains dilator and sphincter pupillae muscles
pupillary reflexes

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16
Q

what is melanoma

A
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17
Q

what is retina

A

neurofibre layer of the eye specialised organ of phototransduction
has many layers

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18
Q

what does the retina produce

A

vitreous humour - acts as a collagen scaffold, helps maintain intraocular pressure and is important in the transmission of light

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19
Q

where does light pass through in order to project an image on the retina

A

light passes through the pupil from
the visual field to project an image
onto the retina.

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20
Q

what is the fovea centralis

A

An object that attention is focused on, projects an image that is centred near the posterior pole of the eye along the
visual axis, this point is known as
the FOVEA CENTRALIS

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21
Q

what is the macula latea

A

the surrounding 1cm to the fovea centralis

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22
Q

what is the retina specially modified for at the fovea centralis and macula latea

A

for maximal visual acuity (resolving power)

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23
Q

what is the optic disk

A
  • a region medial to the macula
  • where retinal axons accumulate to
    leave the eye
  • optic nerve forms here
  • photoreceptors are absent in this region - so its called the blind spot
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24
Q

how much of the cornea is responsible for retractive power

A

2/3
the other 1/3rd comes from the inter ocular lense

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25
Q

unique feature of inter ocular lens

A

never stops growing throughout life
keeps producing cells in ECM
problem of this - develop cataracts

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26
Q

what happens to lens as it grows

A

becomes less pliable - less responsive

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27
Q

what is presmyopia

A

as people age they become more long sighted

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28
Q

how many layers in cornea

A

5

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29
Q

what are the 5 components of cornea (from outer to inner)

A
  1. epithelium - can be regenerated
  2. bowman’s layer
  3. stroma
  4. descemets layer
  5. endothelium - cannot be regenerated
30
Q

what does endothelium do

A

keeps cornea hydrated by actively pumping water out of stroma
keeps cornea clear
(since water molecules alter
the regular spacing between collagen
fibres & cause opacity)

31
Q

what does ciliary body do

A

holds lens and suspensory ligaments in place as it contracts and expands

made of smooth muscle, which controls accommodation; the
adjustment of the lens in the eye so that clear images of objects at
different distances are formed on the retina

32
Q

where does ciliary body get innervation from

A

the parasympathetic system

33
Q

most anterior aspect of choroid

A

iris

34
Q

function of iris

A

Contains & controls the size of the pupil which lets light in
- Sphincter muscles (circular fibres) make the pupil smaller
[parasympathetic]
- Dilator muscles (radial fibres) make the pupil larger [sympathetic]

Gives eyes their colour

35
Q

what does posterior segment refer to

A

anything from posterior segment of lens to back of eye

36
Q

what does anterior segment refer to

A

divided into anterior and poster chambers

37
Q

what does the lens divide

A

anterior and posterior segment

38
Q

what do ciliary bodies produce

A

aqueous humour
maintains pressure of eye
bathes anterior chamber
travels from ciliary body, through pupil , out to anterior chamber and then drains through anterior chamber at an angle between iris and cornea

39
Q

what is glaucoma

A

increased pressure in eye
damages nerves

40
Q

what does outer retina contain and what does it do

A

photoreceptor cells
send signals inwards to retina
then chemical reactions happen
synapses with other cells eventually send signal back

41
Q

2 types of photoreceptor cells

A

rods and cones

42
Q

what is retinal pigement epithelium (RPE)

A

Contains photoreceptors (rods &
cones) so it is able to convert light into
electric impulses (PHOTOELECTRIC
TRANSDUCER) which are transmitted
to ganglion cells which go on to make
optic fibres and eventually the optic
nerve

43
Q

difference between rods and cones

A

cones give colour rods are black and white
cones give high resolution rods give low resolution

44
Q

when are rods more important

A

in dim lighting
they are very sensitive to light
also important for peripheral vision

45
Q

location of rods and cones

A

the more central u get the more cones u get
the more peripheral u get the more rods u get

46
Q

what is the macula latea

A

central area of retina
responsible for central vision and clarity and colour

47
Q

does damage to peripheral affect vision

A

no you can still see
but damage to any point or macula will affect vision

48
Q

configuration of rods and cones

A

rods - many to one
cones - one to one

49
Q

what do rods and cones do

A

send signals to bipolar cells

50
Q

photo transduction

A

light photons come in
they cause a chemical change
signal goes down
changes conformation
recycled back through and enzyme

51
Q

what is emmetropia

A

6/6 vision

52
Q

what is myopia

A
53
Q

what is hypermetropia

A

refractive power is too low
image forms on back of retina instead of in retina
can see far but not close
these people are given a plus lens

54
Q

causes of hypermetropia

A

corneal curvature too shallow
lens not flexible enough
axial length of eyeball too short

55
Q

causes of myopia

A

corneal curvature too steep
axial length of eyeball too lomg

56
Q

what is adnexae

A

term used for near by objects

57
Q

function of lids

A

protects eye
tear fill distribution
blocks light

58
Q

what does tarsal plate do

A

separate eyes into 2 layers

59
Q

3 components to tear film

A

anterior lipid - prevents evaporation
middle aqueous - gives fluidity and nutrition
posterior mucus - maintains rest of tear film

60
Q

describe anterior lipid layer of tear film

A

secreted by meibomium glands, provides a hydrophobic barrier to prevent the aqueous layer evaporating

61
Q

describe middle aqueous layer of tear film

A

secreted by lacrimal
glands, regulates transport through the cornea and prevent infection

62
Q

describe posterior mucus layer of tear film

A

secreted by goblet cells, provides a hydrophilic layer that allows for the even distribution of the tear film

63
Q

eyes blood supply

A

via the ophthalmic artery
- is a branch of the internal carotid artery, arising immediately distal to the cavernous sinus.

  • ophthalmic artery gives rise to many branches, which supply different components of the eye.
64
Q

what supplies the inner surface of the retina

A

The central artery of the retina

Occlusion of this artery will quickly result in blindness.

65
Q

venous drainage

A

superior and inferior ophthalmic veins. These drain into the cavernous sinus, a dural venous sinus in close proximity to the eye.

66
Q

where is lymphatic drainage from

A

the conjuctiva
not from eye
drainage to submandibular and pre auricular nodes

67
Q

what does the glandular epithelium do

A

produces; aqueous humour & nutrients for cornea & lens

68
Q

what is aqueous humour made of

A

mainly water and electrolytes

69
Q

what does aqueous humour do

A

maintains intraocular pressure (15mmHg)

70
Q

why is choroid darkly pigmented

A

so it can absorb stray photons

71
Q

what are the layers that which a photon must travel through the eye (12)

A
  1. Tear film (transmission)
  2. Cornea (transmission & refraction (contributes to 2/3rds of refraction)
  3. Aqueous humour (transmission)
  4. Lens (transmission & refraction)
  5. Vitreous humour (transmission)
  6. Ganglion cell (transmission)
  7. Amacrine cell (transmission)
  8. Bipolar cell (transmission)
  9. Horizontal cell (transmission)
  10. Cone (transduction)
  11. Rods (transduction)
  12. Pigmented epithelium (absorption of excess photons)

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