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LCRS Neuro > Structure & Function of the Eye > Flashcards

Structure & Function of the Eye Flashcards

1
Q

what are the 3 types of tear production?

A

1) basal tears (constantly produced)
2) reflex tears (response to irritation)
- afferent CnV1
- efferent PNS fibres of CnVII
3) crying/emotional tears

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2
Q

pathway of tears in lacrimal system

A
  • lacrimal glands
  • drainage through two puncta
  • via superior and inferior canaliculi
  • collect in tear sac
  • drain through tear duct in nose (via inferior nasal meatus)
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3
Q

afferent and efferent reflex tear

A

afferent: CN V1
efferent: PNS

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4
Q

4 functions of the tear film?

A

1) maintains smooth corneal-air surface
2) facilitate oxygen supply to cornea
3) remove debris
4) bactericide

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5
Q

what are the 3 layers of the tear film?

A

1) superficial oily layer
- reduce tear film evaporation
2) aqueous layer
- contains bactericides
3) mucin layer
- maintains wet corneal layer for diffusion

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6
Q

what produces the superficial oily layer?

A

Meibomian glands

superficial layer made of lipids to prevent evaporation

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7
Q

what produces the aqueous layer of tear film?

A

tear glands

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8
Q

what is the conjunctiva?

A

a thin transparent tissue that covers the outside surface of the eye.

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9
Q

position of the conjunctiva?

A

begins at outer edge of cornea
covers visible surface of eye
lines eyelids
nourished by near-invisible blood vessels

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10
Q

what are the 3 layers of the eye?

A

1) sclera (superficial)
2) choroid
3) retina (deep)

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11
Q

sclera

A

tough and opaque
white tissue, continuous with the cornea
high water content

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12
Q

choroid

A
  • component of the uvea
    (uvea= choroid+iris+ciliary body)
  • composed of vascular layer
  • pigmented
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13
Q

what are the components of the uvea?

A

iris
ciliary body
choroid

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14
Q

choroid and sclera water content

A

choroid: low water content
sclera: high water content

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15
Q

how much of the focusing power does the cornea provide?

A

66%

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16
Q

refractive index of cornea

A

provides 2/3 of the refractive power
(low water content compared to sclera)
- higher than air due convex structure

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17
Q

5 layers of the cornea (from superficial to deep)

A

1) epithelium
2) Bowman’s membrane
3) stroma (thickest, has nerve endings)
4) Descemet’s membrane
5) Endothelium

stroma is the thickest and avascular so receives nutrients from corneal nerves

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18
Q

function of the corneal endothelium

A

(last layer) pumps fluid out of the cornea, so prevent corneal oedema

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19
Q

pathology related to corneal endothelial

A
  • only 1 cell thick, has no capacity to regenerate
  • cell density decreases with age–> corneal oedema and corneal cloudiness
  • responsible for pumping out fluid to prevent corneal oedema
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20
Q

what is the uvea?

where does it lie?

A

iris+choroid+ ciliary body
vascular coat of the eye ball
lies between the sclera and the retina

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21
Q

what is the lens suspended by?

A 
lens zonules (fibrous ring) made of passive connective tissue 
they push and bulge the lens
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22
Q

what is the visible part of the optic nerve called?

A

optic disk

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23
Q

what is located near the optic nerve connection to the eye?

A

macula, temporal to the optic nerve

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24
Q

what is the macula?
what is it involved in?
what is located in the macula?

A
  • small and highly sensitive part of the retina
  • involved in detailed central vision
  • the fovea is in the centre of the macula
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25
Q

what are the boundaries of the anterior segment of the eye?

what is this area filled with?

A

between the cornea and the lens

filled with clear fluid for nutrition

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26
Q

what is the posterior segment? what is filled in it?

A

behind the lens (collagenous)

filled with vitreous humour

27
Q

what is normal intraocular pressure?

A

12-21/24 mmHg

28
Q

what is the effect of hydration of the cornea?

A

whiteness/cloudiness of cornea due to high water content of sclera

29
Q

what produces the aqueous humour?

A

ciliary body
active process
no correlation to BP

30
Q

2 methods of aqueous humour absorption?

A

1) uveal-scleral outflow

2) Canal of Schlemm and trabecular meshwork

31
Q

where does the aqueous leave in uveal-scleral outflow?

A

between sclera and choroid

Prostaglandins can target this

32
Q

where does aqueous humour go into via the CoS?

A

into the blood stream

33
Q

proportion of drainage in U-S outflow and CoS?

A

U-S outflow 20%

CoS into blood stream- 80%

34
Q

what are the 2 characteristics of glaucoma?

A

retinal ganglionic cell death

enlarged optic disk cupping

35
Q

main consequences of glaucoma

A

increased IOP

visual field loss and blindness

36
Q

2 types of glaucoma?

A

1) primary open angle (most common, trabecular dysfunction)

2) closed angle (acute or chronic, lens/iris bulge restricting outflow)

37
Q

what is the cause of primary open angle glaucoma?

A

trabecular meshwork dysfunction

38
Q

what is the mechanism of closed angle glaucoma?

A

increased IOP causes lens/iris to bulge out
this restricts the access to the TM and therefore outflow of the aqueous

acute or chronic issue

39
Q

risk factors of closed angle glaucoma

A

having a small eye and naturally small angle

40
Q

how can closed angle glaucoma be treated?

A

peripheral laser iridotomy to create drainage holes

41
Q

concentrations of cones and rods in macula?

A

highest conc of cones

lowest conc of rods

42
Q

how can the fovea be clinically assessed?

A

Optical Coherence Tomography

43
Q

what are the uses of central vision?

A
  • detailed day vision

- reading and facial recognition

44
Q

pathology and assessment of central vision

A

macular degeneration affects acuity

assessed by visual acuity assessment

45
Q

what are the uses of peripheral vision?

A

for shape, movement and night vision

46
Q

assessment of peripheral vision

A

visual field assessment

47
Q

the 3 layers of the retina?

A

outer- 1st order neurones

middle- 2nd order neurones

inner layer- 3rd order neurones

48
Q

1st order neurones (outer)

A

(photoreceptors detect light)

49
Q

2nd order neurones (middle)

A

(bipolar cells regulate/improve sensitivity and process light)

50
Q

3rd order neurones (inner)

A

(retinal ganglionic cells for signal transmission to the brain)

51
Q

receptor position in retina

A

proximal to pupil

light hits the retinal pigment epithelium first, at the back, then reflects onto the receptors in proximity

52
Q

outer segment of cones vs rods

A

rods has a longer outer segments that is 100x more sensitive to light

53
Q

light sensitivity of cones vs rods

A

rods more sensitive than cones

54
Q

response speed of cones vs rods

A

rods are slower in response than cones

55
Q

what is the rod (scotopic vision) responsible for?

A

peripheral
night vision
recognise motion

56
Q

what is the cone (photopic vision) responsible for?

A

central colour
day vision
detail

57
Q

relative populations of cones and rods in the eye

A

120 million rods

6 million cones

58
Q

fovea photoreceptors

A

no rods found

59
Q

what is the commonest form of colour vision deficiency?

A

red-green confusion (deuteranomaly)

M and L cone peaks are very close to each other

60
Q

at what wavelength is the rods peak sensitivity?

A

500nm

61
Q

what is the test for red-green deficiencies?

A

Ishihara test (numbers in dots)

62
Q

adaptation of cones and rods in the dark

A

increase in light sensitivity

cones initially most sensitive (7mins) than rods adapt and become more sensitive (30mins)

happens as a biphasic process

63
Q

what happens in light adaptation?

A

neuro-adaptation
bleaching of photopigments
inhibition of rod and cone function

LCRS Neuro (19 decks)

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