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LCRS Neuro > Structure & Function of the Eye > Flashcards

Structure & Function of the Eye Flashcards

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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
what are the boundaries of the anterior segment of the eye? what is this area filled with?
between the cornea and the lens filled with clear fluid for nutrition
26
what is the posterior segment? what is filled in it?
behind the lens (collagenous) | filled with vitreous humour
27
what is normal intraocular pressure?
12-21/24 mmHg
28
what is the effect of hydration of the cornea?
whiteness/cloudiness of cornea due to high water content of sclera
29
what produces the aqueous humour?
ciliary body active process no correlation to BP
30
2 methods of aqueous humour absorption?
1) uveal-scleral outflow | 2) Canal of Schlemm and trabecular meshwork
31
where does the aqueous leave in uveal-scleral outflow?
between sclera and choroid | Prostaglandins can target this
32
where does aqueous humour go into via the CoS?
into the blood stream
33
proportion of drainage in U-S outflow and CoS?
U-S outflow 20% | CoS into blood stream- 80%
34
what are the 2 characteristics of glaucoma?
retinal ganglionic cell death | enlarged optic disk cupping
35
main consequences of glaucoma
increased IOP | visual field loss and blindness
36
2 types of glaucoma?
1) primary open angle (most common, trabecular dysfunction) | 2) closed angle (acute or chronic, lens/iris bulge restricting outflow)
37
what is the cause of primary open angle glaucoma?
trabecular meshwork dysfunction
38
what is the mechanism of closed angle glaucoma?
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
risk factors of closed angle glaucoma
having a small eye and naturally small angle
40
how can closed angle glaucoma be treated?
peripheral laser iridotomy to create drainage holes
41
concentrations of cones and rods in macula?
highest conc of cones | lowest conc of rods
42
how can the fovea be clinically assessed?
Optical Coherence Tomography
43
what are the uses of central vision?
- detailed day vision | - reading and facial recognition
44
pathology and assessment of central vision
macular degeneration affects acuity | assessed by visual acuity assessment
45
what are the uses of peripheral vision?
for shape, movement and night vision
46
assessment of peripheral vision
visual field assessment
47
the 3 layers of the retina?
outer- 1st order neurones middle- 2nd order neurones inner layer- 3rd order neurones
48
1st order neurones (outer)
(photoreceptors detect light)
49
2nd order neurones (middle)
(bipolar cells regulate/improve sensitivity and process light)
50
3rd order neurones (inner)
(retinal ganglionic cells for signal transmission to the brain)
51
receptor position in retina
proximal to pupil | light hits the retinal pigment epithelium first, at the back, then reflects onto the receptors in proximity
52
outer segment of cones vs rods
rods has a longer outer segments that is 100x more sensitive to light
53
light sensitivity of cones vs rods
rods more sensitive than cones
54
response speed of cones vs rods
rods are slower in response than cones
55
what is the rod (scotopic vision) responsible for?
peripheral night vision recognise motion
56
what is the cone (photopic vision) responsible for?
central colour day vision detail
57
relative populations of cones and rods in the eye
120 million rods | 6 million cones
58
fovea photoreceptors
no rods found
59
what is the commonest form of colour vision deficiency?
red-green confusion (deuteranomaly) M and L cone peaks are very close to each other
60
at what wavelength is the rods peak sensitivity?
500nm
61
what is the test for red-green deficiencies?
Ishihara test (numbers in dots)
62
adaptation of cones and rods in the dark
increase in light sensitivity cones initially most sensitive (7mins) than rods adapt and become more sensitive (30mins) happens as a biphasic process
63
what happens in light adaptation?
neuro-adaptation bleaching of photopigments inhibition of rod and cone function

LCRS Neuro (19 decks)

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