1
Q
the eye is divided into —- chambers by the —-
A
chambers; lens
2
Q
define the lens
A
a transparent disk that focuses light onto the retina
3
Q
how is the lens suspended?
A
by ligaments called zonules
4
Q
aqueous humor
A
plasma-like fluid that fills the interior chamber in front of the lens
5
Q
what is the purpose of the aqueous humour?
A
to help maintain intraocular pressure
6
Q
vitreous body/humour
A
a clear jelly that helps to maintain the eyeball’s shape, located in the vitreous chamber behind the lens
7
Q
how does light enter the eye?
A
through the cornea
8
Q
cornea
A
a transparent bulge at the front of the eye, continuous with the sclera
9
Q
sclera
A
- the white of the eye - the outer wall of the eyeball
- dense connective tissue
- maintains eyeball shape and protects delicate internal structures
10
Q
what is the function of the cornea and lens?
A
to focus light onto the retina
11
Q
retina
A
the inner lining of the eye that contains the photoreceptors
12
Q
pupil
A
a hole in the iris through which light passes from the cornea to the lens
13
Q
optic disk
A
- site of accumulation and exit of ganglion cells
- vertically elongated, with Hd of 1.7mm and Vd of 1.9mm
14
Q
describe the aqueous humor pathway and IOP regulation
A
produced by the ciliary processes, aqueous humour flows from the posterior chamber -> pupil -> anterior chamber -> drains via trabecular meshwork -> Canal of Schlemm
14
Q
trabecular meshwork
A
porous pressure gate
15
Q
Canal of Schlemm
A
circular drainage pipe that runs around the eye
16
Q
what is the importance of the aqueous humor pathway?
A
it is critical for nourishing the avascular cornea and maintaining intraocular pressure - disruption can lead to glaucoma
17
Q
why is it important for the sclera and cornea o be avascular?
A
light would otherwise scatter
18
Q
is the sclera solely localised to the eye?
A
no; it continues into the dura mater (outermost meningeal layer surrounding the brain and spinal cord)
19
Q
give an example of how the eyes can reflect problems occurring in the brain
A
- if pressure builds up in the scull (tumour/injury), it can be transmitted along the subarachnoid space surrounding the optic nerve to the back of the eye due to CSF pressure
- this can lead to papilledema, which is swelling of the optic disk
- when you look at the back of the eye during a fundoscopic exam, you can see a swollen optic disk with blurred margins.
20
Q
glaucoma
A
if drainage pathway is blocked, you put pressure on the optic nerve where the nerve fibres exit the eye, leading to vision loss
21
Q
5 layers of the cornea, from outermost to innermost
A
outermost
- epithelium
- Bowman’s layer
- stroma
- Descemet’s membrane
- endothelium
innermost
22
Q
describe the structure/contents of the vitreous humour
A
- does not circulate, static
- formed during development
- 99% water, with collagen and hyaluronic acid
- not part of the 3 classical histological layers
23
Q
describe the function of the vitreous humour
A
- important for maintaining the shape of the eyeball, holds retina in place
- shock absorber and light transmitter
24
how can the vitreous humour change with aging?
it can liquefy and detach from the retina, causing 'floaters'
25
hyaloid canal
- transparent tube that runs through the centre of the vitreous humour
- in fetus, it supplies the hyaloid artery which supplies the developing lens
- after birth, the artery regresses and the canal becomes nonfunctional and faint
26
cornea - epithelium
protection, acts as a barrier against foreign material
27
cornea - Bowman's layer
tough supportive layer located just beneath the epithelium, composed of collagen fibers.
28
cornea - stroma layer
The thickest layer, making up about 90% of the cornea's thickness, and is made of collagen and water
29
cornea - Descemet's membrane
thin but strong layer that acts as a barrier to protect against injury and infection.
30
cornea - endothelium
- endothelial layer is in contact with the aqueous layer/chamber
- monolayer of specialised cells that help regulate the fluid and maintain the corneal clarity
- within this layer you have Na+-K+ pumps
31
what is the importance of Na+-K+ pumps in the corneal endothelium?
- nutrients from the humour are allowed to pass through passive diffusion into the corneal space
- to keep the cornea clear and dehydrated, these pumps actively move excess water and ions from the corneal stroma back into the aqueous humour
32
Fuchs endothelial corneal dystrophy
- caused by damage to endothelial cells
- autosomal dominant genetic condition that causes cells to die off
- inability to maintain the corneas dehydrated state, causing corneal edema (swelling) and vision loss
- potential treatment is hypertonic saline solution
33
3 components of the uvea layer
- iris
- ciliary body
- choroid
34
iris
coloured part of the eye - made up of two smooth muscle groups, circular and radial muscle
35
describe the urea layer
highly vascularised and regulates blood flow
36
ciliary body
- helps to compact/change lense shape
- ciliary processes produce aqueous humour
37
choroid layer
- between sclera and retina
- rich in blood vessels and melanin pigment
- can absorb light but also feeds retina nutrients
38
label a diagram of the eye
39
describe how the pupil can change size
- in bright light the pupils constrict (shrink) to 1.5mm across, reducing the amount of light reaching the lens
- in the dark the pupils dilate (enlarge) to 8mm, ~20 times bigger in area, to let in more light
40
describe the range of illumination over which the eye operates
huge - eg. a sunny afternoon is 100 million times brighter than a moonless night
41
how is pupil size controlled?
by smooth muscles in the iris
- in bright light, parasympathetic signals from the brain contract the circular pupillary constrictor muscle, shrinking the pupil
- in the dark, sympathetic signals contract the radial pupillary dilator muscle of the iris, dilating the pupil
42
how does the pupil help to focus light?
- most rays are blocked by the sclera or miss the pupil as a result of its small size
- a small pupil ensures that each point on the retina receives light from just one direction in space (focus!)
43
how does the pupil help to control depth of field
- when the pupil is tightly constricted, we have full depth of field (everything we see is in focus)
- when the pupil is dilated, we have a shallow depth of field (only objects near one specific distance are in focus)
44
two functions of pupils
- focuses light
- helps to control depth of field
45
what is the problem with using the pupil alone to focus light?
- with pinhole-focusing, the retinal image is dim because the pinhole doesn't admit much light
- enlarging the hole makes the image brighter but blurrier
46
how can we get a retinal image that is both bright and in focus?
by using refraction
47
define refraction
when light bends as it enters a medium with a different refractive index
48
angle of refraction depends on
the difference in density of two milieus with distinct optical densities
49
how does refraction in the eye work?
our corneas are made of clear collagen. they bend light strongly because there is a big difference between the refractive indices of air and collagen
50
why is the refraction of light when it hits the eye in water much weaker than in air?
because the refractive indices of collagen and water are similar
51
what is responsive for refracting light in the eye?
- the cornea is responsible for 2/3 of the eye's refraction
- the lens is responsible for 1/3 of the eye's refraction
52
describe the make-up of the lens
- mesh of long (12mm) clear cells without nuclei, packed with clear proteins called crystalline and zippered together in concentric layers for flexibility
- has no blood supply but absorbs nutrients from the aqueous humour
53
is the lens convex or concave and why?
- the lens is convex, meaning it is fatter in the middle and thinner at the edges.
- this ensures that light rays converge to a focal point
54
concave lenses
- thinner in the middle and fatter at the edges
- disperse light
55
what does refraction depend on?
the angle of incidence
56
angle of incidence
the angle at which the light ray hits the lens surface
57
what does the angle of incidence depend on?
the shape of the lens and the direction of the light ray
58
simplest case of angle of incidence
if a ray strikes the lens at right angles then it doesn't bend at all
59
where must the focal point fall for clear vision?
on the retina
60
rounder lens
bends light more, so has a closer focal point
61
what happens if the object draws closer but the lens stays flat
focus falls behind the retina
62
to bring a closer object into focus
parasympathetic nerve signals contract the ring-shaped, smooth ciliary muscle, reducing tension in the zonules, making the lens rounder, so light rays bend more and the focal point moves forward
63
to bring a further object into focus
sympathetic nerve signals relax the ring-shaped, smooth ciliary muscle, increasing tension in the zones, making the lens flatter, so light rays bend less and the focal point moves backwards
64
accommodation
rounding the lens for near vision
65
pupillary light reflex
1. light is shined on the right eye only
2. action potentials from the right eye reach both he right and left pretectal nuclei
3. the pretectal nuclei stimulate both sides of the Eddinger-Westphal nucleus even though the light was only perceived only in the right eye
4. the right and left sides of the Eddinger-Westphal nuclei generate action potentials through the right and left oculomotor nerves, causing both pupils to constrict
66
miosis
contraction/shrinking of the pupil
67
describe the competing autonomic control that the pupil is under
the pupil is under competing autonomic control in response to light levels hitting the retina:
- the sympathetic system dilates the pupil when the retina is not receiving enough light
- the parasympathetic system constricts the pupil when too much light hits the retina
68
near point of accommodation
closest point a person can focus on
69
presbyopia
with advancing age the lens stiffens and the ciliary muscles weaken, hindering accommodation
70
hyperopia
- far-sightedness
- focal point falls behind the retina
- the lens and cornea are not providing enough focusing power to be able to converge light rays to the retina or the eyeball may be shorter than normal in the front-back direction
71
how is hyperopia solved?
by a convex lens in front of the eye
- corrects the fact that the lens of the eye is bending the light rays too little
72
myopia
- near-sightedness
- focal point falls in front of the retina
- the lens and cornea are providing too much focusing power to be able to converge light rays to the retina or the eyeball may be longer than normal in the front-back direction
73
how is myopia solved?
by a concave lens in front of the eye
- corrects the fact that the lens of the eye is bending the light rays too much
PSL300
flashcards
Decks in class (55)
# Cards
-
L140
-
L216
-
L340
-
L431
-
L532
-
L638
-
L733
-
L857
-
L930
-
L1041
-
L1138
-
L1227
-
L1362
-
L1453
-
L1546
-
L1646
-
L1756
-
L1824
-
L1971
-
L2053
-
L2174
-
L2286
-
L2344
-
L2457
-
L2563
-
L2644
-
L2748
-
L2832
-
L2926
-
L3042
-
L3127
-
L3248
-
L3375
-
638
-
733
-
857
-
930
-
1041
-
1138
-
1228
-
1453
-
1546
-
1824
-
1971
-
2053
-
2174
-
2286
-
2563
-
2644
-
2748
-
270
-
2832
-
3127
-
3248
-
3375
