Structure and Function of the Eye Flashcards
(139 cards)
1
Q
Where does the eye sit
A
Orbit
2
Q
The sclera is…
A
the white part of the eye
3
Q
medial canthus is…
A
medial corner of the eye
4
Q
The lateral canthus is…
A
lateral corner of the eye
5
Q
The palpebral fissure is…
A
where the upper eyelet bends back
6
Q
The limbus is…
A
the border between the cornea and sclera
7
Q
the border between the cornea and sclera is known as…
A
the limbus
8
Q
where the upper eyelid bends back is known as…
A
palpebral fissure
9
Q
the white part of the eye is known as…
A
sclera
10
Q
the corners of the eye is known as…
A
canthus
11
Q
the pink bit near the medial canthus is known as…
A
caruncle
12
Q
The caruncle is …
A
the pink bit near the medial canthus
13
Q
Why is the pupil black
A
black because the inside of the eye is coated in pigment epithelium which doesn’t allow light to escape
14
Q
What are basal tears
A
tears produced to keep the cornea wet
15
Q
The three types of tears the cornea produces?
A
Basal, reflex and crying tears
16
Q
Afferent and efferent nerves, and NT of the tear production reflex
A
ACh, afferent - ophthalmic branch of the trigeminal
Efferent- Parasympathetic
17
Q
- Tear produced by …
A
lacrimal gland
18
Q
- Tear drains through …
A
the two puncta, opening on medial lid margin
19
Q
What are the puncta
A
hole where tears drain through
20
Q
- Tear flows through the … (2)
A
superior and inferior canaliculi
21
Q
- Tears gather in the…
A
tear sac
22
Q
Tearsexits the tear sac through the XX and into XX
A
through the tear duct into the nose cavity
23
Q
Describe the route tears take from production to drainage (5)
A
- Tear produced by lacrimal gland
- Tear drains through the two puncta, opening on medial lid margin
- Tear flows through the superior and inferior canaliculi
- Tear gathers in tear sac
- Tears exits the tear sac through the tear duct into the nose cavity
24
Q
Purposes of the tear film? (4)
A
- Tear film maintains smooth cornea-air surface
- Oxygen supply to cornea- normal cornea has no blood vessels
- Removal of debris (tear film & blinking)
- Bactericide
25
Blood supply to the cornea?
There is none physiologically
26
Three layers of the tear film?
Superficial oily layer
Aqueous tear film
Mucinous layer
27
Purpose of the Mucinous layer in tear film
on the corneal surface to maintain surface wetting
28
Purpose of the Superficial oily layer in tear film
to reduce tear film evaporation (produced by a row of Meibomian glands along the lid margins)
29
What produces the Superficial oily layer in tear film and where are these cells found
Meibomian glands along the lid margins
30
What is the CONJUNCTIVA
The thin, transparent tissue that covers the outer surface of the eye
31
What is the cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber
32
Nourishment of the cornea is through...
tiny blood vessels that are nearly invisible to the naked eye
33
The conjunctiva begins where and lines what
begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids
34
Retina is made of..
nerve tissue
35
Where is the uvea and what does it consist of (3)
around the retina- it consists of the iris, ciliary body and choroid
36
What is the choroid and its purpose?
a spongey vessel structure that nourishes the retina
37
what is the sclera made of and its function
collagen structure that protects the eye posterior
38
From out to in, order the sclera, choroid and retina
sclera, choroid, retina
39
purpose of the Cornea
protects eye anteriorly
40
Choroid colour and function
Pigmented and vascular
41
refractive index of cornea vs air
higher refractive index than air
42
Water content of the cornea and why is not as such
- Low water content Dehydrated by corneal endothelium in order to remain transparent
43
Cornea is continuous with X layer
scleral
44
5 layers of the cornea?
1. EPITHELIUM
2. BOWMAN’S MEMBRANE
3. STROMA
4. DESCEMET’S MEMBRANE
5. ENDOTHELIUM
45
2 names membranes in the cornea? which layer of the cornea are they?
2 - Bowmans is outer
| 4 - Descemet in inner
46
Endothelial cell dysfunction may result in ... (2)
corneal oedema and corneal cloudiness
47
3 parts of the uvea?
1. Iris
2. Ciliary body
3. Choroid
48
photoreceptors in retina are cells that transforms X into Y
photons into electrons
49
Choroid is between ...
- Between retina and sclera
50
choroid is mainly composed of ...
posed of layers of blood vessels that nourish the back of the eye
51
Choroid vessels nourish what part of the eye
posed of layers of blood vessels that nourish the back of the eye
52
What is the loss of transparency in the lens known as
cataracts
53
Three functions of the lens?
- Transparency
- Refractive power
- Accommodation
54
Lens is suspended by a fibrous rings known as...
lens zonulae
55
lens zonulae are ...
fibrous rings suspending the lens
56
When the muscle constricts, the pressure on the zonula is X so the lens gets smaller and thicker
released
57
Optic nerve connects to the eye near the X
macula
58
Visible portion of the optic nerve is known as...
Optic disc
59
MACULA is located roughly ...
In the centre of the retina
60
MACULA is slightly [temporal/nasal] to the X
temporal
| optic nerve
61
- The fovea is the ...
very centre of the macula
62
What divides the eye into the anterior and posterior segments
lens
63
the anterior chamber is between the....
cornea and the lens
64
the anterior chamber is filled with....
aqueous humour
65
What secretes aqueous humour
ciliary body
66
ciliary body is responsible for ...
secreting aqueous humour
67
X drains the fluid out of the eye
trabecular meshwork
68
What does the trabecular meshwork do
drains the fluid out of the eye
69
Purpose of the aqueous humour?
Provide nutrients to the eye
70
Describe the flow of the aqueous humour starting with entering the anterior chamber and its 2 methods of exit
- Enters anterior chamber and is then reabsorbed by Trabecular meshwork (then can escape meshwork via Canal of Schlemm that will push aqueous humour into the venous stream (80-90%), OR can escape passively via passive flow inside the uvea and sclera (uveal-scleral flow= 10-20%))
71
Prostaglandins to treat glaucoma work how
increase uveal-scleral flow
72
What is glaucoma
MEDICAL CONDITION OF SUSTAINED RAISED INTRAOCULAR PRESSURE
73
What does glaucoma result in (2 things and this causes 2 things)
- Retinal Ganglion cell death and enlarged optic disk cupping
- Visual field loss, blindness
74
2 types of glaucoma?
PRIMARY OPEN ANGLE GLAUCOMA
| CLOSED ANGLE GLAUCOMA
75
Which is the most common type of glaucoma
PRIMARY OPEN ANGLE
76
What is at fault in PRIMARY OPEN ANGLE glaucoma
Trabecular meshwork dysfunction
77
What happens in closed ANGLE glaucoma
Increased pressure pushing iris/lens complex forwards, blocking trabecular meshwork- vicious cycle
78
risk factors for closed angle glaucoma (2)
small eye (hypermetropia), narrow angle at trabecular meshwork
79
Presentation of glaucoma (2)
sudden painful red eye with acute drop in vision
80
surgical treatment for glaucoma ?
peripheral laser iridotomy to create a drainage hole on the iris
81
Why is there a blind spot in the eye and where is it
- Where the optic nerve meets the retina there are no light sensitive cells
82
concentration of rods and cones in the fovea?
highest concentration of cones, but a low concentration of rods
83
- Loss of foveal vision results in what acuity
poor visual acuity
84
2 categories of visual function?
Central and peripheral
85
how to assess central vision?
visual acuity assessment
86
how to assess peripheral vision?
visual field assessment
87
Loss of peripheral vision manfests as....
unable to navigate environment, patient may need white stick even with perfect acuity
88
what nerves are in the outer layer of the retina and what do they do
Photoreceptors (1st order neurons)- detection of light
89
what nerves are in the middle layer of the retina and what do they do
Bipolar cells (2nd order neurons)- Local sign processing to improve contrast sensitivity, regulate sensitivity
90
what nerves are in the inner layer of the retina and what do they do
Retinal ganglion cells (3rd order neurons)- Transmission of signal from the eye to the brain
91
What is the fovea
pit at the centre of the macula due to absence of overlying ganglion cell layer
92
What causes the pitting of the fovea
pit at the centre of the macula due to absence of overlying ganglion cell layer
93
Where is the highest concentration of photoreceptors
- Fovea
94
Physical difference between rod and cone cells?
- Longer outer segment in rod cells
95
difference in light sensitivity between rod and cone cells?
- rods 100x more sensitive to light than cones
96
difference in speed of response to light between rod and cone cells?
rods are Slower in response to light
cones are faster
97
difference abundance of rod and cone cells
120m rods
| 6m cones
98
What cells are responsible for night vision
rods
99
What cells are responsible for day vision
cones
100
What cells are responsible for colour vision
cones
101
What is day light colour vision known as
Phototopic
102
What is nightvision known as
scotopic
103
Map out the distribution of cone and rod cells (like it would look on a chart)
DO it
104
S-cones - wavelength and colour
short wavelength = blue
105
M-cones - wavelength and colour
medium wavelength = green
106
L-cones - wavelength and colour
long wavelength = red
107
rod wavelengths that are detected between X and Y cones
M and S
108
Deuteranomaly ...
the most common colour vision deficiency as involves not being able to see red well
109
Example of a colour perception test?
ISHIHARA TEST
110
What colour vision does the Ishihara test test?
red green deficiencies only
111
Speed of cone dark adaptation?
7 minutes
112
Speed of rod dark adaptation?
30 minutes
113
Why is the Speed of rod dark adaptation fairly long
it has to regenerate rhodopsin
114
how long does full light adaptation take
- Occurs over 5 minutes
115
what happens to rod/cone function in the light adaptation?
inhibited
116
what mediums does light have to travel through (6)
light has to go through tear film, cornea, aqueous humour, lens, vitreous humour and the retina
117
What is EMMETROPIA
Adequate correlation between axial length and refractive power
- Parallel light falls on to the retina- no accommodation
NO PROLEM
118
What is AMMETROPIA
Mismatch between axial length and refractive power
| - Parallel light rays don’t fall on the retina- no accommodation
119
What is MYOPIA
Parallel rays converge at a focal point anterior to the retina
- Near sightedness
120
What is HYPEROPIA
Parallel rays converge at a focal point posterior to the retina
- Far sightedness
121
What is AMBLYOPIA
uncorrected hyperopia >5D, difference between 2 eyes whereby one eye is very hyperopic- the brain begins to ignore the hyperopic eye
122
What is ASTIGMATISM
Parallel rays come to focus in 2 focal lines rather than a single focal point
123
What is PRESBYOPIA
Naturally occurring loss of accommodation (focus on near objects
124
Aetiology of MYOPIA
Unclear, genetic factor
125
Aetiology of ASTIGMATISM
Hereditary
126
Aetiology of HYPEROPIA
Unclear, inherited
127
Physical cause of myopia? (2)
Excessive long globe (axial myopia) (more common)
| Excessive refractive power (refractive myopia)
128
Physical cause of hyperopia?
Excessive short globe (axial hyperopia) (more common)
| Insufficient refractive power (refractive hyperopia)
129
Physical cause of astigmatism?
Refractive media is not spherical Refracts differently along one meridian than along meridian perpendicular to it 2 focal points (punctiform (dot-like) object is represented as 2 sharply defined lines)
130
- Asthenopic symptoms of hyperopia? (4)
Eye pain
Headache in frontal region
Burning sensation in eyes
Blepharoconjunctivitis
131
What is near vision adaptation
Pupillary mitosis by the sphincter pupillae to increase depth of field
Convergence by the medial recti to a near object
Accommodation by the circular ciliary muscle to increase the refractive power of the lens for near vision
132
5 options for optical correction?
```
SPECTACLE LENSES
CONTACT LENSES
INTRAOCULAR LENSES
SURGICAL CORRECTION
CLEAR LENS EXTRACTION + IO
```
133
Accommodation mechanism via the circular muscle? What nerve mediates this?
The lens is suspended by a ring of zonules and is anchored to the ciliary body. When the circular ciliary muscle within the ciliary body contracts, it pushes the inner edge of the ciliary body towards the lens and relaxes the passive zonules. This allows the lens to return to its natural thicker curved configuration, thus increasing its refractive power.
This process is mediated by the efferent CN III.
134
A sty is infection of the ...
Meibomian glands
135
What layer of the eye goes red during infection/inflammation
Conjunctiva
136
The posterior chamber is filled with ...
vitreous humour
137
The function of the corneal endothelium is to...
o Pumps fluid out of the cornea and prevents corneal oedema
138
Why is injury or disease of the corneal endothelium quite serious
There is no regenerative power in it
139
2 layers of the iris and what they're composed of?
2 layers: a THIN POSTERIOR pigmented epithelial layer and a THICK ANTERIOR layer composed of stromal tissue and smooth muscles
