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Ocular Physiology > Block 10 > Flashcards

Block 10 Flashcards

1
Q

What is the most anterior portion of the uveal tract

A

Iris

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2
Q

What does the iris separate

A

Anterior and posterior chambers of the eye

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3
Q

What surrounds the iris

A

Aqueous

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4
Q

T/F the iris rests on the lens

A

True but lightly

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5
Q

How much is the iris magnified when viewed through the cornea

A

1/8th

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6
Q

T/F the iris increases depth of field

A

True

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7
Q

The pupil that is seen is what?

A

Magnified virtual virtual image of the real object

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8
Q

What is the thickness of the iris at the root?

A

About 500 microns

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9
Q

What is the average diameter of the iris

A

12 mm

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10
Q

Where is the pupil located in relation to the iris

A

Slightly nasal and inferior to iris center

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11
Q

What is a Decentered pupil?

What effect does it have

A

Ectopic

Degrade optical quality

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12
Q

How does aqueous humor flow

A

From posterior into anterior chamber through he pupil

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13
Q

T/f the pupil is in a constant dynamic fluctuation

A

True

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14
Q

What are some things that cause this fluctuation

A

Slide 5

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15
Q

What is the posterior portion of the iris dervied from

A

Neurepithelium

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16
Q

The shape of the pupil varies in animals, what is the shape in humans

A

Round

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17
Q

How has the largest eyes in animal kingdom

A

Squid

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18
Q

What are the layers of the posterior iris

A

Dilator
Sphincter
Post pigmented epithelium

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19
Q

What is the anterior iris derived from

A

Mesoderm

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20
Q

What are the layers of the anterior iris

A

Stroma
Vessels
Here’s
Chromatophores

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21
Q

What are teh r4 layers of the iris anterior or posterior

A

Anterior border layer
Stroma and sphincter muscle
Anterior epithelium and dilator
Posterior and dilator

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22
Q

What layer of the iris has both mesoderm and ectoderm

A

Stroma and sphincter

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23
Q

What are the functions of the iris

A

Regulate retinal illumination, glare, optical aberrations, depth of focus; non-verbal communication and social signaling, attraction/mate selection

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24
Q

Where are glare and aberrations seen

A

Larger pupils

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25
Q

What are the only parts of the iris that facilitate movement

A

Muscles

The other elements are made to adapt to movement

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26
Q

What happens in mitosis

A

The pupillary portion of the iris gathers into pleas

Ciliary portion smooths out

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27
Q

What happens in mydriasis

A

Stroma and pupillary zone flatten

Ciliary area contracts

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28
Q

Is blood flow impeded in miosis and mydriasis

A

NO

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29
Q

T/F the stroma and iris vessels are elastic

A

False

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30
Q

Describe the stroma of the iris

A

It is loose but orderly meshwork of collagen fibers with aqueous fluid.

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31
Q

Describe iris vessels

A

Thin walled layer of endothelium

Outer covering of collagen fibrils

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32
Q

What is the thickest portion of the iris

A

Stroma

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33
Q

what is the function of the iris stroma

A

No active part in movement

Acts as an anchor for sphincter muscle, dilator-post-epith plate, nerves, and vessels

adapts to constant movement

Folds and unfolds with minimal resistance to minimize energy usage

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34
Q

How does the iris stroma protect nerves and vessels

A

It protects against stretching and kinking

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35
Q

T/F ALL elements of the iris maintain their identity and characteristics across millions of iris movements over decades

A

True

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36
Q

What is the anterior border layer

A

Porous
Fibroblasts interlaced with melanocytes
More solid and dense layers in pigmented eyes

Can have nevi

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37
Q

What causes blue iris color

A

Light scatter

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38
Q

T/F newborns can be born with blue eyes that darker with age

A

True

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39
Q

What leads to darker eye colors

A

Development of anterior stromal melanocytes and production of pigment granules

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40
Q

How is eye color determined

A

Genetics
Dark: dominant
Light: recessive

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41
Q

Where is iris blood flow dervied from

A

Ophthalmic artery from 2 long posterior ciliary Artie’s and anterior ciliary arteries

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42
Q

Does the iris bleed when cut

A

No

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43
Q

Anterior ciliary arteries run along what

A

Rectors muscles

Each has 2 except the lateral rectus (it has 1)

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44
Q

What are perivascualr collagen sheaths

A

They are unique to iris vessles (nowhere else in the body)

Allows for little distention an folding of vessels during the constant movement of the iris

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45
Q

Do humans react to light stimulation of the iris?

A

No, we react to stimulation of the retina

This can occur in some animals though

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46
Q

What is the light reflex important for

A

Testing the integrity of the retina, optic nerves, chiasm, and optic tracts

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47
Q

What variables affect the pupil

A 
Light intensity 
Light Adaptation 
Temporal frequency
Stimulus duration 
Retinal area 
Retinal location 
Stimulus wavelength
Spatial frequency 
Motion
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48
Q

What affect to bright (photopic) lights have on the pupil

A

Pupil constricts

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49
Q

What affect ones the dark (scotopic) have on the pupil

A

Dilation

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50
Q

Where does the pupil start to reduce in size

A

In the mesopic range of light

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51
Q

What occurs in dark adapted eyes

A

Pupillary reactions occur at intensities below photopic range (due to rods)

Parafovea and peripheral more sensitive than fovea

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52
Q

T/f the pupil contracts at the same rate

A

True

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53
Q

If the pupil stimulus is too short what happens

A

There isn’t enough time for it to react

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54
Q

T/f the pupil is more constricted when light covers a greater area when light is equally bright

A

True

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55
Q

The pupil sums afferent impulses regardless of spatial distribution

A

True

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56
Q

Spectral sensitives math well with pupillary reactions

A

Yes

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57
Q

Look at slide 51 spatial freq

A

Read it

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58
Q

Does the pupil react to motion

A

Yes

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59
Q

Myopes have larger pupils than hyperopes

A

Not really, there is a 1% difference

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60
Q

What is the optimal pupil size

A

2 mm

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61
Q

What effect do large pupils have

A

Image degradation and glare

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62
Q

Does pupil size change with age

A

Yes it decreases

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63
Q

What range of diameters can he human eye vary in

A

2-8 mm

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64
Q

Does the pupil play a large role in regulating light levels

A

No, it is minimal

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65
Q

What is the near vision triad

A

Convergence
Miosis
Accommodation

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66
Q

What is the 3rd nerve nucleus

A

Eddinger-Westphal

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67
Q

Near vision pupillary contraction amplitude for young people is equal to what

A

Contraction from bright light

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68
Q

What are the sphincter and dilator muscle derived from

A

Neural ectoderm

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69
Q

What innervates the iris sphincter

A

PNS

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70
Q

What innervates the iris dilator

A

SNS

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71
Q

What causes Horner Syndrome

A

Interference with blood supply from carotid artery

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72
Q

When are pupils smaller

A

During sleep and after death

73
Q

When are pupils larger

A

During waking hours and when frightened (Jill)

74
Q

Drugs/disease that treat the CNS often have what effects

A

Pupil effects

75
Q

Alphagan alphagan in a tree

A

This sucks and I’m sleepy

We’re not tested on this

76
Q

As stimulus become less arousing what effect does that have on pupillary reaction

A

Less reaction

77
Q

When stimuli become more infuriating over time what effect does it have on pupillary reaction

A

Greater reaction

78
Q

What are some theories for reduction in pupil size

A

Reduced strength of dilator
Greater resistance of stroma
Iris fatigue
CNS fatigue

79
Q

Pupils are round and smooth with ______ age

A

Advanced

80
Q

Light reflex is brisk in _____

A

Middle age

81
Q

Reduction in pupil size is what process

A

Linear

82
Q

Does the thickness of the dilator muscle change with age

A

No

83
Q

When does pupil size decrease begin

A

Healthy eyes

84
Q

What is the cocaine test used for

A

Horner’s syndrome check

The pupil will dilate less than the normal pupil

85
Q

What effect does apraclonidine have in Horners

A

Increased dilation in affected side

86
Q

What effects does IR radiation have on pupil

A

High levels can burn ocular structures

Posterior Iris absorbs heat
Iris sphincter contracts when heated
Have iritis

87
Q

What are the functions of the ciliary body?

A

Aqueous production
Aqueous outflow
Accommodation

88
Q

Why is the ciliary muscle atypical for smooth muscles

A

Rapid contraction speed
Large motor neurons
Distance between muscle and motor neurons
Structure of ciliary M resembles skeletal M

89
Q

What are the 4 layers of ciliary angle (in order)

A

Schwalbes line
Trabecular meshwork
Scleral spur
Ciliary body

90
Q

What provides a large surface area of ciliary body

A

Finest rated capillaries and the number and shape of the processes

91
Q

How is aqueous humor made

A
  1. Diffusion
  2. Ultrafiltration (negligible)
  3. Active secretion (80-90%)
92
Q

Movement of what drives secretion in the posterior chamber

A

Na and Cl

93
Q

What ion has an indirect role in moderating Cl flux

A

Bicarb

94
Q

Where does aqueous production occur

A

In the ciliary processes

95
Q

What is the purpose of aqueous production

A 
Provide nutrients to cornea
Prevents oxidative damage 
Prevents light scatter (low protein)
Carries wastes from cornea and lens 
High lactate concentration from lens and cornea
96
Q

What is the rat of aqueous production

A

2.5 uL/min

97
Q

What is the purpose of zonular fibers

A

Stabilize lens
70-80 nm diameter
Allows flow from posterior to vitreous chamber

Superficial attachment to lens

98
Q

T/F accommodation declines gradually until it is completely lost at age 50

A

True

99
Q

What is accommodation

A

Contraction of the longitudinal fibers of the ciliary muscle pills the choroid forward, contraction of the circular fibers draws the ciliary body closer to the lens
Decreases the diameter of the ring formed by the ciliary body

Releases tension on the zonular fibers and allows the lens to become more spherical (more powerful)

100
Q

What is the lens enclosed in

A

Lens capsule

101
Q

Where do the zoules attach to the lens

A

At the equator

102
Q

What is happening during far vision

A

Ciliary is relaxed

Zonular fibers are in tension

103
Q

When the ciliary muscle contracts what is happening to the zonules

A

They relax, increases the power of lens

104
Q

T/F changes in illumination do not alter pupil diameter

A

False, it does

105
Q

Accommodation and convergence stimulate what

A

Miosis

106
Q

Pupil constriction aids in clarity due to

A

Larger depth of field

107
Q

Accommodative amplitude increases/decreases with age

A

Decreases

108
Q

Contractile strength shows reduction with increasing age?

A

NO

109
Q

What is presbyopia

A

Loss of ability to accommodate

Normal age related change

110
Q

What changes occur/do not occur with presbyopia

A

Ciliary muscle contractive power increases UNTIL presbyopia

No change in zonular length

111
Q

T/F the limiting factor for accommodation is the ciliary muscle

A

False, it is the movement and shape of the lens

112
Q

T/F ciliary muscle contraction can change the configuration of the trabecular meshwork

A

True

113
Q

What is he ciliary muscle derived from

A

Mesoderm

114
Q

What is teh Tyndall phenomenon

A

Breakdown of blood-aqueous barrier

Cells and flares are visible
Aqueous is invisible
Leukocytes
Whitefish
Can form hypopyon
115
Q

What is hyphema

A

Trauma to head or whiplash can tear the iris
Break blood vessels entering the major arterial circle of iris

Blood settles inferiorly

116
Q

What is aqueous humor

A

Clear, colorless fluid that fills the anterior and posterior chamber of the eye

117
Q

What is the function of the aqueous humor

A

It supplies nutrients and oxygen/removes wastes from the anterior tissues

Inflates the eye and creates IOP

Transport ascorbic acid into the anterior segment where it is antioxidative

Facilitates the local immune responses during inflammation and infection

118
Q

What is the primary site of aqueous humor formation

A

Pars plicata

119
Q

What tissue forms aqueous humor

A

Non-pigmented ciliary epithelium

120
Q

How much aqueous humor is there

A

250-300 uL

121
Q

What is the refractive index of aqueous

A

1.333

122
Q

What is the pH of aqueous

A

7.2

123
Q

Aqueous is hyperosmotic or hypoosmotic

A

Hyperosmotic

124
Q

What is the rate of aqueous formation

A
  1. 75 uL/min (day)

1. 08 uL/min (night)

125
Q

What is higher in ascorbic acid AH or BP

A

AH

126
Q

What is higher in proteins AH or BP

A

BP

127
Q

How is aqueous produced

A
  1. Blood flows to vascular bed of ciliary stroma
  2. Loading of solute from stroma into PE cells
  3. Translocation of solute through gap junctions into NPE cells
  4. Exclusion of solute from NPE to posterior chamber
  5. Osmotic gradient made by the solutes facilitates the passive flow of water
128
Q

What are the mechanisms of solutes across the CE

A

Diffusion (passive movement due to concentration difference)

Ultrafiltration (passive movement due to pressure)

Active transport (energy consuming process, moves against gradient)

129
Q

What is the major mechanism of solutes moving across the CE

A

Active transport

130
Q

What enzyme is responsible for the production of HCO3

A

Carbonic anhydrase

131
Q

What affect does carbonic anhydrase inhibitor have

A

Reduces AH formation

132
Q

What does vasopressin do?

A

Supports active transport of Na ions across CE and increases AH

133
Q

What do A2 agonists do

A

Decrease AH formation

134
Q

What do B2 agonists do?

A

Increase AH formation

135
Q

What is the blood aqueous barrier

A

Barrier to the movement of intermediate and high molecular weight substances (protein)

Protects the eyes from entry of toxic substances and maintains homeostatic control

136
Q

What explains how drugs that are taken orally or IV can barely reach therapeutic levels in intraocular tissues

A

Blood aqueous barrier

137
Q

What is the BAB made up of

A
  1. Tight junctions are present on NPCE
  2. Endothelial of inner schlemms canal are joined tightly to prevent retrograde movement of solutes and fluid
  3. Tight jxns are at iridologist vascular endothelium as well as between iris epithelia
138
Q

Where are tight jxns present?

What do they do

A

Between NPCE

Constitute an effective barrier to intermediate and high molecular weight substances (proteins)

139
Q

What happens when the BAB breaks down

A

Aqueous becomes cloudy due to leakage of plasma proteins into the posterior and anterior chamber

Inflammatory cells may also be present

140
Q

What are some causes of BAB breakdown

A

Ocular injuries (trauma, inflammation, disorders, tumor)

Ocular hypotony (IOP of 5mmHG or less)

141
Q

What are the mechanisms of BAB breakdown due to injury/inflammation

A

Release of cytokines and growth factor

Activation of immune response

Breakdown

142
Q

What are the mechanisms of BAB breakdown due to hypotony

A

Opening of non-penetrated endothelial layer of iris capillaries and tight jxns of ciliary epithelium
Increases episcleral venous pressure

Breakdown

143
Q

What is the vitreous humor

A

Clear gel in the posterior chamber

144
Q

Where is vitreous located

A

Between crystalline lens and retina (80% of the volume of the eyeball)

145
Q

What is primary vitreous

A

3-4 gestational age

Optic cup filled by a system of fibrillation material (secreted by embryonic retinal cells)

VEGF released by lens induces vasculogenesis
Hyaloid artery penetration

146
Q

What is secondary vitreous (6 weeks gestation)

A

Increasing size of vitreous cavity

Anti-angiogenesis factor present, regression of hyaloid artery and it leaves a Cloquets canal surrounded by 2ndary vitreous

Vitreous gel formed

147
Q

What is tertiary vitreous

A

Controversial

Secreted by NPCE of pars plana and persists in adult as suspensory ligament of lens (zonular fibers)

148
Q

What is Bergmeisters Papillae?

A

Center of optic disc

Small tuft of fibrous tissue that is a remnant of fetal hyaloid artery

149
Q

What is Mittendorfs dot:

A

Small circular opacity on posterior lens capsule (nasal)

Anterior attachment of hyaloid artery

150
Q

What is Cloquets canal

A

Tubular structure continuing remnant of primary vitreous

Located at posterior aspect of lens and the retina (in vicinity of optic disc)

151
Q

Vitreous cortex:

A

Outer surface (hyaloid surface)

152
Q

Center zone:

A

Cloquets canal

153
Q

Intermediate zone

A

Inner to cortex and surrounds the center canal

154
Q

What is the uvea

A

Middle layer of the eye

155
Q

What are the regions of the uvea

A

Iris
Ciliary body
Choroid

156
Q

Where is the choroid located

A

Extends from ora serrata to optic nerve

Between sclera and retina

157
Q

What absorbs excess light

A

Darkly pigmented choroid

158
Q

What is the function of the vascular choroid

A

It provides nutrients to and removes waste from the outer retina

159
Q

What is so different about the macula

A

It is avascular

No vessels

160
Q

What supplies blood to the macula

A

Choriocapillaries

161
Q

What arteries supply/pass the choroid

A

Long posterior ciliary (2)
Short posterior ciliary (20)
Ciliary artery
Ophthalmic A

162
Q

What nerves supply/pass the choroid

A

Long ciliary and short ciliary nerves

163
Q

Where are the nerves and vessels that supply the choroid held

A

Suprachoroid space

164
Q

Long ciliary nerve carry what info

A

Sensory

Sympathetic

165
Q

Short ciliary nerves carry what info

A

Sympathetic

Parasympathetic

166
Q

T/F the choroid can rapidly change its thickness, and the vary the location of the retina and the state of focus of the eye

A

True

167
Q

What are the functions of the choroid (4)

A
  1. Provide nutrients and remove wastes from outer retina
  2. Passage of nerves and vessels
  3. Absorb excess light
  4. Regulate emmetropization
168
Q

What changes occur in the iris

A

Loss of pigmentation
Dilator muscle atrophic
Sphincter muscle sclerotic

169
Q

What changes occur in the ciliary body with age

A
  1. Elasticity decreased due to amount of connective tissue increased in the ciliary body
  2. Formation of aqueous humor decreases with age
170
Q

At age 80 with the production of aqueous compared to younger

A

25%

171
Q

What changes occur to the choroid with aging

A
  1. Choriocapillaries decrease in density and diameter, choroidal blood flow decreases
  2. Bruchs membrane thickens
  3. Various substances and particles accumulate in Bruchs
172
Q

What is Bruchs membrane

A

Nutrient from choriocapillaries and waste product from retina must pass though Bruchs membrane

173
Q

What is Drusen

A

Calcification and ellow deposits in teh inner collagenous layer of Bruchs layer
Made of the remaining damaged cells from oxidative stress

174
Q

What is Lipfuscin

A

Yellow-brown pigment granules composed of lipid-containing residues from oxidative stress

175
Q

What does accumulation of drusen do?

A

Makes Bruchs membrane hypdrophobic

Barrier to water movement
Inhibits passage of metabolites

176
Q

Accumulation of water between Bruchs and RPE can cause what

A

Detachment

177
Q

What serious condition is associated with drusen

A

AMD

178
Q

What are some stimulus types that can cause dilation

A

Sensory
Emotional
Mental

Ocular Physiology (8 decks)

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