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Ocular Phys Block 10 > Function Of The Iris > Flashcards

Function Of The Iris Flashcards

1
Q

Which of the following is not a function of the iris

A

Reduce depth of focus

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2
Q

The pupil that is seen is actually a

A

Magnified virtual image of the real object

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3
Q

Most anterior portion of uveal tract

A

Iris

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4
Q

What does the iris separate

A

The anterior and posterior chambers of the eye

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5
Q

What is the iris surrounded by

A

Aqueous

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6
Q

First relationship with the lens

A

Rests lightly upon the lens

  • not flat
  • shallow truncated cone
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7
Q

Magnification of the iris

A

Magnified by 1/8th when viewed through cornea

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8
Q

Diameters of iris

A

12mm white to white

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9
Q

Thickness at the thinnest point, the iris root

A

500microns

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10
Q

How is pupil centered

A

Slightly nasal and inferior to iris center

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11
Q

Abnormally decentered pupil is

A

Ectopic

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12
Q

Optical quality in irregular or ectopic pupils

A

Degrades it

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13
Q

What does the pupillary margin rest on

A

Anterior surface of the lens

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14
Q

How does the aqueous humor flows

A

From posterior into anterior chamber through the pupil

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15
Q

Pupil fluctuation

A

In constant state of dynamic fluctuation, always changing size

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16
Q

Stimulus variables that contribute to the constant state of fluctuation of the pupil

A
  • light level
  • spectral composition
  • spatial configuration: field size, spatial structure of the field
  • monocular/binocular view
  • non visual stimuli: pain and noise
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17
Q

Observer variables that contribute to the constant fluctuation of the pupil

A
  • individual differences
  • age
  • day to day within observer variance
  • biomechanical factors: respirations, heart beat
  • cognitive factors: arousal, attentions, fright, workload, hedonistic content
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18
Q

Pupils in other animals

A

Varies in other animals based on their environment and visual needs

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19
Q

What part of the iris is broader in humans

A

Temporal iris in humans broader than nasal iris

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20
Q

Giant squid eyes

A

10.5” across and 3.5” pupil filled with water

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21
Q

What animal has the largest eyes

A

Giant squid

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22
Q

Largest eyes relative to body size

A

Tarsier

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23
Q

Posterior portion of the iris is derived from

A

Neuroepithelium

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24
Q

What iris structures are derived from the neuroepithelium

A
  • dilator muscle
  • sphincter muscle
  • posterior pigmented epithelium
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25
Q

Anterior portion of the iris is derived from

A

Mesoderm

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26
Q

Iris structures derived from the mesodermal

A
  • iris stroma
  • iris vessels
  • iris nerves
  • chromatophores
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27
Q

The different embryonic tissue can cause

A

Anterior and posterior portions are torn apart

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28
Q

4 layers of the iris

A

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

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29
Q

Which layer of the following contains both mesoderm and ectoderm

A

Stroma and sphincter muscle

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30
Q

Functions of the pupil

A
  • control of rental illumination
  • reduction in optical aberrations
  • depth of focus

Need 2mm pupil for 2 out of these 3 functions

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31
Q

Functions of the iris

A
  • regulates retinal illumination
  • regulates glare
  • regulates optical aberrations
  • regulates depth of focus
  • provides nonverbal communication and social signaling
  • attraction/mate selection
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32
Q

What is probably the number one reason for the pupil changing shape as much as it does

A

Communication and social signaling as well as mate selection/attraction

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33
Q

Dilator muscle attaches to these at the collarette

A

Michels spur

Fuchs spur

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34
Q

Only elements that are capable of initiating movement in the iris

A

Iris muscles

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35
Q

All other elements of the iris except the muscles when it comes to movement

A

Are constructed so as to adapt to the movement of these muscles

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36
Q

The iris in miosis

A

The pupillary portion of iris gathers into pleats while the culinary portion smooths out

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37
Q

The iris in mydriasis

A

The stroma in the pupillary Zeno pulls flat while contraction furrows appear in the ciliary area

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38
Q

Blood flow of the iris in the miosis or mydriasis

A

Blood flow is not impeded by wither miosis or mydriasis

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39
Q

Elasticity of stroma and iris

A

Not elastic!
Stroma is loose but orderly mesh work of collagen fibers with aqueous fluid. It compresses and expands easily like a sponge

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40
Q

Iris vessels in movements

A

Are thin walled layer of endothelium with an outer covering of collagen fibrils. Keeps it from pinching the vessels

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41
Q

When was the sphincter muscle discovered

A

Middle of the 19th century

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42
Q

When was the dilator muscle discovered

A

Late 1950s with electron microscope

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43
Q

Thickest part of the iris

A

Stroma

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44
Q

Collagenous network of fibrils with scissor-like angles for folding

A

Stroma

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45
Q

Stroma and movement

A

No active part in iris movement

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46
Q

What does the stroma proved anchor for

A
  • sphincter muscle
  • dilator posterior epithelial plate
  • iris nerves
  • iris vessels
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47
Q

Protects the nerves and vessels from stretching and kinking

A

Stroma

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48
Q

Adapts to constant movements

A

Stroma

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49
Q

Folds and unfolds with minimal resistance to minimize energy expenditure

A

Stroma

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50
Q

Identity and characteristics of the iris during movements

A

All elements of the iris system maintain their identity and characteristics across millions of iris movements over decades of time

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51
Q

Constructed more densely than deeper stroma

A

Anterior border layer

52
Q

Porous

A

Anterior border layer

53
Q

Fibroblasts interlaced with melanocytes

A

Anterior border layer

54
Q

More solid and dense with more layers in darkly pigmented eyes

A

Anterior border layer

55
Q

Where do you see nevi on the iris

A

Anterior border layer

56
Q

Compact masses of rounded cells filled with melanin

A

Anterior border layer

57
Q

What layer may require a stronger laser in someone with dark eyes

A

Anterior border layer

58
Q

Causes of blue eyes

A

Just as light scatter in the atmosphere or in water can give a blue appearance, light can scatter in uniform uniformly space stromal tissue to give a blue appearance

59
Q

Newborns iris

A

Have a blue iris which changes darker because of the development of anterior stromal melanocytes and production of pigment granules can lead to a darker color

60
Q

Which iris color is dominant

A

Dark, light colors are recessive

61
Q

Blood flow to the iris is derived from

A

Tow long posterior cilioary arteries and anterior ciliary arteries

62
Q

Iris bleeding

A

Does not bleed much when it is cut, maybe because severed ends retract slightly to heal wound

63
Q

Major and Minor arterial circles

A

Probably not continuous. Anterior ciliary arteries probably bypass the major arterial circle to send radial branches to the iris directly

64
Q

How do the anterior ciliary arteries run

A

Along the reclusive muscle. Two in each muscle except the lateral rectus which has only 1

Could lose blood supply is rectus muscles are severed

65
Q

Surrounding sheaths of vessels

A

Not part of the vessel

66
Q

What is unique to the iris vessels

A

Pervascular collagen sheaths

-they are not found anywhere else’s in the body

67
Q

What does the perivascular sheaths on the blood vessels of the iris do

A

Allows for little dissension and folding of vessels during constant movement of iris

68
Q

Light reflex of the iris

A

Some animals have photosensitive irises, but humans react to light stimulation of the retina rather than the iris

69
Q

What is light reflex important for

A

To discover the integrity of the retina, optic nerves, chiasam, and optic tracts

70
Q

What variables can effect the pupil

A 
Light intensity 
State of light adaptation 
Temporal frequency 
Stimulus duration 
Retinal area 
Perimetric location 
Spectral sensitivity 
Spatial Frequency 
Motion
71
Q

Scotopic vision and pupil size

A

Doesn’t change the pupil size that much if darkness increases if already under scotopic conditions

72
Q

Mesopic light and pupil size

A

Causes a lot of change with changes in illumination

73
Q

Photopic conditions and pupil size

A

Doesn’t change much with illumination if already in photopic lighting

74
Q

What kind of curve do we see with pupil size and mesopic, photopic, and scotopic lighting

A

S curve

75
Q

In _______, pupillaryreactions occur at intensities below photopic range

A

Dark adapted eyes

Paradoxes and peripheral more sensitive than fovea

76
Q

In ________ adapted eyes, the pupillary threshold is much higher

A

Light

Fovea more reactive than periphery

77
Q

Pupil constriction speed

A

Does not depend on the level of brightness

  • max contraction amplitude reached
  • pupil remains in spastic contraction for a few seconds
78
Q

When does the pupil return to normal size

A

3-15 seconds

79
Q

Stimulus duration and pupil

A

Pupil contracts more for a longer duration stimulus

80
Q

Retinal area and pupil

A

The pupil more constricted when light covers greater area when light is equally bright

81
Q

Perimetric location and pupils

A

Pupils sum affront impulses regardless of spatial distribution, both rods and cones

82
Q

Stimulus wavelength and pupil

A

Experiments show that spectral sensitivities match well with pupillary reactions

83
Q

Spatial Frequency and pupil

A

Increased SF=decreased pupil size

84
Q

Motion and pupil

A

The pupil may respond to a motion stimulus even under isolimunant conditions

85
Q

Myopia and pupils

A

Myopes have larger pupils

-enhanced by greater corneal refractive power and deeper anterior chambers

86
Q

Myopes and accommodation

A

Don’t need to accommodate as much

-less than 1% variability based on ametropia

87
Q

Larger pupils and images

A

Result in degradation and glare, common after refractive surgery

88
Q

Pupils that are too small (less than 2mm)

A

Diffraction limit and reduced illumination can effect visual performance

89
Q

Optimal pupil size

A

Around 2mm

90
Q

Pupil size and age

A

DECREASES

91
Q

Pupils role in retinal illumination

A

Minimal role
16 fold change in area
Eye can change with a factor of 10^9, those are quite different numbers
Retina is more responsible

92
Q

Cat pupils

A

Large range of pupil size 0.5mm-13mm

93
Q

What limits round pupil from getting miosis less than 1mm

A

Mechanical

  • iris tissue is not elastic, it is folding
  • containers a meshed network of fibers
94
Q

Near vision triad

A

Convergence, miosis, and accommodation

-miosis can be stimulated with either convergence or accommodation in the absence of the other

95
Q

What is the accommodative triad controlled by

A

Third nerve nucleus, eddinger-westphal

96
Q

Amplitude for young person equal to what

A

Contraction from bright light
Less extensive for older who have los accommodation
Fairly linearly

97
Q

What are the sphincter and dilator muscles derived from

A

Neural ectoderm

98
Q

Iris sphincter muscle innervated by

A

Parasympathetic

No sympathetic innervation but beta adrenergic receptor sites can inhibit function and cause relaxation

99
Q

Iris dilator muscle innervated by

A

Sympathetic

Some inhibtoryu effect of cholinergic net which innervated dilator muscle

100
Q

How thick is the iris dilator

A

3-5 layers

101
Q

Which iris muscle is the strongest

A

Equally strong

102
Q

Reflex dilation

A

Sensory, emotional, or mental stimulus tend to elicit pupillary dilation

103
Q

When are pupils smaller

A

During sleeep and after death

104
Q

When are pupils large

A

During waking hours and when frightened

105
Q

What animal has the most dramatic reaction in pupil reflex dilation

A

Cats

106
Q

Alphagan and pupils

A

Can cause miosis under scotopic conditions. A2 adrenergic action might have inhibitory affect on A1 receptors. Some CNS effect might also be involved

107
Q

CNS and pupillary reactions

A

Fatigue, sleep and arousal contribute to pupillary reactions causing dilation or constriction

108
Q

Drugs treating the CNS and pupils

A

Usually have pupillary effects

109
Q

Disease affecting CNS and pupils

A

Affect the pupils

110
Q

Habituation

A

Some stimuli become less arousing over tine, less pupillary reaction

111
Q

Sensitization

A

Others stimuli become more infuriating and develop greater pupillary reaction

112
Q

Theories for reduction in pupil size with age

A
  • reduced strength of dilator muscle
  • greater resistance in iris stroma
  • iris fatigue
  • fatigue in CNS
113
Q

Response to mydriatic drugs in older eyes

A

Still able to dilate fully

114
Q

Shape of pupil and age

A

Can be round and smooth with advanced age

115
Q

Light reflex in age

A

Can remain brisk into late Middle Ages

116
Q

Reduction in pupil size is a _____ process

A

Linear

117
Q

Thickness of dilator muscle and age

A

No change

118
Q

Decreases in pupil size beings in what kind of eyes

A

Healthy eyes with strong levels of accommodation and brisk reactive pupils

119
Q

Presentation of hornets syndrome

A

Small pupil
Drooping lid
Lack of sweating

Damaged sympathetic on one side

120
Q

Cocaine test is usedfor what

A

Testing for horners syndrome

  • one drop of 10% cocaine in each eye
  • check in 15 minutes
  • horners pupil dilates less than normal pupil
  • cocaine blockers the reuptake of post ganglionic NE resulting in the dilation of a normal pupil from retention of norepinephrine in the synapse
121
Q

High levels of infrared and iris

A

Can burn any ocular structure and have very deep penetration

122
Q

What layer of the iris absorbed heat

A

Black pigment of the posterior iris layer

123
Q

When stimulated directly by heat, what does the iris sphincter do

A

Contracts

124
Q

What is a feature of iritis

A

Long lasting miosis

-mediated by prostaglandins

125
Q

Microwaves and eyes

A

Miosis lasting several days

126
Q

Ultrasonic energy and eyes

A

Dilation

Ocular Phys Block 10 (5 decks)

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