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Uvea - iris Flashcards

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1
Q

What is the middle layer of the eye?

A

The Uvea

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2
Q

What are the three regions the uvea is composed of?

A
  • the iris
  • ciliary body
  • choroid
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3
Q

Why is the uvea sometimes called the vascular layer?

A
  • the choroid is made up of mainly blood vessels that supply the outer retinal layers
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4
Q

Where is the center aperture of the pupil located?

A
  • slightly nasal and inferior to iris center
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5
Q

what’s the range is pupil size?

A
  • 1mm to 9mm
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6
Q

When is the pupil miotic?

A
  • in brightly lit conditions
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7
Q

When is the pupil mydriatic?

A
  • in dim illumination
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8
Q

What’s the average diameter of a iris?

A
  • 12mm
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9
Q

Where is the iris thickest?

A
  • the collarette
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10
Q

Where is the iris collarette located?

A
  • 1.5mm from the pupillary margin
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11
Q

What does the collarette divide the iris into?

A
  • divides iris into pupillary zone and the ciliary zone
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12
Q

where is the pupillary zone located?

A
  • encircles the pupil
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13
Q

Where is the ciliary zone located?

A
  • extends from collarette to iris root
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14
Q

What’s the thickness of the iris root?

A

0.5mm

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15
Q

What’s the thinnest part of the iris?

A
  • iris root
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16
Q

What does the iris root join the iris to?

A
  • anterior part of the ciliary body
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17
Q

What are the four layers of the iris?

A

1) anterior border layer
2) stroma and sphincter muscle
3) anterior epithelium and dilator muscle
4) posterior epithelium

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18
Q

What is the anterior border layer a condensation of?

A
  • the stroma
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19
Q

What is the anterior border layer composed of?

A
  • fibroblasts and pigmented melanocytes
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20
Q

How are the fibroblasts and melanocytes arranged in the anterior border layer?

A
  • the highly branching processes of the cells interweave to form a meshwork
  • fibroblasts on the surface, melanocytes underneath
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21
Q

How might the melanocyte layer vary?

A
  • thickness varies with groups of melanocytes forming freckle like masses
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22
Q

Where is the anterior border layer absent?

A
  • iris crypts
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23
Q

What shape are iris crypts?

A
  • oval
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24
Q

What is the connective tissue stroma composed of?

A
  • pigmented and no pigmented cells
  • collagen fibrils
  • extensive ground substance
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25
What are the pigmented cells of the tissue stroma?
- melanocytes - clump cells
26
What are the non pigmented cells of the tissue stroma?
- fibroblasts - lymphocytes - macrophages - mast cells
27
What's the structure of a clump cell?
- large - round - darkly pigmented - altered macrophages
28
Where are clump cells usually located?
- pupillary portion of the stroma often near sphincter
29
How are the iris arteries structured?
- branches of circular vessels - the major circle of the iris
30
Where is the major circle of the iris located?
- located in the ciliary body near iris root
31
What encircles the iris vessels?
- collagen fibrils from the stroma
32
What do the collagen fibrils that surround the iris vessels do?
- anchor the vessels in place - protects them from kinking and compression during iris movement during miosis and mydriasis
33
What is the iris stroma continuous with?
- stroma of the ciliary body
34
Where is the sphincter muscle located?
- pupillary zone of the iris stroma
35
What is sphincter muscle composed of?
- smooth muscle cells joined by tight junctions
36
What's the shape and width of the sphincter muscle
- circular - 0.75 to 1mm wide
37
What does contraction of the sphincter muscle cause?
- causes pupil to constrict in miosis
38
What is posterior to the iris stroma?
- anterior iris epithelium
39
What is the anterior iris epithelium composed of?
- myoepithelial cells
40
What is the apical portion of the anterior iris epithelium composed of?
- pigmented cuboidal epithelium joined by tight junctions and desmosomes
41
What is the basal portion of the anterior iris epithelium composed of?
- elongated, contractile, smooth muscle processes
42
Where do the muscle fibers of the basal portion of the anterior iris epithelium extend to?
- extend into stroma to form three to five layers of dilator muscle fibers joined by tight junctions
43
Where is the dilator muscle present from?
- from the iris root to point in stroma below midpoint of sphinctor
44
How are the dilator muscle fibers arranged?
- radically
45
What does the radial arrangement of the dilator muscles result in?
- contraction of the dilator muscle pulls the pupillary portion towards the root, enlarging the pupil in mydriasis
46
What does the anterior iris epithelium continue to the pupillary margin as?
cuboidal epithelial cells
47
What does the anterior iris epithelium continue posteriorly as?
- the pigmented epithelium of the ciliary body
48
What is the second layer posterior to the stroma?
- posterior iris epithelium
49
What's the structure of the posterior iris epithelium?
- single layer of heavily pigmented columnar cells
50
How are the posterior iris epithelium cells joined?
- tight junctions and desmosomes
51
How does the posterior iris epithelium change at its periphery?
- begins to lose its pigment as continues to ciliary body as non pigmented epithelium
52
What covers the basal part of the posterior epithelium layer?
- a thin basement membrane that lines the posterior chamber
53
How are the anterior and posterior iris epithelial layers positioned?
- apex to apex
54
What forms the pupillary ruff?
- epithelial cells curl around from posterior iris to anterior surface at pupillary margin
55
What are crypts?
- depressions or openings in the surface of the anterior eye surface
56
Where are crypts located?
- both sides of the collarette(Fuchs crypts) - near the root(peripheral crypts)
57
What do crypts allow for?
- allow the aqueous quick exit and entrance into spaces in the iris stroma as the volume of the iris changes during contraction and dilation
58
What causes circular contraction folds?
- result from tissue moving toward the iris root during pupillary dilation
59
Where circular contraction folds found?
- anterior surface of the ciliary zone
60
what does the anterior iris surface appear like?
- thin, radial, collagenous columns or trabeculae evident in lightly pigmented irises
61
What are the small circular furrows near the pupil on the posterior iris surface?
- Radial contraction furrows(of Schwalbe) - structural furrows of(of Schwalbe)
62
What is iris colour determined by?
- number of melanin granules within the melanocytes and the area they occupy - type of melanin present - arrangement of the connective tissue components
63
Why can an iris appear blue?
- the wavelength seen results from light scatter caused by the arrangement and density of the connective tissue components
64
How's the ciliary body look when viewed from front of eye?
- ring shaped structure
65
ciliary body width?
- 5.9mm nasal - 6.7mm temporal
66
How does the anterior and posterior ciliary body differ?
- posterior ciliary body is fairly flat - anterior contains numerous folds or processes that extend into posterior chamber
67
What are the two parts the ciliary body is divided into?
- pars plicata - pars plana
68
Pars plicata structure?
- wider anterior potion of ciliary - contains ciliary processes - 70 to 80 ciliary processes extend into posterior chamber - regions between ciliary processes called valleys of kuhnt
69
Pars plana structure?
- flatter region of ciliary body - extends from posterior of pars plicata to the ora serrata
70
ora serrata structure?
- transition between ciliary body and choroid - serrated pattern - has forward pointing apices called dentate processes - rounded portions between processes called oral bays - dentate processes are elongations of retinal tissue
71
structure of attachment of the zonule fibers and the lens?
- course from the ciliary body to the lens - some fibers insert into internal limiting membrane of the pars plana region and travel through the valleys between the ciliary processes - some attach to the internal limiting membrane of the valleys of the plars plitata
72
What is ciliary body attached to?
- the vitreous base
73
What is the outermost layer of the ciliary body?
- supraciliaris
74
What is the arrangement of the supraciliaris?
- loose connective tissue arranged in ribbonlike layers containing pigmented melanocytes, fibroblasts and collagen bands
75
What does the arrangement of the supraciliaris allow for?
- arrangement of bands allows for ciliary body to slide agains sclera without detaching or scratching tissue - allows for accumulation of fluid within its spaces, which can lead to displacement from the sclera
76
ciliary muscle structure
- composed of smooth muscle fibers oriented in longitudinal, radial and circular directions - fibers bundle interweaving from layer to layer - various connective tissue found amongst muscle bundles
77
longitudinal muscle fibers(of Brucke) location?
- lie adjacent to supraciliaris and parralel to sclera
78
longitudinal muscle fibers(of Brucke) structure?
- each muscle resembles a long narrow V, base at scleral spur and apex in choroid - tendon of origin attaches muscle fibers to sclera spur and trabecular meshwork sheets
79
Where are the radial muscle fibers located?
- inner to the longitudinal fibers
80
radial fibers structure?
- wider shorter interdigitating V's - originate at scleral spur - insert into connective tissue near the base of the ciliary processes - layer is a transition from the longitudinal oriented fibers to the circular fibers
81
What makes up the innermost region of the ciliary muscle?
- (Mullers) annular muscle
82
(Mullers) annular muscle structure
- circular muscle bundles - sphincter type action - located near major circles of the iris
83
ciliarly muscle innervation
- dually innervated by the autonomic nervous system - parasympathetic stimulation activates the muscle contraction - sympathetic innervation likely has inhibitory effect that is a function of the level of parasympathetic activity
84
ciliary stroma location?
- lies between the muscle and epithelial layers - forms core of each ciliary process - continuous with connective tissue that separates the bundles of the ciliary muscle - anteriorly is continuous with iris stroma - thins in pars plana, where is continuous with choroidal stroma
85
What vessels are located within the ciliary stroma?
- the major arterial circle of the iris
86
major arterial circle of iris structure?
- circular artery - formed by anastomosis of the long posterior ciliary arteries and the anterior ciliary arteries - stromal capillaries are large and fenestrated is the ciliary processes
87
ciliary epithelium structure?
- two layers of epithelium - positioned apex to apex - cover the ciliary body, posterior chamber and parts of the vitreous chamber
88
What connects the two ciliary epithelial layers?
- intercellular junctions - desmosomes - tight junctions
89
What's the function of the ciliary epithelium gap junctions?
- allow for cellular communication between the layers - formation of aqueous
90
Why are the two ciliary epithelial layers positioned apex to apex?
- because of the invagination of the neural ectoderm in forming the optic cup
91
ciliary epithelium outer layer structure?
- pigmented and cuboidal
92
what joins the ciliary epithelium outer layer cells?
- desmosomes - gap junctions
93
anteriorly what is the pigmented ciliary epithelium continuous with?
- anterior iris epithelium
94
posteriorly what is the pigmented ciliary epithelium continuous with?
- retinal pigmented epithelium
95
what attaches pigmented ciliary epithelium to the stroma?
- basement membrane
96
What is the ciliary basement epithelium continuous with?
- anteriorly with basement membrane of the anterior iris epithelium - posteriorly with inner basement membrane portion of Bruchs membrane of choroid
97
inner epithelial layer structure
- non pigmented - columnar cells in pars plana - cuboidal cells in pars plicata - lateral walls contain extensive interdigitations
98
What is inner epithelial layer joined by?
- joined near apices - desmosomes - gap junctions - zonula occludens
99
What is the nonpigmented ciliary epithelium continuous with?
- anteriorly with posterior iris epithelium - posteriorly at ora serrata, becoming neural retina
100
nonpigmented epithelial cells function
- metabolically active - active secretion of aqueous humor - diffusion barrier between blood and aqueous
101
Why do the ciliary non pigmented cells have more mitochondria than the pigmented ones?
- higher metabolic activity
102
what provides an extensive surface area to the posterior chamber?
- basal and basolateral aspects of nonpigmented cells have numerous invaginations
103
Where does the choroid extend from?
- ora serrata to optic nerve
104
Where is choroid located?
- between sclera and retina
105
choroid structure and function
- primarily blood vessels - a thin connective tissue layer lies on each side of the stromal vessel layer
106
Suprachoroid lamina structure
- thin - pigmented - ribbonlike branching band of connective tissue - potential space between sclera and choroid vessels - contains features from both sclera and choroidal stroma
107
What does the looseness of the suprachoroid lamina benefit it?
- allows the vascular net to swell without causing detachment
108
What does the suprachoroid lamina carry?
- long posterior ciliary arteries - nerves from posterior to anterior globe
109
Choroidal stroma structure
- pigmented - vascularized - loose connective tissue layer
110
What does the choroidal stroma contain?
- melanocytes - fibroblasts - macrophages - lymphocytes - mast cells
111
Choroidal stroma vessel structure
- collagen fibrils arranged circularly around vessels - branches of short posterior ciliary arteries - vessels with larger lumina on outer layer - medium vessels pass inwards layer - medium vessels branch to form capillary bed - the venules join to become veins that gather in vortex pattern in each quadrant of the eye and exit choroid as four large vortex veins - contain no valves
112
Choroidal vessel innervation
- innervated by autonomic nervous system - sympathetic stimulation causes vasoconstriction and decreased choroidal blood flow - parasympathetic stimunlation causes nitrous oxide responsive vasodilation, resulting in increased choroidal blood flow
113
Whats the choriocapillaris?
- specialized capillary bed

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