Chapter 2: The Eye Flashcards Preview

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Flashcards in Chapter 2: The Eye Deck (163):
1

What is the radius of curvature of the cornea? What is the radius of curvature of the sclera? What effect do the differences in radius of curvature have on the shaper of the eye?

8 mm
11 mm
Therefore, shape of the globe is an oblate spheroid

2

What is the AP diameter of the eye? What is the average transverse diameter of the eye?

23-25 mm

24 mm

3

What are the borders of the anterior chamber? What is the volume of aqueous it holds? How deep is it?

Bordered by the cornea anteriorly and the iris posteriorly

200 micro L

3 mm deep

4

What are the borders of the posterior chamber? What is the volume?

posterior of the iris to the anterior of the lens/face of the vitreous

volume= 60 micro L

5

Vitreous Cavity

comprises 2/3 of the volume of the eye
5-6 mL

6

What is the total volume of the average eye?

65-70 mL

7

What are the layers of the eyeball?

outermost= cornea + sclera
Middle= Uvea (choroid, ciliary body, iris)
Inner= Retina

8

What are the three layers of the pre corneal tear film?

outer= superficial oily layer (produced by meibomian glands)
middle= aqueous layer (produced by lacrimal glands)
bottom= Deep mucin layer (produced by conjunctival goblet cells)

9

What are the functions of the pre corneal tear film?

lubrication
provides nutrients and 02 via diffusion
provides a clear smooth optical surface
contains Ig's, lysozymes, and lactoferrin

10

What are the dimensions of the avg cornea? How much refractive power does the cornea provide?

dimensions: 12 mm wide x 11 mm tall x 0.5-1.0 mm thick (0.5 in center, 1.0 at periphery--due to posterior surface being more curved than anterior surface)

Cornea provides 2/3 of refractive power of the eye, or about +43 diopters

Note; center of cornea is nearly spherical, with a diameter of 4.0 mm and a thickness of 0.5 mm

11

Is the thinning of the cornea toward the periphery symmetrical in all quadrants?

No, it becomes more flat in the nasal and superior quadrants then in the inferior and temporal quadrants.

12

Embryologically, what is the anterior surface of the cornea derived from?

Surface Ectoderm

13

What kind of cells cover the anterior surface of the cornea?

non-keratinized stratified squamous epithelium

14

What cells cover the basal lamina of the outer layer of the cornea?

2-3 layers of polygonal "wing cells"

15

Are the surface of the wing cells smooth? If not, how does the body compensate for this?

The surfaces of the cells are covered with microplicae and microvilli, causing it to be irregular. The body compensates via the pre corneal tear film

16

Where do the corneal epithelial cells originate from?

They originate from limbal stem cells and migrate centripetally.

17

What non-epithelial cells are found in the outer layers of the cornea?

wandering histiocytes, macrophages, lymphocytes, and pigmented melanocytes.

antigen-presenting langerhans cells found peripherally (migrate centrally with keratitis or old age)

18

Where is Bowmans layer located? Does it regenerate after injury?

located beneath the basal lamina of the corneal epithelium, is a tough layer consisting of randomly dispersed collagen fibrils 8-12 micrometers thick

Is not restored after injury--becomes scar tissue

19

Corneal Stroma

constitutes 90% of corneal thickness, composed of collagen-producing keratocytes, ground substance, and collagen lamellae

20

How are the collagen fibrils in the cornea oriented?

In the anterior 1/3 of the stroma, the fibers are oriented obliquely

In the posterior 2/3 of the stroma, they are oriented parallel

21

What factors about the collagen promotes corneal transparency?

uniform fibril size and separation

22

What types of collagen are found in the corneal stroma?

Type I, III, V, VII

23

What is the ground substance found in the cornea? How does it contribute to corneal edema?

Ground substance consists of proteoglycans, which are highly charged, and contribute to swelling during corneal edema.

24

How many keratocytes are found in the cornea? How are they distributed within the stroma?

There are 2.4 x 10^6 keratocytes in the average adult cornea. There is a higher density of keratocytes anteriorly (1058 cells/mm^2) compared to posteriorly (771 cells/mm^2)

25

How do the keratocytes contribute to corneal transparency?

They have a flat profile and an even distribution within the coronal plane that minimizes the disturbance of light transmission

26

What is Descemets Membrane?

a true basement membrane, the basal lamina of the corneal endothelium

PAS +

Rich in Type IV Collagen

27

T/F: The thickness of descemets membrane increased with age?

True. At birth, it is between 3-4 mm thick, and increased in size until adulthood, where it is 10-12 mm thick.

28

What are the parts of Descemets Membrane?

Anterior banded zone that develops in utero, and a posterior non-banded zone that develops throughout life.

29

What are Hansall-Henle Warts?

Peripheral excrescences of descemets membrane that are common findings in the elderly

30

Describe the make-up of the corneal endothelium? From what embryonic layer are they derived?

Consists of a single layer of mainly hexagonal cells

Derived from neural crest cells

31

Describe the orientation of the endothelial cells and their function

The cells are oriented that their apical surface faces away from descemets membrane. They function as an ion pump that helps maintain corneal deturgescence and transparency.

32

Can you replace corneal endothelial cells?

Endothelial mitosis is limited. Therefore, when injury occurs, residual cells typically spread and enlarge, decreasing cell density.

33

What is the sclera?

covers 4/5 of the posterior surface of the globe

is covered by Tenons capsule

34

Where is the sclera the thinnest? Where is it the thickest?

It is thinnest behind the insertions of the rectus muscles (0.3 mm)

It is thickest at the posterior pole around the ON head (1.0 mm)

35

When scleral rupture occurs due to blunt trauma, where is the most common location of rupture?

The superonasal quadrant near the limbus

36

What is the blood supply of the sclera?

It is essentially avascular, except for the superficial episcleral vessels and the interscleral vascular plexus

37

What are Emissaria?

they are numerous channels that penetrate the sclera allowing for passage of arteries/veins/nerves

38

What are Axenfeld Loops?

They are branches of the ciliary nerve that supply the cornea, that sometimes leave the sclera to form loops posterior to the limbus

39

What is the episclera?

consists of dense vascular CT that merges with the superficial sclera and tenons capsule/conjunctiva

40

What part of the sclera contains the fibers with the largest diameter?

The outer collagen fibers have a larger diameter (1600 A) compared to the inner fibers (1000 A)

41

What is the opaque appearance of the sclera attributed to?

Two factors:
1- increased variation in the collagen fibril separation and diameter

2- increased degree of fibril interweaving

42

What is the limbus?

the transition zone b/w the peripheral cornea and the sclera (occurs over 1.0-1.5 mm)

43

What structures comprise the limbus?

There are 5 structures in total:
1- conjunctival and limbal palisades
2-Tenons Capsule
3- Episclera
4- Corneoscleral stroma
5- Aqueous outflow apparatus

44

How is the surgical limbus divided?

Into 2 zones.
1- Anterior blue-gray zone: overrides the clear cornea and extends from bowman's membrane to schwalbes lines

2- Posterior White Zone: overlies the TM and extends from schwalbes line to the scleral spur (iris root)

45

What structures comprise the Anterior Chamber Angle?

1- Schwalbes Line (termination of Descemets)
2- Schlemm Canal and TM
3- Scleral Spur
4- Anterior border of Ciliary Body
5- Iris

46

Under what conditions is the angle deeper? More Shallow?

The angle is deeper in patients who are aphakic, pseudophakic, and myopic

The angle is more shallow in hyperopic patients

47

How deep is the angle at the center (typically)?

3 mm

48

What is the volume of the anterior chamber in the emmetropic eye?

200 micro L

49

What are the paths that the aqueous can drain through?

Primary drainage via the TM
Seconary drainage via the uveoscleral pathway

50

In what population does 50% of the aqueous drain via the uveoscleral pathway?

Young people

51

Internal Scleral Sulcus

accommodates schlemms canal externally and TM internally

52

Insertion and action of the longitudinal ciliary muscle? Innervation?

Inserts onto the scleral spur. Contraction causes the TM to open and therefore increased drainage.

Nerve fibers mediated via sympathetic, sensory, and pterygopalatine pathways

53

What is the Trabecular Meshwork?

a circular sponge work of CT lined by trabeculocytes consisting of 3 laters. Its apex is located at Schwalbes line and its base at the scleral spur and ciliary body

54

What are the three layers of the TM?

The Uveal Portion, the Corneoscleral Meshwork, and the Juxtacanalicular Tissue.

55

Uveal Portion of the TM

Composed of cord-like trabeculae

Has fewer elastic fibers than corneroscleral meshwork

apertures are larger and less circular than that of the corneroscleral meshwork

56

Corneoscleral Portion of TM

a series of thin, flat, perforated CT sheets arranged in a laminar pattern

each beam is covered by a monolayer of thin trabecular cells

57

Juxtacanalicular Tissues

Invest the extent of Schlemms Canal, including endothelial meshwork

58

What is the Endothelial Meshwork, and what is its significance?

= a multilayered network of cells b.w the outermost layers of the corneoscleral meshwork and the endothelial lining of schlemms canal

Significance: contributes most to outflow resistence

59

Why does the endothelial meshwork contribute most to outflow resistance?

thought to contribute due to it being a narrow and tortuous pathway that can also be blocked by glycosaminoglycans and proteoglycans

60

What is Schlemms Canal?

a circular tube resembling a lymphatic vessel formed by a continuous monolater of non-fenestrated endothelium with a thin CT wall

Endothelial cells are connected by tight junctions

61

What are the collector channels? What are they also known as?

arising from Schlemms canal, are 25-30 channels that drain into either the deep, midscleral, or episcleral venous plexuses.

Channels that drain into the episcleral venous plexuses are also known as "aqueous veins"

62

What is the uveal tract?

the main vascular component of the eye consisting of the iris, choroid, and ciliary body

63

What are the attachment sites of the uveal tract?

There are 3 attachment sites:
- Scleral Spur
-Exit points of the vortex veins
- Optic Nerve

64

What is the Iris?

The most anterior portion of the uveal tract

made up of blood vessels and CT

mobility allows the pupil to change size

65

What is the Iris Stroma?

composed of pigmented cells (melanocytes) and non-pigmented cells, collagen fibrils, and a matrix (containing hyaluronic acid)

66

What forms the bulk of the Iris Stroma?

Blood vessels and nerves of the Iris, most of which follow a radial course and arise from the major arterial circle

anastomoses occurs between the arteries and veins at the collarette (thickest part of the stroma) to form the minor vascular circle of the Iris.

67

Where is the Major Arterial Circle located?

In the apex of the Ciliary Body

68

Facts about the posterior pigmented Iris Epithelium

densely pigmented and continuous with non-pigmented epithelium of the ciliary body

polarity is maintained from embryogenesis

curves around the pupillary margin and extends for a short distance onto the anterior border layer of the Iris Stroma (aka a "Pigment Ruff")

69

What is the dilator muscle of the Iris embryologically derived from?

From the Optic Cup (therefore, neuroectoderm)

70

Where is the dilator muscle located in the Iris?

it lies parallel and anterior to the posterior pigmentary epithelium

71

Describe the innervation of the dilator muscle of the iris. What kind of stimulation leads to contraction?

has dual sympathetic and parasympathetic innervation, with alpha 1 adrenergic stimulation causing contraction

72

Describe the sympathetic chain

1st Order Neurons: originates in the posterior ipsilateral hypothalamus, travels inferiorly down the SC and synapses in the intermediolateral gray matter of T1.

2nd Order Neuron: The nerve fiber leaves the SC, travels over the pulmonary apex, through the stellate ganglion (without synapsing), and synapses on the Superior Cervical Ganglion

3rd Order Neuron: Post-Ganglionic fibers travel with ICA plexus, enter the cavernous sinus, travels with the ophthalmic division of CN V to the dilator muscle

73

What embryological tissue is the Iris sphincter muscle derived from?

Neuroectoderm

74

What is the sphincter muscle composed of? Where is it located?

A circular band of smooth muscle. It is located near the pupillary margin in the deep stroma anterior to the pigmented posterior iris epithelium

75

What is the primary innervation of the sphincter muscle?

Myelinated parasympathetic fibers originating in CN III nucleus that responds to muscarinic stimulation.

76

What is the pathway of the parasympathetic fibers that innervate the Iris sphincter muscle?

Fibers leave the edinger-westphal nucleus and follow the inferior division of CN III after bifurcating in the cavernous sinus. They continue with the branch that supplies the IO muscle, exit, and synapse on the ciliary ganglion. Post-ganglionic fibers then travel with the short ciliary nerves to the iris sphincter

77

What is the Ciliary Body?

Bridges the anterior and posterior aspects uveal tract.

It is triangular in shape with its apex directed posteriorly toward the ora serrate

Its base gives rise to the Iris

78

Where does the ciliary body attach to the sclera?

It attaches at the scleral spur, where the longitudinal muscle fibers also insert

79

What are the two functions of the ciliary body?

aqueous humor production and lens accomodation

80

What is the size of the ciliary body? What makes up the ciliary body?

6-7mm wide

Pars Plana and Pars Plicata

81

What is the Pars Plana?

a relatively avascular smooth pigmented zone, 4 mm wide, extending from the ora serrate to the ciliary process

82

What is the Pars Plicata?

richly vascularized, consisting of 70 residual folds/ciliary processes

83

Where do the zonular fibers attach to the pars plicata and what is their blood supply?

The zonular fibers attach to the valleys of the ciliary processes, whose blood supply is capillary plexuses that are fed via the major arterial circle.

84

What kind of epithelium lines the ciliary body?

a double layer of pigmented and non-pigmented epithelium



85

Where is the non-pigmented ciliary body epithelium located? What kind of epithelium makes up the non-pigmented epithelium?

Non-Pigmented Layer: located b/w the aqueous humor and the pigmented layer of the CB

In the pars plana, the epithelium is cuboidal. In the pars plicata, the epithelium is columnar.

86

What are some characteristics of the pigmented ciliary body epithelium?

cells are relatively uniform, with each cuboidal cell having multiple basal infoldings, a large nucleus, mitochondria, an extensive endoplasmic reticulum, and many melanosomes

ER and golgi apparatus are important in the formation of the aqueous humor

87

What is the major blood supply of the Ciliary Body? Venous Drainage?

Anterior and Long Posterior Ciliary Arteries, which join together to form a multi-layered arterial plexus

Consists of the superficial episcleral plexus, a deeper intramuscular plexus, and an incomplete major arterial circle (located in CB, NOT IRIS)

Drains via the vortex system

88

How many muscle layers are there in the ciliary muscle and what are they?

There are 3 layers to the ciliary muscle, which function as a normal smooth muscle unit

Longitudinal Layer (outer), radial layer (middle), and circular layer (inner)

Note: Rich in type VI collagen

89

What is the largest muscle layer of the ciliary muscle, and where does it insert?

The longitudinal (outer) layer, which inserts into the scleral spur

90

What is the primary innervation for the ciliary muscle?

parasympathetic fibers of CN III via the short ciliary nerves. Cholinergic stimulation causes contraction

91

What is the Choroid?

the most posterior aspect of the uveal tract

provides nourishment to the outer retina

92

How many layers make up the choroid, and what are they?

Innermost: Choriocapillaris
Middle: layer of small vessels
Outer: layer of large vessels

93

What is the blood supply of the choroid? Venous drainage?

long and short posterior ciliary arteries and perforating anterior ciliary arteries

Therefore, has a higher 02 concentration than most of the eye, being 2-3 percent below normal arterial level

Venous drainage via the vortex system

94

What is Bruchs Membrane?

a seroes pf CT sheets resulting from fusion of the basal lamina of the RPE and the choriocapillaris

95

What are the components of Bruchs Membrane?

- RPE basal lamina
- inner collagenous zone
- thick porous band of elastic fibers
- outer collagenous zone
- basal lamina of choriocapillaris

96

What is the choriocapillaris? How does this differ from the middle and outer layers of the choroid?

a continuous fenestrated layer of large capillaries (40-60 micrometers in diameter) lying in a single plane beneath the RPE

Differs from the other layers of the choroid in that it is fenestrated, whereas the others are not.

97

What is the Lens?

a biconvex structure located directly behind the posterior chamber and pupil that contributes +20D to the total refractive power of the eye.

98

What are the dimensions of the lens?

Diamter: @ birth- 6.5 mm Adulthood- 9-10 mm
Width: @ Birth- 3 mm Adulthood- <=6 mm

99

What effect does ciliary muscle contraction have on the lens?

When contracting, the ciliary muscle moves forward and inward, easing tension on the zonular fibers and allowing the lens to assume a more globular shape, allowing for accommodation.

100

Why does the power of the lens decrease with age?

- increased size of the lens
- altered mechanical relationship
- increased stiffness of lens nucleus (due to changes in the crystalline lens fibers)
- alterations in the geometry of zonular attachments occurring with age
- changes in lens capsule elasticity

101

What is the blood supply and innervation of the lens?

Trick question--lens is avascular, lacks innervation, and receives all nutrients via the aqueous and vitreous.

102

When does the lens capsule develop?

During embryologic development in utero

103

What does the lens capsule consist of?

consists of fine filaments of type IV collagen arranged in lamellae arranged parallel to the surface.

104

What are the differences between the anterior and posterior lens capsule?

Anterior capsule- synthesis continues throughout life until an adult thickness of around 15.5 micrometers is reached; contains laminin (a fibrogranular material)

Posterior capsule: only synthesized during embryogenesis, and therefore maintains a constant thickness of around 2.8 micrometers

105

Where is the lens epithelium located?

epithelium is located between the anterior and equatorial capsule, but NOT the posterior capsule

central zone- represents a stable population of cells whose # decreased with age

Intermediate zone- show occasional mitosis

Peripheral zone- rows of cuboidal post-equatorial cells that form the germinative zone (undergo mitosis)

Note: if cells from the peripheral zone are left behind during phacoemulsification, PCO can occur

106

What part of the lens fibers are present at birth? What part develops post-natally?

The nucleus

The Cortex

107

Where do fibers differentiate into the adult cortex in the lens?

In the superficial and deep regions

108

What are characteristics of lens fibers?

hexagonal in cross section

spindle-shaped

possess numerous finger-like projections (interdigitation of these form the lens sutures)

109

What attribute of the lens fibers allows for high refractive index?

Increased concentration of lens crystallins (alpha, bravo, and gamma crystallins)

110

What do the zonular fibers do? Where do they originate from? Where do they attach to?

They hold the lens in place

Originate from the ciliary body (valleys of the ciliary processes of the pars plana and pars plicate)

attach to the lens capsule anterior and posterior to the equator

111

What are the zonular fibers made of?

multiple filaments of fibrillin

112

What happens to the zonules in distance vision? Near vision?

Distance vision- zonules are held under tension (ciliary muscle is relaxed) and lens is flat

Near Vision- zonules are relaxed due to ciliary muscle contraction and the lens assumes a globular shape

113

What is the Retina?

a thin transparent structure that developes from the inner and outer layers of the optic cup

114

How many layers are there in the retina? What are they?

10 layers: ILM, NFL, GCL, IPL, INL, MLM, OPL, ONL, ELM, rod and cone outer segments

115

what does the term "fundus oculi" mean?

refers to the part of the posterior eye visible via ophthalmoscopy, consisting of the retina, vessels, and ON head.

116

What is the macula?

5-6 mm in diameter, is the area of the retina that is rich in cones and responsible for color vision/high acuity vision.

Located b/w the temporal arcades

117

What is the Ora Serrata?

the junction b/w the pars plana and the retina

118

Why does the ocular fundus have a reddish color?

The red color is due to the transmission of light reflected from the posterior sclera through the capillary bed of the choroid

119

What is the RPE?

Retinal pigment epithelium, is a monolayer of hexagonal cells that extends anteriorly from the optic disc to the ora serrata

Note: at the ora, it merges with pigmented epithelium of ciliary body)

120

What are the functions of the RPE?

- vitamin A metabolism - blood/retina barrier
-phagocytosis of photoreceptor outer segments
- production of mucopolysaccharaide matrix surrounding photoreceptor outer segments
- active transport of materials into and out of RPE
- heat exchange - formation of basal lamina of bruchs membrane - absorption of light (decreases scatter)

121

How are cells of the RPE attached to one another?

Zona occludentes and Zona adherentes, which provide structural stability and help to maintain the blood-retina barrier

122

How do RPE cells differ in the fovea compared to the retinal periphery?

Foveal cells are taller, thin, and contain an increased number of larger melanosaomes

At the periphery, RPE cells are shorter, broader, and less pigmented

123

What are lipofuscin granules?

thought to arise from the discs of photorecepter outer segments that are residual s/p phagocytosis by RPE

124

What are phagosomes?

membrane-enclosed packets of disc outer segments that have been engulfed by RPE

125

What are Drusen?

accumulation of incompletely digested residual bodies, lipofuscin granules, phagosome, and other material excreted beneath the RPE basal lamina

typically located b/w basement membrane of RPE and inner collagenous zone of Bruchs membrane

126

What are the neuronal elements of the neurosensory retina?

Consists of highly specialized rods and cones, horizontal cells, bipolar cells, and amacrine cells

127

Description of a Rod

consists of an outer segment that contains multiple laminated discs resembling a "stack of coins" and a central connecting cilium

microtubules have a 9+0 configuration

128

What are the elements of the rod inner segment?

1- an outer ellipsoid containing numerous mitochondria
2- an inner myoid containing a large amount of glycogen

129

Extrafoveal cones v Foveal cones

Extrafoveal Cones: have conical ellipsoids and myoids, and their nucleri are closer to the ELM than rod nuclei

Foveal Cones: have cylindrical inner segments, but are otherwise identical to extrafoveal cones

130

What are horizontal cells?

neuron that makes synaptic connections with many rod spherules and cone pedicles; also spread processes throughout the OPL

131

What are bipolar cells?

vertically oriented neurons whose dendrites synapse with either rod or cone synaptic bodies, and their axons make contact with ganglion/amacrine cells in the IPL

132

How many nerve fibers are in the optic nerve?

1x10^6, or a little over 1 million

133

What glial elements are found in the neurosensory retina?

Mullers cells, astrocytes, etc....that provide structural support and nutrition to the retina

134

What are muller cells?

glial cells that extend vertically from the ELM inward to the ILM; nuclei are located in the INL

135

What is the blood supply of the inner portion of the retina?

branches of the central retinal artery

macula is supplied by a cilioretinal artery, a branch from ciliary circulation

136

How do retinal vessels help maintain the blood-retinal barrier?

Retinal vessels contain a single layer of non-fenestrated endothelial cells covered by a basal lamina that is attached to mullers cells and other glial elements

137

What is the difference between rod and cone nuclei?

Rod discs do not attach to the cell membrane (therefore, are discrete structures)

Cone discs are attached to the cell membrane, and thought to be renewed by membranous replacement

138

How do retinal vessels differ from other vessels throughout the body?

Retinal vessels lack an IEL and a continuous layer of smooth muscle cells

139

How far into the retina do the retinal vessels typically extend?

Up until the middle limiting membrane

140

What part of retinal vessels do vaso-occlusive phenomena occur, and why?

They typically occur at AV junctions, as the vessels share a basement membrane

141

What is the External Limiting Membrane (ELM)

the outermost layer of the neurosensory retina, and not considered a true membrane.

Is formed by attachments of adjacent photoreceptors and muller cells

Is highly fenestrated is

142

What is the outer plexiform layers?

second outermost layer of neurosensory retina, composed of interconnections b/w the photoreceptor synaptic bodies and horizontal/bipolar cells

143

What is the Fiber Layer of Henle?

the OPL in the macula, where it is thicker and contains more fibers (because axons or rods and cones become longer and more oblique as they deviate from the fovea)

144

What is the Inner Nuclear Layer?

contains the nuclei of muller cells as well as bipolar/amacrine/horizontal cells

145

What is the middle limiting membrane?

a zone of desomosome-like attachments in the region of the synaptic bodies of photoreceptors

146

What is the Inner Plexiform Layer?

consits of axons of bipolar/amacrine cells, dendrites of ganglion cells, and their synapses

147

What is the ganglion cell layer?

consists of bodies of ganglion cells that lie near the inner surface of the retina

148

What is the nerve fiber layer?

formed by axons of ganglion cells (typically not myelinated until they exit via the lamina cribosa)

149

What is the internal limiting membrane?

formed by the footplates of muller cells and their attachments to the basal lamina

not a true membrane

150

How are the cells/layers of the retina oriented?

In the outer/middle layers of the retina, the cells are oriented perpendicularly to the retina.

In the inner layer, the cells are oriented parallel to the retinal surface

151

What the Macula?

an area of the retina responsible for high acuity vision that histologically contains >1 layer of ganglion cell nuclei

typically yellow in color

152

Why is the macula yellow in color?

the presence of carotenoid pigments, lutein and zeaxanthin

high proportion of lutein corresponds to more rod-dense areas, which higher proportions of zeaxanthin correspond to more cone-dense areas.

153

What is the fovea?

a concave central retinal depression around 1.5 mm in diameter

154

What is the parafovea?

the area around the fovea, around 0.5 mm wide

where the GCL/INL, OPL are the thickest

155

What is the perifovea?

surrounds the parafovea

1.5 mm wide

156

What is the foveola?

a central depression within the fovea consisting only of cones, muller cells, and other glial elements

0.35 mm wide x 0.1 mm thick

foveal cones are shaped more like rods, but are cytologically the same as extrafoveal cones

157

Why is the foveal avascular zone important?

it is an important clinical landmark in the treatment of subretinal neovascular membranes by laser photocoagulation

158

What is the Ora Serrata?

the bounday b/w the pars plana and retina

a watershed zone b/w the anterior and posterior ciliary vascular systems

159

What is the volume of the vitreous?

makes up 4/5 of ocular volume, or 4 mL

160

What is the vitreous made of? What percentage of the vitreous is water?

Fine collagen fibrils (mainly type II) and hyalocytes

99%

161

Why is the vitreous important?

important to the metabolism of ocular tissues, as it provides a route for their metabolites

162

What are the sites of attachment of the vitreous?

- the retina peripherally at the vitreous base
- at the disc margin
- at the perimacular region
- along retinal vessels
- at the periphery of the posterior lens capsule

163

What are the remnants of fetal vasculature that can occur in the eye?

Cloquet canal= an s shaped canal that passes sinuously from a point slightly nasal to the posterior pole of the lens (known as the mittendorf dot)

Remnants can also occur on the nerve head (vascular loops, Bergmeister papillae)