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FRCOphth part 1 Anatomy Eyeball > Retina > Flashcards

Retina Flashcards

Page 158-176

1
Q

What is the retina?

A

The internal layer of the eyeball where the optical image is formed

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2
Q

What occurs in the retina that leads to the creation of nerve impulses?

A

Photo-chemical transduction

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3
Q

What is the thickness of the retina at the optic disc?

A

0.56 mm

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4
Q

What is the thickness of the retina at the ora serrata?

A

0.1 mm

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5
Q

Where is the retina thinnest?

A

At the center of the fovea

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6
Q

What does the retina become continuous with posteriorly?

A

The optic nerve

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7
Q

What is the retina continuous with anteriorly?

A

Epithelium of the ciliary body and iris

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8
Q

What is the outer surface of the retina in contact with?

A

Bruch’s membrane of the choroid

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9
Q

What is the inner surface of the retina in contact with?

A

The vitreous body

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10
Q

Where is the retina firmly attached?

A

At the margins of the optic disc and at the anterior termination of ora serrata

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11
Q

What is the ora serrata?

A

The anterior edge of the retina that forms a wavy ring

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12
Q

Which side of the retina extends more anteriorly? Which structure of the eye is this side therefore closer to?

A

The medial side => ora serrata on this side is closer to limbus

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13
Q

What are the landmarks the outside of the eyeball that indicate roughly where the retina is attached to the ora serrata medially and laterally?

A

medially = insertion of medial rectus
laterally = insertion of lateral rectus

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14
Q

What are the two layers of the retina?

A

An outer pigmented layer and an inner neurosensory layer

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15
Q

From which embryological structure are the layers of the retina derived?

A

Neuroectoderm
Outer layer - from outer layer of optic cup
Inner layers - from inner layer of optic cup

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16
Q

What is the anterior, nonreceptive part of the retina at the ora serrata continuous with?

A

The pigmented and nonpigmented columnar cell layers of the ciliary body and its processes

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17
Q

Fill in the blank: The posterior, receptive part of the retina extends forward from the optic nerve to a point just posterior to the _______.

A

Ciliary body

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18
Q

True or False: The retina has a purplish-red color in living subjects.

A

True - it is actually a transparent membrane which has a purple-red colour in living subjects

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19
Q

What happens to both layers of the retina at the iris?

A

Become pigmented and continue onto posterior surface of iris

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20
Q

What is the macula lutea?

A

An oval, yellowish area in the centre of the retina responsible for the most distinct vision

It contains the fovea centralis at its center.

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21
Q

What is the fovea centralis?

A

The central depression of the macula lutea

It is the area of the retina with the highest visual acuity.

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22
Q

Where does the optic nerve leave the retina?

A

At the optic disc, about 3 mm to the medial side of the macula lutea

The optic disc is where the central retinal artery and vein pierce the retina.

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23
Q

What is the optic disc referred to as, and why?

A

The blind spot, due to the complete absence of rods and cones

It is insensitive to light.

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24
Q

How does the optic disc appear on ophthalmoscopic examination?

A

Pale pink, much paler than the surrounding retina

This indicates the lack of photoreceptive cells in that area.

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25
Q

What is the retinal pigment epithelium (RPE)?

A

A single layer of cells extending from the optic nerve to the ora serrata

It continues forward as the pigmented ciliary epithelium.

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26
Q

What shape do the cells of the RPE take on tangential section?

A

Hexagonal

They are tall and narrow in the posterior region and flattened near the ora serrata.

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27
Q

Describe the structure of the basal ends vs the apical ends of the cells of the RPE

A

Basal end - infolded, rests on basement membrane
apical - multiple microvilli 5-7microns long

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28
Q

What structures do the microvilli of the RPE cells project between? Do they have special attachments?

A

The outer segments of the rods and cones
No special attachments

These microvilli are involved in the interaction with photoreceptor cells.

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29
Q

What is the role of glycosa-minoglycans in the RPE?

A

They may act as an adhesive binding the pigment layer to the neural layer

This helps maintain structural integrity in the retina.

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30
Q

What are the zonula adherens and zonula occludens?

A

Types of tight junctions in the RPE

They maintain the isolation of the retina from systemic circulation.

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31
Q

Where are cell nuclei in the RPE cells?

A

They occupy the basal part of the cytoplasm

This positioning is important for cellular function.

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32
Q

Describe which organelles are found in RPE cells

A
  • nuclei near basal aspect
  • melanin granules (lots), extend into microvilli
  • granular and agranular enoplasmic reticulum
  • golgi apparatus
  • LOTS of lysosomes = Phagosomes
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33
Q

What happens to the outer ends of the rods in relation to the RPE?

A

1) They are continuously eroded by the apical microvilli of the RPE
2) pigment cells phagocytose the debris generated from this process (this includes lamellar structures in outer processes of photoreceptor cells)
3) lysocomes break down content of phagosomes to form lipofuscin

The

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34
Q

Role of pigmented cells

A

1) absorption of light
2) participation in the turnover ofthe outer segments ofthe photoreceptors
and
formation of rhodopsin and iodopsin by storing and releasing vitamin A, which is a precursor of the photosensitive pigments.
4) These cells may also have a secretory function.

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35
Q

What mechanism do pigment cells use to absorb light?

A

Antireflection mechanism

This mechanism prevents the return of light into the photoreceptive layer of the neural retina, which would result in a loss of image sharpness.

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36
Q

What are the two main components developed from the optic cup?

A
  • Pigmented epithelium (outer layer)
  • Rods and cones (inner layer)
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37
Q

What separates the RPE from the rods + cones? Where is this derived from?

A

Potential space, constitues remains of cavity of optic vesicle

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38
Q

What condition occurs when the layers of the retina become separated?

A

Detached retina

This condition can occur despite the layers being very close together.

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39
Q

What is the Blood-Retina Barrier?

A

A barrier formed by tight junctions between pigment epithelial cells

This barrier limits ion flow and prevents large toxic molecules from diffusing from choroid capillaries to photoreceptors.

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40
Q

What is a characteristic of albinism in the eye?

A

Lack of melanin pigment in pigment cells (ie still have normal number of pigment cells, but MELANIN is low)

This condition leads to transillumination of the iris, allowing visualization of the ciliary processes and lens.

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41
Q

In oculocutaneous and ocular albinism, what is observed during clinical examination?

A
  • Iris is transparent (transillumination)
  • Pupil appears red
  • Fundus is light red
  • Retinal and choroidal vessels visible against white sclera

Despite the normal number of pigment cells, melanin pigment is deficient.

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42
Q

Fill in the blank: The _______ is a condition where the layers of the retina become separated.

A

Detached retina

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43
Q

True or False: The Blood-Retina Barrier allows large toxic molecules to pass freely from the choroid capillaries to the photoreceptors.

A

False

The Blood-Retina Barrier is designed to prevent this diffusion.

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44
Q

What is the neural retina embryologically derived from?

A

The inner layer of the optic cup

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45
Q

Name the three main groups of neurons in the neural retina.

A
  • Photoreceptors
  • Bipolar cells
  • Ganglion cells

and horizontal, amacrine and supporting cells

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46
Q

What are the two types of photoreceptors?

A
  • Rods
  • Cones
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47
Q

What are the functions of rods in vision?

A

Responsible for vision in dim light and produce images of varying shades of black and white

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48
Q

Which nerves in the visual pathway are considered to be akin to relay neurons?

A

Ganglion cells. Also considered to be second order neurons.

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49
Q

What is the primary function of cones?

A

Adapted to bright light and can resolve fine details and color vision

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50
Q

How many rods are estimated to be in the retina?

A

About 110 to 125 million

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51
Q

What is the estimated number of cones in the retina?

A

6.3 to 6.8 million

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52
Q

Where are rods absent in the retina?

A

At the fovea.
Rise in number toward periphery and then dimish at the extreme periphery.

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53
Q

What is the density of rods at the extreme periphery of the retina?

A

About 30,000 rods per square millimeter

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54
Q

Where are cones most dense in the retina?

A

At the fovea. Numbers decrease towards periphery.

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55
Q

What is the approximate number of ganglion cells in each retina?

A

About 1 million

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56
Q

How many photoreceptor cells are estimated to activate a single ganglion cell?

A

About 100 photoreceptor cells

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57
Q

What do the axons of ganglion cells form after passing through the lamina cribrosa?

A

The optic nerve

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58
Q

What type of cells form the myelin sheaths of ganglion cell axons?

A

Oligodendrocytes
NOT schwann cells

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59
Q

True or False: The optic nerve is comparable to a tract within the peripheral nervous system.

A

False. It is comparable to a tract in the CENTRAL nervous system.

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60
Q

What is the role of the lateral geniculate body in the visual pathway?

A

Most axons terminate by synapsing with nerve cells

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61
Q

What type of neurons are formed by the nerve cells of the lateral geniculate body?

A

Third-order neurons

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62
Q

Fill in the blank: The number of neurons involved in conducting light impulses from the retina to the visual cortex is the same as that found in other _______.

A

[sensory pathways]

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63
Q

Name the three main parts of a photoreceptor cell

A

Outer segment (name describes shape of this part, eg rod vs cone)
connecting stalk
Inner segment

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64
Q

What are the two types of photoreceptor cells in the retina?

A

Rods and cones

Rods are responsible for vision in low light, while cones are responsible for color vision and detail.

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65
Q

What is the primary function of the outer segment of rod cells?

A

It is the true photoreceptor of the cell containing rhodopsin (light-sensitive pigment crucial for vision.)

Rhodopsin is a light-sensitive pigment crucial for vision.

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66
Q

How long are rod cells approximately?

A

100 to 120 micrometers long

This length contributes to their function in the phototransduction process.

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67
Q

What structures do the outer segments of rod cells contain?

A

600 to 1000 membrane-bound transversly arranged lamellae (discs)

These discs are crucial for the phototransduction process.

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68
Q

What is the diameter of each disc in the outer segment of rod cells and how thick is each disc?

A

Approximately 2 microns
The thickness of each disc is about 14 nanometers.

The thickness of each disc is about 14 nanometers.

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69
Q

What happens to the discs at the tip of the rod cell’s outer segment?

A

They are phagocytosed by the cells of the pigment epithelium

This process is part of a 24-hour cycle of disc shedding.

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70
Q

When does the majority of disc shedding occur in rod cells?

A

Most shed at once in the early morning

This cyclical shedding is part of the rod cells’ renewal process.

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71
Q

What is found in the connecting stalk of rod cells? How does it differ to other similar structures found in the body.

A

A modified cilium - it has the nine doublet microtubules but lacks a central pair.

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72
Q

What is the basal body of rod cells?

A

It is the origin point of the modified cilium (of the connectign stalk), found in the inner segment. Essential for structural integrity of the cilium.

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73
Q

True or False: A slight degree of transillumination of the iris is a normal finding in approximately 10 percent of the population.

A

True

This finding is considered normal and not indicative of any pathology.

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74
Q

What are the two areas of the inner segment of a rod cell called? How are they orientated?

A

Ellipsoid and myoid

Ellipsoid = next to connecting stalk, myoid = closer to vitreous

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75
Q

What structures are contained in the ellipsoid of the inner segment?

A

Basal body and numerous mitochondria

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76
Q

What is contained in the myoid of the inner segment?

A

Granular and agranular endoplasmic reticulum, free ribosomes, Golgi apparatus

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77
Q

What connects the inner segment to the cell body in rod cells?

A

Rod outer fiber

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78
Q

What does the rod inner fiber contain?

A

Numerous microtubules

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79
Q

What is the name of a rod cell’s synaptic ending? What shape does it have and what does it contain?

A

Rod Spherule. Pear-shaped and contains many presynaptic vesicles

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80
Q

With which type of cells does the rod spherule synapse?

A

Bipolar cells

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81
Q

What is the length of cone cells?

A

About 65 to 75 microns

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82
Q

How does the outer segment of cone cells differ from that of rod cells?

A

Conical and wider at the base, tapering to a rounded tip

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83
Q

What is unique about the membranes of the discs in cone cells compared to those in rods?

A

Continuous with the outer plasma membrane

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84
Q

Are the tips of cone cells phagocytosed by pigment cells?

A

No (UNLIKE RODS!!)
=> lamallae are continuous with extracellular space

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85
Q

What are the photochemicals found in cones called?

A

Iodopsins

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86
Q

Where are the photosensitive pigments in rods and cones found?

A

Incorporated into the disc membrane

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87
Q

What connects the outer segment of cone cells to the inner segment?

A

Connecting stalk containing Modified cilium (9 doulet microtubules but missing central pair)

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88
Q

Are the inner segments of rods and cones similar?

A

YES!

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89
Q

What does the body of cone cells contain?

A

Large, pale-staining nucleus

90
Q

What is the name of the synaptic ending of cones?

A

Cone pedicle

91
Q

What type of cells do bipolar cells synapse with?

A

Photoreceptor cell terminals

92
Q

Describe the orientation of bipolar cells.

A

Radial orientation

93
Q

What is the function of rod bipolar cells?

A

Connect several rod cells to one to four ganglion cells

94
Q

What do flat or diffuse bipolar cells connect?

A

Many cone cells with many ganglion cells

95
Q

Which cell types do midget bipolar cells connect?

A

a single cone cell with a single midget ganglion cell => there is a direct pathway between from a singular cone to a singular optic nerve fibre

96
Q

Where are ganglion cells located?

A

Inner part of the retina

97
Q

What is the diameter range of ganglion cells?

A

10 to 30 microns.
Most are small cells, but a few are latge

98
Q

How many layers of ganglion cells are found in retina vs the macula?

A

Retina = single, Macula = up to 10 layers

99
Q

What type of neurons are ganglion cells?

A

Non-myelinated multipolar cells (=> one axon, multiple dendites)

100
Q

Which cell types do ganglion cells synapse with?

A

Dendites synapse with axons of bipolar and amacrine cells

Midget ganglion cells linked by midger bipolar cells to a single cone cell

101
Q

What happens to ganglion cell axons when they reach the inner surface of the retina?

A

They make a right-angled turn and converge at exit of optic nerve at optic disc

102
Q

What is the site called where optic nerve fibers pass through the sclera?

A

Lamina cribrosa

103
Q

What type of cells are horizontal cells?

A

Multipolar neurons

104
Q

What is the length of the long process of horizontal cells?

A

Up to 1 mm

105
Q

How many cone spherules do horizontal cells synapse with?

A

Have synaptic junctions with seven cone pedicles

106
Q

How many rod spherules do horizontal cells associated with rods synapse with?

A

10 to 12 rod spherules

107
Q

The ganglion cells’ axons become myelinated after piercing which structure?

A

Lamina cribrosa

108
Q

True or False: The ganglion cells are the first neurons in the visual pathway.

A

False

109
Q

Fill in the blank: The cytoplasm of horizontal cells contains an organelle called _______.

A

Kolmer’s crystalloid (tubular membranes covered by ribososmes)

110
Q

What is the role of horizontal cells?

A

Thought to respond to neurotransmitter released by rods and cones (after they have been excited by light), to release inhibitory transmitter that inhibits activity of bipolar cells

111
Q

What inhibitory transmitter is released by rods and cones following excitation by light?

A

Gamma-aminobutyric acid (GABA)

112
Q

What is the role of GABA in the retina?

A

Inhibits the activity of bipolar cells, sharpening contrast and increasing spatial resolution

113
Q

What is the primary function of horizontal cells in the retina?

A

Integrate visual stimuli

114
Q

Describe the appearance of amacrine cells

A
  • Large cell bodies
  • abundant cytoplasm
  • lobulated indented nuclei
  • no axons
  • long processes (that synapse with other cells)
115
Q

Where are amacrine cells located in the retina?

A

Close to the ganglion cells

116
Q

What do amacrine cells synapse with?

A

Each other, dendrites of ganglion cells, and axonal endings of bipolar cells

117
Q

What stimulates amacrine cells?
Which cells do amacrine cells stimulate?

A

Stimulated by bipolar cells
Stimulate ganglion

118
Q

Describe the structure of muller cells

A

long, narrow, pale-staining, long processes that extend from it throughtout almost the entire thickness of the neural retina + branches that extend horizontally and surround/support nerve cells

119
Q

What is the function of Müller cells in the retina?

A

Support nerve cells and fill space not occupied by neurons

120
Q

What structure is traditionally called the outer limiting membrane?

A

A row of zonulae adherentes between photoreceptor cells and Müller cell processes

Note - outer limiting membrane is a misnomer

121
Q

What forms the inner limiting membrane in the retina?

A

Expanded Müller cell terminations covered by a basement membrane

122
Q

What role do Müller cells play regarding blood capillaries?

A

Make extensive contacts with the walls of blood capillaries

123
Q

What are some functions of Müller cells?

A

Support neurons, assist in nourishing retinal neurons, uptake neurotransmitters, electrical insulation

124
Q

What are retinal microglial cells known for?

A

Phagocytic function and probable immunologic functions

125
Q

How many layers is the retina traditionally said to be composed of?

A

10 layers

126
Q

Fill in the blank: The _____ cells are glial-like cells found in the retina.

A

Müller

127
Q

What are the ten layers of the retina?

A

1) The pigment epithelium
2) The rods and cones
3) The external limiting membrane
4) The outer nuclear layer
5) The outer plexiform layer
6) The inner nuclear layer
7) The inner plexiform layer
8) The ganglion cells
9) The nerve fiber layer
10) The internal limiting membrane

The layers are functional components and may not represent real layers upon electron microscopy examination.

128
Q

What does the outer nuclear layer consist of?

A

The nuclei of the rod and cone cells

The outer nuclear layer plays a crucial role in phototransduction.

129
Q

What is the composition of the outer plexiform layer?

A

Synapses between the terminal processes of the rod and cone cells, bipolar cells, and horizontal cells

This layer is essential for the processing of visual information.

130
Q

What is contained in the inner nuclear layer?

A

Nuclei of the bipolar cells, horizontal cells, amacrine cells, and Müller cells

The inner nuclear layer is involved in the integration of visual signals.

131
Q

What is the function of the inner plexiform layer?

A

Synaptic connections between the bipolar, amacrine, and ganglion cells

This layer is critical for transmitting visual signals to the brain.

132
Q

What comprises the ganglion cell layer?

A

Nuclei of the ganglion cells

Ganglion cells are the final output neurons of the retina.

133
Q

What does the nerve fiber layer consist of?

A

Axons of the ganglion cells converging toward the optic disc

This layer is important for transmitting visual information to the optic nerve.

134
Q

What is the macula lutea?

A

An oval, yellowish area at the center of the posterior part of the retina measuring about 4.5 mm in diameter, lies 3mm lateral to optic disc

The macula is crucial for high acuity vision.

135
Q

What causes the yellow coloration of the macula lutea?

A

A yellow carotenoid pigment called xanthophyll

This pigment is present in the retinal layers from the outer nuclear layer inward.

136
Q

What is the fovea centralis?

A

A depressed area in the center of the macula lutea measuring about 1.5 mm in diameter

The fovea is where visual acuity is highest due to its structure.

137
Q

What are the sides and floor of the fovea called?

A

Sides = clivus, floor = foveola

138
Q

Why is the fovea depressed?

A

Nerve cells and fibresof inner layers of retina are displaced peripherally => only photoreceptors found here.
No blood vessels here either, or rods, only cones.

139
Q

What is the significance of the arrangement of cells in the fovea centralis?

A

It allows greater access of incoming light to the photoreceptors

This arrangement contributes to the fovea’s ability to provide the most distinct vision.

140
Q

How many cones are present per square millimeter in the fovea?

A

147,000 cones per square millimeter

This high density of cones is essential for detailed vision.

141
Q

Where is the optic disc located relative to the macula lutea?

A

About 3 mm medially to the macula lutea

The optic disc is also known as the blind spot because it contains no photoreceptors.

142
Q

What is the appearance of the optic disc?

A

Pale pink or almost white, measuring about 1.5 mm in diameter

The optic disc is the point where the central retinal vessels enter and leave the eye.

143
Q

Describe the edge vs the central part of the optic disc. Where do the central retinal vessels enter and leave the eye?

A

Edge = slightly raised, centre = slightly depressed. Central retinal vessels enter and leave eye in depression.

144
Q

True or False: The fovea centralis contains rod cells.

A

False

The fovea has no rod cells, only cones, which enhances visual acuity.

145
Q

What happens at the optic disc?

A

The optic nerve fibers exit the eye by piercing the sclera.

146
Q

What is a consequence of a rise in pressure inside the eyeball?

A

The lamina cribrosa can bulge out.

147
Q

What effect does an increase in cerebrospinal fluid pressure have on the optic disc?

A

It may cause the optic disc to bulge into the eyeball.

148
Q

What is believed to cause the swelling of the optic disc?

A

External pressure on the optic nerve impeding axon flow.

149
Q

Are optic nerve fibres myelinated?

A

Posterior to the optic disc, the fibers are myelinated; anterior to the disc, they are nonmyelinated.

150
Q

What is the significance of the absence of rods and cones at the optic disc?

A

It is insensitive to light and is referred to as the blind spot.

151
Q

What is the ora serrata?

A

The scalloped anterior margin of the retina.

152
Q

Fill in the blank: The _______ is the area where the nervous tissues of the retina end.

A

ora serrata

153
Q

What part of the retina extends forward from the ora serrata?

A

The anterior, non-receptive part of the retina

This part consists of a single layer of pigment cells with a deeper layer of nonpigmented columnar epithelium.

154
Q

What are the two layers of cells on the posterior surface of the iris?

A

Both layers of cells are pigmented

The anterior part of the retina consists of a single layer of pigment cells and a deeper layer of nonpigmented columnar epithelium.

155
Q

How far is the ora serrata from the limbus?

A

About 8.5 mm

Nasally, it is 1 mm closer to the root of the iris than on the temporal side.

156
Q

What are the two sources of blood supply to the retina?

A

1) Choroidal capillaries for outer laminae (rods, cones, outer nuclear layer) - NB vessels do not enter these layers, tissue fluid exudes between these cells

2) Central artery and vein for inner laminae

The outer laminae include the rods and cones and outer nuclear layer.

157
Q

What type of arteries are the retinal arteries described as?

A

Anatomic end arteries

There are no arteriovenous anastomoses in the retina.

158
Q

True or False: The integrity of the retina depends on both the choidal vessels and central retinal vessels.

A

True

Neither the choroidal capillaries nor the central artery and vein alone is sufficient for the retina’s integrity.

159
Q

Fill in the blank: The outer laminae of the retina are supplied by _______.

A

choroidal capillaries

Tissue fluid exudes between the cells of the outer laminae.

160
Q

Fill in the blank: The inner laminae of the retina are supplied by _______.

A

central artery and vein

These vessels play a crucial role in the blood supply to the inner layers of the retina.

161
Q

What is the first branch of the ophthalmic artery?

A

The central retinal artery

162
Q

What is the diameter of the central retinal artery?

A

About 0.3 mm

163
Q

How does the central retinal artery run forward to eye?

A

Adherant to dural sheath of optic nerve

164
Q

Where does the central retinal artery enter the optic nerve?

A

The inferior and medial side of the optic nerve about 12 mm posterior to the eyeball

NB central retinal vein pierces dural sheath further away from eyeball than central retinal artery

165
Q

What coverings does the central retinal artery obtain after piercing the dura and arachnoid?

A

A covering from both the dura and arachnoid

166
Q

What happens to the central retinal artery within the sub-arachnoid space?

A

It bends forward and then turns at a right angle to enter the optic nerve

167
Q

What does the central retinal artery acquire upon entering the optic nerve?

A

A sheath derived from the pia mater

168
Q

What surrounds the central retinal artery as it reaches the center of the optic nerve?

A

A sympathetic plexus and the central vein

169
Q

What does the central retinal artery pierce to enter the eyeball?

A

The lamina cribrosa

170
Q

What forms an anastomotic circle in the sclera around the optic nerve?

A

The posterior ciliary arteries

171
Q

What do small branches from the posterior ciliary artery anastomotic circle supply?

A

The optic disc and the adjacent retina

172
Q

What is the occasional larger connection between the posterior ciliary arteries and the central retinal artery called?

A

Cilioretinal artery

173
Q

How does the central retinal artery divide after entering the eyeball?

A

Into two equal superior and inferior branches

174
Q

What branches do the superior and inferior branches of the central retinal artery further divide into?

A

Superior and inferior nasal and temporal branches

175
Q

Where does the last division of the central retinal artery take place?

A

Either inside the optic nerve or on the surface of the optic disc

176
Q

Where do the branches of the central artery and vein usually emerge from the optic disc?

A

Usually toward the nasal side

177
Q

Is there any overlap or anastomosis between branches within a quadrant of the retina?

A

No - each quadrant supplied by own branch of central retinal artery

178
Q

Describe the course of the nasal branches of the central retinal artery.

A

They run a relatively straight course toward the ora serrata

179
Q

Describe the course of the temporal branches of the central retinal artery.

A

They arch above and below the fovea centralis and then pass to the ora

180
Q

Where do the arterial branches run in the retina?

A

In the nerve fiber layer close to the internal limiting membrane

(This membrane serves as the basement membrane of the Müller cells.)

181
Q

What is the internal limiting membrane characterized by?

A

It is extremely thin and transparent

This transparency allows retinal blood vessels to be seen with the ophthalmoscope.

182
Q

To which layer do the arterioles in the retina reach?

A

The internal nuclear layer

183
Q

Do the retinal arterioles have anastomoses?

A

No

184
Q

What structural feature is absent in retinal arterioles compared to typical arterioles?

A

Internal elastic lamina

185
Q

Where are smooth muscle cells found in the retinal arterioles?

A

In the tunica adventitia

186
Q

What do the arterioles give rise to in the retina?

A

A diffuse capillary network

187
Q

What type of endothelial cells line the walls of the retinal capillaries?

A

Nonfenestrated endothelial cells

188
Q

What are located outside the endothelial layer of retinal capillaries?

A

Pericytes

189
Q

What is the foveal avascular zone?

A

A capillary-free zone approximately 500microns in diameter

190
Q

Where are the capillary networks most concentrated in the retina?

A

In the macula

191
Q

What happens to the diameter of the avascular zone in diabetes mellitus?

A

It becomes enlarged

192
Q

How do the numbers of capillaries change at the periphery of the retina?

A

They are less numerous

193
Q

At what location are capillaries absent in the retina?

A

At the ora serrata and the foveal avascular zone

194
Q

What type of nerve fibers innervate the arteries of the retina?

A

Sympathetic postganglionic fibers

195
Q

What mechanism protects the retina from circulating molecules of large size?

A

Presence of nonfenestrated endothelium of capillaries and tight junctions of RPE

196
Q

How does the diameter of the central vein of the retina (and its branches) compare to that of their corresponding artery?

A

About one-third to one-fourth larger

197
Q

Where do the veins lie in relation to the arteries in the retina?

A

deep to the arteries (ie arteries are closer to vitreous and cross over veins)

198
Q

What forms the central vein of the retina?

A

Tributaries that accompany the arteries

199
Q

Where does the central vein of the retina leave the eyeball?

A

Through the lamina cribrosa (lateral to central retinal artery)

200
Q

Which structure does the central vein of the retina drain into?

A

Cavernous sinus or superior ophthalmic vein

201
Q

What protects the outer third of the neural retina from large molecular toxic substances?

A

Zonulae occludentes between RPE and pigment layer

202
Q

What is absent in the retina regarding lymphatic vessels?

A

No lymphatic vessels

203
Q

Where is the neural retina firmly attached to the underlying pigment epithelium?

A

At the optic disc and the ora serrata

204
Q

What three factors keep the two neural retina and the pigment epithelium in apposition?

A

1) Negative pressure from fluid absorption
2) Viscous mucopolysaccharides between microvilli of pigment cells and photoreceptor cells
3) Electrostatic force between the retina parts

205
Q

What can cause pathological separation of the neural retina from the pigment epithelium?

A

Trauma
degenerative changes
Vitreous traction
hole/tear

206
Q

What does the separation of the neural retina from the pigment epithelium represent?

A

Reopening of the lumen of the embryonic optic vesicle

207
Q

Which structure separates the neural retina into two halves?

A

outer plexiform layer

208
Q

Which artery supplies the inner vitreal half of the retina?

A

Central retinal artery

209
Q

Fill in the blank: The attachment of the neural retina is particularly weak in the region just posterior to the _______.

A

Ora serrata

210
Q

What supplies the outer half of the sensory retina?

A

Choroid capillaries derived from the ciliary vasculature

The outer half of the sensory retina contains no blood vessels.

211
Q

Why does retinal degeneration occur in retinal detachment?

A

neural retina separated from underlying choroidal vascular supply

This produces outer retinal degeneration.

212
Q

Where do complete or partial central artery occlusions most commonly occur? why?

A

At the level of the lamina cribrosa.
Bc here central retinal artery is like a medium sized artery adn subject to atherosclerosis, whereas four major fundus vessels are like arterioles

This is just before the artery enters the retina.

213
Q

What is seen with the ophthalmoscope in the presence of disease changes in the arteriolar wall?

A

Nickings or narrowing of the venous blood column

This occurs as the arterioles cross internal to the venules.

214
Q

What is the result of complete central artery occlusion?

A

Sudden onset of unilateral blindness

This is a critical clinical sign.

215
Q

What occurs in branch arteriole occlusion?

A

Partial loss of sight corresponding to the sector supplied by the arteriole

This indicates localized retinal issues.

216
Q

How long must total arterial occlusion last to produce irreversible retinal degeneration?

A

About 1½ hours

This is a crucial time frame for potential recovery.

217
Q

Where do changes begin in the retina due to central artery occlusion?

A

In the inner vitreal half of the retina

These changes are clinically seen as white discoloration of the fundus.

218
Q

What remains unaffected by central artery occlusion?

A

The outer half of the foveal retina

It is nourished by the underlying capillaries of the chorion.

219
Q

What clinical appearance is observed surrounding the fovea centralis in retinal artery occlusion?

A

A rounded red area surrounded by grayish-white discolored retina

This indicates the preservation of the foveal area despite occlusion.

220
Q

Which nerves in the visual pathway are considered first order neurons?

A

bipolar cells

FRCOphth part 1 Anatomy Eyeball (10 decks)

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