Retina Flashcards
Page 158-176 (220 cards)
1
Q
What is the retina?
A
The internal layer of the eyeball where the optical image is formed
2
Q
What occurs in the retina that leads to the creation of nerve impulses?
A
Photo-chemical transduction
3
Q
What is the thickness of the retina at the optic disc?
A
0.56 mm
4
Q
What is the thickness of the retina at the ora serrata?
A
0.1 mm
5
Q
Where is the retina thinnest?
A
At the center of the fovea
6
Q
What does the retina become continuous with posteriorly?
A
The optic nerve
7
Q
What is the retina continuous with anteriorly?
A
Epithelium of the ciliary body and iris
8
Q
What is the outer surface of the retina in contact with?
A
Bruch’s membrane of the choroid
9
Q
What is the inner surface of the retina in contact with?
A
The vitreous body
10
Q
Where is the retina firmly attached?
A
At the margins of the optic disc and at the anterior termination of ora serrata
11
Q
What is the ora serrata?
A
The anterior edge of the retina that forms a wavy ring
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
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
14
Q
What are the two layers of the retina?
A
An outer pigmented layer and an inner neurosensory layer
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
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
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
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
19
Q
What happens to both layers of the retina at the iris?
A
Become pigmented and continue onto posterior surface of iris
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.
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.
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.
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.
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.
25
What is the retinal pigment epithelium (RPE)?
A single layer of cells extending from the optic nerve to the ora serrata
## Footnote
It continues forward as the pigmented ciliary epithelium.
26
What shape do the cells of the RPE take on tangential section?
Hexagonal
They are tall and narrow in the posterior region and flattened near the ora serrata.
27
Describe the structure of the basal ends vs the apical ends of the cells of the RPE
Basal end - infolded, rests on basement membrane
apical - multiple microvilli 5-7microns long
28
What structures do the microvilli of the RPE cells project between? Do they have special attachments?
The outer segments of the rods and cones
No special attachments
## Footnote
These microvilli are involved in the interaction with photoreceptor cells.
29
What is the role of glycosa-minoglycans in the RPE?
They may act as an adhesive binding the pigment layer to the neural layer
## Footnote
This helps maintain structural integrity in the retina.
30
What are the zonula adherens and zonula occludens?
Types of tight junctions in the RPE
## Footnote
They maintain the isolation of the retina from systemic circulation.
31
Where are cell nuclei in the RPE cells?
They occupy the basal part of the cytoplasm
## Footnote
This positioning is important for cellular function.
32
Describe which organelles are found in RPE cells
- nuclei near basal aspect
- melanin granules (lots), extend into microvilli
- granular and agranular enoplasmic reticulum
- golgi apparatus
- LOTS of lysosomes = Phagosomes
33
What happens to the outer ends of the rods in relation to the RPE?
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
## Footnote
The
34
Role of pigmented cells
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.
35
What mechanism do pigment cells use to absorb light?
Antireflection mechanism
## Footnote
This mechanism prevents the return of light into the photoreceptive layer of the neural retina, which would result in a loss of image sharpness.
36
What are the two main components developed from the optic cup?
* Pigmented epithelium (outer layer)
* Rods and cones (inner layer)
37
What separates the RPE from the rods + cones? Where is this derived from?
Potential space, constitues remains of cavity of optic vesicle
38
What condition occurs when the layers of the retina become separated?
Detached retina
## Footnote
This condition can occur despite the layers being very close together.
39
What is the Blood-Retina Barrier?
A barrier formed by tight junctions between pigment epithelial cells
## Footnote
This barrier limits ion flow and prevents large toxic molecules from diffusing from choroid capillaries to photoreceptors.
40
What is a characteristic of albinism in the eye?
Lack of melanin pigment in pigment cells (ie still have normal number of pigment cells, but MELANIN is low)
## Footnote
This condition leads to transillumination of the iris, allowing visualization of the ciliary processes and lens.
41
In oculocutaneous and ocular albinism, what is observed during clinical examination?
* Iris is transparent (transillumination)
* Pupil appears red
* Fundus is light red
* Retinal and choroidal vessels visible against white sclera
## Footnote
Despite the normal number of pigment cells, melanin pigment is deficient.
42
Fill in the blank: The _______ is a condition where the layers of the retina become separated.
Detached retina
43
True or False: The Blood-Retina Barrier allows large toxic molecules to pass freely from the choroid capillaries to the photoreceptors.
False
## Footnote
The Blood-Retina Barrier is designed to prevent this diffusion.
44
What is the neural retina embryologically derived from?
The inner layer of the optic cup
45
Name the three main groups of neurons in the neural retina.
* Photoreceptors
* Bipolar cells
* Ganglion cells
and horizontal, amacrine and supporting cells
46
What are the two types of photoreceptors?
* Rods
* Cones
47
What are the functions of rods in vision?
Responsible for vision in dim light and produce images of varying shades of black and white
48
Which nerves in the visual pathway are considered to be akin to relay neurons?
Ganglion cells. Also considered to be second order neurons.
49
What is the primary function of cones?
Adapted to bright light and can resolve fine details and color vision
50
How many rods are estimated to be in the retina?
About 110 to 125 million
51
What is the estimated number of cones in the retina?
6.3 to 6.8 million
52
Where are rods absent in the retina?
At the fovea.
Rise in number toward periphery and then dimish at the extreme periphery.
53
What is the density of rods at the extreme periphery of the retina?
About 30,000 rods per square millimeter
54
Where are cones most dense in the retina?
At the fovea. Numbers decrease towards periphery.
55
What is the approximate number of ganglion cells in each retina?
About 1 million
56
How many photoreceptor cells are estimated to activate a single ganglion cell?
About 100 photoreceptor cells
57
What do the axons of ganglion cells form after passing through the lamina cribrosa?
The optic nerve
58
What type of cells form the myelin sheaths of ganglion cell axons?
Oligodendrocytes
NOT schwann cells
59
True or False: The optic nerve is comparable to a tract within the peripheral nervous system.
False. It is comparable to a tract in the CENTRAL nervous system.
60
What is the role of the lateral geniculate body in the visual pathway?
Most axons terminate by synapsing with nerve cells
61
What type of neurons are formed by the nerve cells of the lateral geniculate body?
Third-order neurons
62
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 _______.
[sensory pathways]
63
Name the three main parts of a photoreceptor cell
Outer segment (name describes shape of this part, eg rod vs cone)
connecting stalk
Inner segment
64
What are the two types of photoreceptor cells in the retina?
Rods and cones
## Footnote
Rods are responsible for vision in low light, while cones are responsible for color vision and detail.
65
What is the primary function of the outer segment of rod cells?
It is the true photoreceptor of the cell containing rhodopsin (light-sensitive pigment crucial for vision.)
## Footnote
Rhodopsin is a light-sensitive pigment crucial for vision.
66
How long are rod cells approximately?
100 to 120 micrometers long
## Footnote
This length contributes to their function in the phototransduction process.
67
What structures do the outer segments of rod cells contain?
600 to 1000 membrane-bound transversly arranged lamellae (discs)
## Footnote
These discs are crucial for the phototransduction process.
68
What is the diameter of each disc in the outer segment of rod cells and how thick is each disc?
Approximately 2 microns
The thickness of each disc is about 14 nanometers.
## Footnote
The thickness of each disc is about 14 nanometers.
69
What happens to the discs at the tip of the rod cell's outer segment?
They are phagocytosed by the cells of the pigment epithelium
## Footnote
This process is part of a 24-hour cycle of disc shedding.
70
When does the majority of disc shedding occur in rod cells?
Most shed at once in the early morning
## Footnote
This cyclical shedding is part of the rod cells' renewal process.
71
What is found in the connecting stalk of rod cells? How does it differ to other similar structures found in the body.
A modified cilium - it has the nine doublet microtubules but lacks a central pair.
72
What is the basal body of rod cells?
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.
73
True or False: A slight degree of transillumination of the iris is a normal finding in approximately 10 percent of the population.
True
## Footnote
This finding is considered normal and not indicative of any pathology.
74
What are the two areas of the inner segment of a rod cell called? How are they orientated?
Ellipsoid and myoid
Ellipsoid = next to connecting stalk, myoid = closer to vitreous
75
What structures are contained in the ellipsoid of the inner segment?
Basal body and numerous mitochondria
76
What is contained in the myoid of the inner segment?
Granular and agranular endoplasmic reticulum, free ribosomes, Golgi apparatus
77
What connects the inner segment to the cell body in rod cells?
Rod outer fiber
78
What does the rod inner fiber contain?
Numerous microtubules
79
What is the name of a rod cell's synaptic ending? What shape does it have and what does it contain?
Rod Spherule. Pear-shaped and contains many presynaptic vesicles
80
With which type of cells does the rod spherule synapse?
Bipolar cells
81
What is the length of cone cells?
About 65 to 75 microns
82
How does the outer segment of cone cells differ from that of rod cells?
Conical and wider at the base, tapering to a rounded tip
83
What is unique about the membranes of the discs in cone cells compared to those in rods?
Continuous with the outer plasma membrane
84
Are the tips of cone cells phagocytosed by pigment cells?
No (UNLIKE RODS!!)
=> lamallae are continuous with extracellular space
85
What are the photochemicals found in cones called?
Iodopsins
86
Where are the photosensitive pigments in rods and cones found?
Incorporated into the disc membrane
87
What connects the outer segment of cone cells to the inner segment?
Connecting stalk containing Modified cilium (9 doulet microtubules but missing central pair)
88
Are the inner segments of rods and cones similar?
YES!
89
What does the body of cone cells contain?
Large, pale-staining nucleus
90
What is the name of the synaptic ending of cones?
Cone pedicle
91
What type of cells do bipolar cells synapse with?
Photoreceptor cell terminals
92
Describe the orientation of bipolar cells.
Radial orientation
93
What is the function of rod bipolar cells?
Connect several rod cells to one to four ganglion cells
94
What do flat or diffuse bipolar cells connect?
Many cone cells with many ganglion cells
95
Which cell types do midget bipolar cells connect?
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
Where are ganglion cells located?
Inner part of the retina
97
What is the diameter range of ganglion cells?
10 to 30 microns.
Most are small cells, but a few are latge
98
How many layers of ganglion cells are found in retina vs the macula?
Retina = single, Macula = up to 10 layers
99
What type of neurons are ganglion cells?
Non-myelinated multipolar cells (=> one axon, multiple dendites)
100
Which cell types do ganglion cells synapse with?
Dendites synapse with axons of bipolar and amacrine cells
Midget ganglion cells linked by midger bipolar cells to a single cone cell
101
What happens to ganglion cell axons when they reach the inner surface of the retina?
They make a right-angled turn and converge at exit of optic nerve at optic disc
102
What is the site called where optic nerve fibers pass through the sclera?
Lamina cribrosa
103
What type of cells are horizontal cells?
Multipolar neurons
104
What is the length of the long process of horizontal cells?
Up to 1 mm
105
How many cone spherules do horizontal cells synapse with?
Have synaptic junctions with seven cone pedicles
106
How many rod spherules do horizontal cells associated with rods synapse with?
10 to 12 rod spherules
107
The ganglion cells' axons become myelinated after piercing which structure?
Lamina cribrosa
108
True or False: The ganglion cells are the first neurons in the visual pathway.
False
109
Fill in the blank: The cytoplasm of horizontal cells contains an organelle called _______.
Kolmer's crystalloid (tubular membranes covered by ribososmes)
110
What is the role of horizontal cells?
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
What inhibitory transmitter is released by rods and cones following excitation by light?
Gamma-aminobutyric acid (GABA)
112
What is the role of GABA in the retina?
Inhibits the activity of bipolar cells, sharpening contrast and increasing spatial resolution
113
What is the primary function of horizontal cells in the retina?
Integrate visual stimuli
114
Describe the appearance of amacrine cells
- Large cell bodies
- abundant cytoplasm
- lobulated indented nuclei
- no axons
- long processes (that synapse with other cells)
115
Where are amacrine cells located in the retina?
Close to the ganglion cells
116
What do amacrine cells synapse with?
Each other, dendrites of ganglion cells, and axonal endings of bipolar cells
117
What stimulates amacrine cells?
Which cells do amacrine cells stimulate?
Stimulated by bipolar cells
Stimulate ganglion
118
Describe the structure of muller cells
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
What is the function of Müller cells in the retina?
Support nerve cells and fill space not occupied by neurons
120
What structure is traditionally called the outer limiting membrane?
A row of zonulae adherentes between photoreceptor cells and Müller cell processes
*Note - outer limiting membrane is a misnomer*
121
What forms the inner limiting membrane in the retina?
Expanded Müller cell terminations covered by a basement membrane
122
What role do Müller cells play regarding blood capillaries?
Make extensive contacts with the walls of blood capillaries
123
What are some functions of Müller cells?
Support neurons, assist in nourishing retinal neurons, uptake neurotransmitters, electrical insulation
124
What are retinal microglial cells known for?
Phagocytic function and probable immunologic functions
125
How many layers is the retina traditionally said to be composed of?
10 layers
126
Fill in the blank: The _____ cells are glial-like cells found in the retina.
Müller
127
What are the ten layers of the retina?
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
## Footnote
The layers are functional components and may not represent real layers upon electron microscopy examination.
128
What does the outer nuclear layer consist of?
The nuclei of the rod and cone cells
## Footnote
The outer nuclear layer plays a crucial role in phototransduction.
129
What is the composition of the outer plexiform layer?
Synapses between the terminal processes of the rod and cone cells, bipolar cells, and horizontal cells
## Footnote
This layer is essential for the processing of visual information.
130
What is contained in the inner nuclear layer?
Nuclei of the bipolar cells, horizontal cells, amacrine cells, and Müller cells
## Footnote
The inner nuclear layer is involved in the integration of visual signals.
131
What is the function of the inner plexiform layer?
Synaptic connections between the bipolar, amacrine, and ganglion cells
## Footnote
This layer is critical for transmitting visual signals to the brain.
132
What comprises the ganglion cell layer?
Nuclei of the ganglion cells
## Footnote
Ganglion cells are the final output neurons of the retina.
133
What does the nerve fiber layer consist of?
Axons of the ganglion cells converging toward the optic disc
## Footnote
This layer is important for transmitting visual information to the optic nerve.
134
What is the macula lutea?
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
## Footnote
The macula is crucial for high acuity vision.
135
What causes the yellow coloration of the macula lutea?
A yellow carotenoid pigment called xanthophyll
## Footnote
This pigment is present in the retinal layers from the outer nuclear layer inward.
136
What is the fovea centralis?
A depressed area in the center of the macula lutea measuring about 1.5 mm in diameter
## Footnote
The fovea is where visual acuity is highest due to its structure.
137
What are the sides and floor of the fovea called?
Sides = clivus, floor = foveola
138
Why is the fovea depressed?
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
What is the significance of the arrangement of cells in the fovea centralis?
It allows greater access of incoming light to the photoreceptors
## Footnote
This arrangement contributes to the fovea's ability to provide the most distinct vision.
140
How many cones are present per square millimeter in the fovea?
147,000 cones per square millimeter
## Footnote
This high density of cones is essential for detailed vision.
141
Where is the optic disc located relative to the macula lutea?
About 3 mm medially to the macula lutea
## Footnote
The optic disc is also known as the blind spot because it contains no photoreceptors.
142
What is the appearance of the optic disc?
Pale pink or almost white, measuring about 1.5 mm in diameter
## Footnote
The optic disc is the point where the central retinal vessels enter and leave the eye.
143
Describe the edge vs the central part of the optic disc. Where do the central retinal vessels enter and leave the eye?
Edge = slightly raised, centre = slightly depressed. Central retinal vessels enter and leave eye in depression.
144
True or False: The fovea centralis contains rod cells.
False
## Footnote
The fovea has no rod cells, only cones, which enhances visual acuity.
145
What happens at the optic disc?
The optic nerve fibers exit the eye by piercing the sclera.
146
What is a consequence of a rise in pressure inside the eyeball?
The lamina cribrosa can bulge out.
147
What effect does an increase in cerebrospinal fluid pressure have on the optic disc?
It may cause the optic disc to bulge into the eyeball.
148
What is believed to cause the swelling of the optic disc?
External pressure on the optic nerve impeding axon flow.
149
Are optic nerve fibres myelinated?
Posterior to the optic disc, the fibers are myelinated; anterior to the disc, they are nonmyelinated.
150
What is the significance of the absence of rods and cones at the optic disc?
It is insensitive to light and is referred to as the blind spot.
151
What is the ora serrata?
The scalloped anterior margin of the retina.
152
Fill in the blank: The _______ is the area where the nervous tissues of the retina end.
ora serrata
153
What part of the retina extends forward from the ora serrata?
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
What are the two layers of cells on the posterior surface of the iris?
Both layers of cells are pigmented
## Footnote
The anterior part of the retina consists of a single layer of pigment cells and a deeper layer of nonpigmented columnar epithelium.
155
How far is the ora serrata from the limbus?
About 8.5 mm
Nasally, it is 1 mm closer to the root of the iris than on the temporal side.
156
What are the two sources of blood supply to the retina?
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
## Footnote
The outer laminae include the rods and cones and outer nuclear layer.
157
What type of arteries are the retinal arteries described as?
Anatomic end arteries
## Footnote
There are no arteriovenous anastomoses in the retina.
158
True or False: The integrity of the retina depends on both the choidal vessels and central retinal vessels.
True
## Footnote
Neither the choroidal capillaries nor the central artery and vein alone is sufficient for the retina's integrity.
159
Fill in the blank: The outer laminae of the retina are supplied by _______.
choroidal capillaries
## Footnote
Tissue fluid exudes between the cells of the outer laminae.
160
Fill in the blank: The inner laminae of the retina are supplied by _______.
central artery and vein
## Footnote
These vessels play a crucial role in the blood supply to the inner layers of the retina.
161
What is the first branch of the ophthalmic artery?
The central retinal artery
162
What is the diameter of the central retinal artery?
About 0.3 mm
163
How does the central retinal artery run forward to eye?
Adherant to dural sheath of optic nerve
164
Where does the central retinal artery enter the optic nerve?
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
What coverings does the central retinal artery obtain after piercing the dura and arachnoid?
A covering from both the dura and arachnoid
166
What happens to the central retinal artery within the sub-arachnoid space?
It bends forward and then turns at a right angle to enter the optic nerve
167
What does the central retinal artery acquire upon entering the optic nerve?
A sheath derived from the pia mater
168
What surrounds the central retinal artery as it reaches the center of the optic nerve?
A sympathetic plexus and the central vein
169
What does the central retinal artery pierce to enter the eyeball?
The lamina cribrosa
170
What forms an anastomotic circle in the sclera around the optic nerve?
The posterior ciliary arteries
171
What do small branches from the posterior ciliary artery anastomotic circle supply?
The optic disc and the adjacent retina
172
What is the occasional larger connection between the posterior ciliary arteries and the central retinal artery called?
Cilioretinal artery
173
How does the central retinal artery divide after entering the eyeball?
Into two equal superior and inferior branches
174
What branches do the superior and inferior branches of the central retinal artery further divide into?
Superior and inferior nasal and temporal branches
175
Where does the last division of the central retinal artery take place?
Either inside the optic nerve or on the surface of the optic disc
176
Where do the branches of the central artery and vein usually emerge from the optic disc?
Usually toward the nasal side
177
Is there any overlap or anastomosis between branches within a quadrant of the retina?
No - each quadrant supplied by own branch of central retinal artery
178
Describe the course of the nasal branches of the central retinal artery.
They run a relatively straight course toward the ora serrata
179
Describe the course of the temporal branches of the central retinal artery.
They arch above and below the fovea centralis and then pass to the ora
180
Where do the arterial branches run in the retina?
In the nerve fiber layer close to the internal limiting membrane
(This membrane serves as the basement membrane of the Müller cells.)
181
What is the internal limiting membrane characterized by?
It is extremely thin and transparent
## Footnote
This transparency allows retinal blood vessels to be seen with the ophthalmoscope.
182
To which layer do the arterioles in the retina reach?
The internal nuclear layer
183
Do the retinal arterioles have anastomoses?
No
184
What structural feature is absent in retinal arterioles compared to typical arterioles?
Internal elastic lamina
185
Where are smooth muscle cells found in the retinal arterioles?
In the tunica adventitia
186
What do the arterioles give rise to in the retina?
A diffuse capillary network
187
What type of endothelial cells line the walls of the retinal capillaries?
Nonfenestrated endothelial cells
188
What are located outside the endothelial layer of retinal capillaries?
Pericytes
189
What is the foveal avascular zone?
A capillary-free zone approximately 500microns in diameter
190
Where are the capillary networks most concentrated in the retina?
In the macula
191
What happens to the diameter of the avascular zone in diabetes mellitus?
It becomes enlarged
192
How do the numbers of capillaries change at the periphery of the retina?
They are less numerous
193
At what location are capillaries absent in the retina?
At the ora serrata and the foveal avascular zone
194
What type of nerve fibers innervate the arteries of the retina?
Sympathetic postganglionic fibers
195
What mechanism protects the retina from circulating molecules of large size?
Presence of nonfenestrated endothelium of capillaries and tight junctions of RPE
196
How does the diameter of the central vein of the retina (and its branches) compare to that of their corresponding artery?
About one-third to one-fourth larger
197
Where do the veins lie in relation to the arteries in the retina?
deep to the arteries (ie arteries are closer to vitreous and cross over veins)
198
What forms the central vein of the retina?
Tributaries that accompany the arteries
199
Where does the central vein of the retina leave the eyeball?
Through the lamina cribrosa (lateral to central retinal artery)
200
Which structure does the central vein of the retina drain into?
Cavernous sinus or superior ophthalmic vein
201
What protects the outer third of the neural retina from large molecular toxic substances?
Zonulae occludentes between RPE and pigment layer
202
What is absent in the retina regarding lymphatic vessels?
No lymphatic vessels
203
Where is the neural retina firmly attached to the underlying pigment epithelium?
At the optic disc and the ora serrata
204
What three factors keep the two neural retina and the pigment epithelium in apposition?
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
What can cause pathological separation of the neural retina from the pigment epithelium?
Trauma
degenerative changes
Vitreous traction
hole/tear
206
What does the separation of the neural retina from the pigment epithelium represent?
Reopening of the lumen of the embryonic optic vesicle
207
Which structure separates the neural retina into two halves?
outer plexiform layer
208
Which artery supplies the inner vitreal half of the retina?
Central retinal artery
209
Fill in the blank: The attachment of the neural retina is particularly weak in the region just posterior to the _______.
Ora serrata
210
What supplies the outer half of the sensory retina?
Choroid capillaries derived from the ciliary vasculature
## Footnote
The outer half of the sensory retina contains no blood vessels.
211
Why does retinal degeneration occur in retinal detachment?
neural retina separated from underlying choroidal vascular supply
## Footnote
This produces outer retinal degeneration.
212
Where do complete or partial central artery occlusions most commonly occur? why?
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
## Footnote
This is just before the artery enters the retina.
213
What is seen with the ophthalmoscope in the presence of disease changes in the arteriolar wall?
Nickings or narrowing of the venous blood column
## Footnote
This occurs as the arterioles cross internal to the venules.
214
What is the result of complete central artery occlusion?
Sudden onset of unilateral blindness
## Footnote
This is a critical clinical sign.
215
What occurs in branch arteriole occlusion?
Partial loss of sight corresponding to the sector supplied by the arteriole
## Footnote
This indicates localized retinal issues.
216
How long must total arterial occlusion last to produce irreversible retinal degeneration?
About 1½ hours
## Footnote
This is a crucial time frame for potential recovery.
217
Where do changes begin in the retina due to central artery occlusion?
In the inner vitreal half of the retina
## Footnote
These changes are clinically seen as white discoloration of the fundus.
218
What remains unaffected by central artery occlusion?
The outer half of the foveal retina
## Footnote
It is nourished by the underlying capillaries of the chorion.
219
What clinical appearance is observed surrounding the fovea centralis in retinal artery occlusion?
A rounded red area surrounded by grayish-white discolored retina
## Footnote
This indicates the preservation of the foveal area despite occlusion.
220
Which nerves in the visual pathway are considered first order neurons?
bipolar cells
