THE RETINA Flashcards
(89 cards)
1
Q
Which 5 of the following retinal layers are supplied by the central retinal artery?
A
Inner plexiform layer Internal limiting membrane Ganglion cell layer Nerve fiber layer Inner nuclear layer
2
Q
Which of the following junction types creates the outer blood retina barrier?
A
Zonula occludens
3
Q
Consider the image. Which of the following photoreceptor components is being highlighted by the red arrow?
A
Outer segment
other answers include connecting stalk, inner segment, pedicle, spherule, cell body
4
Q
Amacrine cells synapse with which 3 of the following cells in the inner plexiform layer?
A
Interplexiform cells, ganglion cells, bipolar cells
5
Q
Muller cells extend between which 2 of the following retinal layers?
A
Internal limiting membrane, External limiting membrane
6
Q
The external limiting membrane is composed of which type of junction?
A
Zonula adherens
7
Q
Which 3 of the following components are found at rod synaptic sites?
A
Horizontal cell, bipolar cell, spherule
8
Q
Which 4 of the following cells make connections in the inner plexiform layer?
A
Interplexiform cells, amacrine cells, bipolar cells, ganglion cells
9
Q
The loss of the foveal light reflex is a result of which of the following retinal layers thickening with age?
A
Internal limiting membrane
10
Q
Which 6 of the following retinal layers are found at the fovea?
A
Outer nuclear layer, photoreceptor layer, internal limiting membrane, external limiting membrane, retinal pigmented epithelium, outer plexiform layer
11
Q
What are exudates?
A
Lipids and proteins that collect from the plasma of leaking blood vessels
12
Q
Which of the following cells have extended processes that form Henle’s fiber layer?
A
Cone photoreceptors
13
Q
Zonula occluden junctions at which of the following locations forms the inner blood retina barrier?
A
Endothelium of the retinal capillaries
14
Q
Which of the following locations best describes the position of the deep capillary network?
A
Inner nuclear layer near the outer plexiform layer
15
Q
Development of retinal microaneurysms is due to the loss of which of the following cells?
A
Pericyte cells
16
Q
The central retinal vein will most likely drain into which of the following structures?
A
Cavernous sinus
17
Q
Which of the following vessels is NOT supplied by the central retinal artery?
A
Cilioretinal artery
(other choices include deep capillary network, superficial capillary network, radial peripapillary capillary plexus)
*It is supplied by the SPCA
18
Q
The equator of the eyeball can be identified clinically when viewing which of the following structures?
A
Vortex ampullae
19
Q
Flame and dot/blot retinal defects can be found in which layer of the retina?
A
Flame = nerve fiber layer Dot/blot = inner nuclear layer
20
Q
Consider the image. The highlighted hemorrhages are most likely due to damage of which of the following retinal vascular supplies?
A
Deep capillary network (red dots on pale fundus photo)
other choices: central retinal artery branch, choriocapillaris, superficial capillary network
21
Q
Consider the image. Which of the following layers is being highlighted by the arrow?
A
Inner nuclear layer
22
Q
Which neurons synapse in the OPL and with which cells? In the IPL?
A
The OPL contains the synaptic connections between the photoreceptor terminals and bipolar cell dendrites + horizontal cell processes; also contains processes of Muller cells
In the inner plexiform layer bipolar cell terminals (ribbon synapses) contact ganglion cell dendrites and amacrine cell processes; also contains processes of Muller cells
23
Q
What forms the ELM?
A
It is a dense-staining line that appears to separate the INNER SEGMENTS of rods/cones from outer nuclear layer. It is not a true membrane, as it is merely composed of ZONULA ADHERENS junctions between Muller cells + inner photoreceptor segments and between Muller cells themselves
24
Q
Blood supply to the outer retinal layers is provided by ______
The inner retinal layers are supplied by the _________
A
Choriocapillaris; Central Retinal Artery
25
You look at the retina and see gray-green colored blood. Where is the blood located in the eye?
Between _________ & ________
Why?
Between Bruch's membrane and the RPE; it appears gray-green because the clinician is looking at the blood through the pigment of the RPE. The source of blood is the choriocapillaris, and probably leaked through Bruch's membrane.
26
How are RPE cells and photoreceptor outer segments held together?
The space between the RPE cells and outer segments of the rods/cones is called the "intraretinal space".
RPE cells and photoreceptor outer segments remain in close approximation to each other across the intraretinal space due to several factors including lOP, presence of the vitreous, interdigitations of the RPE cell microvilli with the photoreceptor outer segments, and the presence of a material in the intraretinal space, called interphotoreceptor matrix (IPM).
27
What structures lie in the nerve fiber layer of the retina? Be complete; include blood vessels.
Axons from the ganglion cell layer and Muller cell processes. The ganglion cell axons are arranged in arcades delineated by the Muller cells. While in the NFL, ganglion cells are unmyelinated. They are myelinated after they exit the lamina cribosa.
Throughout the retina, retinal vessels also lie in the nerve fiber layer. These are the tiny branches coming from the CRA and have a strong adhesion to the ILM.
28
What are the differences between rod spherule and cone pedicle in terms of the structures that extend into their invaginating sites? Include numbers of processes and which cells' processes are located in the center vs. periphery of the invaginating site.
In general, the cone pedicles are much larger than the rod spherules.
At the rod synaptic site in the OPL, the rod spherule is invaginated by: 2 horizontal cell processes (from two different horizontal cells) and 1-4 different rod bipolar cell dendrites. The rod bipolar cell dendrite(s) are the central element and the horizontal cell processes are located on either side (creating the "surround" of a bipolar cell's receptive field).
At cone synaptic sites, there are 2 TYPES of synaptic sites: (1) invagination synaptic sites (there are more of these due to size of pedicle) and (2) flat synaptic sites. The central element is the dendrite of an invaginating midget bipolar cell. Laterally, there are processes coming from 2 horizontal cells.
- While cones only have one bipolar cell dendrite at a synaptic site, rods can have up to 4 central bipolar dendrites at a synaptic site.
- Invaginating midget bipolar cells are "on" bipolar cells
- Flat midget bipolar cells (FMB) are "off" bipolar cells
29
Which cells contact the flat synaptic sites of cone pedicles? Are these "on" or "off" cells?
At flat cone synaptic sites, dendrites of flat midget bipolar cells (FMB) contact the flat base of the cone pedicle. Flat midget bipolar cells are "off" bipolar cells.
30
What forms the ILM of the retina?
How does the ILM change with age?
Why does the foveal light reflex "dim" with increased age?
The innermost layer of the retina (ILM) is formed by the basement membrane (basal lamina) of the expanded terminations (footplates) of the Muller cells. It is made of type 4 collagen and proteoglycans.
When light reflects off the ILM, it gives the posterior retina a white "sheen" evident in young patients, seen as a circular white macular reflex. The sheen is less evident in older individuals, because the ILM thickens with age.
Thickness of the ILM can also cause the foveal reflex to dim.
31
How is RPE involved in the blood retinal barrier?
Selective transport of substances between neural retina and choroidal circulation (via blood-retinal barrier formed by the zonula occludens junctions of RPE)
32
Which cells have cell bodies in the inner nuclear layer (INL)? What structures lie in the outer nuclear layer (ONL)?
The INL contains the cell bodies and nuclei of bipolar, horizontal, amacrine, interplexiform & Müller cells
The ONL contains the cell bodies and nuclei of rod/cone photoreceptors and the processes of Muller cells.
33
What causes the white sheen on the retinas of young children?
See previous question (right reflected off the thin ILM of the retina)
34
When a retinal detachment occurs, WHY does the RPE stay with the choroid and not detach with the other 9 retinal layers?
Fine filaments from the basement membrane of the RPE cells merge with collagen fibrils in the inner collagenous zone of Bruch’s membrane, which helps maintain a strong adhesion between the RPE cells of the retina and Bruch’s membrane, as seen with a retinal detachment (i.e. the detachment occurs between the RPE cells & photoreceptors: RPE cells remain attached to Bruch’s membrane)
35
Where is the retina thinnest?
The retina is thinnest at the ora serrata and thickest near the optic disc.
36
(CO) 1. Name the 10 layers of the retina and in the proper order
Internal to external
1. Internal Limiting Membrane
2. Nerve Fiber Layer (axons of ganglion cells)
3. Ganglion cell layer (cell bodies of ganglion cells)
4. Inner plexiform layer (area of synapse of bipolar cell terminals with ganglion cell dendrites and amacrine cell processes)
5. Inner nuclear layer (cell bodies of bipolar, horizontal, amacrine, interplexiform, and Muller cells)
6. Outer plexiform layer (areas of synapses between photoreceptor terminas, bipolar cell dendrites, and horizontal cell processes)
7. Outer nuclear layer (cell bodies of photoreceptors)
8. External (outer) limiting membrane
9. Photoreceptor layer (inner and outer segments of photorceptors)
10. Retinal pigmented epithelium
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(CO) 2. Know where the retina is thickest and thinnest
see previous question
38
(CO) 3. Know where a retinal detachment occurs (i.e. which layers are separated) and why there?
▪ Know what the RPE cells are tightly attached to & how the RPE is attached to it!
see previous question
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(CO) 4. **Describe the contents of all 10 layers of the retina. Additionally be sure to include:
▪ Names of the cells whose cell bodies are present in the ONL, INL & GCL
▪ Which processes of which cells synapse in the OPL and IPL
▪ What the photoreceptor layer (layer of rods and cones) contains
▪ What the nerve fiber layer (NFL) contains
▪ What layers of the retina do the retinal neurons & Muller cells extend through?
▪ Functions of Muller cells
▪ Where (and with what cells) the Muller cells have zonula occludens junctions and zonula
adherens junctions
▪ What the ILM (overlying retina) & ELM are formed by and their location?
▪ What forms the ILM over the optic disc and why?
▪ Contents of the layer of rods and cones (=photoreceptor layer)
▪ Names of the cells whose cell bodies are present in the ONL, INL & GCL
ONL: cell bodies (and nuclei) of rod/cone photoreceptors + processes of Muller cells
INL: cell bodies and nuclei of bipolar, horizontal, amacrine, interplexiform & Müller cells
GCL: cell bodies of ganglion cells + Muller cell processes
▪ Which processes of which cells synapse in the OPL and IPL
OPL: synaptic connections between photoreceptor terminals + bipolar cell dendrites + horizontal processes + processes of Muller cells
IPL: synapse of bipolar cell terminals with ganglion cell
dendrites & amacrine cell processes
▪ What the photoreceptor layer (layer of rods and cones) contains
inner & outer segments of the rods and cones
▪ What the nerve fiber layer (NFL) contains
axons of ganglion cells
▪ What layers of the retina do the retinal neurons & Muller cells extend through?
Extend from the external limiting membrane (ELM) to the internal limiting membrane (ILM))
▪ Functions of Muller cells
– Provide structural support & help maintain alignment of retinal neurons
– Provide insulation for the photoreceptors and neurons
– Help maintain extracellular pH
– Play a role in retinal metabolism (metabolize, synthesize & store glycogen)
▪ Where (and with what cells) the Muller cells have zonula occludens junctions and zonula adherens junctions
End feet contact exist between Müller cells & retinal neurons, except at the ELM where zonula adherens junctions lie between Müller cells & photoreceptor inner segments & between adjacent Müller cells
▪ What the ILM (overlying retina) & ELM are formed by and their location?
ILM: formed by the basement membrane (basal lamina) of the expanded terminations (footplates) of the Müller cells (type 4 collagen and proteoglycans)
ELM: composed of zonula adherens junctions between Müller cells & the inner segments of photoreceptors and between adjacent Müller cells
▪ What forms the ILM over the optic disc and why?
The ILM DOES extend over the optic disc as well, but the ILM here is formed by fibrous astrocytes (cells that will support the ganglion cell axons in the optic disc), which replace the Müller cells! Because the retina is NOT present at the optic disc & therefore Müller cells are NOT present!
▪ Contents of the layer of rods and cones (=photoreceptor layer)
The rod and cone photoreceptors both consist of outer and inner segments joined by a connecting stalk, cell body, & a synaptic terminal.
> The inner segment is subdivided into an outer ellipsoid and an inner myoid region
– Ellipsoid -contains numerous mitochondria (energy source)
– Myoid - contains free ribosomes, rough & smooth endoplasmic reticulum, golgi apparatus
The remainder of the photoreceptors is made of the:
– Cell body containing a nucleus
– Terminal ending called:
• Rod spherule (small) • Cone pedicle (large)
40
(CO) 5. Describe the blood supply to the retina: which layers receive blood supply from CRA vs. choroid
see previous question
41
(CO) 6. Describe the RPE cells. Be sure to include anatomy of the cells (contents of apical and basal ends and microvilli), location, functions, location of gap junctions & zonula occludens junctions
▪ Describe how the RPE and sensory retina are held together (junctions? Matrix, how?)
RPE is hexagonal in shape; taller and narrower near macula and flatter near ora serrata
Apex of RPE faces apex of photoreceptors (outer segments), with melanin granules and numerous long microvilli that envelop photoreceptor outer segments.
Basal end has numerous infoldings and is firmly attached to basement membrane forming Bruch's membrane.
There are NO intercellular junctions between the RPE cells and outer segments. Only the microvilli surrounding the outer third of the segments plus other factors (see previous question) keep RPE and photoreceptors together.
42
(CO) 7. Compare rods and cones. Be sure to include:
▪ Synaptic terminals (rod spherule and cone pedicle)
▪ Description of the rod and cone synaptic endings in the OPL, including differences and
similarities in the terminal endings, neuron processes that synapse with them and their location and number in the invagination, how many invaginating sites rod spherules have vs. cone pedicles, etc. Know what region of the cone the flat vs. invaginating midget bipolar cells processes synapse with and which are "on" bipolar cells and which are "off" bipolar cells.
see previous question
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(CO) 8. Describe differences between P and M ganglion cells in terms of functions and which photoreceptor they receive information from.
"P" GANGLION CELLS
– Color vision (since receive input from cones)
– Fine detailed vision (central vision, since found in the fovea)
– Recognition of objects
• “P” ganglion cells have small cell bodies
"M" GANGLION CELLS
The "M" ganglion cells are involved in:
– Less detailed vision since they receive input from rods & cones
– Night vision
– Motion detection
• "M"ganglion cells have large cell bodies
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(CO) 9. How are the ipRGC different from the other ganglion cells? What unique function do they provide especially to someone with damaged photoreceptors?
They are a type of ganglion cell, morphologically distinguished by having larger cell body and extremely large dendritic field. They have melanopsin which absorbs light in the blue portion (like third type of photoreceptor).
They allow patients with poor vision due to photoreceptor disease to still have light sensitivity, plus normal circadian rhythms and preserved pupil light reflex.
45
(CO) 10. Know where ganglion cell axons are first myelinated as they head toward the optic chiasm.
Ganglion cell axons are normally myelinated after they exit the lamina cribrosa
46
(CO) 11. Describe what “myelinated nerve fibers” are and their effects on vision
For a few patients, myelination of the ganglion cells extends to the posterior pole of the eye, appearing as superficial white opacities with feathery edges that can block underlying retinal vessels.
It is a forward continuation of totally normal myelin onto ganglion cell axons anterior to the lamina cribosa, and will not affect vision unless the myelination is very dense. Then, there could be a scotoma.
47
(CO) 12. Where are zonula occludens junctions found within the retina (i.e. what cells are they
interconnecting)?
RPE apico-lateral border: junctional complexes (zonula occludens, adherens, and desmosomes); the occludens lie closest to apex of cells.
Retinal capillaries are also made continuous with a continuous epithelium joined by zonula occulsions, continuous basement membrane, and pericytes.
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(CO) 13. Where are zonula adherens junctions found within the retina (i.e. what cells are they
interconnecting)?
The ELM is composed of zonula adherens junctions between Muller cells and inner segments of photoreceptors + between Muller cells
49
The fovea is supplied with nutrients by the _______
Choriocapillaris vessels
50
The macula is supplied with nutrients by the _______
Choriocapillaris + CRA
51
A sub-retinal hemorrhage is located between these two structures: ______ & ________
The hemorrhage is ______ color because ________
RPE and photoreceptors
The hemorrhage is red in color because the blood lies deep to the sensory retina but anterior to the RPE from the clinician's view
52
A sub-RPE hemorrhage is located between these two structures: ______ &________
The hemorrhage is _______ color because __________________________________
between Bruch's membrane and RPE
| Gray-green in color because the bleeding is deep to the RPE which is heavily pigmented
53
Where are zonula occludens junctions located in the retina? Be specific and complete.
see previous question
54
Flame-shaped hemorrhages are located in this layer of the retina: _________
Why are they that shape?
Dot and blot hemorrhages are located in these layers of the retina:
Why are they that shape?
Flame-shaped hemorrhages are seen in the nerve fiber layer amount patients with hypertensive retinopathy (where NFL is thickest). The hemorrhages have a linear shape because blood is in the NFL and the ganglion cells run horizontally below.
Dot and blot hemorrhages are seen in deeper retinal layers such as the INL and OPL. They appear this way because of the vertical orientation of retinal cells.
55
Pre-retinal hemorrhages are located here:
Anterior or posterior to the ILM depending on the source of blood
POSTERIOR TO ILM: significant bleeding of superficial capillary plexus or damage to branches of CRV/CRA in a PVD due to mechanical tugging
ANTERIOR TO ILM: retinal neovascularization
56
What forms the ILM over the retina?
It is formed by the basement membrane (basal lamina) of the expanded terminations (footplates) of the Müller cells.
57
Which layers of the retina are seen in the fovea?
Retinal layers present in the "fovea" are: RPE, photoreceptor layer, ELM, ONL, OPL & ILM
58
What is Henle's fiber layer and what does it contain?
Processes (axons) of the cones had to elongate & run almost parallel to the retinal surface in the outer plexiform layer (OPL) to maintain their synaptic connections with the bipolar cells and horizontal cells which were displaced. Collectively, the horizontally-oriented cone processes running through the OPL are called Henle’s fibers and this part of the OPL is Henle’s fiber layer (HL)
59
Describe the major characteristics of the fovea that make it the area of highest visual acuity.
The fovea is the area of highest visual acuity in the retina because:
– Only cone photoreceptors are present here
– The cone photoreceptors have the highest packing density here compared to other areas of
the retina (cones are more elongated here compared to cones in other retinal areas)
– there is a 1:1 ratio between cones & ganglion cells here, providing maximum visual discrimination
– Retinal vessels are absent here so there is no blood in front of the cones to absorb & scatter light
60
What is the origin of the cilioretinal artery? What does it supply? Where is it located relative to the optic disc?
The cilioretinal artery is really an arteriole that originates either directly from a short posterior ciliary artery (SPCA) or the choroid; it emerges from the temporal edge of the optic disc (NOT from the optic cup) & travels towards the macula.
In ~15-20% of all eyes, a cilioretinal artery provides additional blood to that part of the retina between the optic disc and the macula called the papillomacular bundle
* If a CRA occlusion occurred in someone with a cilioretinal artery, realize that both the fovea and papillomacular bundle would remain vascularized.
61
The deep capillary plexus is located in this retinal layer__________
The superficial capillary plexus is located in these retinal layers__________
• The superficial capillary network lies in the ganglion cell layer (GCL) and nerve fiber layer (NFL)
• The deep capillary network lies in the inner nuclear layer (INL) near the OPL
• Nutrients will diffuse from the capillaries in these layers to the adjacent layers of
the "inner" retina
62
Exudates in the ________ create a star-like pattern in this part of the retina: __________
Why?
Exudates in Henle's fiber layer create a star-like pattern (macula star) in the OPL of the fovea because of the arrangement of cone processes running horizontally in Henle's fiber layer. Photoreceptors are reaching over to their displaced bipolar cell.
63
Where is the lumen of the CRA narrowest? Be specific?
If the CRA was occluded where it is narrowest, could the distal part of the CRA (anterior to the occlusion) still supply blood to some of the retina or not?
If "yes" then how could the CRA still supply the retina?
The wall of the CRA has focal constrictions at 2 sites along its path:
• One constriction occurs where the CRA
pierces the dura of the three meningeal layers surrounding the optic nerve to enter the optic nerve
– Here the lumen of the CRA is narrowest & this is the most common site for emboli to lodge and lead to a CRA occlusion
Yes; the CRA forms several anastomoses with pial blood vessels originating from other arteries (ophthalmic, recurrent branches of circle of Zinn Haller, CRA, SPCA) which provide blood supply to CRA in event of an occlusion at the site where it pierces the dura of the optic nerve.
64
```
Which layer(s) of the retina do the retinal blood vessels lie in as seen with direct ophthalmoscopy?
What is the histological classification of the blood vessels called the superior and inferior temporal arteries?
```
The retinal vessels visible during ophthalmoscopy are branches of the central retinal artery (CRA) & central retinal vein (CRV) and they lie in the nerve fiber layer of the retina
Note that as the superior nasal & temporal branches and inferior nasal & temporal branches of the CRA entered the retina they further lost their internal elastic membrane and they now have a smaller diameter (~100 μm) so these retinal branches are now histologically classified as arterioles, not arteries.
65
Which cells mop up debris in the retina?
Phagocytic cells such as microglia (tissue injury but without disruption of blood vessels), macrophages (ischemic retinal changes such as diabetic retinopathy), astrocytes (only present in retinal layers containing blood vessels).
Not present in photoreceptor layer, ELM, ONL, OPL, peripheral retina, fovea.
66
If the RPE cells lose some pigment with increased age, what blood vessels would become more visible during ophthalmoscopy of the fundus?
Choroidal vessels are more prominent when the fundus is lighter in color.
67
Are astrocytes present in the retina? What is their function?
YES!
- Form ILM over the fovea (ILM is thickest over fovea)
- structural support by surrounding retinal vessels as part of their adventitia and by filling in spaces not occupied by neurons & their processes
68
When looking with the direct ophthalmoscope, what would be the boundaries of the posterior pole?
Major vascular arcades(?)
69
Why are there no retinal capillaries at the ora serrata?
Because the retinal layers have thinned considerably and 0.5 mm before the ora serrata several layers have disappeared including the NFL, GCL &OPL and the ONL is reduced in thickness with malformed cones replacing rods here.
Any remaining retina is adequately supplied by the choriocapillaris so there is no nutritional need for additional capillaries from the central retinal artery to be here.
70
At what two locations is the central retinal vein at risk of being occluded?
1. at the lamina cribrosa where the CRA & CRV share a common adventitial sheath and pass through a narrow opening in the lamina cribrosa
2. immediately posterior to the lamina cribrosa in the adjacent retrolaminar region.
71
What forms the blood retinal barrier?
The zonula occludens between adjacent RPE cells (forming a blood-retinal barrier) ensure that substances reaching the outer layers of the retina from the choriocapillaris first passed through the RPE cells
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(CO) 1. For the following retinal landmarks know:
▪ Define the posterior pole, including its relative boundaries
▪ The location of the macula relative to the optic disc and its relative diameter
▪ The location of the fovea relative to optic disc and its relative diameter
POSTERIOR POLE
Some authors describe it as the central posterior part of the eye bounded by the major vascular arcades.
The optic nerve exits the back of the eyeball slightly nasal to the posterior pole of the eyeball.
MACULA
clinical term for the oval, yellowish (due to xanthophyll carotenoids) darkened area in the center of the posterior pole
-temporal to the optic disc with avg. diameter 1.5mm (approx. size of optic disc)
FOVEA
macula’s center (floor of macula), retinal layers are thinner, producing a concave indentation, the "fovea", where a "pinpoint light reflex" is seen with ophthalmoscopy (avg. diameter 0.35mm)
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(CO) 2. What is Henle’s fiber layer?
▪ What does it contain?
▪ What is the orientation of the neuron processes in it and why?
▪ Why is it susceptible to accumulating extracellular fluid? Clinical relevance (i.e. macular
star and exudates)
The OPL of the fovea, containing horizontally-oriented cone processes (fibers running radially out from the center of the fovea)
The lateral displacement disturbs normal retinal architecture of the Müller cells, so the tissue is less compact & more susceptible to accumulating large amounts of extracellular fluid (fluid, proteins & maybe cells that leak from blood vessels) and/or exudates (lipids leaking from blood vessels) as seen in hypertensive retinopathy
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(CO) 3. Know the major anatomical differences between the macula (fovea centralis) and fovea
(foveola). Be sure to include retinal layers forming them or absent from them, & differences in blood supply.
▪ Describe the specialized anatomy of the fovea and its characteristic features & what makes it the area of highest visual acuity
▪ Which layers of the retina are seen in the fovea?
Macula still has all the layers. The "fovea" is formed by the peripheral displacement of the inner retinal layers leaving
only the photoreceptors in the center and its downward-sloping border is called the "clivus".
The retinal layers present in the "fovea" are: RPE, photoreceptor layer, ELM, ONL, OPL & ILM
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(CO) 4. Describe the differences between the branches of the CRA and CRV as seen with direct ophthalmoscopy in terms of color, diameter, more superficial location at A/V crossings from clinical view point. Also:
▪ Be able to state the origin of the CRA and what vessel(s) the CRV drains directly into.
▪ What layer of the retina do they initially lie in as you observe them with direct
ophthalmoscopy?
▪ Where do they have a focal constriction where they are at risk of being occluded by an
embolus or thrombus?
▪ Discuss the fact that the CRA and CRV share the same tunica adventitia and that the
artery overlies the vein and its clinical significance.
▪ Where they emerge from the optic cup
▪ What do the terms “superior and inferior nasal and temporal arcades” refer to?
o Classify these blood vessels histologically. Are they arteries or arterioles?
▪ Be able to state the origin of the CRA and what vessel(s) the CRV drains directly into.
Originates from the ophthalmic artery, piercing 3 meningeal layers of the optic nerve and entering on its inferior-medial aspect. The CRV exits the optic nerve more posterior to CRA entrance and terminates in cavernous sinus or superior ophthalmic vein.
▪ What layer of the retina do they initially lie in as you observe them with direct ophthalmoscopy?
Nerve Fiber Layer
▪ Where do they have a focal constriction where they are at risk of being occluded by an embolus or thrombus?
> One constriction occurs where the CRA pierces the dura of the three meningeal layers surrounding the optic nerve to enter the optic nerve
– Here the lumen of the CRA is narrowest & this is the most common site for emboli to lodge and lead to a CRA occlusion
> A second constriction is at the lamina cribrosa where the CRA & CRV share a common adventitial sheath and pass through a narrow opening in the lamina cribrosa.
– Here the wall of the CRA loses its external elastic lamina
▪ Discuss the fact that the CRA and CRV share the same tunica adventitia and that the artery overlies the vein and its clinical significance. (see above)
▪ Where they emerge from the optic cup
The central retinal artery (CRA) emerges from the optic cup slightly nasal to the optic cup’s center and nasal to the central retinal vein (CRV).
▪ What do the terms “superior and inferior nasal and temporal arcades” refer to? Classify these blood vessels histologically. Are they arteries or arterioles?
Superior & inferior temporal branches arch around the macular area on their way to the ora serrata
– The temporal retinal branches are therefore clinically referred to as the "superior and inferior temporal arcades"
They are arterioles.
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(CO) 5. Which blood vessels related to the eye would and would not be directly affected by giant cell
arteritis? Why?
must research
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(CO) 6. How many CRV trunks might a person have in the optic nerve? Which number is more
common?
During the 3rd month of intrauterine life there are always two trunks of the CRV in the optic nerve (1 on either side of the CRA) and one usually disappears before birth.
However in 20% of eyes a dual- trunked CRV persists into adult life.
So, there is usually just 1 CRV in the optic nerve but in 20% of eyes there are two trunks of the CRV in the optic
nerve. This congenital anomaly helps explain how some patients can develop a “hemi-central retinal vein occlusion rather than a complete CRVO.
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(CO) 7. State the origins of the cilioretinal artery, part of the retina it supplies, and where it is located
in the eye and clinical significance as discussed in class.
▪ Classify the cilioretinal artery histologically.
Origin: The cilioretinal artery is really an arteriole that originates either directly from a short posterior ciliary artery (SPCA) or the choroid
Supplies: the retina between the optic disc and the macula called the papillomacular bundle
Located: it emerges from the temporal edge of the optic disc (NOT from the optic cup) & travels towards the macula
Clinical: If a CRA occlusion occurred in someone with a cilioretinal artery, realize that both the fovea and papillomacular bundle would remain vascularized.
▪ So, an island of vision would be spared, corresponding to the areas of the retina still supplied by the cilioretinal artery and the choriocapillaris of the choroid.
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(CO) 8. What is/are the anatomical reason(s) why the retina appears so white within the temporal
arcades of a patient with a recent onset CRAO?
what creates the “cherry red spot” and why?
In a complete CRA occlusion (CRAO), the retina (mainly retina surrounded by the temporal retinal arcades) appears opaque (whiter in color) due to acute ischemia of the ganglion cells & the associated edema of the ganglion cell axons in the NFL.
Since the retinal ganglion cells are piled up in several layers in the GCL at the edge of the fovea where the inner retinal layers were displaced during foveal development, the opacification is more obvious here then further out where the thickness of the GCL is just one cell layer thick.
The fovea remains visible as a reddish area (cherry red spot) because the fovea receives nutrients from the choroid, which is not affected in a CRA occlusion
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(CO) 9. Describe the dual blood supply to the retina including what supplies outer and inner layers of
retina and exactly which layers they supply.
• Blood supply to the retina is from TWO sources:
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1. Central retinal artery & vein
▪ Supply inner layers of sensory retina:
inner nuclear layer (INL)
inner plexiform layer (IPL) ganglion cell layer (GCL)
nerve fiber layer (NFL)
internal limiting membrane (ILM)
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2. Choriocapillaris of the choroid
▪ Supplies the outer layers of the sensory retina
– RPE
– Photoreceptor inner & outer
segments
– ELM
– ONL (outer nuclear layer)
– OPL (outer plexiform layer)
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(CO) 10. State the locations of the two capillary beds in the retina, types of capillaries they are, what
structures lie in the capillary wall, etc.
▪ Why is there a capillary free zone by the fovea?
▪ Are retinal capillaries present in the peripheral retina? If you answer “NO”, then what is
the source of nutrients to the cells in the peripheral retina?
There are 2 capillary beds in the retina that assume a "meshwork" configuration to ensure adequate perfusion to the retina.
• The superficial capillary network lies in the ganglion cell layer (GCL) and nerve fiber layer (NFL)
• The deep capillary network lies in the inner nuclear layer (INL) near the OPL
• Nutrients will diffuse from the capillaries in these layers to the adjacent layers of the "inner" retina
The fovea lies within a capillary-free zone (cfz) within the macula. The lack of blood vessels allows light to pass unobstructed to the photoreceptors
No; choriocapillaris is all that is needed. There are few blood vessels in the peripheral retina.
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(CO) 11. For the following hemorrhages, know where the blood is specifically located, color of the
blood and the source of that blood:
▪ Sub-RPE hemorrhage
▪ Subretinal hemorrhage
▪ Intraretinal hemorrhage
▪ Pre-retinal hemorrhage
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Sub-RPE: between Bruch’s membrane & the RPE; gray-green
-source = choriocapillaris through Bruch's membrane
Subretinal: between RPE and photoreceptor outer segments; red
-source = choriocapillaris through Bruch's and blood retinal barrier
Intraretinal: within 9 sensory layers of the retina; red
-source = central retinal artery or choriocapillaris
Pre-retinal: anterior or posterior to ILM; red
- posterior to ILM: significant bleeding of superficial capillary plexus or damage to branches of CRV/CRA in a PVD due to mechanical tugging
- anterior to ILM: retinal neovascularization
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(CO) 12. Be able to explain how blood could get into the intraretinal space between RPE and outer segments of photoreceptors and source of the blood.
▪ State the name of such a hemorrhage that would lie between RPE and photoreceptor outer segments
see previous question
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(CO) 13. Describe what forms the blood-retinal barrier and where it is located. Should be two sites.
Realize that the endothelium of the retinal arteries, arterioles & capillaries are interconnected by zonula occludens junctions (forming the “inner” blood retinal barrier).
▪ The “outer” blood retinal barrier is formed by the zonula occludens junctions at the apico-lateral borders of the RPE cells.
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(CO) 14. Describe the location of the zonula occludens in the retina. Function?
see previous question
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(CO) 15. How would you know you were looking at choroidal vessels in the fundus while doing direct
ophthalmoscopy? (i.e. What is the appearance and location of choroidal vessels compared to the CRA and CRV?)
- Exactly which blood vessels of the choroid are you looking at when you see choroidal blood vessels in a patient’s fundus? Be specific.
Not as easy to see as CRA/CRV
The choroidal vessels:
▪ appear as thick, criss-crossing orange vessels
▪ are much lighter in color and thicker (ribbon-like or band-like) compared to the
branches of the central retinal artery and vein
▪ lie at a deeper level compared to the retinal vessels (so, to the clinician, the branches of
the CRA & CRV would appear to cross above the choroidal vessels).
These visible choroidal vessels are the blood vessels in Haller’s and Sattler’s layers of the choroid, NOT the choriocapillaris!
- The capillaries in the choriocapillaris are too small to be seen.
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(CO) 16. Describe the region of the ora serrata, including what structures interdigitate there.
▪ What the RPE and sensory retina are continuous with anteriorly.
▪ What are the dentate processes and ora bays? And are they part of retina or part of pars plana?
▪ In general, how the retina has changed in terms of layers or numbers of layers present and blood supply
It is named this because in this region the retina’s dentate processes interdigitate with the
rounded ora bays of the ciliary body’s pars plana creating a “scalloped “ or “serrated“ pattern
As the ora serrata is approached, the
retina has thinned to ~0.1 mm because the retinal layers have been decreasing in thickness
At the ora serrata the sensory retina becomes a single layer of columnar cells that continue forward as the non- pigmented epithelium of the ciliary body
At the ora serrata the RPE cells (simple cuboidal epithelium) continue forward as the pigmented epithelium of the ciliary body
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(CO) 17. Explain dot and blot hemes and flame shaped hemorrhages in terms of retinal layers they
might be in and why they are the shape they are.
see previous question
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(CO) 18. Know the specific functions of the microglial cells, migrating phagocytic cells (monocytes) and astrocytes in the retina!
Microglia: prominent in response to tissue injury; scavengers that ingest debris in the retina by phagocytosis + transporting to blood vessels for disposal.
Monocytes: migrating phagocytic cells complementing microglia in scavenging; if there is significant blood vessel damage, these are recruited
Astrocytes: present in retinal layers containing blood vessels and provide structural support by surrounding vessels as part of their adventitia and by filling in spaces not occupied by neurons & their processes
