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Ocular Anatomy & Physiology II > Retina > Flashcards

Retina Flashcards

1
Q

General retina information

What is the retina?

Layer
Location
Appearance

A
  • Innermost layer of the eye
  • Neural layer
  • Located between choroid and vitreous
  • Transparent but appears reddish due to choroid and retinal pigment epithelium
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2
Q

General retina information

What is the ora serrata?

A

Anterior limit of the neural retina

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3
Q

General retina information

Where is the retina thickest?

A

The retina is thickest in the macular region and thins out as the retina goes further out in the periphery

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4
Q

General retina information

What is the function of the retina?

A

The retina receives light and transmits neural impulses to the brain for interpretation
Photoreceptors transform photons into neural signals via phototransduction and sends the signal to the optic nerve and then the brain

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5
Q

Zones in the retina

What are the retinal zones?

Try to picture them in your head too!

A
  1. Posterior pole (central retina)
  2. Peripheral retina
  3. Ora serrata

Peripheral retina consists of mid-periphery, equator, and far periphery

Vitreous base straddles the ora serrata and far periphery

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6
Q

Posterior pole

What is the posterior pole?

Identify:
1) Retinal portion
2) Function
3) Vision type - photoreceptors

A
  1. Central retina - takes up a small part of the total retina
  2. Designed for visual acuity and detecting detail and color
  3. Critical for good photopic vision due to majority of cones being here
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7
Q

Posterior pole

What key structures can be found in the posterior pole?

A
  1. Optic nerve
  2. Macula
  3. Vascular arcades
  4. Arcuate retinal nerve fibers
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8
Q

Where is the temporal optic disc located in relation to the fovea?

A

3.4 mm away from the fovea

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9
Q

Peripheral retina

What is the peripheral retina?

Identify:
1) Retinal portion
2) Function
3) Vision type - photoreceptors

A
  1. Makes up most of the retina - includes equator, mid-periphery, far periphery
  2. Detects gross form and motion - objects appear less detailed and clear
  3. Critical good scotopic vision - majority of rods found here
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10
Q

Peripheral retina

What key structures can be found in the peripheral retina?

A
  1. Short ciliary nerves
  2. Long ciliary nerves
  3. Short ciliary arteries
  4. Long ciliary arteries
  5. Vortex veins
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11
Q

Peripheral retina

What are short ciliary nerves?

Describe:
1) Amount of short ciliary nerves
2) Location
3) Pathway
4) Meridian and division

A
  1. 8-10 per eye
  2. 2, 4, 8, 10 o’clock (in between notches)
  3. Ciliary ganglion (origin) -> nasociliary branch (V1) of CN V (sensory); CN III and CN VIII (sympathetic and parasympathetic) -> sphincter of iris -> ciliary body -> cornea

Represents the vertical meridian of the retinas
Divides peripheral retina into the nasal and temporal half

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12
Q

Peripheral retina

What are long ciliary nerves?

Describe:
1) Amount of long ciliary nerves
2) Location
3) Pathway
4) Meridian and division

A
  1. 2 per eye
  2. 3 and 9 o’clock
  3. Nasociliary branch (V1) of CN 5 (origin) -> conjunctiva -> cornea -> dilator muscle of iris -> ciliary body

Represents the horizontal meridian (180 axis)
Divides retina into superior and inferior half

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13
Q

Peripheral retina

What are the short ciliary arteries?

Describe:
1) Origin
2) Amount
3) Interaction

A
  1. Arises from ophthalmic artery
  2. Divides into 10-20 branches
  3. Entwine with short ciliary nerves
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14
Q

Peripheral retina

What are the long ciliary arteries?

Describe:
1) Origin
2) Amount
3) Interaction

A
  1. Arises from opthalmic artery
  2. Divides into 2 branches
  3. Entwine with long ciliary nerves
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15
Q

Peripheral retina

What are vortex veins?

Describe:
1) Composition
2) Function
3) Amount
4) Location

A
  1. Composed of tributary veins that come together at ampulla
  2. Drains vasculature of choroid
  3. About 4-8 per eye
  4. Oblique regions of the retina (IN, IT, SN, ST)
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16
Q

Peripheral retina

Where is the equator located?

A
  • 2 DD posterior to the tributary veins
  • Right at the posterior edge of the ampulla of a vortex vein

DD is disc diameter

Kind of like the more central edge or border of the ampulla

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17
Q

What is the vitreous base?

Identify:
1) Description
2) Function
3) Anterior border
4) Posterior border

A
  1. Site of strongest attachment of the vitreous to the retina
  2. Straddles ora serrata
  3. Extends 1.5 mm into pars plana anteriorly
  4. Extends 2-3 mm into the ora serrata posteriorly

Posterior border is closer to 3 mm when nasal and closer to 2 mm when temporal

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18
Q

How is the retina measured?

Identify:
1) Typical unit/measurement definition
2) Conversions for DD, microns, mm, and degrees

A
  1. Disc diameter: optic disc size equivalent
  2. 1 DD = 1,500 mircons
  3. 100 microns = 0.1 mm
  4. 1 degree = 300 microns
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19
Q

Retinal testing

Fluorescein Angiography

Identify:
1) Purpose
2) Application
3) General description of the image

A
  1. Highlights the optic nerve and retinal+choroidal circulation
  2. Useful for detection of subclinical retinal/choroidal/optic nerve changes secondary to vascular conditions - diagnose retinal, choroidal, optic nerve head vascular disorders
  3. Vasculature should be highlighted white with a grey/darker retinal background

Aids in treatment decisions and guides retinal laser therapy

Image will show leakage of dye if there is damage

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20
Q

Retinal testing

Optical Coherence Tomography (OCT)

Identify:
1) Purpose
2) Application
3) General description of image

A
  1. Visualizes all layers of the retina
  2. Instrumental in diagnosing various pathologies (ex: macular edema, vitreomacular traction)
  3. Grey scale image that’s layered like sand art with a small blip in the center
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21
Q

Retinal testing

Optical Coherence Tomography Angiography (OCT-A)

Identify:
1) Purpose
2) Application
3) General description of image

A
  1. Visualize vessels of the retina and choroid non-invasively and is based on active blood flow
  2. Provides good view of blood flow structure - not really for leakage
  3. Similar grey-scale image to FA (grey retina/background with white vasculature)
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22
Q

Retinal testing

Fundus Autofluorescence (FAF)

Identify:
1) Purpose
2) Application
3) General description of image
4) AF result interpretation - increased AF
5) AF result interpretation - decreased AF

A
  1. Reflects lipofuscin at the RPE layer/level
  2. Useful for detecting issues with RPE
  3. Image is “opposite” of FA - vasculature appears dark/black with a lighter grey retinal background
  4. Increased AF means excess lipofuscin accumulation
  5. Decreased AF means loss or death of RPE cells

Lipofuscin is formed when RPE ingests shedded outer segments of photoreceptors via phagocytosis - it’s a normal wear and tear pigment

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23
Q

Retinal testing

B-Scan Ocular Ultrasound

Identify:
1) Mechanism
2) Purpose
3) Application
4) General description of image

A
  1. High frequency sound waves are transmitted from a probe to the eye using transmission gel
  2. Helps in localizing and defining shape and extension of posterior segment pathology
  3. Useful for detecting retinal detachments or other posterior segment pathology
  4. Image shows darker area as vitreous and optic nerve and the lighter area as retina

Literally ultrasound for the eye

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24
Q

Retinal layers

What are the main layers of the retina in order from anterior to posterior (inner to outer)?

Anterior/inner - closer to vitreous; Posterior/outer - closer to choroid

A
  1. Internal limiting membrane (ILM)
  2. Retinal nerve fiber layer (NFL)
  3. Ganglion cell layer (GCL)
  4. Inner plexiform layer (IPL)
  5. Inner nuclear layer (INL)
  6. Outer plexiform layer (OPL)
  7. Outer nuclear layer (ONL)
  8. External limiting membrane (ELM)
  9. Photoreceptor layer
  10. Retinal pigment epithelium (RPE)

Mneomonic: INGIIOOEPR (“in geeoo EPR)

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25
Q

Retinal layers

What retinal layers make up the inner layers?

(between what layers is the distinction between inner and outer made)

A
  1. Internal limiting membrane
  2. Retinal nerve fiber layer
  3. Ganglion cell layer
  4. Inner plexiform layer
  5. Inner nuclear layer

Distinction is between INL and OPL

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26
Q

Retinal layers

What retinal layers make up the outer layers?

(between what layers is the distinction between inner and outer made)

A
  1. Outer plexiform layer
  2. Outer nuclear layer
  3. External limiting membrane
  4. Photoreceptor layer
  5. Retinal pigment epithelium

Distinction is between INL and OPL

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27
Q

Retinal layers

What layer is contained in the OPL?

A

Henle fiber layer

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28
Q

Retinal layers

What three components make up the photoreceptor layer?

A
  1. Myoid zone
  2. Ellipsoid zone
  3. Outer segments of photoreceptors
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29
Q

Retinal layers

What is the interdigitation zone (IDZ)?

A

Junction that sits between the photoreceptor layer and RPE

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30
Q

Retinal layers - RPE

Retinal pigment epithelium (RPE)

Describe:
1) Location
2) Composition
3) Unique traits

A
  1. Outermost layer (deepest) - lies between Bruch’s membrane and the photoreceptor layer
  2. Single cell thick - composed of pigmented hexagonal cells which appear more cube-like when viewed as a cross section
  3. Highly metabolic and appears darker due to melanin (contained in melanosomes and lipofuscin)

Melanin is densest in the RPE cells at the macula followed by the equator

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31
Q

Retinal layers - RPE

RPE Melanin

Identify:
1) Densest melanin in RPE
2) Effect of age on melanin
3) Pigment distribution

A
  1. Melanin in RPE is densest at the macula followed by the equator
  2. Increasing age results in more melanin/pigment due to increased pigmented bodies, lipofuscin, and breakdown of phagocytic material
  3. Pigment distribution is unequal - gives more granular appearance (primarily seen/is more apparent at the macula)
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32
Q

Retinal layers - RPE

What types of junctions are found in the RPE?

Identify:
1) Junction types
2) Function

A
  • Zonulae occludens (tight) - forms BBB, prevents passage of material in between cells but can sometimes allow material through
  • Zonulae adherens (anchoring) - forms BBB, prevents cells from sliding out of position and can sometimes allow material to pass through
  • Desmosomes (anchoring) - provides structural support between RPE cells and can sometimes allow material to pass through
  • Hemidesmosomes (anchoring) - provides structural support between RPE cell and basement membrane (Bruch’s) by connecting intermediate filaments with strong adhesion
  • Gap junctions - permit electrical and chemical communication between RPE cells
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33
Q

Retinal layers - RPE

RPE Physical Appearance

Identify:
1) Physical appearance at macula
2) Physical appearance in periphery
3) Density pattern

A
  1. RPE cells are longer and narrower at the macula
  2. RPE cells become wider and flatter further out in the periphery and ora serrata
  3. RPE cells are most dense at the macula (fovea) and decrease in density further out in the periphery

Mnemonic: Macula is a model - long and narrow shape

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34
Q

Retinal layers - RPE

RPE Cell - Basal

(try to visualize diagram)

Identify:
1) Location
2) Organelle present
3) Function

A
  1. Closest component to Bruch’s membrane
  2. Majority of mitochondria found here
  3. Strong adhesion to innermost layer of Bruch’s membrane (basement membrane of RPE)
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35
Q

Retinal layers - RPE

Why is there such strong adhesion to Bruch’s membrane at the basal component?

A
  1. Basal aspect contains infoldings of plasma membranes which allows tight adherence
  2. Innermost layer of Bruch’s membrane is composed of extracellular matrix proteins that includes large adhesive glycoproteins that bind strongly to the basal surface
  3. Hemidesmosomes in the basal aspect allow stable adhesion to Bruch’s

Bruch’s membrane separates RPE from choroicapillaries

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36
Q

Retinal layers - RPE

RPE Cell - Central

(try to visualize diagram)

Identify:
1) Location
2) Organelle present

A
  1. Between basal component and apical component
  2. Large oval nucleus
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37
Q

Retinal layers - RPE

RPE Cell - Apical

(try to visualize diagram)

Identify:
1) Location
2) Organelle present
3) Function

A
  1. Closest to photoreceptors
  2. Microvilli - extend to outer segment tips of photoreceptors
  3. Composed of melanin granules which help to absorb scattered light and stabilize free radicals
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38
Q

Retinal layers- RPE

What junctions are present at the RPE - Photoreceptor interface?

A
  • No intracellular junction connect the RPE to the photoreceptors - results in potential space in between the RPE and photoreceptors (sub-retinal space)
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39
Q

Retinal layers- RPE

How does the RPE-photoreceptor interface stay attached?

A
  1. IOP
  2. Osmotic pressure
  3. Vitreous
  4. Apical microvilli of the RPE
  5. Interphotoreceptor matrix (IPM) is composed of sticky proteins and glycosaminoglycans
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40
Q

Retinal layers - RPE

What are some functions of the interphotoreceptor matrix (IPM)?

A
  • Sticky proteins and glycosaminoglycans found in the extracellular space between RPE and photoreceptors - helps with RPE-photoreceptor attachment
  • Matrix surrounds outer segments of photoreceptors - provides support, allows exchange of nutrients, provides optimal orientation to capture light, and helps with transfer of pigment and nutrients
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41
Q

Retinal layers - RPE

Where is the RPE-photoreceptor interface absent?

Identify location and clinical significance

A

Absent along the peripapillary ring around the optic disc as well as the ora serrata - retina is strongly attached at these areas and will never detach

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42
Q

Retinal detachment

Describe:
1) What condition is
2) Clinical consequence

A
  1. Separation between the RPE and photoreceptor layer
  2. Separation prevents photoreceptors from getting nutrients from the choroid and leads to photoreceptor death
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43
Q

Retinal layers - RPE

What are the functions of the RPE?

A
  1. Absorption of scattered light - improves optical quality and reduces photo-oxidative stress on the retina
  2. Control fluid, nutrient, and waste product transport to and from the sub-retinal space and photoreceptor layer
  3. Visual pigment regeneration and synthesis
  4. Essential for the visual cycle
  5. Synthesis of signaling molecules (PDGF, PEDF, VEGF, TGF)
  6. Phagocytosis of photoreceptor waste
  7. Involved in regeneration and repair if there is retinal damage
  8. Stores vitamin A
  9. Synthesizes IPM
  10. Acts as the outer-blood retina barrier (tight junctions in RPE)
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44
Q

Retinal layers - RPE

What are the signaling molecules synthesized by the RPE and their functions?

Identify:
1) Signaling molecule
2) Function

A
  1. PDGF - controls cell growth and healing
  2. PEDF - neuroprotectant
  3. VEGF - stimulates normal vascular growth and neovascularization
  4. TGF - controls inflammation

Mnemonic: PDGF - growth and flourish
Mnemonic: PEDF - defense
Mnemonic: VEGF - veggies need new (neo) water (vascular)
Mnemonic:

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45
Q

What is the interdigitation zone (IDZ)?

Describe:
1) General description
2) Visible area
3) Retinal area make up

A
  • Where apices of the RPE cells encase part of the cone and rod outer segments
  • Only visible in the posterior pole usually
  • Part of the sub-retinal space
46
Q

What is Verhoeff membrane?

A
  • Anatomical structure that surrounds the apical portion of the RPE and composed of the tight junctions between RPE cells
  • Found in the IDZ

(doesn’t do anything functional)

47
Q

Photoreceptors

How many photoreceptors are there?

(rods and cones)

A
  • 120 million rods
  • 60 million cones
48
Q

Photoreceptors

Describe photoreceptor densities and locations

1) Rod vs cone densities throughout retina
2) Rod vs. cone densities at fovea
3) Rod and cone density at ora serrata
4) Greatest rod density location
5) Rod and cone density at optic nerve

A
  1. Rod density > cone density throughout the retina EXCEPT
  2. Cone density > rod density at the macular/foveola - no rods are at the foveola
  3. Rod density and cone density decrease towards the ora serrata
  4. Rod density is greatest concentrically 3 mm from the fovea
  5. No photoreceptors at the optic nerve
49
Q

Photoreceptors

What are the layers/parts of the photoreceptor and their respective functions?

(posterior to anterior) or (closest to RPE to OPL)

A
  1. Outer segment - contains visual pigment molecules that convert light into a neural signal
  2. Cilium - connecting stalk
  3. Inner segment (ellipsoid + myoid zones) - contains metabolic material and is involved in protein synthesis
  4. Outer fiber
  5. Cell body - forms outer nuclear layer
  6. Inner fiber - forms outer plexiform layer and usually ends in a synaptic terminal
50
Q

Photoreceptors - Outer Segment

What is the outer segment?

Identify:
* Composition
* Shapes
* Base and apical contacts

A
  • Composed of a stack of discs - contain visual pigment molecules
  • Shape denotes name for rods and cones
  • Outer segment base is in contact with cilium
  • Outer segment tip is in contact with IDZ
51
Q

Photoreceptors - Cilium

What is the cilium?

Identify:
* Anatomy/connection points

A
  • Connects inner segment with outer segment
52
Q

Photoreceptors - Inner Segment

What is the inner segment?

Identify:
* Comprised of
* Function

A
  • Composed of the ellipsoid zone and myoid zone
  • Ellipsoid zone is nearest to the outer segment and directly connected to the cilium - contains mitochondria which provides energy to photoreceptors
  • Myoid zone is nearest to the cell body and directly connected to the outer fiber - contains other organelles and is the site for protein synthesis
53
Q

Photoreceptors - Outer Fiber

What is the outer fiber?

Identify:
* Anatomy/connection points

A
  • Connects the inner segment to the cell body
54
Q

Photoreceptors - Cell Body

What is the cell body?

Idenfity:
* Composition
* Corresponding retinal layer

A
  • Contains the nucleus
  • Forms outer nuclear layer
55
Q

Photoreceptors - Inner Fiber

What is the inner fiber?

Identify:
* Composition
* Corresponding retinal layer

A
  • Composed of axons with microtubules that connects the cell body to the synaptic terminals
  • Forms outer plexiform layer
56
Q

Photoreceptors - Rods

Rods

Describe:
* Length
* Type(s)
* Shape
* Active conditions
* Function

A
  • 40-60 microns long
  • Only one type of rod (visual pigment based)
  • Longer and thinner compared to cones
  • More active in scotopic conditions - most effective after 20-30 minutes of dark adaptation
  • Responsible for sensing contrast, brightness, and motion
57
Q

Rods - Outer Segment

Outer segment of rods

Describe:
* Width (disc width)
* Disc traits
* Plasmalemma traits
* Cone comparison

A
  • Discs are uniform in width (about 600-1000 discs per rod)
  • Discs contain visual pigment
  • Discs are separate from surrounding discs
  • Plasmalemma is separate from the membranes that surround the discs
  • Outer segment is longer than cone outer segments EXCEPT at the macula/fovea region where they are about the same length

Plasmalemma is a plasma membrane that encloses the outer segment of the rod

58
Q

Rods - Outer Segment

What is the visual pigment found in rods?

Identify:
1. Pigment
2. Wavelength absorbed

A
  1. Rhodopsin
  2. Maximum wavelength absorption of 498 nm

Only one type of rhodopsin means only one type of rod (monochromatic)

59
Q

Rods - Outer Segment

Describe the renewal system of the outer segment in rods

Identify:
1. Steps of the renewal system
2. Renewal system timing

A
  1. Components of the disc membrane are made in the inner segment which will move to be a part of the discs in the base of the outer segment
  2. Old discs are displaced outward by formation of new discs
  3. Old discs come off the tip of the outer segment and are phagocytized by RPE cells
  4. Constant renewal - discs are shed regularly, especially in the early mornings or in bright environments
60
Q

Rods - Other Components

Compare the components of a rod to a cone

Describe:
* Rod vs. cone inner segment size
* Rod inner segment vs. rod outer segment width
* Rod vs. cone ellipsoid area mitochondria
* Rod vs. cone outer fiber size
* Rod vs. cone nuclei size
* Rod vs. cone cell body and nuclei location
* Rod vs. cone inner fiber
* Rod spherule vs. cone pedicle

A
  • Rod inner segment is thinner than the cone inner segment
  • Rod inner segment and outer segment are about the same width
  • Rod ellipsoid area of inner segment contains less mitochondria than cone ellipsoid area
  • Rod outer fiber is longer than cone outer fiber
  • Rod nuclei are typically further from the outer retina or external limiting membrane than cone nuclei
  • Rod cell body and nuclei are smaller than cone cell body and nuclei
  • Rod inner fiber is shorter than cone inner fiber (inner fiber connects cell body to synaptic complex)
  • Rod spherule is smaller compared to cone pedicle
61
Q

Rods

What neurotransmitter is released from the rod spherule?

62
Q

Photoreceptors - Cones

Cones

Describe:
* Length
* Type(s)
* Shape
* Active conditions
* Function

A
  • 40-50 microns long
  • 3 types of cones (based on visual pigment)
  • Cones tend to be overall shorter and thicker than rods EXCEPT at the macula/foveola where cones appear more rod-like (thinner and longer)
  • More active in photopic conditions
  • Responsible for sensing fine resolution, spatial resolution, and color
63
Q

Cones - Outer Segment

Outer Segment of Cones

Describe:
* Width (disc width)
* Disc traits
* Plasmalemma traits
* Rod comparison

A
  • Discs at the base are wider in width than at the tip (1000-1200 discs per cone)
  • Discs are connected to each other - not separate like in rods
  • Plasmalemma is continuous with the membranes that surrounds the discs in the outer segment
  • Cone outer segments are shorter and sometimes may not reach the RPE EXCEPT at the macula/fovea where they are just as long as rod outer segments

RPE microvilli on the apical surface can reach and surround cone segments when they are too short

64
Q

Cones - Outer Segment

What is the visual pigment found in cones?

Identify:
1) Pigment
2) Types
3) Wavelength absorbed by each type

A
  • Photopsin
  • Blue cone (short wavelength) - maximum wavelength absorption is 420 nm
  • Green (medium) - maximum wavelength absorption is 531 nm
  • Red (long) - maximum wavelength absorption is 588 nm
65
Q

Cones - Outer Segment

Describe the outer segment renewal system in cones

Describe:
* Renewal process/mechanism
* Renewal time period

A
  • New discs are formed while old discs come off the tip of the outer segment and the RPE cells will phagocytize the old discs
  • Not constantly renewed - discs are shed periodically, typically at the end of the day or in dark environments
66
Q

Cone - Other Components

Describe some of the differences between cones and rods

Describe:
* Cone vs. rod inner segment size
* Cone vs. rod ellipsoid mitochondria
* Cone vs. rod outer fiber
* Cone vs. rod nuclei location
* Cone vs. rod cell body/nuclei size
* Cone vs. rod inner fiber
* Cone pedicle vs. rod spherule size

A
  • Cone inner segment is thicker than the rod inner segment - contribute to cone shape
  • Cone ellipsoid area of the inner segment contains more mitchondria
  • Cone outer fiber is shorter and may even be missing
  • Cone nuclei tend to be found closer to the outer retina or external limitng membrane
  • Cone cell body and nuclei are larger
  • Cone inner fiber is longer
  • Cone pedicle is larger than rod spherule
67
Q

Cones

What is the neurotransmitter released by cones?

68
Q

Photoreceptors - External Limiting Membrane

What is the external limiting membrane?

Identify:
* Description
* Composition
* Location
* Functions

A
  • Not a true membrane
  • Composed of zonula adherens junctions (anchoring junctions) between photoreceptor cells as well as photoreceptor and Muller cells at inner segments
  • Located between the outer nuclear layer and photoreceptor cell inner segments
  • Function: acts a metabolic barrier to prevent passage of large molecules, stabilizes the transducing portion of photoreceptors

Transduction is the process by which light is converted into electrical signals in the rod and cone cells

69
Q

Photoreceptors - Outer Nuclear Layer

What is the outer nuclear layer?

Describe:
* Composition
* Cone nuclei layer
* Rod nuclei layer
* Rod vs. cone nuclei throughout retina and at fovea

A
  • Contains rod and cone cell bodies and nuclei
  • Cone outer fibers are very short or even absent so the nuclei tend to be in a single layer close to the external limiting membrane
  • Rod cell bodies are found in different rows inner to the cone cell bodies because rod outer fibers tend to be longer
  • Rod nuclei outnumber cone nuclei throughout the retina except at the fovea where there are only cone nuclei
70
Q

Photoreceptors - Outer Nuclear Layer

Describe the outer nuclear layer thickness levels in order

(thickest to thinnest)

Identify:
1. Retinal portion
2. Number of photoreceptor rows
3. Microns

A
  1. Thickest at the fovea - 10 rows of cone nuclei (50 microns thick)
  2. Nasal to the optic nerve - 8-9 rows of both cone and rod nuclei (45 microns thick)
  3. Rest of the retina - 1 row of cones and 4 rows of rods (27 microns thick)
  4. Temporal to the optic nerve - 4 rows of both rod and cone nuclei (22 microns thick)
71
Q

Photoreceptors - Outer Plexiform Layer

What is the outer plexiform layer?

(AKA outer synaptic layer)

Identify:
* Outer aspect composition
* Inner aspect composition
* Thickest area
* Function

A
  • Outer aspect of OPL made up of the inner fibers of the rods and cones
  • Inner aspect of OPL made up of the synaptic terminals
  • Thickest in the macula region (51 microns)
  • Prevents spread of any fluid to other layers of the retina

This is the last layer where parts of the photoreceptor can be found

72
Q

Rods - Outer Plexiform Layer

Rods in the OPL

Describe:
* What structures spherules synapse to
* Synapse complex amount
* Spherule invagination composition
* Synapse type

A
  • Rod spherules synapse with bipolar cell dendrites and horizontal cell axons
  • 2-7 synaptic complexes per spherule
  • Rod spherules have deep invaginations where synapses occur - each invagination contains 1 or more rod bipolar dendrites surrounded by 2 horizontal cell axons
  • Synaptic ribbon is found on rod spherule adjacent to invagination
73
Q

Rods - Outer Plexiform Layer

What is a ribbon synapse?

  • Description
  • Function
A
  • Membranous plate that is found on the rod spherule adjacent to the invagination
  • Allows for fast and sustained neutransmitter release
74
Q

Cones - Outer Plexiform Layer

Cones in the OPL

Describe:
* What structures pedicles synapse to
* Synapse complex amount
* Pedicle invagination composition
* Other cells/connections outside of the triad
* Synapse type

A
  • Cone pedicles synapse with bipolar cell dendrties and horizontal cell dendrites
  • 25 synaptic complexes per pedicle
  • Cone pedicles have superficial invaginations where synapses occur - each invagination in a cone pedicle contains an invaginating midget bipolar dendrite surrounded by two horizontal cell dendrites (triad)
  • 1-2 flat midget bipolar dendrites exist outside of the triad
  • Flat bipolar dendrites can also be found outside the invaginations
  • Synaptic ribbon is found on the cone pedicle adjacent to the invagination
75
Q

Photoreceptors - Outer Plexiform Layer

What other synapses are present in the OPL that don’t involve pedicle/spherule invaginations?

Identify:
* Horizontal cell synapses and junctions
* Spherule synapses and junctions
* Pedicle synapses and junctions

A
  • Horizontal cells synapse with bipolar dendrites via gap junctions
  • Horizontal cells synapse with horizontl cells via gap junctions
  • Rod spherules synapse with cone pedicles and other spherules via gap junctions
  • Cone pedicles synapse with rod spherule and other pedicles via gap junctions EXCEPT blue cones - don’t have gap junctions with other cones and rods

Gap junctions allow current to pass directly between cells quickly, creating an electrical synapse with no chemical mediator

76
Q

Photoreceptors - Outer Plexiform Layer

What is the Henle fiber layer?

A
  • Outer plexiform layer at the fovea
  • Cone pedicles, neurons, and axons are displaced laterally at the fovea

Allows for unobstructed area at the fovea

77
Q

Middle Limiting Membrane

What is the middle limiting membrane?

  • Description
  • Function
A
  • Composed of desmosome-like attachments called synaptic densities that are found within branching, interwoven bipolar dendrites and horizontal cells
  • Prevents leaking from the inner retinal vasculature from getting in the outer retina

Inner retinal vasculature does not extend beyond middle limiting membrane

78
Q

Inner Nuclear Layer

What is the inner nuclear layer?

  • Description
  • Composition
  • Foveola significance
A
  • Contains cell bodies of horizontal cells, bipolar cells, amacrine cells, interplexiform neurons, Muller cells, and displaced ganglion cells - basically all cell cell bodies except for rods, cones, and normal ganglion cells!
  • Composed of 8-12 rows of closely packed nuclei
  • Disappears at the foveola
79
Q

Inner Plexiform Layer

What is the inner plexiform layer?

(inner synaptic layer)

  • Description
  • Inner half
  • Outer half
  • Synapses
A
  • Synaptic junctions between higher-order neurons
  • Axon of invaginating midget bipolar cell ends in the inner half
  • Flat midget bipolar cell ends in the outer half
  • Synapses between amacrine processes and bipolar axons, ganglion cell dendrites, other amacrine processes; synapses between amacrine cells and interplexiform neurons
  • Disappears at the foveola
80
Q

Which plexiform layer is stronger?

A

Inner plexiform layer tneds to be stronger than the outer plexiform layer

81
Q

Retinal layers - Ganglion Cell Layer

What is the ganglion cell layer?

  • Ganglion cell amount
  • Composition
  • Ganglion cell separation
  • Foveola significance
A
  • 1.12-2.22 million ganglion cells
  • Contains the cell body of ganglion cells
  • Each ganglion cell is separated by Muller cells
  • Disappears at the foveola
82
Q

Retinal layers - Ganglion Cell Layer

How thick is the ganglion cell layer?

  • General thickness
  • Macula thickness
  • Temporal ON thickness
  • Ganglion cell amount/pattern
A
  • Single cell thickness!
  • EXCEPT at the macula - 8-10 cells thick
  • EXCEPT temporal to the optic nerve - 2 cells thick
  • Number of ganglion cells decrease significantly further out in the peripheral retina
83
Q

Rods - Ganglion Cell Layer

Convergence of rods in the GCL

  • Rod vs. cone convergence
  • Function
  • Rod pathway
A
  • Rods have greater convergence into a ganglion cell - due to sheer number of rods vs. cones
  • Allows increased sensitivity to light and motion
  • Rod pathway involves a 4 neuron chain due to involvement of amacrine cells

Bottleneck convergence

84
Q

Retinal layers - Ganglion Cell Layer

Convergence of cones in the GCL

  • Cone vs. rod convergence
  • Function
  • Cone pathway
A
  • Cones converge less than rods - less cones synapse with bipolar cells and small amount of cone bipolar cells synapse with a single ganglion cell
  • Some areas have 1:1 ratio between cones and ganglion cells
  • Allows ability to discriminate detail
  • A cone pathway involves a 3 neuron chain
85
Q

Retinal layers - Ganglion Cell Layer

What is the convergence pathway for a rod?

A

Rod (75,000) -> Bipolar cells (500) -> Amacrine cells (250) -> Ganglion cell (1)

first order -> second order -> third order -> fourth order

Bottleneck convergence

86
Q

Retinal layers - Ganglion Cell Layer

What is the convergence pathway for a cone?

A

Cones (1-5) -> Bipolar cells (1-5) -> Ganglion cell (1)

first order -> second order -> third order

87
Q

Retinal layers - Nerve Fiber Layer

What is the nerve fiber layer?

  • Description
  • Thickest area
A
  • Consists of ganglion cell axons that should be unmyelinated - run parallel to the retina surface and go to the optic disc and through the lamina cribosa
  • Thickest at the margins of the optic disc
  • Disappears at the foveola

Axons become myelinated at the lamina cribosa

88
Q

Retinal layers - Nerve Fiber Layer

What are the nerve fiber layer bundles?

A
  1. Papillomacular fibers
  2. Nasal radial fibers
  3. Superior arcuate fibers
  4. Inferior arcuate fibers
89
Q

Retinal layers - Nerve Fiber Layer

Papillomacular fibers

Identify:
* Passage
* Function
* Size

A
  • Radiate from the macula to the optic disc
  • Carries information that determines visual acuity
  • Thinnest NFL bundle
90
Q

Retinal layers - Nerve Fiber Layer

Nasal radial fibers

Identify:
* Passage

A
  • Brings information from the nasal retina to the optic nerve
91
Q

Retinal layers - Nerve Fiber Layer

Superior arcuate fibers

Identify:
* Passage

A
  • Brings information from the temporal retina to the optic nerve
92
Q

Retinal layers - Ganglion Cell Layer

Inferior arcuate fiber

Identify:
* Passage

A
  • Brings information from the temporal retina to the optic nerve
93
Q

Retinal layers - Ganglion Cell Layer

What structure divides the superior and inferior arcuate fibers?

A

Horizontal raphe

94
Q

What is a flame hemorrhage?

Identify:
* Blood pool formation
* Retinal layer

A
  • Blood pooling in a horizontal and linear formation
  • In the nerve fiber layer
95
Q

What is a dot/blot hemorrhage?

Identify:
* Blood pool formation
* Retinal layer

A
  • Blood pooling in a vertical and linear formation
  • In the inner nuclear layer
96
Q

Retinal layers - Internal Limiting Membrane

What is the internal limiting membrane?

Describe:
* Description
* Composition
* Continuity
* Retinal appearance

A
  • Innermost boundary of the retina that adheres to the posterior hyaloid face of the vitreous
  • Composed of terminations of Muller cells (footplates) as well as collagen fibrils, proteoglycans, other glial cells, and basal lamina
  • Becomes continuous with the internal limiting membrane of the ciliary body
  • Gives off relfections - results in bright sheen on retina
97
Q

Bipolar Cells

Bipolar cells

  • Amount
  • Highest concentration
  • Composition
  • Visual pathway order
  • Types (number)
A
  • 35.68 million bipolar cells in the retina
  • High concentration at the fovea
  • Composed of single axon with multiple terminals, cell body with large nucleus, single dendrite with multiple terminals
  • Second order neuron in the visual pathway
  • 11 types total - all associated with cones except rod bipolar cell
98
Q

Bipolar Cells

What is the function of bipolar cells?

  • Output to
  • Input from
  • Neurotransmitter released
A
  • Relays information from the photoreceptor cells to the horizontal, ganglion, and amacrine cells
  • Receives synaptic feedback from amacrine cells
  • Releases glutamate
99
Q

Bipolar Cells

Rod Bipolar Cells

  • Description
  • Appearance
  • Contact points in central vs. peripheral
  • Function
  • Synapses on
A
  • The only bipolar cell that connects to rods
  • Composed of a large cell body
  • Appears ~1 mm away from the fovea and continues into the retina periphery
  • Dendrite of a single rod bipolar cell comes in contact with 15-20 rods in the central retina and 80 in the peripheral retina - leads to better sensitivity but less recognition of detail
  • Axon synapses with amacrine cells (which synapse with ganglion cells)
100
Q

Bipolar Cells

Midget Bipolar Cells

  • Contacts in central vs. peripheral
  • Anatomy and shape
A
  • Only contacts one cone in the central retina
  • Can contact multiple cones in the peripheral retina
  • Composed of a small cell body
  • Can be flat or invaginating
101
Q

Bipolar Cells

Flat Midget Bipolar Cells

  • Contact area
  • Contact # in central
  • Contact # in peripheral
  • Axon synapse
A
  • Makes contact with only the flat area of the cone pedicle
  • Only contacts one cone in the central retina - better recognition of detail
  • Contacts 2-3 cones in the peripheral retina
  • Axon synapses with ganglion cells of all types
102
Q

Bipolar Cells

Midget Bipolar Cells

  • Contact area - #
  • Adjacent structure - #
  • Cone contact in central
  • Cone contact in peripheral
  • Axon synapse
A
  • Makes contact with only the invaginating area of the cone pedicle - can have up to 12-25 invaginating areas
  • Flanked on both sides by a horizontal cell dendrite - can have up to 12-25 triads
  • Only contacts one cone in central retina - better detail recognition
  • Contacts 2-3 cones in the peripheral
  • Axon synapses with dendrite of a single midget ganglion cell with amacrine processes

Like contacting different homes in a neighborhood

103
Q

Bipolar Cells

Diffuse Cone Bipolar Cells

(Flat bipolars, brush bipolars)

  • Contact area
  • Contact cone types - central
  • Contact cone types - peripheral
A
  • Makes contact with only the flat area of the cone pedicle
  • Contacts 5 neighboring cones in the central
  • Contacts 10-15 neighboring cones in the peripheral

(only contacts cones in close proximity to each other)

104
Q

Bipolar Cells

Blue Cone Bipolar Cells

  • Contact area
  • Synapse
  • Contact cone types
A
  • Makes contact with only the flat area of the cone pedicle
  • Can synapse with up to 3 cone pedicles
  • Contacts widely spaced cones rather than neighboring cones

Like contacting different states

105
Q

Bipolar Cells

Giant Cone Bipolar Cells

  • Contact area
  • Dendrite description
A
  • Makes contact with only the flat area of the cone pedicle
  • Giant dendrite that branches into 3 trees which cluster into multiple processes - ends up being size of cone pedicle
106
Q

Ganglion Cells

Ganglion Cells

Describe:
* Neuron order for both rods and cones
* Shape(s)
* Visual pathway significance

A
  • Third order neuron (cones), fourth order neuron (rods)
  • Can be bipolar or multipolar
  • Second cell in the visual pathway to respond with an action potential

Amacrine cells are the first

107
Q

Ganglion Cells

Describe the axons of ganglion cells

  • Axon description (runs where, comes together)
  • Majority of termination
  • Minority of termination
  • Neurotransmitter released
A
  • Each ganglion cell has a single axon that runs parallel to the inner surface of the retina
  • Axons come together at the optic nerve
  • Termination for 90% of these axons are at the LGN -> visual cortex
  • Termination for 10% of these axons are in subthalamic areas involved with pupillary reflexes
  • Releases glutamate
108
Q

Ganglion Cells

How are ganglion cells classified?

  • Based on
  • Cell types
A
  • P cells
  • M cells
  • K cells
  • Based on lateral geniculate nucleus layer in which they terminate
109
Q

Ganglion Cells

P Cells

  • Terminate in which layer
  • Portion of ganglion cells
  • Input
  • Majority found (location)
  • Cell body size
  • Axon speed
  • Function
A
  • Terminate in parvocellular layer of LGN
  • Majority of ganglion cells (80%)
  • Input is from cones (medium and long)
  • Found in central retina
  • Composed of small cell bodies
  • Fast axon conduction
  • Specialized for determining color vision, detail, and form
110
Q

Ganglion Cells

P1 Cells

  • Cell type
  • AKA
  • Cell size and dendrite #
  • Connection and function
  • Location found
A
  • Most common P cell
  • Also known as midget ganglion cell
  • Small cell with single dendrite
  • Exclusively conntected to only one midget bipolar cell which might be connected to only one cone receptor - allows processing of high contrast detail and color resolution
  • Likely found in the fovea region
111
Q

Ganglion Cells

M Cells

  • Terminate in which layer
  • AKA
  • Input
  • Majority found (location)
  • Cell body size
  • Axon speed
  • Function
A
  • Terminate in the magnocellular layer of the LGN
  • AKA parasol ganglion cell because synapses made over wide area
  • Input is from rods
  • Majority found in the peripheral retina (only 5% of ganglion cells are M cells in central)
  • Composed of large cell bodies
  • Axon conduction is slow
  • Specialized for seeing motion

FTT visual field test specifically tests for M cells

112
Q

Ganglion Cells

K Cells

  • Terminate in which layer
  • Input
  • Majority found (location)
  • Function
A
  • Terminate in the koniocellular layer of the LGN
  • Input from cones (short)
  • Found throughout the retina
  • Thought to be involved with some aspect of color vision but function not fully understood

Ocular Anatomy & Physiology II (2 decks)

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