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Ophthalmology > Day 7 (2): Anatomy of the Internal Eye > Flashcards

Day 7 (2): Anatomy of the Internal Eye Flashcards

1
Q

What are the parts of the Internal Eye/Posterior Segment?

A
  1. Posterior Lens Capsule
  2. Uvea: Iris, Ciliary Body, Choroid
  3. Vitreous Gel
  4. Retina
  5. Optic Nerve
  6. Posterior Sclera
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2
Q

What are the boundaries of the Posterior Segment?

A

Anterior most structure: Lens
Posterior most structure: Fovea

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3
Q

Imaginary line delineating the superior from the inferior half of the retina

A

Horizontal Raphe
- passes through the optic nerve

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4
Q

Most posterior portion of the retina

A

Fovea/Foveola

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5
Q

Junction of the retina and the ciliary body and the anterior most portion of the retina

A

Ora Serrata

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6
Q

Landmarks when drawing the retina

A

4 Inner Concentric Circles
- differentiated based on histologic findings and organization of retinal cells
- no clear demarcation in between areas

  1. Foveola
    - corresponds to the Foveal Avascular Zone
    - at the center of the Fovea
    - bordered by the Clivus or Foveal Slope
    - diameter: 0.35 mm
    - ROD-free zone
    - highest density of CONE receptors: 199,000 cones/sq. mm
    - decreasing cone density the farther away from the foveola
  2. Fovea/Fovea Centralis
    - diameter: 1.5 mm (~ optic disc size)
    - located 3 mm from temporal border of optic disc, slightly below the horizontal raphe
    - cone density: 20,000 cones/sq. mm
    - (+) macula lutea: made of xanthophylls, a protective pigment, concentrated in this area
  3. Macula/Posterior Pole/Area Centralis
    - area encompassing the Foveola, Fovea, Parafovea and Perifovea
    - diameter: 4.5 - 6.0 mm
    - cone density: 5,000 cones/sq. mm
    - central and photopic vision
    - PARAfovea: 0.50 mm area around the fovea
    - PERIfovea: 1.5 mm area around the parafovea
  4. Optic Disc
    - corresponds to the optic nerve head
    - nasal to the fovea

3 Outer Concentric Circles:

  1. Equator: innermost
    - circle connecting the vortex veins
  2. Ora Serrata: middle
    - anterior termination of the retina and the junction between the retina and the ciliary body
  3. Pars Plana: outermost
    - located between the Ora Serrata and the Limbus

2 Sets of Lines:

  1. Major Arterioles or Vascular Arcades
    - 4 in number at 2, 4, 8 and 10 o’ clock positions
  2. Vortex Veins
    - along the equator
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7
Q

What is the Spiral of Tillaux?

A
  • External landmark of the Ora Serrata
  • Corresponds to the insertions of all four recti muscles
  • Any injury posterior to this area will highly involve the retina
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8
Q

What is the Pars Plana?

A
  • Located midway between the Spiral of Tillaux/Ora Serrata and the Limbus
  • 3 - 4 mm from the limbal edge
  • Safe zone for retinal surgery
    1. Pars Plana Vitrectomy
    2. Intravitreal Injections
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9
Q

What is the Foveal Avascular Zone?

A
  • 500 um dark area at the center of the fovea/macula
  • NO retinal capillaries (retinal circulation)
  • Relies only on choriocapillaries
    + from CHOROIDAL circulation: via Posterior Ciliary Arteries
    + INNER retinal layers (INL, IPL, GCL, NFL) which are supplied by the RETINAL circulation (via Central Retinal Artery), are ABSENT from the fovea
  • High concentration of xanthophylls
  • RPE: tall and dense

Appearance:
1. Fundus Photo: dark area at the center of the macula
2. Fluorescein Angiography: hypofluorescent (dark)
- leak outside the FAZ: EXTRA-foveal
- leak within the FAZ: SUB-foveal
3. Indocyanine Green Angiography: cherry red spot

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10
Q

What are the cell types found in the retina?

A

Neuronal Cells: signal transduction of light to vision

  1. Vertical
    - Photoreceptors (Rods and Cones)
    - Bipolar Cells
    - Ganglion Cells
  2. Horizontal/Interneurons
    - Horizontal Cells
    - Amacrine Cells

Glial Cells: supportive cells

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11
Q

Why is the retina considered to be an inverted structure?

A
  • Light rays must traverse the entire thickness of the retina to reach the photoreceptors at the OUTERMOST layer to begin signal transduction
  • Light stimulus is then converted into chemical and electrical signals which are propagated back INWARDS, passing again through the entire thickness of the retina
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12
Q

What is the 3 Cell Pathway of phototransduction?

A

Cell 1: Photoreceptors
- photons strike the photopigments in the photoreceptors
- photopigments split creating a chemical signal

Cell 2: Bipolar Cells
- intermediary/interneurons
- connects the two cells

Cell 3: Ganglion Cells
- axons carry signal through the optic nerve into the brain

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13
Q

What are the 10 layers of the retina?

A

Innermost to Outermost:

  1. Internal Limiting Membrane (ILM)
    - inner/basal footplate of the Muller cells
    - separates neurosensory retina from the vitreous
  2. Nerve Fiber Layer (RNFL): axons of ganglion cells
  3. Ganglion Cell Layer (GCL): cell bodies of ganglion cells
  4. Inner Plexiform Layer (IPL): axons of BC synapsing with GC
  5. Inner Nuclear Layer (INL): cell bodies of bipolar cells
  6. Outer Plexiform Layer (OPL): axons of PRs synapsing with BC
  7. Outer Nuclear Layer (ONL): cell bodies of photoreceptors
  8. Outer Limiting Membrane (OLM)
    - outer/apical footplate of the Muller cells
    - between inner segment of PRL and ONL
  9. Photoreceptor Layer (PRL): inner and outer segments of PRs
  10. Retinal Pigment Epithelium (RPE)
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14
Q

What are photoreceptors and their parts?

A
  1. Axons (LIGHT Band) = Outer Plexiform Layer
    - synapses of photoreceptors with bipolar cells
  2. Nucleus (DARK Band) = Outer Nuclear Layer
    - cell body/nucleus of photoreceptors
    ——————-ELM (LIGHT Band)——————-
  3. Inner Segment = Photoreceptor Layer
    - contains cytoplasm
    - Myoid Zone (DARK Band): other organelles
    - Ellipsoid Zone (LIGHT Band): mitochondria; junction of inner and outer segments
  4. Outer Segment (DARK Band) = Photoreceptor Layer
    - comprised of disks or modified cilia containing opsin-retinal complex
    - closer to the choroid and sclera
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15
Q

What are the FOUR HYPERreflective outer retinal bands seen in the SS-OCT?

A

(DARK) Outer Nuclear Layer
(LIGHT) External Limiting Membrane : apical processes of Muller Cells
(DARK) Myoid Zone of Inner Segment
(LIGHT) Ellipsoid Zone of Inner Segment
- densely packed with mitochondria causing increased backscattering of light and high refractive index
- junction of inner segment and outer segment
(DARK) Outer Segment
(LIGHT) Interdigitation Zone : junction of outer segment and RPE
(DARK + LIGHT) RPE/Bruch’s Membrane Complex

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16
Q

What are Bipolar Cells?

A
  • Interneurons
  • Connects Photoreceptors to Ganglion Cells
    1. Horizontal Cells
    2. Amacrine Cells
    3. Interplexiform Cells
  • Corresponds to 3 layers of the neurosensory retina:
    1. Outer Plexiform Layer: axons of PRs synapsing with bipolar cells
    2. Inner Nuclear Layer: cell bodies of bipolar cells
    3. Inner Plexiform Layer: axons of BCs synapsing with ganglion cells
17
Q

What are Ganglion Cells?

A
  • Connects the neurosensory retina to the brain
  • 1.2 M in number
  • Density depends on the area of the retina:
    + Foveola: Absent
    + PERIfovea: 8 - 10 rows; greatest thickness
    + Beyond the macula: 1 row only
  • Corresponds to 3 layers of the neurosensory retina:
    1. Inner Plexiform Layer: axons of BCs synapsing with ganglion cells
    2. Ganglion Cell Layer: cell bodies of ganglion cells
    3. Nerve Fiber Layer: axons of ganglion cells passing into the ON
18
Q

What is the Nerve Fiber Layer?

A
  • Axons of the ganglion cells which coalesce to form the Optic Nerve
  • Connects the retina to the brain

Optic Disc
- convergence point of all ganglion cell axons from the macula and peripheral retina
- corresponds to the optic nerve head

Papillo-Macular Bundle
- dense concentration of axons coming from the macula
- severe vision loss if damaged

19
Q

What are glial cells?

A

Non-neuronal cells which provide supportive functions to the retina
1. Microglia
2. Oligodendrocytes
3. Astrocytes
4. Muller Cells: main supporting structure encompassing the entire retina
- corresponds to 2 layers of the neurosensory retina:
1. Internal Limiting Membrane
+ inner footplate of the Muller cells
+ separates the neurosensory retina from the vitreous
2. External Limiting Membrane
+ outer footplate of the Muller cells
+ separates PRL from ONL

20
Q

What is the Retinal Pigment Epithelium?

A
  • Outermost layer of the retina
  • Supports the neurosensory retina and provides the substrates needed to initiate phototransduction process
  • Able to proliferate under pathologic conditions
  • (+) Lipofuscin: accumulates with age
  • (+) Potential space: between the photoreceptor layer and RPE
  • (+) Tight Junctions/Zonula Occludens: OUTER Blood Retina Barrier
21
Q

What is the Bruch’s Membrane?

A
  • Layer between the Retinal Pigment Epithelium and Choriocapillaris
  • (+) Drusen: in ARMD
  • Composed of 5 sublayers: innermost to outermost
    1. Basement membrane of RPE
    2. Inner collagenous layer
    3. Central elastic layer
    4. Outer collagenous layer
    5. Basement membrane of choriocapillaris
22
Q

Regional differences in the retinal structure of the eyes.

A

Macula
- all 10 layers are complete

Peripheral Retina
- all 10 layers are complete

Fovea
- innermost layers are ABSENT: INL, IPL, GCL, NFL
- (+) Henle’s Layer: part of OPL; high concentration of CONES
- NO RODS
- (+) Foveal Avascular Zone

Ora Serrata
- peripheral termination of the retina
- (+) Junctional complexes: between NSR and RPE; tightly adherent and NO potential space
- Neurosensory Retina –> NON-pigmented ciliary epithelium
- Retinal Pigment Epithelium –> PIGMENTED ciliary epithelium

23
Q

Appearance of retinal layers in Optical Coherence Tomography?

A

Hyporeflective (dark) layers: nuclear layers (GCL, INL, ONL)
Hyperreflective (bright) layers: axons and synapses (NFL, IPL, OPL)
Red/orange layer: RPE
Hazy layer underneath the RPE: Choroid

24
Q

What is Serous Neurosensory Detachment?

A

Central Serous Chorioretinopathy: if detachment is in the macula

Pathology: Extravasation or leakage of fluid due to a defect or dysfunction of the RPE (OUTER BRB)

  1. OCT: collection of hyporeflective fluid between the PRL and RPE
  2. FA: smokestack pattern (extravasating fluorescein rises to the top of the defect)
25
Q

What is the appearance of Diabetic Retinopathy on OCT and FA?

A
  • Dysfunction of the endothelium of the retinal vessels (INNER BRB)
  • Extravasation or leakage of blood or intraluminal contents into the retinal stroma

OCT: stromal cystic spaces interspersed in between retinal layers
FA: multiple cloud-like blotches due to leakage of dye

26
Q

What is a Macular Hole?

A

Absence of retinal layers at the macula

Full-thickness: complete absence of ALL layers
Partial-thickness: some layers are absent

27
Q

What is the appearance of Choroidal Neovascular Membrane on OCT?

A

Fusiform hyperreflective irregular lesions (blood vessels) involving the RPE and choroid

28
Q

Distribution of ocular blood flow.

A

Highly metabolic organ with increased blood flow

80%: Choroid
15%: Iris and Ciliary Body
5%: Retina

29
Q

Describe the blood supply and drainage of the retina.

A

Internal Carotid Artery –> Ophthalmic Artery –> either:

  1. Retinal Circulation
    - Anterior 2/3 (INNER) retina: NFL, GCL, IPL, INL
    - INNER Blood Retina Barrier:
    + retinal vessel lining are endothelium with tight junctions/zonula occludens
    + prevents seepage of intraluminal contents like blood and proteins
    - Central Retinal Artery –> Retinal Arterioles (vascular arcades) –> capillaries –> venules –> Central Retinal Vein –> Ophthalmic Vein
    –> Cavernous Sinus
  2. Choroidal Circulation
    - Posterior 1/3 (OUTER) retina: OPL, ONL, PRL, RPE
    - OUTER Blod Retina Barrier: Retinal Pigment Epithelium
    - ONLY blood supply of the FAZ and extreme retinal periphery (ora serrata)
    - blood vessels are fenestrated –> intraluminal contents can diffuse into the choroidal layer
    - Posterior Ciliary Artery (Medial and Lateral) –> Long (1) and Short (multiple) Posterior Ciliary Arteries –> Choriocapillaries –> venules
    –> Vortex Veins –> Ophthalmic Vein –> Cavernous Sinus
30
Q

Differentiate the use of Fluorescein Angiography and Indocyanine Green Angiography?

A

FA
- delineates retinal vessels
- choroidal circulation NOT seen
- FAZ: dark area

IGA
- delineated BOTH retinal circulation and LARGE choroidal vessels
- FAZ: cherry red

31
Q

How to differentiate arterioles and venules in a fundus photo?

A

Arterioles: smaller in caliber, bright red
Venules: larger, dark red

32
Q

What are the two blood retina barriers in the eye?

A
  • Regulates supply of oxygen and other molecules into the retina
  • Pathology leads to extravasation of intraluminal contents into the retinal layers
  1. Inner BRB: endothelium of the retinal vessels
  2. Outer BRB: retinal pigment epithelium
33
Q

Differentiate CRAO vs CRVO vs BRVO based on fundus photo.

A

Central Retinal Artery Occlusion
- whitening or pallor of the entire retina due to loss of blood supply
- cause: cardiac EMBOLUS
- fovea: cherry red or chico-brown spot because pallor of the entire retina accentuates the patent choroidal circulation underneath

Central Retinal Vein Occlusion
- occlusion of the central retinal vein at the level of the lamina cribrosa posterior to the optic disc/optic nerve head
- cause: THROMBOSIS
- (+) dot hemorrhages present on all quadrants
- (+) tortuous and dilated venules

Branch Retinal Vein Occlusion
- (+) segmental hemorrhagic area RESPECTING the horizontal raphe
- cause: venule compression by an adjacent thickened arteriole due to a common adventitial sheath

34
Q

What is the Hyaloid Circulation?

A
  • In-utero vascular circulation which involutes at around 12-36 weeks
  • Usually with NO visual consequence
  • Pathologies:
  1. Mittendorf Dot: on the lens
  2. Bergmeister’s Papilla: elevated membrane at the ONH
  3. Persistent Fetal Vasculature: membrane emanating from the disc to the posterior lens capsule/retinal periphery; remnant of the hyaloid artery
  4. Persistent Pupillary Membrane
35
Q

Characteristics of the retinal blood supply and drainage.

A
  1. Dual BUT non-overlapping circulation
    - Retinal (Central Retinal Artery): INNER retina (NFL, GCL, IPL, INL)
    - Choroidal (Posterior Ciliary Arteries): OUTER retina (OPL, ONL, PRL, RPE)
    - NO collateral circulation or anastomosis between the two thus doubly vulnerable to loss of blood supply
  2. ENDARTERIAL arrangement
    - a single retinal arteriole supplies a single capillary bed
    - interruption of that supply causes a loss of supply to the area of the retina being supplied by the capillary bed
  3. COMMON adventitial sheath between adjacent artery and vein
    - pathology in either vessel will affect the other due to their close proximity
  4. LOW venous hydrostatic pressure
    - susceptible to compression and obstruction due to elevated IOP, intraorbital pressure or ICP
36
Q

What is the vitreous gel?

A

Composition:
1. Water - most abundant component
2. Hyaluronan - primary solid component
3. Collagen fibrils - main structural framework

3 Parts:
1. Central Vitreous
2. Cortical Vitreous
3. Vitreous Base

37
Q

Primary sites of attachment of the vitreous?

A
  • strands of collagen fibrils are adherent to certain areas of the posterior segment
    1. Vitreous Base: where vitreous is MOST adherent to the retina; most common location of retinal detachments and tears
    2. Optic Nerve Head
    3. Along vascular arcades
    4. Macula
    5. Posterior Lens Capsule
38
Q

Common pathologies of the retina related to the vitreous.

A

Retinal Tear
- tearing of the retina due to traction by the vitreous most commonly at the vitreous base at the retinal periphery

VitreoMacular Traction –> Macular Hole
- posterior vitreous pulls on its attachment at the fovea resulting to cystic changes on OCT

Proliferative Diabetic Retinopathy
- (+) florid neovascularization
- (+) fibrous membrane formation: grow from the retinal surface to attach to the vitreous gel
- in later stages of the disease, traction by the vitreous causes retina to detach
- treatment: membranolysis/adhesiolysis to sever the attachment of retina to the vitreous and vitrectomy to prevent recurrence

Ophthalmology (44 decks)

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