Reviewing retina

Question 1

Name 10 layers of retina

From outwards to inwards

Answer 1

Chroid

1. Pigment epithelium
2. Rods and cones
3. Outer limiting membrane
4. Outer nuclear layer
5. Outer plexiform (molecular) layer
6. Inner nuclear layer
7. Inner plexiform (molecular) layer
8. Ganglion cell layer
9. Nerve fibre layer
10. Internal limiting membrane

Vitreous

Question 2

Retinal pigment epithelium (RPE)

1. Extension from where to where?
2. Relationship to choroid?

Answer 2

Retinal pigment epithelium (RPE)

• Single layer of cells which extend from the optic nerve to the ora serrata
• The base of each cell rests on a basement membrane which forms part of the Bruch’s membrane of the choroid

Question 4

The neural retina

1. Photoreceptors ? 2 types?
2. First order and second order neurons?

Answer 4

The neural retina

1. Photoreceptors Rods & cones
2. The bipolar cells form the 1st order neurones

The ganglion cells form the 2ndorder neurones & become myelinated after passing through the lamina cribrosa

NB: their axons form the optic nerve

Question 5

Retinal blood supply

Sources of blood supply?

Answer 5

2 sources of blood supply to the retina:

1. central retinal artery
2. choroidal blood vessels

Question 6

1. Greatest source of retinal blood supply? Supply what part of retina?
2. What is the remaining? Supply what part of retina

Answer 6

1. The choroid receives the greatest blood flow (65-85%) and is vital for the maintenance of the outer retina (particularly the photoreceptors)
2. The remaining 20-30% flows to the retina through the central retinal artery from the optic nerve head to nourish the inner retinal layers.

Question 7

CENTRAL RETINAL ARTERY

1. How many branches in retina?
2. Where do they emerge from? Describe their course?

Answer 7

1. The central retinal artery has 4 main branches in the human retina
2. The vessels emerge from the optic nerve head & run in a radial fashion, curving towards the fovea

Question 8

Label the branches

Answer 8

Question 9

CHOROID

1. What is it?
2. Extension?
3. Thickest and thinnest where?

Answer 9

1. Thin, soft brown coat on the inner surface of sclera
   Extremely vascular
2. Extends from the optic nerve to the ciliary body
3. Thickest posteriorly (0.2mm) & gradually thins anteriorly (0.1mm)

Question 10

CHOROID

1. Name of space between sclera and choroid
2. Structure run across this space?
3. What other structure it contains?

Answer 10

1. There is a perichoroidalspace which sits between the sclera and choroid
2. Suprachoroid lamina runs across this space (pigmented connective tissue)
3. Short post. ciliary arteries & nerves are also here

Question 11

CHOROID

How many layers? Name?

Answer 11

1. Vessel ( External)
2. Capillary ( Middle)
3. Brunch’s membrane ( Internal)

Question 12

CHOROIDAL LAYERS

Describe Vessel layer: Tissue? Vessels?

Answer 12

• Loose connective tissue
• Medium & large blood vessels embedded

Question 13

CHOROIDAL LAYERS

Capillary layer?

Function? Density?

Answer 13

• Network of capillaries
• Arteries & veins from vessel layer are responsible for feeding & drainage of these capillaries
• Density of capillaries is greatest at the macula

Question 14

CHOROIDAL LAYERS

Bruch’s membrane

Name components?

Answer 14

5 components

• Basement membrane of the endothelium of the capillaries of the capillary layer
• Outer collagen fibre layer
• Elastic fibre layer
• Inner collagen fibre layer
• Basement membrane of the pigment epithelium of the retina

Question 15

CHOROID

Primary function?

Answer 15

• nourish the outer layers of the retina by blood supply → nutrition to the retina

Question 16

Retinal vessels

Any variation in appearance? What’s common?

Answer 16

• vary in appearance between people
• common variation is that in some people small arteries run from the disc to the macula = cilioretinal vessels

Question 17

FUNDUS COLOUR

1. What factors detemine colour?
2. Relationship with other structure?

Answer 17

1. how much MELANIN is in the Retinal pigment epithelium
   Melanocytes in the choroid
   Haemoglobin in the retinal & choroidal vasculature
2. Relationship between fundus colour and the person’s:
   Skin colour
   Hair colour
   Iris colour

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Question 18

FUNDUS COLOUR

Variation between races?

Answer 18

Question 19

Retinal landmarks

Macula lutea

1. Position in relation to disc and retina?
2. Colour?
3. Name of depression?

Answer 19

Macula lutea

1. At the centre of the posterior part of the retina
   Always temporal to the disc
2. Slightly darker in colour to the surrounding retina
3. Has a central depression = Fovea

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Question 20

MACULA

1. Distinguising Characteristics?
2. Structure allowing light fall directly on photopigment?

Answer 20

1. The macula contains only cones.
   * The density of the cones is greater than for any other region of the retina.
2. The neural elements of the inner retina are pushed aside to allow light to fall directly on the photopigment-containing outer segments of cones ⇒ foveal pit.

Question 21

The fovea
1. Vascular network? Metabolic nourishment?

2. Significance of this adaptation?

Answer 21

1. Avascular
   Metabolic nourishment from the choroid rather than directly from the blood vessels.
2. Prevents the scattering of light by retinal vessels, maximising the visual resolution provided by the fovea.

Question 23

Looking at the retina & choroid
Ways to view retina?

Answer 23

• Ophthalmoscopy
  Direct
  Indirect
• Photography
  Colour
  Red free
• AngiographyFundus Fluorescein (FFA)
• Optical Coherence Tomography (OCT)

Question 24

• *Fundus Fluorescein Angiograms (FFA)**
  1. How to do it?

2. What is it?

Answer 24

1. Fluorescein (orange water-soluble dye) injected intravenously circulates in the blood

2 types used when performing FFA

Ensures that blue light enters the eye & only yellow-green light enters the camera

2. Photographing the passage of the dye through the retinal & choroidal circulations

Question 25

**FFA Filters** Name 2 filters?

Answer 25

1. **Blue excitation filter** White light from the camera passes through this Blue light emerges & enters the eye Excites the fluorescein molecules in retina 2. **Yellow-green barrier filter** Blocks reflected blue light from the eye Allows only yellow-green light to pass through 36

Question 26

**FFA technique?**

Answer 26

Patient sits on front of the camera Fluorescein injected intravenously Images taken at ~ 1 sec intervals, 5-25 seconds after the injection

Question 27

**FFA –adverse effects ?**

Answer 27

* Skin & urine discolouration * Mild Nausea, vomiting Flushed skin Itching, hives Sneezing * Serious (rare) Laryngeal oedema Bronchospasm Anaphylaxis Syncope (lapse in consciousness)

Question 28

FFA -phases 1. Where does fluorescein enter eye and its course? 2. Why difficult to see choroidal circulation?

Answer 28

1. Fluorescein enters eye through **ophthalmic artery** & passes to *choroidal circulation slightly before retinal circulation* 2. b/c it **fills quickly with free fluorescein & the RPE blocks the view of choroidal fluorescence**

Question 29

**FFA -phases** 1. **Phases? How many ?**

Answer 29

5 phases : 1. Choroidal 2. Arterial 3. Arteriovenous 4. Venous 5. Late

Question 30

FFA –phases -choroidal 1. Other name ? 2. Time? 3. Appearance of choroid? 4. What artery fills?

Answer 30

1. Pre-arterial phase 2. 8-12 seconds after dye injected 3. Patchy filling of choroid as fluorescein leaks through the choriocapillaries 4. Cilioretinal artery (if present) fills now

Question 31

**FFA –phases -Arterial**

Answer 31

* Arterial filling seen * Choroidal filling continues

Question 32

**FFA –phases -Arteriovenous**

Answer 32

* Complete filling of arteries & capillaries * Lines the venous walls leaving a strip * Choroidal fluorescence increases (not so obvious in highly pigmented eyes)

Question 33

**FFA –phases -venous** **1. Early?** **2. Mid?** **3. Late?**

Answer 33

1. **Early** Complete arterial & capillary filling 2. **Mid** Almost complete venous filling 3. **Late** ​Complete venous filling Decreased concentration of dye in arterie

Question 34

**FFA –phases -late** Effects? Intensity? How long no longer seen? How long to get eliminated?

Answer 34

* Late/elimination phase - excrete via urine * Shows effects of continuous recirculation, dilution & elimination of the dye * Intensity of fluorescein becomes weaker * Fluorescein no longer seen on FFA after 10 mins * Eliminated from body within 24 hours

Question 35

**Hyperfluorescence** 1. Cause? 2. Types?

Answer 35

1. **↑ fluorescence** could be c/b ***normal density*** of fluorescein in the fundus or **↑ in fluorescein content** in the tissues 2. **Types of hyperfluorescence (abnormal)** Transmission/window defect Pooling Leakage Staining

Question 36

**Hyperfluorescence** **Transmission/window defect** Cause?

Answer 36

**Atrophy/absence of the RPE**

Question 37

**Hyperfluorescence** - **Pooling** Causes?

Answer 37

**Dye pools** in the anatomical space as a result of ***breakdown of the outer blood-retina barrier***

Question 38

**Hyperfluorescence​- Leakage** Causes?

Answer 38

Can arise from abnormal choroidal vessels (**neovascularisation**)

Question 39

Hypofluorescence 1. Cause ? 2. Types? (3)

Answer 39

1. ↓ in presence of fluorescein **optical obstruction** of normal density of fluorescein in the tissue or by **low perfusion of tissue** 2. _Types of hypofluorescence (abnormal)_ Blockage of retinal fluorescence Blockage of background choroidal fluorescence Filling defects 50

Question 40

* *Hypofluorescence** * *Blockage of retinal fluorescence** Causes?

Answer 40

* Can be due to **lesions anterior** to the retina such as **severe bleeding**

Question 41

**Hypofluorescence Blockage of background choroidal fluorescence** Cause?

Answer 41

Caused by conditions which **block fluorescence of BOTH choroid and retina**

Question 42

**Hypofluorescence- Filling defects** Cause?

Answer 42

Caused by **vascular occlusion** or **loss of vascular bed**

Question 43

What to look for in FUNDUS? 1. Disc? 2. Vessel? 3. Macula? 4. Peripheral retina?

Answer 43

Look carefully at the 1. Disc Clear/blurry edges? Oval/irregular shape? Cupping? 2. Vessels Blockages/leakage? 3. Macula Slightly darker red? Deposits/abnormalities? 4. Peripheral retina Colour/abnormalities?

Question 44

**Optical Coherence Tomography​ Types of OCT**

Answer 44

1. Stratus OCT 2. Cirrus OCT