Unit 3 - Imaging Flashcards

1
Q

What are top 3 most reflective layers on OCT?

A
  1. RNFL
  2. Ellipsoid zone (junction between inner segment and outer segments)
  3. RPE/Bruchs
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2
Q

Current OCT instruments use which wavelength of what type of light?

A

IR light of about 840nm

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3
Q

What absorbs light between 200-600nm?

A

haemoglobin

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4
Q

What absorbs light above 1000nm?

A

Water in tissue

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5
Q

What does doppler OCT measure?

A

Velocity of blood flow in eye

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6
Q

What spacing are the ETDRS grids?

A

1,3,6mm

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7
Q

What is the average retinal thickness?

A

250um

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8
Q

Which people tend to have thinner retinas?

A
  1. Myopes
  2. Older patients
  3. Women
  4. African patients
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9
Q

What drug may cause IRF?

A

Latanoprost

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10
Q

What do vitelliform lesions look like on OCT?

A

Yellow, round elevated lesions below neurosensory retina

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11
Q

What do pseudcysts look like on OCT and what causes them?

A

Round or oval cystic spaces

Represent a loss of muller cells and may be a precursor to a macula hole

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12
Q

What do tubulations look like on OCT?

A

round/oval lesions surrounded by hyperflectivity caused by a rearrangement of the photoreceptor layer in response to injury.

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13
Q

What colour light do you use to take RNFL photos?

A

Short wavelength i.e. blue

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14
Q

What colour light do you use to take choroid photos?

A

Long wavelength i.e. red

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15
Q

What blocks green light?

A

Pigment in RPE, useful for viewing nerve fibre layer, diabetic retinopathy, ERMs and PED.

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16
Q

What size are microanuerysms?

17
Q

When is an FFA better than an OCTA?

A

With larger PED

18
Q

What are the pros of OCTA?

A
  1. Quick, non-invasive
  2. Can see different layers
  3. Good sensitivity and specificity
  4. Can help differentiate immature, mature and hypermature lesions
19
Q

What are the cons of OCTA?

A

Don’t work well with PED
Extreme flow patterns may be undetected
Can be noisy and difficult to spot leak

20
Q

What are the cons of FFA?

A
  1. Labour intensive
  2. Uncomfortable for patient
  3. Danger of anaphylaxis
  4. Side effects of Fluorescein
  5. Can’t see different layers
21
Q

What are the side effects of fluorescein?

A

Flushing
Erythema
Nausea
Vomiting
Hypersensitivity reacion
Anaphylactic shock and death

22
Q

How is a projection artefact caused in OCTA?

A

Light is reflected at a deeper level than it should be causes blood flow signals where they should be absent.

23
Q

What do motion artefacts look like on OCTA?

A

Horizontal white lines

24
Q

What can cause areas that look like non-perfusion on OCTA?

A

Media opacities

25
What is the best OCTA scan for looking at nAMD?
6 x 6mm
26
When would you use a 12X12 OCTa scan?
RVO and DR Covers macula and just beyond arcades
27
What are the two clasification systems for CNVM?
One based on OCT images, Type 1, type 2 and type 3 One based on FFA images, Classic, occult
28
Where do Type 1 CNVM form?
Sub-RPE
29
Where do Type 3 CNVM form?
Within retina
30
What are outer retinal corrugations?
Undulating sheets of hyperreflective material above Bruchs
31
What is the difference between drusen and outer retinal corrugations?
Drusen sit within Bruchs
32
What are the two types of focal choroidal excavation?
Conforming (no separation between posterior retina and RPE) and non-conforming (separation between posterior retina and RPE)
33
Who does focal choroidal excavation effect most?
Myopic asian males
34
What other conditions are associated with FCE ?
ERM, CSR, dry AMD, PCV,
35
What percentage of FCE may develop CNVM?
10%
36
In FAF what lesions will show increased flurophore?
Lipofuscin related i.e. Bests, Stargardts, Pattern dystrophy, CSCR Other fluorophores i.e. disc drusen, astryocyic hamatomas
37
When do you get reduced fluorescence in FAF?
Loss of lipofuscin, reduced RPE metabolic demand