Unit 3 - Retinal imaging Flashcards

1
Q

What is an OCT?

A
  1. Non-contact
  2. Topographical
  3. Biomicoscopic device producing High res, cross-sectional digital images in vivo
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2
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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3
Q

What spacial resolution does OCT give?

A

as good as 2um

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4
Q

Current instruments use which wavelenght of what type of light?

A

IR light of about 840nm

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5
Q

What absorbs light between 200-600nm?

A

haemoglobin

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6
Q

What absorbs light above 1000nm?

A

Water in tissue

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7
Q

What does dopper OCT measure?

A

Velocity of blood flow in eye

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8
Q

What spacing are the ETDRS grids?

A

1,3,6mm

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9
Q

What is the average retinal thickness?

A

250um

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10
Q

Which people tend to have thinner retinas?

A
  1. Myopes
  2. Older patients
  3. Women
  4. African patients
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11
Q

What percentage of OCT scans have artefacts?

A

90%

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12
Q

What percentage of OCT scans have clinically significant artefacts?

A

5-8%

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13
Q

How many A-scans per second are taken in time domain, spectral and swept source OCTs?

A

400

15000- 40k

100k

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14
Q

What is the axial resolution in time domain, spectral and swept source OCTs?

A

10mics

6-7mics

3mics

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15
Q

What drug may cause IRF?

A

Latanoprost

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16
Q

What do vitelliform lesions look like on OCT?

A

Yellow, round elevated lesions below neurosensory retina

17
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

18
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.

19
Q

What causes ring flare on fundus photography?

A

Being too close

20
Q

What causes a blue haze on fundus photography?

A

Being too far away

21
Q

How do you deal with IOLs on fundus photography?

A

Set exposure lower

22
Q

How can you take A/C photos?

A

Pull back and focus on pupil margin.

23
Q

What colour light do you use to take RNFL photos?

A

Short wavelength i.e. blue

24
Q

What colour light do you use to take choroid photos?

A

Long wavelength i.e. red

25
What blocks green light?
Pigment in RPE, useful for viewing nerve fibre layer, diabetic retinopathy, ERMs and PED.
26
What do types of digital sensor are there?
Charged coupled devices Complimentary Metal Oxide Semiconductors (CMOS)
27
What are the advantages of CMOS?
Easier to produce Use less power Chips of choice
28
What are the advantages of CCDs?
Produce very high quality images but very expensive to produce.
29
What types of picture file formats are there?
* JPEG (Joint photographic experts group) * TIFF (Tagged image file format)
30
Which are bigger JPEG or TIFF?
TIFF
31
What images are captured in diabetic screening?
2 x 45 degrees once centred on macula one on disc
32
What size are microanuerysms?
30um
33
What resolution must be set for diabetic screening?
30um
34
What screen should images be viewed on?
1200 x 1080, laptops are considered unsuitable.