Unit 3 - Retinal imaging

Question 1

What is an OCT?

Answer 1

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

Question 2

What are top 3 most reflective layers on OCT?

Answer 2

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

Question 3

What spacial resolution does OCT give?

Answer 3

as good as 2um

Question 4

Current instruments use which wavelenght of what type of light?

Answer 4

IR light of about 840nm

Question 5

What absorbs light between 200-600nm?

Answer 5

haemoglobin

Question 6

What absorbs light above 1000nm?

Answer 6

Water in tissue

Question 7

What does dopper OCT measure?

Answer 7

Velocity of blood flow in eye

Question 8

What spacing are the ETDRS grids?

Answer 8

1,3,6mm

Question 9

What is the average retinal thickness?

Answer 9

250um

Question 10

Which people tend to have thinner retinas?

Answer 10

1. Myopes
2. Older patients
3. Women
4. African patients

Question 11

What percentage of OCT scans have artefacts?

Answer 11

90%

Question 12

What percentage of OCT scans have clinically significant artefacts?

Answer 12

5-8%

Question 13

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

Answer 13

400

15000- 40k

100k

Question 14

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

Answer 14

10mics

6-7mics

3mics

Question 15

What drug may cause IRF?

Answer 15

Latanoprost

Question 16

What do vitelliform lesions look like on OCT?

Answer 16

Yellow, round elevated lesions below neurosensory retina

Question 17

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

Answer 17

Round or oval cystic spaces

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

Question 18

What do tubulations look like on OCT?

Answer 18

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

Question 19

What causes ring flare on fundus photography?

Answer 19

Being too close

Question 20

What causes a blue haze on fundus photography?

Answer 20

Being too far away

Question 21

How do you deal with IOLs on fundus photography?

Answer 21

Set exposure lower

Question 22

How can you take A/C photos?

Answer 22

Pull back and focus on pupil margin.

Question 23

What colour light do you use to take RNFL photos?

Answer 23

Short wavelength i.e. blue

Question 24

What colour light do you use to take choroid photos?

Answer 24

Long wavelength i.e. red

Question 25

What blocks green light?

Answer 25

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

Question 26

What do types of digital sensor are there?

Answer 26

Charged coupled devices

Complimentary Metal Oxide Semiconductors (CMOS)

Question 27

What are the advantages of CMOS?

Answer 27

Easier to produce

Use less power

Chips of choice

Question 28

What are the advantages of CCDs?

Answer 28

Produce very high quality images but very expensive to produce.

Question 29

What types of picture file formats are there?

Answer 29

• JPEG (Joint photographic experts group)
• TIFF (Tagged image file format)

Question 30

Which are bigger JPEG or TIFF?

Answer 30

TIFF

Question 31

What images are captured in diabetic screening?

Answer 31

2 x 45 degrees once centred on macula one on disc

Question 32

What size are microanuerysms?

Answer 32

30um

Question 33

What resolution must be set for diabetic screening?

Answer 33

30um

Question 34

What screen should images be viewed on?

Answer 34

1200 x 1080, laptops are considered unsuitable.