OCT

Question 1

What are the positives of OCT?

Answer 1

-allows you to see 3D structures of retina, vitreous and optic nerve head as it has a high resolution
-gives quantifiable measurements like intrea-retinal layer thickness and volumes
-allows for statistical analysis by giving normative values and progression
-requires no patient prep so no dilation or anaesthetic, its quick and gives images instantly

Question 2

what are the three types of oct from oldest to newest?

Answer 2

-time domain (TD)
-spectral domain (SD) (mosy current octs are this one)
-swept source (SS)

Question 3

what properties were that of TD?

Answer 3

-slow
-low resolution
-max 400 A scans / s
-axial resolution of max 10 micrometers
-could see from vitreous surface to RPE
-wavelengths from 810-840nm

Question 4

what are the properties of SD OCT?

Answer 4

-faster/ higher res
-27,000-70,000 A scans/ s
-axial resolution 5-7 micrometres
-can see from post vitreous surface - sclera (possible in EDI mode)
-wavelengths of around 840-870nm

Question 5

what are the properties of swept source OCT

Answer 5

-fastest highest res
-100,000-400,000 A scans /s
-axial resolution 5 micrometers
-sees from post vitreous to sclera (more reliable in EDI mode)
-wavelength 1050nm

Question 6

whats the name of the oct that uses swept source?

Answer 6

Topcon Triton

Question 7

be able to label oct of anterior eye and cornea

Answer 7

check optom ss or google docs

Question 8

what can OCT allow you to see?

Answer 8

Looking at anterior eye structures
Looking at layers of cornea
Anterior chamber angle
Looking at retina and choroid
Seeing optic nerve head

Question 9

what are normal retinal and choroidal oct features

Answer 9

-Foveal bulge
-Thick blood vessels in the choroid compared to fine blood vessels which are the choriocapillaris, these are closer to the retina than the thick blood vessels
-Sclera is the line below the choroid
-Lines going into the sclera are blood vessels coming from choroid into sclera

Question 10

make sure to look at the google doc page 15 to label the diagrams

Answer 10

ok

Question 11

what are the 3 types of macular scans?

Answer 11

Grid
Radial
Raster - good if you have macular pathology in a small area as it gives you good quality scans

Question 12

what are macular cube scans? What are they used for?

Answer 12

-Oct scans that are made of lots of grid scans layered together and gives you a good sense of retinal volume.
-Used for analysis of the retinal layers to compare with the normal database so can give you the retinal thickness relative to normal

Question 13

give 3 things that make a good OCT image

Answer 13

-good technical skills of the one operating the OCT
-compliant patient
-free from artefacts

Question 13

what are the 4 scan protocols?

Answer 13

-Wide scan on Topcon Triton protocol gives you disc and macula in one scan
-Disc scan
-Macular cube
-Macular scan

Question 14

what are the 6 OCT artefacts?

Answer 14

-blink artefacts
-degraded image
-mirror artefact
-motion artefact
-out of register
-misalignment artefact

Question 15

what happens to light entering the eye in an OCT scan?

Answer 15

-Passes through clear ocular structures - disease can cause shadows and opacities which will affect the oct signal and will be evident on the scan
-Refracted by structures
-Absorption

Question 16

how can you get a better quality OCT on a patient with cataract?

Answer 16

use a longer wavelength OCT which may give better penetration through the cataract

Question 17

what does posterior hyaloid mean in OCT?

Answer 17

fairly common finding especially in myopes but you should consider PVD or RD so talk to the patient about flashes and floaters

Question 18

why may a patient get false OCT results?

Answer 18

Some databases for OCTs do not fully represent all populations so some people may be given a false result because their population has not been represented

Question 19

what are the first 2 steps in analysing OCT images?

Answer 19

-check scan quality
-make sure to scan through the OCT B-scan

Question 20

what can you do to help prevent segmentation errors?

Answer 20

• Look at the reports produced by the
  OCT
• If the patient has had an OCT before
  using the follow up setting when
  taking an image is helpful

Question 21

Are measurements
from different
devices
comparable?

Answer 21

no

Question 22

how can you tell between cotton wool spots and drusen in OCT?

Answer 22

cotton wool spots appears in the nerve fibre layer whereas drusen appears in the retinal pigment epithelium