OCT Flashcards

1
Q

List the retinal layers from innermost to outermost

A

Inner Limiting Membrane
Nerve Fibre Layer
Ganglion Cell Layer
Inner Plexiform Layer
Inner Nuclear Layer
Outer Plexiform Layer
Outer Nuclear Layer
Outer Limiting Membrane
Inner Photoreceptor Segments
Outer Photoreceptor Segments
RPE
Choroid

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2
Q

How does OCT work?

A

Interferometry:
IR light is sent towards a beamsplitter which sends some light to a mirror (at a known distance) and some towards the retina.
The delay in light returning to the detector from the retina allows an image to be build up via interference patterns when compared with the light returning from the mirror.
A longer delay indicates further depth, and longer wavelengths can be used to penetrate deeper.

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3
Q

What do bright bands in an OCT image represent?

A

Layers with high reflectivity (RPE, NFL, plexiform layers)

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4
Q

What do dark bands in an OCT image represent?

A

Layers with low reflectivity (cell bodies, blood vessels)

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5
Q

What is an A-scan?

A

Vertical, 1D scan

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6
Q

What is a B-scan?

A

Multiple A-scans of varying depths combined, allowing for a 3D image to be created

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7
Q

How many A-scans are in a B-scan?

A

512-1024

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8
Q

What was the first type of OCT? What was its light source peak and how many A-scans per sec could it do?

A

Time-domain (TD)
Light source peak: 830nm
A-scans per sec: 400

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9
Q

What was the second type of OCT? What was its light source peak and how many A-scans per sec could it do?

A

Spectral-domain (SD)
Light source peak: 830nm
A-scans per sec: 20,000-40,000

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10
Q

What additional features does an SD-OCT have over a TD OCT?

A

Takes fundus photo
Takes multiple B scans in one area and averages them giving better resolution and reduced noise, motion artefact and chance of missing lesions

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11
Q

What is the most modern type of OCT? What is its light source peak and how many A-scans per sec could it do?

A

Swept-source (SS)
Light source peak: 1050-1060nm
A-scans per sec: 100,000-400,000

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12
Q

What advantages does an SS-OCT have over the older versions?

A

Increased light source peak allows for deeper tissue penetration

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13
Q

What are the disadvantages of TD OCT?

A

Time-consuming
Only produced cross-sectional images

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14
Q

What are the limitations of OCT?

A

Requires patient cooperation: no blinks or movement
Opacities can interfere with images
Operator error can result in unfocused scans

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15
Q

What are the advantages of OCT?

A

Non-contact
Relatively easy for patient
Allows easy and instant imaging of cornea, retina, choroid, optic nerve head and anterior chamber angle
Can monitor over time
High repeatability

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16
Q

What are 3D scans useful for?

A

Imaging of large area of retina

17
Q

What are radial scans useful for?

A

Monitoring macular lesions and ONH

18
Q

What are raster scans useful for?

A

Detailed (higher resolution) scans of a particular area in any angle needed

19
Q

What is OCT clinically useful for?

A

Monitoring conditions
Having a baseline on record for future detection
Objective records - can be compared in the future (easier than interpreting notes)

20
Q

What is the Zeiss workstation?

A

Combines HFA visual fields results alongside OCT scans so link between VFs and RGC loss can be seen more easily

21
Q

What is the Hood report?

A

Predicts VF loss from OCT scan RNFL loss and aids understanding of the link between the two

22
Q

What are the possible artefacts that you could get on an OCT?

A

Blinking
Movement
Opacities
Degraded image
Out of register
Mirror
Misalignment

23
Q

What can a degraded image artefact result in?

A

Misidentification of layers
Retina looks broken (when it’s not)
Central thickness map incorrect

24
Q

What can an out-of-register artefact result in?

A

Part of scan cut off - central thickness map incorrect due to this

25
Q

What can a mirror artefact result in? How can it be avoided?

A

Image folded in on itself - often in high myopes
Use vertical scans to avoid

26
Q

What can a blink artefact result in?

A

Part of scan missing

27
Q

What can a motion artefact result in?

A

Parts of scan repeated

28
Q

What can a misalignment artefact result in?

A

Disc located in the wrong place between OCT and photo - makes normative data incorrect