Unit 3 - Imaging Flashcards
What are top 3 most reflective layers on OCT?
- RNFL
- Ellipsoid zone (junction between inner segment and outer segments)
- RPE/Bruchs
Current OCT instruments use which wavelength of what type of light?
IR light of about 840nm
What absorbs light between 200-600nm?
haemoglobin
What absorbs light above 1000nm?
Water in tissue
What does doppler OCT measure?
Velocity of blood flow in eye
What spacing are the ETDRS grids?
1,3,6mm
What is the average retinal thickness?
250um
Which people tend to have thinner retinas?
- Myopes
- Older patients
- Women
- African patients
What drug may cause IRF?
Latanoprost
What do vitelliform lesions look like on OCT?
Yellow, round elevated lesions below neurosensory retina
What do pseudcysts look like on OCT and what causes them?
Round or oval cystic spaces
Represent a loss of muller cells and may be a precursor to a macula hole
What do tubulations look like on OCT?
round/oval lesions surrounded by hyperflectivity caused by a rearrangement of the photoreceptor layer in response to injury.
What colour light do you use to take RNFL photos?
Short wavelength i.e. blue
What colour light do you use to take choroid photos?
Long wavelength i.e. red
What blocks green light?
Pigment in RPE, useful for viewing nerve fibre layer, diabetic retinopathy, ERMs and PED.
What size are microanuerysms?
30um
When is an FFA better than an OCTA?
With larger PED
What are the pros of OCTA?
- Quick, non-invasive
- Can see different layers
- Good sensitivity and specificity
- Can help differentiate immature, mature and hypermature lesions
What are the cons of OCTA?
Don’t work well with PED
Extreme flow patterns may be undetected
Can be noisy and difficult to spot leak
What are the cons of FFA?
- Labour intensive
- Uncomfortable for patient
- Danger of anaphylaxis
- Side effects of Fluorescein
- Can’t see different layers
What are the side effects of fluorescein?
Flushing
Erythema
Nausea
Vomiting
Hypersensitivity reacion
Anaphylactic shock and death
How is a projection artefact caused in OCTA?
Light is reflected at a deeper level than it should be causes blood flow signals where they should be absent.
What do motion artefacts look like on OCTA?
Horizontal white lines
What can cause areas that look like non-perfusion on OCTA?
Media opacities
What is the best OCTA scan for looking at nAMD?
6 x 6mm
When would you use a 12X12 OCTa scan?
RVO and DR
Covers macula and just beyond arcades
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
Where do Type 1 CNVM form?
Sub-RPE
Where do Type 3 CNVM form?
Within retina
What are outer retinal corrugations?
Undulating sheets of hyperreflective material above Bruchs
What is the difference between drusen and outer retinal corrugations?
Drusen sit within Bruchs
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)
Who does focal choroidal excavation effect most?
Myopic asian males
What other conditions are associated with FCE ?
ERM, CSR, dry AMD, PCV,
What percentage of FCE may develop CNVM?
10%
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
When do you get reduced fluorescence in FAF?
Loss of lipofuscin, reduced RPE metabolic demand
