Imaging Part 2 Flashcards
which types of OCTs are currently on the market (general)?
3rd gen “time domain”
4th gen “spectral domain”
what generation is the stratus OCT
3rd gen
what is the depth/axial resolution of the Stratus OCT?
8-10 microns
anything less than that it can not resolve
how does the Stratus OCT display in “false color” scale?
red-white: high reflectivity (RPE and RNFL)
blue-green: low reflectivity (cell bodies, photoreceptors and choroid)
black: very low reflectivity (vitreous)
reflectivity rules for:
layers oriented perpendicular to the pathway of light
- higher reflectivity
- red
- RNFL, RPE
reflectivity rules for:
layers oriented parallel to the pathway of light
- lower reflectivity
- nuclear layers or cell body layers
reflectivity rules for vitreous
very low reflectivity (black)
how many retinal layers can be resolved with Stratus OCT vs. 4th gens OCTs
Stratus (3rd gen): maybe 4-5 layers well
4th gen: all layers well (everything)
how is Stratus OCT at retinal nerve fiber layer analysis
can show thinning of the RNFL thickness which is an early indicator of glaucoma (stratus can segment out of the RNFL)
how is Stratus OCT at optic nerve head analysis
- glaucomatous cupping can be measured with OCT
- a series of radial line scans are used to represent the whole ONH- there is much interpolation b/w line scans
how is Stratus OCT in macular thickness maps
- stratus cannot segment out the ganglion cell layer, IPL, and RNFL (Ganglion Cell Complex)
- stratus can only show the total retinal thickness
describe the Stratus OCT’s RNFL analysis and how it works
- circular scans around ONH at a radius of 1.73mm from the center of the ONH
- begins temporally
- 3 scans and they are all averaged
describe the Stratus OCT’s ONH analysis and how it works
- radial scanning across ONH
- six 4mm line scans are taken
- each line scan is composed of 128 A-scans for the “fast ONH” scan, 512 for the regular ONH scan
what are types of 4th gens OCTs
- Fourier Domain
- Spectral Domain
- High Def Domain
major advantages of SD OCT over TD OCT
-SD is much faster, (cleaner images, more data acquired at once), better resolution (more retinal layers segmented out, more structures, finer details of abnormalities), and can perform all 3 OCT CPT codes
what optovue avanti scans do you use for glaucoma
- ONH scan
- RNFL scan
- Ganglion (GCC) complex scan
what does the ganglion cell (GCC) scan do?
-segments out the portions of the retina that include parts of the retinal ganglion cells: ganglion cell layer, inner plexiform layer, and RNFL layer
why is the GCC scan important?
50% of retinal ganglion cells (RGCs) are located in central 4.5mm (16 degrees) of retina
-paramacular RGCs are lost in early glaucoma
macular changes in glaucoma- advantages of the spectral domain
- has twice the depth resolution
- allows consistent imaging and segmentation of the GCC
- much faster scan speed, allows for greater density of sampling points
- reduces artifacts from eye-movements (because its faster)
what do you need to check about the GCC on the RTVue/Avanti Symmetry Printout?
- on the GCC deviation map, the area of a true defect should be at least the size of the foveal mask (grey area at the center of the scan- the foveal area is not scanned)
- GCC defects will very often respect the temp horizontal midline in early/moderate glaucoma (be cautious if GCC defect crosses the temp horizontal midline in an older patient)
the RTVue/Avanti RNFL provides trend analysis (not change analysis) for:
RNFL: average thickness trended
GCC: average thickness trended
how does the the RTVue/Avanti RNFL provides trend analysis for RNFL/GCC Change?
trend line is analyzed to determine whether the slope is significantly different than 0
(however there is a normal loss of axons with age, so the line will not have a slope of 0, so some judgement is needed to judge if the slope is faster than “normal”
