Imaging Part 2

Question 1

which types of OCTs are currently on the market (general)?

Answer 1

3rd gen “time domain”

4th gen “spectral domain”

Question 2

what generation is the stratus OCT

Answer 2

3rd gen

Question 3

what is the depth/axial resolution of the Stratus OCT?

Answer 3

8-10 microns

anything less than that it can not resolve

Question 4

how does the Stratus OCT display in “false color” scale?

Answer 4

red-white: high reflectivity (RPE and RNFL)
blue-green: low reflectivity (cell bodies, photoreceptors and choroid)
black: very low reflectivity (vitreous)

Question 5

reflectivity rules for:

layers oriented perpendicular to the pathway of light

Answer 5

• higher reflectivity
• red
• RNFL, RPE

Question 6

reflectivity rules for:

layers oriented parallel to the pathway of light

Answer 6

• lower reflectivity

- nuclear layers or cell body layers

Question 7

reflectivity rules for vitreous

Answer 7

very low reflectivity (black)

Question 8

how many retinal layers can be resolved with Stratus OCT vs. 4th gens OCTs

Answer 8

Stratus (3rd gen): maybe 4-5 layers well

4th gen: all layers well (everything)

Question 9

how is Stratus OCT at retinal nerve fiber layer analysis

Answer 9

can show thinning of the RNFL thickness which is an early indicator of glaucoma (stratus can segment out of the RNFL)

Question 10

how is Stratus OCT at optic nerve head analysis

Answer 10

• 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

Question 11

how is Stratus OCT in macular thickness maps

Answer 11

• stratus cannot segment out the ganglion cell layer, IPL, and RNFL (Ganglion Cell Complex)
• stratus can only show the total retinal thickness

Question 12

describe the Stratus OCT’s RNFL analysis and how it works

Answer 12

• 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

Question 13

describe the Stratus OCT’s ONH analysis and how it works

Answer 13

• 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

Question 14

what are types of 4th gens OCTs

Answer 14

• Fourier Domain
• Spectral Domain
• High Def Domain

Question 15

major advantages of SD OCT over TD OCT

Answer 15

-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

Question 16

what optovue avanti scans do you use for glaucoma

Answer 16

• ONH scan
• RNFL scan
• Ganglion (GCC) complex scan

Question 17

what does the ganglion cell (GCC) scan do?

Answer 17

-segments out the portions of the retina that include parts of the retinal ganglion cells: ganglion cell layer, inner plexiform layer, and RNFL layer

Question 18

why is the GCC scan important?

Answer 18

50% of retinal ganglion cells (RGCs) are located in central 4.5mm (16 degrees) of retina
-paramacular RGCs are lost in early glaucoma

Question 19

macular changes in glaucoma- advantages of the spectral domain

Answer 19

• 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)

Question 20

what do you need to check about the GCC on the RTVue/Avanti Symmetry Printout?

Answer 20

• 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)

Question 21

the RTVue/Avanti RNFL provides trend analysis (not change analysis) for:

Answer 21

RNFL: average thickness trended
GCC: average thickness trended

Question 22

how does the the RTVue/Avanti RNFL provides trend analysis for RNFL/GCC Change?

Answer 22

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”