Technology Flashcards
What is OCT?
optical coherence tomography; uses low coherence laser light to evaluate reflection of laser light off different tissues (the science not the instrument)
What manufacturers make OCTs?
Spectralis (Heidelberg), Cirrus (Zeiss), RTVue (Optovue), 3-D OCT 1000 (Topcon), etc
What light wavelength does an OCT use?
843 nm (near infrared)
How does the OCT work?
interference signal from retina is compared to reference beam via spectrometry
What does a spectrometer do?
evaluates changes in wavelength between reference beam and reflected beam
What is the size of the Zeiss reference circle?
r=3.64 mm around the center of disk
What is Zeiss data compared to?
adult age matched norms 19 yo+, 256 scans
What does yellow mean?
1-5% percentile
What does red mean?
<1% of normals in this range
What does the triangle on the Zeiss machine allow you to do?
check how close the value is to the next probability level
What is the ICD-10?
the diagnosis, linked to the CPT
How do you code the OCT of ONH?
92133 (OCT of ONH) linked to H40.113_ (glaucoma ICD-10)
How does CPT reimbursement work?
paid for the technical and professional components (without interpretation it’s incomplete), CPTs are now bilateral procedures
What is the ganglion cell complex?
evaluation of ganglion cells, dendrites and axons about the macula
Is the GCC preferentially affected in glaucoma?
possibly, 15% of glaucoma pts have early central change
What is contained in the GCC?
inner plexiform, ganglion cell layer, retinal nerve fiber layer
Where is the GCC densest?
macula
When does ganglion cell loss occur and what does it cause?
early in glaucoma, results in isolated paracentral damage
What is the floor effect?
loss of RNFL down to the vessels and other tissues where the machine picks up the connective tissue and vessels
What is the problem with the floor effect?
it makes the OCT look stable over time even if the 10-2 field loss is progressing– insurance may not cover the test if floor effect is exhibited
T/F GCC loss is always glaucoma
false
What does the cirrus ganglion cell analysis measure?
ganglion cell and inner plexiform layers GCIPL
What does the optovue ganglion cell complex measure?
IPL, ganglion cells and RNFL
What does the spectralis measure in terms of GCC?
measures each layer individually: IPL, GC, NFL
Which machine does not have normative data?
spectralis
What did Moreno find?
GCC and pRNFL in early GLC– 40% identified GCC only, 33% pRNFL only, 27% identified on both aka use both measurements
What did Kim find?
early v moderate v severe– inferior GCC detected early and severe glaucoma best, mean GCC was more effective than mean RNFL, global loss volume accurate for GLC
What did Rolle find?
pre-perimetric glaucoma, GCC and global loss volume comparable to pRNFL, high specificity, lower sensitivity, challenging with early stage
What are the most effective GCC parameters of the cirrus?
minimum ganglion cell and inner plexiform layer, inferotemporal GCIPL, average GCIPL, comparable to pRNFL
What are the most effective GCC parameters of the optovue?
global loss volume, thickiness in inferior quadrant
Why is inferior/inferior-temporal macula so important?
anatomically fibers from the I/IT macula enter ONH at inferior aspect of ONH which is a higher risk area (superior macular is able to enter ONH temporally)
What is the average disc area?
1.84 mm squared
How does disc size impact OCT RNFL thickness measurement?
a larger optic nerve will have the RNFL measured closer to the edge and will measure thicker regardless of disease level aka mask glaucoma
What happens when the reference ring of the OCT is further from the edge of the ONH like in a small nerve?
RNFL will measure thinner, may over diagnose glaucoma
What is the panomap feature?
On Zeiss the RNFL and GCC maps are on the same printout
What should you keep in mind about the panomap?
it is not comparing the exact same tissue, one is RNFL and one is ganglion cell + IPL
How does Zeiss show progression?
guided progression analysis of pRNFL, 2 baseline tests with up to 6 total
What does the guided progression analysis work?
(zeiss) gives the best-fit slope line of the average RNFL thickness, superior thickness, inferior thickness, and CD ration
Which guided progression analysis aspect goes up instead of down with progression?
cup to disc ratio
What did JH Na find?
poor correlation of OCT GPA to progression of expert analysis on ONH and HVF/HVF GPA– this is the point…. software should be better than clinicians
What is Optovue data compared to?
330 normative database
What does the optovue printout contain?
ring color codes on the ONH map (difference between normative data), GCC, TSNIT graph, focal loss volume and global loss volume, graph comparing OD to OS
What is in the optovue RNFL interpretation?
RNFL thickness (warmer color is thicker), probability plots for norms, optic nerve assessment in middle
What is the size of the optovue/rtvue reference circle?
4 mm
What does NHM4 protocol mean?
the nerve head map reference circle is 4 mm (difference from Zeiss 3.64 mm)
T/F you can compare data optic disk data across instruments
false, the reference circles are different sizes
How high above the RPE is the RTVue reference line?
150 microns above RPE
What is in the Optovue progression analysis?
RNFL trend analysis and 6 regions of ONH graphed out
What are the most effective parameters of the Optovue GCC?
global loss volume, GCC thickness inferiorly
What is the Spectralis GMPE?
glaucoma module premium edition– evaluates RNFL and macula
What is the APS?
anatomic positioning system of the spectralis, compensates for head tilts
How does the APS work?
maps macula then nerve then the axis between them and then takes the measurement
What is the BMO-MRW?
spectralis’ bruchs membrane opening minimum rim width
What is BMO?
bruch’s membrane opening is set as the anatomical border of the NRR
How is BMO-MRW measured?
rim tissue is measured from the MBO to the closest appearance of ILM and NRR thickness is measured perpendicular to the path of the axons
What is the spectralis progression analysis?
event: circumpapillary RNFL; trend: sector RNFL measures
