Imaging Part 1 Flashcards
GDx is what type of instrument and measures what
- a scanning laser polarimetry (SLP)
- measures thickness of RNFL
HRT is what type of instrument and measures what
- confocal scanning later ophthalmoscopy/ tomography (CSLO)
- topography of the ONH
what does OCT measure?
thickness of paramacular ganglion cell complex
problems with stereo ONH photography
- requires clear media, dilated pupil, and skilled photographer
- poor inter observer agreement, even between experts
- progression can be missed, may not always have high quality results, and time consuming
what is the biggest “pro” of glaucoma imaging devices? (glaucoma change now vs. change over time)
change over time, comparing the patient to him/herself
3 glaucomatous and nonglaucomatous changes that CODI is not designed to detect
- drance heme (flame heme)
- peripapillary atrophy
- pallor
what is the current standard of care for glaucoma?
stereoscopic ONH eval
-stereo ONH photos and CODI images may start becoming standard of care too
problems with clinical RNFL evaluation
- difficult especially with media opacities, small pupils, light fundus
- subjective, qualitative only
- very difficult to detect diffuse RNFL loss, easier to detect localized defects
general disadvantages of GDx
- measures RNFL thickness only, not ONH topography or GCC/GCA (RNFL loss if nonspecific for glaucoma, can be from other ON diseases, anterior seg diseases, and congenital abnormalities)
- things other than RNFL cause retardation or change the retardation (media opacities for example)
- rate of artifact such as anomalous bifridgement pattern is too high (ECC technology on Pro version addresses this)
what is the GDx deviation map
- compares the individual’s entire nerve fiber layer scan to a normal database
- color coded defects
what is the TSNIT graph?
displays the thickness values along the calculation circle (1.73mm from the center of ONH)
how do you interpret a TSNIT graph?
normal values are within the shaded green zone, if abnormal it falls below the shaded green zone (double hump one)
what is the nerve fiber indicator (NFI)?
- a one number index of the degree of RNFL damage or thinness such as is due to congenital anomalies such as ON hypoplasia
- based on both focal and diffuse RNFL loss
what is the most sensitive parameter for discriminating normal from glaucoma from GDx?
nerve fiber index (NFI)
what does a higher number of NFI mean?
more likely RNFL is abnormal
what is the atypical birefringement pattern on the GDx?
an artifact that thickens the RNFL measurements, mainly temporally and it causes the GDx measurements to be thicker than they actually are and thicker than what it is on OCT
-may hide true RNFL loss, most correlated to age
what is the ECC on GDx?
enhanced corneal compensation only available on GDx pro which eliminates atypical birefringence pattern
what is the progression software for HRT called?
topographic change analysis (TCA)
what are 2 multiple interpretation tools for HRT?
moorefields probability score (MRA) and glaucoma reliability score (GPS)
what are some problems with the HRT?
- only for ONH topography
- false positives (b/c of large ONH)
- false negatives (b/c of small ONH)
what is the contour line on the HRT?
- drawn once around the ONH by the operator and automatically transferred to future HRTs
- doesn’t need to be changed after the first visit since TCA isn’t based off it
what is the reference plane in HRT?
- automatically determined, go 50 microns be;ow ON fiber layer between 350 and 356 degrees (papillomacular bundle)
- stereometric measures (height/depth) are relative to this
what structures are above and below the reference plane and what colors do they show up as?
- above: rim tissue, green
- below: cup, red
what are some glaucoma detection NOW strategies for HRT?
- Moorfields Regression Analysis (MRA)
- Stereometric parameters of ONH
- Glaucoma Probability Score (GPS)
what are some detection of change over time strategies for HRT?
- Topographical Change Analysis (TCA): an event analysis to detect change
- Progression trend analysis: a trend analysis of stereo metric parameters
what does the Moorfieldo Regression Analysis (MRA) do?
it is a relationship between the rim area and optic disc size is combined in a linear regression equation
- adjusted for age- related changes in the rim
- performed on whole OHN and 6 sectors
what is the difference between tracking ONH stereo metric parameters with time and TCA?
- ONH change tracking is trend analysis (may go up/down)
- TCA is an analysis of local surface height, local change probabilities
pros/cons of progression analysis vs TCA?
trend analysis: not good for detection of localized change
TCA: shows you exactly where the change is (area of significant excavation will be red)
when is change on TCA significant?
- if it is repeated in at least 2 (better 3) consecutive follow-up exams
- if it is region of at least 20 connected super pixels (large area)
