Imaging Part 1

Question 1

GDx is what type of instrument and measures what

Answer 1

• a scanning laser polarimetry (SLP)

- measures thickness of RNFL

Question 2

HRT is what type of instrument and measures what

Answer 2

• confocal scanning later ophthalmoscopy/ tomography (CSLO)

- topography of the ONH

Question 3

what does OCT measure?

Answer 3

thickness of paramacular ganglion cell complex

Question 4

problems with stereo ONH photography

Answer 4

• 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

Question 5

what is the biggest “pro” of glaucoma imaging devices? (glaucoma change now vs. change over time)

Answer 5

change over time, comparing the patient to him/herself

Question 6

3 glaucomatous and nonglaucomatous changes that CODI is not designed to detect

Answer 6

• drance heme (flame heme)
• peripapillary atrophy
• pallor

Question 7

what is the current standard of care for glaucoma?

Answer 7

stereoscopic ONH eval

-stereo ONH photos and CODI images may start becoming standard of care too

Question 8

problems with clinical RNFL evaluation

Answer 8

• difficult especially with media opacities, small pupils, light fundus
• subjective, qualitative only
• very difficult to detect diffuse RNFL loss, easier to detect localized defects

Question 9

general disadvantages of GDx

Answer 9

• 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)

Question 10

what is the GDx deviation map

Answer 10

• compares the individual’s entire nerve fiber layer scan to a normal database
• color coded defects

Question 11

what is the TSNIT graph?

Answer 11

displays the thickness values along the calculation circle (1.73mm from the center of ONH)

Question 12

how do you interpret a TSNIT graph?

Answer 12

normal values are within the shaded green zone, if abnormal it falls below the shaded green zone (double hump one)

Question 13

what is the nerve fiber indicator (NFI)?

Answer 13

• 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

Question 14

what is the most sensitive parameter for discriminating normal from glaucoma from GDx?

Answer 14

nerve fiber index (NFI)

Question 15

what does a higher number of NFI mean?

Answer 15

more likely RNFL is abnormal

Question 16

what is the atypical birefringement pattern on the GDx?

Answer 16

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

Question 17

what is the ECC on GDx?

Answer 17

enhanced corneal compensation only available on GDx pro which eliminates atypical birefringence pattern

Question 18

what is the progression software for HRT called?

Answer 18

topographic change analysis (TCA)

Question 19

what are 2 multiple interpretation tools for HRT?

Answer 19

moorefields probability score (MRA) and glaucoma reliability score (GPS)

Question 20

what are some problems with the HRT?

Answer 20

• only for ONH topography
• false positives (b/c of large ONH)
• false negatives (b/c of small ONH)

Question 21

what is the contour line on the HRT?

Answer 21

• 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

Question 22

what is the reference plane in HRT?

Answer 22

• 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

Question 23

what structures are above and below the reference plane and what colors do they show up as?

Answer 23

• above: rim tissue, green

- below: cup, red

Question 24

what are some glaucoma detection NOW strategies for HRT?

Answer 24

• Moorfields Regression Analysis (MRA)
• Stereometric parameters of ONH
• Glaucoma Probability Score (GPS)

Question 25

what are some detection of change over time strategies for HRT?

Answer 25

• Topographical Change Analysis (TCA): an event analysis to detect change
• Progression trend analysis: a trend analysis of stereo metric parameters

Question 26

what does the Moorfieldo Regression Analysis (MRA) do?

Answer 26

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

Question 27

what is the difference between tracking ONH stereo metric parameters with time and TCA?

Answer 27

• ONH change tracking is trend analysis (may go up/down)

- TCA is an analysis of local surface height, local change probabilities

Question 28

pros/cons of progression analysis vs TCA?

Answer 28

trend analysis: not good for detection of localized change

TCA: shows you exactly where the change is (area of significant excavation will be red)

Question 29

when is change on TCA significant?

Answer 29

• 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)