Lec.4: Imaging Devices Flashcards
what is the gold standard of glaucoma imaging?
simultaneous stereo photography
with early intervention, what are the chances that a patient with early glaucoma will go blind?
very low
can you have VF defect before there is cell death?
yes
can you have NFL cell death before VF defect is seen?
yes
does structural cell death always precede function deficit?
NO, sometime we measure functional deficits before we can measure cell death
what c/d ratio indicates that a patient has glaucoma?
0.7-0.8 (watch in African Americans, because this can be a normal c/d)
what type of device has software that allows data to be transferred from one generation device to the next?
Heidelberg retina tomograph (HRT)
how many series of 2-D images does the HRT take in order to generate a 3-D topographical image?
up to 64 series of the individual optical section images are combined to create a single 3-D topographical image
what is the mean number of HRT images used to make the 3-D image?
3
is HRT measurement taken from the reference plane or surface plane?
reference plane
what are the 4 sections of the HRT-3 OU printout?
patient demographics and quality checks, optic disc cup, neuroretinal rim, retinal nerve fiber layer (RNFL)
ideally what value should the standard deviation be for HRT-3 measurements?
less than 30 microns (lower SD means a good quality measurement)
what should you do if your standard deviation quality has a score of greater than 30 microns?
re-take the images
what does the following indicate: p> 0.05
95% of normality
what does the following indicate: 0.001<p><0.05
suspect (borderline)
what does the following indicate: p<0.001
high chance of being abnormal
what is a small optic disc size?
<1.6 mm2
what is an average optic disc size?
1.6-2.5 mm2
what is a large optic disc size?
> 2.5
as the disc size increases, what happens to rim tissue?
increases
how does peripapillary atrophy affect an HRT-3 reading?
makes it difficult to read the NFL
is rim area the best area to determine if the patient is a suspect?
yes
what is the relationship between neuroretinal rim and optic disc area?
neuroretinal rim increases withthe increases in optic disc area (proportional relationship)
what modeling device is able to eliminate technician error by determining disc border automatically?
Glaucoma Probability Score (GPS)
in GPS modeling how many parameters are used?
5 (3 parameters describe the optic disc and 2 parameters describe the RNFL)
what parameters describe the optic disc?
rim steepness, cup size and cup depth
in the 3-D model what does steep curvature represent?
NFL is present (normal and healthy cup)
in the 3-D model what does the flat curvature represent?
NFL is missing (likely glaucoma)
what does flattening of the RNFL surface indicate?
loss of ganglion cells and their axons
according to OHTS study, which is the best parameter to predict glaucoma?
MRA
what is the advantage of GDX over HRT?
GDX has a polarizer
what makes up total birefringence?
cornea+lens+RNFL
how does the amount of retardation from the RNFL relate to RNFL thickness?
directly proportional
in the eye what is the birefringent structure that is of interest?
RNFL
if you want to save the results of a GDX screening test, what must you remember to do?
print it out (machine will not save the results)
do corneal and lens birefringence properties change over a patient’s lifetime?
no (unless they have surgery)
if you get the color red in a GDX measurement, what does it indicate?
less than 0.5% chance of being normal
what does a nerve fiber indicator score of < 30 represent?
low likelihood of glaucoma
what does a nerve fiber indicator score of >50 represent?
high likelihood of glaucoma
what can cause an atypical birefringence pattern?
less choroidal pigment, cataracts and high myopia
what is the draw back of HRT and GDX?
they dont measure the macula
in OCT how are b-scans created?
a series of a-scans (axis scans) are used to create the image of a b-scan
in OCT how many radial scans are taken in order to create optic disc imaging?
6 radial scans are combined to create a 3-D image
why is it better to take 256 a-scans rather than 512 a-scans?
faster to take 256 a-scans, so less chance for eyemovement to effect the image
what type of OCT is known for breaking down components mathematically (sine and cosine waves)?
Fourier Domain-OCT
what are the advantages of Fourier Domain OCT?
has a stationary mirror for faster capture of scans, its range of wavelength allows it to be more accurate
between Time Domain OCT and Fourier OCT, which is faster than eyemovements, takes the entire A-scan at once and can take 26,000-40,000 A-scans per second?
Fourier Domain OCT
in OCT, what is the best diagnostic parameter in identifying glaucoma?
inferior average thickness
in OCT what does the red color indicate?
less than 1% chance of being normal
in OCT what does the yellow color indicate?
less than 5% chance of being normal
in OCT what does the green color indicate?
95% chance of being normal
are clockhours repeatable in OCT imaging?
no, quadrants are
on average what is the inferior average thickness?
93 microns (OCT is 85% accurate at measuring inferior thickness)
what proportion of fibers go to the macula?
50%
what are the 3 main instrument used for macula analysis?
Ganglion cell complex (Optovue), Ganglion cell analysis (Zeiss) and Heidelberg spectralis
why do you take a risk by running screening test on all patients?
increase chance of false positives (screenings are only appropriate for the appropriate populations)
do VF’s tend to fluctuate in early glaucoma?
yes
in OCT what does a significant p-value indicate?
glaucoma is progressing
in OCT, what happens to image quality at deeper Z depths?
image quality decreases
what should be the pupil diameter before running an OCT?
at least 3 mm in bright light
what does a line across your image data indicate?
patient most likely blinked
what are the required 3 parts of an OCT interpretation report?
clinical findings, comparison and plan
