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Glaucoma > Lec.4: Imaging Devices > Flashcards

Lec.4: Imaging Devices Flashcards

1
Q

what is the gold standard of glaucoma imaging?

A

simultaneous stereo photography

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2
Q

with early intervention, what are the chances that a patient with early glaucoma will go blind?

A

very low

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3
Q

can you have VF defect before there is cell death?

A

yes

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4
Q

can you have NFL cell death before VF defect is seen?

A

yes

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5
Q

does structural cell death always precede function deficit?

A

NO, sometime we measure functional deficits before we can measure cell death

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6
Q

what c/d ratio indicates that a patient has glaucoma?

A

0.7-0.8 (watch in African Americans, because this can be a normal c/d)

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7
Q

what type of device has software that allows data to be transferred from one generation device to the next?

A

Heidelberg retina tomograph (HRT)

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8
Q

how many series of 2-D images does the HRT take in order to generate a 3-D topographical image?

A

up to 64 series of the individual optical section images are combined to create a single 3-D topographical image

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9
Q

what is the mean number of HRT images used to make the 3-D image?

A

3

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10
Q

is HRT measurement taken from the reference plane or surface plane?

A

reference plane

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11
Q

what are the 4 sections of the HRT-3 OU printout?

A

patient demographics and quality checks, optic disc cup, neuroretinal rim, retinal nerve fiber layer (RNFL)

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12
Q

ideally what value should the standard deviation be for HRT-3 measurements?

A

less than 30 microns (lower SD means a good quality measurement)

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13
Q

what should you do if your standard deviation quality has a score of greater than 30 microns?

A

re-take the images

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14
Q

what does the following indicate: p> 0.05

A

95% of normality

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15
Q

what does the following indicate: 0.001<p><0.05

A

suspect (borderline)

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16
Q

what does the following indicate: p<0.001

A

high chance of being abnormal

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17
Q

what is a small optic disc size?

A

<1.6 mm2

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18
Q

what is an average optic disc size?

A

1.6-2.5 mm2

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19
Q

what is a large optic disc size?

A

> 2.5

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20
Q

as the disc size increases, what happens to rim tissue?

A

increases

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21
Q

how does peripapillary atrophy affect an HRT-3 reading?

A

makes it difficult to read the NFL

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22
Q

is rim area the best area to determine if the patient is a suspect?

A

yes

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23
Q

what is the relationship between neuroretinal rim and optic disc area?

A

neuroretinal rim increases withthe increases in optic disc area (proportional relationship)

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24
Q

what modeling device is able to eliminate technician error by determining disc border automatically?

A

Glaucoma Probability Score (GPS)

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25
Q

in GPS modeling how many parameters are used?

A

5 (3 parameters describe the optic disc and 2 parameters describe the RNFL)

26
Q

what parameters describe the optic disc?

A

rim steepness, cup size and cup depth

27
Q

in the 3-D model what does steep curvature represent?

A

NFL is present (normal and healthy cup)

28
Q

in the 3-D model what does the flat curvature represent?

A

NFL is missing (likely glaucoma)

29
Q

what does flattening of the RNFL surface indicate?

A

loss of ganglion cells and their axons

30
Q

according to OHTS study, which is the best parameter to predict glaucoma?

A

MRA

31
Q

what is the advantage of GDX over HRT?

A

GDX has a polarizer

32
Q

what makes up total birefringence?

A

cornea+lens+RNFL

33
Q

how does the amount of retardation from the RNFL relate to RNFL thickness?

A

directly proportional

34
Q

in the eye what is the birefringent structure that is of interest?

A

RNFL

35
Q

if you want to save the results of a GDX screening test, what must you remember to do?

A

print it out (machine will not save the results)

36
Q

do corneal and lens birefringence properties change over a patient’s lifetime?

A

no (unless they have surgery)

37
Q

if you get the color red in a GDX measurement, what does it indicate?

A

less than 0.5% chance of being normal

38
Q

what does a nerve fiber indicator score of < 30 represent?

A

low likelihood of glaucoma

39
Q

what does a nerve fiber indicator score of >50 represent?

A

high likelihood of glaucoma

40
Q

what can cause an atypical birefringence pattern?

A

less choroidal pigment, cataracts and high myopia

41
Q

what is the draw back of HRT and GDX?

A

they dont measure the macula

42
Q

in OCT how are b-scans created?

A

a series of a-scans (axis scans) are used to create the image of a b-scan

43
Q

in OCT how many radial scans are taken in order to create optic disc imaging?

A

6 radial scans are combined to create a 3-D image

44
Q

why is it better to take 256 a-scans rather than 512 a-scans?

A

faster to take 256 a-scans, so less chance for eyemovement to effect the image

45
Q

what type of OCT is known for breaking down components mathematically (sine and cosine waves)?

A

Fourier Domain-OCT

46
Q

what are the advantages of Fourier Domain OCT?

A

has a stationary mirror for faster capture of scans, its range of wavelength allows it to be more accurate

47
Q

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?

A

Fourier Domain OCT

48
Q

in OCT, what is the best diagnostic parameter in identifying glaucoma?

A

inferior average thickness

49
Q

in OCT what does the red color indicate?

A

less than 1% chance of being normal

50
Q

in OCT what does the yellow color indicate?

A

less than 5% chance of being normal

51
Q

in OCT what does the green color indicate?

A

95% chance of being normal

52
Q

are clockhours repeatable in OCT imaging?

A

no, quadrants are

53
Q

on average what is the inferior average thickness?

A

93 microns (OCT is 85% accurate at measuring inferior thickness)

54
Q

what proportion of fibers go to the macula?

A

50%

55
Q

what are the 3 main instrument used for macula analysis?

A

Ganglion cell complex (Optovue), Ganglion cell analysis (Zeiss) and Heidelberg spectralis

56
Q

why do you take a risk by running screening test on all patients?

A

increase chance of false positives (screenings are only appropriate for the appropriate populations)

57
Q

do VF’s tend to fluctuate in early glaucoma?

A

yes

58
Q

in OCT what does a significant p-value indicate?

A

glaucoma is progressing

59
Q

in OCT, what happens to image quality at deeper Z depths?

A

image quality decreases

60
Q

what should be the pupil diameter before running an OCT?

A

at least 3 mm in bright light

61
Q

what does a line across your image data indicate?

A

patient most likely blinked

62
Q

what are the required 3 parts of an OCT interpretation report?

A

clinical findings, comparison and plan

Glaucoma (12 decks)

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