Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Year 2 Investigative Techniques > VF Representation of Sensitivity/Stimulus Parameters > Flashcards

VF Representation of Sensitivity/Stimulus Parameters Flashcards

1
Q

What abnormalities does the total deviation map measure?

A

Diffuse and focal i.e. overall loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What abnormalities does the pattern deviation map measure?

A

Focal loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is the pattern deviation map made from the total deviation map?

A

General height adjustment/elevator
Average reduction of the hill of vision (when compared to normal values is added to TD values (subtracted if vision better than average) to reveal focal loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the p-value?

A

Probability analysis of deviation values
Indicates how likely there is to be an abnormality

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

If the p-value is darker, what does this mean?

A

It’s more likely to be abnormal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

If the value of the absolute value is higher, what does this mean?

A

The patient has seen a dimmer stimulus i.e. they have a higher sensitivity at that location

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are some limitations of the grayscale map?

A

Not age-compensated
Not eccentricity compensated
Underestimates/masks early loss
Continuous nature of grayscale means that the difference between each point is cut out, making borders of loss less obvious

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does a Humphrey fields machine change the brightness of the stimulus?

A

Adds progressively darker ND filters in front of the light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What effect does a small pupil have on the results?

A

Diffuse ‘loss’ similar to cataracts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What can cause artefacts?

A

Upper lid
Glasses/trial lens edge
Incorrect positioning

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the VF indices?

A

Mean Deviation (MD)
Pattern Standard Deviation (PSD)
Visual Field Index (VFI)
Short-term Fluctuation (SF)
Corrected Pattern Standard Deviation (CPSD)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Which of the VF indices are present on modern perimeters?

A

Mean Deviation (MD)
Pattern Standard Deviation (PSD)
Visual Field Index (VFI)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Which of the VF indices are present on older perimeters?

A

Mean Deviation (MD)
Pattern Standard Deviation (PSD)
Short-term Fluctuation (SF)
Corrected Pattern Standard Deviation (CPSD)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the equivalent of mean deviation on an Octopus machine? What’s the difference?

A

Mean Defect
Not weighted, and a reduced VF has positive values

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the mean deviation?
What does it give an idea of?

A

A weighted mean of the TD values (weighted centrally - i.e. central values are given more importance)
More negative MD = more abnormal
Value given is how far away from a normal hill of vision the result is
Gives an idea of overall loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a normal MD?

A

~-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is Pattern Standard Deviation (PSD)?

A

The standard deviation of the MD
Gives more idea of the shape of the hill of vision

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does a large difference between TD values indicate (analysed by PSD)?

A

Presence of focal loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What does a more positive PSD score indicate?

A

More severe focal loss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

If the PSD score is over +12dB, what does this indicate?

A

Diffuse loss
Large areas of focal loss becoming confluent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is Short-term Fluctuation?

A

Weighted standard deviation of repeated measurements of sensitivity at the same specified locations - checks px consistency and variability

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What could high SF indicate?

A

Abnormality (increased depth of defect, increased overall severity of loss)
Increased eccentricity
Px bad at doing test!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is a normal value for SF?

A

Equal to or less than 1.5dB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

On a HFA, how is SF tested?

A

10 locations tested twice

24
Q

What is the equivalent of PSD on an Octopus machine? What is the difference?

A

Loss variance
Squared SD, so number is larger

25
Q

What is Corrected PSD?
Why is it helpful?

A

PSD with the SF effects removed
Shows a more consistent shape of the hill of vision, makes focal loss more obvious and gives a good indication of variability

26
Q

What is the Visual Field Index?

A

A centrally weighted percentage based on the probability map - tells you proportion of normal vision

27
Q

Is the VFI clinically useful?

A

No - use as a tool to inform pxs, but be careful as 95% can seem good when it’s not

28
Q

What does the Glaucoma Hemifield Test (GHT) indicate?

A

Whether one hemifield is likely to be glaucomatous when compared to the other hemifield (based on fact that one hemifield becomes glaucomatous before the other)

29
Q

What values does the GHT use for comparison?

A

Pattern deviation probability values (split into boxes of different areas for comparison)

30
Q

What causes the GHT to show “Within normal limits”?

A

No probability values are present in either hemifield

31
Q

What causes the GHT to show “Outside normal limits”?

A

More probability values present in one hemifield than the other

32
Q

What causes the GHT to show “Borderline”?

A

The software is unable to distinguish if it is glaucomatous, but it is not within normal limits

33
Q

What causes the GHT to show a general reduction of sensitivity?

A

An equal increase in probability values in both hemifields

34
Q

What causes the GHT to show an abnormally high sensitivity?

A

Px overclicking

35
Q

What are the stimulus parameters?

A

Colour
Size
Location
Algorithm

36
Q

What colour are the stimuli and background?

A

White

37
Q

What conditions does the white background create? How bright is it?

A

Photopic conditions
31.5ASB

38
Q

What is the standard stimulus size?

A

III
(2.26mm - subtends 0.43 degrees)

39
Q

How many stimuli sizes are available?

A

6

40
Q

For which stimulus sizes are normal values available?

A

III and V

41
Q

By how much does the stimulus size increase between every size?

A

Doubles

42
Q

Why would you increase the stimulus size?

A

Very poor response to standard size - needs bigger size to see stimulus

43
Q

How much of the VF does a 30-2 program measure?

A

27 degrees

44
Q

How much of the VF does a 24-2 program measure?

A

21 degrees

45
Q

What is the difference between a 30-2 and 24-2?

A

Outer locations are removed in a 24-2 (except 2 nasal locations - 1 above and 1 below midline) due to increased variability at peripheral locations.
Nasal are kept to allow for nasal step defect to be detected

45
Q

How much of the VF does a 10-2 program measure?

A

9 degrees

46
Q

What is the difference between a 24-2 and a 24-2c?

A

24-2c has more central locations - allows for earlier detection of glaucoma in central retina

46
Q

Why is it useful to perform a 10-2?

A

Smaller separation of points (2 degrees rather than 3)
Screens central retina
Both of these are useful for any central retina disease or to measure central vision when peripheral is gone (e.g. in end stage glaucoma)

47
Q

What is the staircase method of Threshold estimation?

A

Determines threshold by starting above or below threshold, then descends or ascends in 4dB steps, then returns the opposite way in 2dB

48
Q

What improves threshold accuracy?

A

Reduced step sizes
Increased reversal
Increased repetitions

49
Q

What does increased threshold accuracy result in?

A

Reduces reliability

50
Q

What is the threshold algorithm of FASTPAC (HFA)?

A

3dB steps, single crossing of the threshold

51
Q

What is the threshold algorithm of Dynamic (Octopus)?

A

2-10dB steps dependent on px

52
Q

What is the threshold algorithm of SITA Standard (HFA)?

A

4-2dB steps

53
Q

What is the threshold algorithm of SITA Fast (HFA)?

A

4dB steps

54
Q

What is the Error Related Factor (ERF) on SITA?

A

How similar px’s FOS curve is to normal and glaucomatous FOS curves

55
Q

How does the SITA algorithm reduce time spent doing the test?

A

Tries to get as close as possible to threshold before presenting the stimulus
Adapts stimulus presentation speed to px reaction times

56
Q

What increases the threshold variability?

A

Increased defect depth
Increased eccentricity
Increased overall loss

Year 2 Investigative Techniques (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions