D - Visual Field Assessment in Glaucoma - Week 1

Question 1

Why is visual field assessment essential for glaucoma? (4)

Answer 1

disease detection
disease monitoring
assessing impact on tasks of daily living
fitness to drive

Question 2

In VF testing, what should the false positive rate be less than for the test to be reliable?

Answer 2

20%

Question 3

What could be one potential reason for high fixation losses in an otherwise normal patient? (i.e. not malingering, no motility problems, etc.)

Answer 3

Blindspot in unique position. Test/machine assumes blindspot in average position, resulting in apparent fixation losses

Question 4

What is total deviation? What is it good for?

Answer 4

the dB value you are away from age-matched normals (e.g. +5dB = 5dB better than normals)

good to see if outside normal limits (i.e. 95% CI)

Question 5

What do pattern deviation maps look for?

Answer 5

looks for deviations from your own hill of vision

(e.g. if you are worse than others in sensitivity, that generalised difference gets subtracted out so you can focus specifically on changes to your own hill of vision)

Question 6

What is Mean deviation (MD) in perimetry?

Answer 6

MD measures the mean defect across the visual field (i.e. the average of deviations in all test locations across the visual field)

Question 7

Why would you perform macula testing (10-2) on a glaucoma patient? What is the advantage of a 10-2 over a 24-2?

Answer 7

Macula testing gives you refined detail of defects in central vision compared to the standard 24-2 or 30-2. When 24-2 picks up one deviated spot in the central 10 degrees, macula testing can identify if the region of defect in greater detail.

Because 24-2 only tests vision every 6 degrees apart whereas 10-2 tests vision every 2 degrees apart.

Question 8

What is the main disadvantage of a 10-2?

Answer 8

Doubles testing duration compared to 24-2. This is why we only use it when indicated (i.e. when we see a bit of central defect/loss - even if just one spot)

Question 9

Which perimeter device is better at picking up central defects: Humphrey or Medmont?

Answer 9

Medmont has more locations tested in the fovea so will pick up more central defects by default

Question 10

What type of instruction should you give to patients for visual field testing for the best results? Liberal, Neutral, or Conservative

Answer 10

Realistically it’s fine as long as everyone uses the same instructions. Ideally you’d want neutral instructions however.

Question 11

Give an example of good visual field instruction

Answer 11

“Some lights will be dim, some brighter. We are trying to measure how dim the lights can be for you to just be able to see them. Maintain fixation on the central light. When you see a light, press the button. We also want to know when you can’t see the light, so don’t panic if you don’t see anything”

Question 12

How can the false +ve/false -ve rate be described graphically?

Answer 12

As a psychometric function of probability

Question 13

What does a flat psychometric false+ve/false-ve function for perimetry suggest?

Answer 13

that there is a genuine probability that a light you saw before won’t be seen next time and vice-versa

Question 14

True or False: Psychometric function for seeing or not seeing a stimulus changes across the visual field

Answer 14

true

Question 15

Are visual field results in locations with high confidence intervals reliable for measuring progression of loss or defect?

Answer 15

No

Question 16

What is the main thing you should check for in the visual field of a glaucoma suspect?

Answer 16

Visual field asymmetry + patterns that can be explained by RNFL defect

Question 17

Why can’t you numerically compare HFA vs Medmont results? (3)

Answer 17

They arrange spots in different areas of space (Humphrey = grid, Medmont = ring) and the dB scales + maths is different. And also the max brightness differs too.

Question 18

What is event analysis?

Answer 18

little symbols to indicate progression and show whether it’s been reported consecutively

Question 19

What do global indices show you?

Answer 19

shows how the whole visual field is changing

Question 20

What does trend analysis project?

Answer 20

projects expected change over time based on previous/current data

Question 21

Give one reason why SITA-faster is faster?

Answer 21

it doesn’t check the blindspot location

Question 22

List the criteria used to identify an early glaucomatous defect (stage 1)

Answer 22

MD >/= -6.00 dB and one of the following:
A: Pattern deviation - cluster of 3 or more points in an expected location of the VF depressed below 5% level, at last 1 of which is depressed below the 1% level
B: Corrected pattern stdv./pattern stdv. significant at P<0.05
C: Glaucoma hemifield test “Outside Normal Limits”

Question 23

List the criteria used to identify an moderate glaucomatous defect (stage 2)

Answer 23

MD -6.01 to -12.00dB and one of the following:
A: Pattern deviation - >/= to 25% but <50% of pts depressed below 5% level, and 15-<25% depressed below 1% level
B: At least 1 pt. within central 5deg with sensitivity <15dB but, no point within central 5deg with sensitivity <0dB
C: Only 1 hemifield containing a pt. with sensitivity <15dB within 5deg of fixation

Question 24

List the criteria used to identify an advanced glaucomatous defect (stage 3)

Answer 24

MD -12.01 to -20.00dB and one of the following:
A: Pattern deviation - 50-<75% of pts depressed below 5% level, and 25-<50% depressed below 1% level
B: Any pt. within central 5deg with sensitivity <0dB
C: Both hemifields containing a pt. with sensitivity <15dB within 5deg of fixation

Question 25

List the criteria used to identify a severe glaucomatous defect (stage 4)

Answer 25

MD -20.00dB and one of the following:
A: Pattern deviation - >/=75% of pts depressed below 5% level, and >/=50% depressed below 1% level
B: At least 50% of pts. within central 5deg with sensitivity <0dB
C: Both hemifields containing >50% of pts. with sensitivity <15dB within 5deg of fixation

Question 26

List the criteria used to identify a end stage glaucoma (stage 5)

Answer 26

Unable to perform Humphrey visual fields in “worst eye” attributable to central scotoma or “worst eye” visual acuity of 20/200 or worse attributable to POAG. “Best eye” may be at any stage