LEC 4: REPRESENTATION OF SENSITIVITY & SELECTION OF STIMULUS PARAMETERS

Question 1

True or false- Probability analysis is the most important component diagnostically?

Answer 1

True

Question 2

5 visual field indices?

Answer 2

1.Mean deviation
2.Pattern Standard Deviation
3.Short-term fluctuation
4.Corrected Pattern Standard Deviation
5.Visual Field Index

Question 3

What do visual field incides do?

Answer 3

These indices reduce all the numbers down into a single entity- collapse measured values into 1 value. This 1 value represents what is going on around the entire measured field. They are called data reduction statistics. They reduce the probability analysis data down into 1 single entity.

Question 4

Which indices are shown in the results of visual field indices?

Answer 4

MD (mean deviation), PSD (pattern standard deviation) and VFI (visual field index).

Question 5

Px with controlled hypertension, asides from the visual field, what should the optometrist look at?

Answer 5

Ocular hypertension, structural abnormality- optic nerve, looking for cup within optic nerve head and retinal nerve fiber thickness.

Question 6

2 structural effects of glaucoma?

Answer 6

Glaucoma increases cupping of optic nerve head and reduces retinal nerve fiber layer thickness.

Question 7

Damage to superior visual field- what section in the optic nerve head is examined?

Answer 7

Inferior optic nerve head

Question 8

Between the probability map of total and pattern deviation- which map shows focal loss and which map shows generalized loss?

Answer 8

Total deviation representing generalized loss and focal loss and pattern deviation shows only focal loss.

Question 9

What is the most common cause for generalized loss in probability map?

Answer 9

Cataract

Question 10

What is mean deviation?

Answer 10

*Weighted mean of the Total Deviation values, (which are the difference between the measured value and the average normal value for the age of the patient).
*Signifies overall severity of loss (diffuse + focal)

Question 11

What is the theoretical value if mean deviation was normal, effect of MD value as field becomes worse?

Answer 11

If normal theoretically- the value would be 0dB.
As field becomes worse, value becomes more negative.

Question 12

MD (Mean deviation) is weighted towards central deviation more, why?

Answer 12

Central deviations are diagnostically more important than those at the edges and the Px is likely to generate these values more accurately than those at the edges. THAT IS WHY IT IS WEIGHTED

Question 13

MD (Mean deviation) shows focal and general loss

Answer 13

Both focal and general loss

Question 14

Describe the math’s behind calculating MD?

Answer 14

Add up all the total deviations and divide by the number of locations.
Before you add the numbers- more weight applied to central deviations.

Question 15

Mean deviation is what in terms of octopus perimeter? +ve values in this octopus perimeter corresponds to?

Answer 15

Mean defect
+Ve value is abnormal.

Question 16

Octopus perimeter uses unweighted or weighted mean for MD?

Answer 16

Unweighted mean of the difference between the average normal value for the age of the patient and the measured value.

Question 17

Relationship between standard deviation and mean?

Answer 17

Wider the SD the less representative the mean is

Question 18

What is patterned standard deviation (PSD)?

Answer 18

The Standard Deviation (mean) of the values in the Total Deviation plot.

Question 19

PSD is indicative of?

Answer 19

Indication of the non-uniformity. Demonstrates whether the Total Deviation values are all approximately the same (PSD ≈ 1.0dB) or are different from one another

Question 20

Relation between focal loss and PSD?

Answer 20

As focal loss increases, PSD becomes increasingly more +ve

Question 21

PSD Value greater than 12dB?

Answer 21

Greater than 12 dB suggests visual field loss is due to focal loss becoming more diffused.

Question 22

What does mean and standard deviation represent?

Answer 22

Mean: Statical uniformity
Standard deviation: gives the non- uniformity of mean.
Wider the SD the less reprehensive the mean is.

Question 23

What is short term fluctuation index?

Answer 23

This incides is no longer used.
It is the weighted SD of repeated measurements of sensitivity at different locations. It measures how inconsistent a Px was with responses.

Question 24

3 factors that increase fluctuations/ variability in threshold?

Answer 24

1. (Relative) defect depth- Deeper the defect less consistent Px responses.
2. Eccentricity- Variability gets worse in the periphery compared to the center.
3. Overall severity of field loss

Question 25

What is corrected standard pattern deviation ?

Answer 25

Not used a anymore
PSD with effects of short term fluctuation removed.
Signifies focal loss.

Question 26

Corrected standard pattern deviation equivalent to what in Octopus Perimeter ?

Answer 26

Corrected loss variance

Question 27

What is VFI?

Answer 27

Based upon pattern deviation

Question 28

VFI indicates?

Answer 28

Focal loos + central weighed loss

Question 29

How is total deviation calculated?

Answer 29

Difference between measured value and average normal value for the age of the Px

Question 30

Why does focal loss interfere with measured visual field?

Answer 30

Because focal loss is localized

Question 31

What is glaucoma hemifield test (GHT)

Answer 31

Hemi-field comparison of pattern deviation probability values top vs bottom

Question 32

What does -2 stimulus offset mean?

Answer 32

Stimulus is offset by 2- not aligned in the vertical and horizontal merdian

Question 33

Why is stimulus offset?

Answer 33

To overcome microsaccades. To ensure stimuli are presented are independent of micro-eyemovements

Question 34

30-2 vs 24-2 in detecting glaucoma?

Answer 34

30-2 : previously used to detect glaucoma
24-2: detect glaucoma now, it is faster so px does not get tired when used, gives diagnostically more significant locations

Question 35

Early glaucoma on gray scale?

Answer 35

Seen in paracentral locations