LEC 3- REPRESENTATION OF SENSITIVITY 2

Question 1

What is a probability analysis?

Answer 1

Probability analysis used to identify the likelihood of the measured value lying in the normal range.

Question 2

How are the values obtained from a visual field exam interpreted?

Answer 2

1.Necessity for comparison of the measured sensitivity with that of the age-corrected normal sensitivity.
2.Necessity for a probability analysis of the above comparison.
3.Separation of the extent of the focal loss (Pattern Deviation) from the extent of the diffuse and the focal loss, combined (Total Deviation).
4.Concept of the elevator by which the separation is achieved.

Question 3

Separation of overall loss (generalized loss) that occurs from?

Answer 3

Occurs from media opacities, small pupils, poor or no correction of Rx.

Question 4

Moving from total deviation map to pattern deviation map is using an?

Answer 4

elevator/ general height adjustment

Question 5

What do absolute values represent ?

Answer 5

The numbers that represent sensitivity to a spot of light.

Question 6

What is difference (deviation) values?

Answer 6

Difference from age corrected normal values.

Question 7

To move from total deviation to pattern deviation:
What does 0, -ve and +ve values indicate?

Answer 7

Measured (estimated) sensitivity – age corrected normal sensitivity.
-> 0 indicates the measured sensitivity is the same as the average value.
-> -ve value indicates that the measured value is worse than the average.
-> +ve value indicates that the measured value is better than the average.

Question 8

Why do you move from total deviation to pattern deviation?

Answer 8

This map removes the influence of media opacities, cataracts, small pupils, etc. to identify focal damage.

Question 9

How is the elevator value identified by the software?

Answer 9

The software removes the locations In the outer region. The software ranks the deviations from the most positive/ least negative. These are arbitrary values. The software then selects the 7th most positive or least negative 7th number.

Question 10

Why is the 7th number used in identification of the elevator?

Answer 10

To remove guessing that can occur, and it is the 85th percentile.

Question 11

After ranking numbers and finding the elevator value as -3, how is this value used?

Answer 11

Visual field is -3 worse than the expected normal. Visual field is -3 worse than the expected normal

Question 12

Why is the software not very useful in determination of the elevator value?

Answer 12

The software in the instrument goes to 1-2 decimal places. Whereas whole numbers are used in the printed-out result.

Question 13

If software finds the ranked 7th number as 2, what is the value of the elevator?

Answer 13

-2dB

Question 14

Describe the role of elevator in relation to hill of vision?

Answer 14

Elevator adjusts the measured hill of vision up and down to normal hill of vision.

Question 15

Within the probability analysis map, dark symbols represent?

Answer 15

The darker the symbol the less likelihood of the deviation lies within the normal range.

Question 16

What do the symbols represent in the probability analysis map?

Answer 16

The symbols do not indicate the depth of the defect it is the statistic probability of the deviation lying within the normal range.

Question 17

What does it indicate when total deviation and pattern deviation have a similarity in the probability map?

Answer 17

Similarity between maps: because nothing is obstructing light coming in the eye- no cataract, no corneal or vitreous opacity. Px is better than normal.

Question 18

In a “hyper normal person” hill of vision is brought down when using an elevator, why

Answer 18

increases defected area by movement caused by elevator

Question 19

Influence of cataract on the luminance level values?

Answer 19

Absorption and scatter reduce luminance level of the spot before it even reaches the retina.
This lowers the numbers then what is expected.

Question 20

Grey scale usefulness in early or advanced detection? And why?

Answer 20

Grey scale USELESS for identification of EARLY loss. ONLY use for ADVANCED loss. Grey scale can mask or underestimate visual field loss.

Question 21

Movement from total probability deviation map to pattern probability deviation map removes?

Answer 21

Diffused component

Question 22

Influence of cataract on absolute values?

Answer 22

Reduces the number value

Question 23

Why do probability symbols decreases as movement from total probability deviation map to pattern probability deviation map is made?

Answer 23

The symbols exists because diffused or measured hiller vision lies outside the lower limit of the normal range.