HVF interpretations

Question 1

explain how fixation loss test runs.

what is the cut off value and the cause for fixation loss?

Answer 1

how it works:
occurs at random intervals throughout test.
px responds when target is flashed on blind spot (actually not supposed to see)

cut off value: norm < 20%

cause:
px cannot maintain regard of fixation target

Question 2

interpret the following fixation loss result.

fixation losses: 18/19 xx

Answer 2

18/19 times light flashed on blind spot, px detected

xx= FL > 20%

Question 3

explain how false positive occurs.

what is the cut off value and the cause for FP?

Answer 3

px pressing button when no target is presented (trigger happy)

cut off: <15% (norm)
cause: px anyhow click/ unsure of what to look out for

Question 4

explain how false negative occurs.

what is the cut off value and the cause for FN?

Answer 4

px fail to respond to a brighter target but responded to dimmer target

cut off: <20%

possible cause for FN: px inattentive, fatigue, advanced glaucoma or maligners

Question 5

explain when gaze tracker is done? explain upward and downward deflection.

Answer 5

done throughout test

upward deflection: fixation instability
downward deflection: blinks, interference by lids/lashes

Question 6

what can be done to improve test reliability?

Answer 6

instruct the px to fixate on the target
tape lids (elderly)
repeat test

Question 7

explain glaucoma hemifield test (GHT)

Answer 7

AI software to compare upper and lower VF (e.g 4A and 4B) according to common glaucomatous VF defects
only sensitive to glaucomatous VF defect

Question 8

what is the purpose of GHT?

Answer 8

detect any glaucomatous VFD

detect possible glaucoma

Question 9

what are the possible outcomes of GHT?

Answer 9

1. within normal limits
2. outside normal limits: 1 pair zone differ, < 1% (abnormal)
3. borderline: 1 pair zones differ, < 3% (abnormal)
4. abnormally high sensitivity (trigger happy)
5. general depression (cataract)

Question 10

explain visual field index (VFI)

Answer 10

has central focus, a single number that summarizes each px’s VF status as % of norm age-corrected sensitivity
central test points (higher ganglion cell density) given higher weight than peripheral point.

Question 11

what is the purpose of VFI

Answer 11

to get any average deviation from norm

Question 12

what is the norm for VFI?

Answer 12

norm 100%

blind (abnormal): 0%

Question 13

what is mean deviation?

Answer 13

average of all the deviation values of the TD numerical plot. has higher weightage for periphery

Question 14

what is the purpose of MD?

Answer 14

to see how much better/worse px performs compared to norm.

Question 15

what are the possible results for MD? what is the norm?

Answer 15

(+) value: px better than norm
(-) value: px worse than norm

norm: >-2.00 dB
* if MD lower than 10% of normal px, a significant level (P<10%) will be printed

Question 16

what is pattern standard deviation? what is its purpose?

Answer 16

the diff between expected data and px data

reflects irregularities in the field, such as those caused by localised field defects e.g glaucoma

Question 17

what is the norm for PSD?

Answer 17

small, close to zero (both in norm and blindness)

Question 18

what is abnormal for PSD

Answer 18

more (+) is highly abnormal, peaks at moderate levels of localized field loss
low=norm

Question 19

explain what the first number in a test pattern refer to

e,g 30-2

Answer 19

it refers to thee degrees of the field tested

e.g 30-2 means the machine tests 30 deg around the fovea.

Question 20

explain what the second number of the test pattern refers to

Answer 20

the testing protocol. -1 and-2

-1: tests points directly at the horizontal and vertical axis
uncommon, defects found directly on axis is difficult to interpret

-2; tests points on either side of the horizontal and vertical axis

Question 21

explain the advantages and disadvantages of 30-2

Answer 21

+:defects sometimes found earlier due to increased testing locations

-: more testing points= longertesting time and poorer reliability

higher chance of lid/rim artefacts

Question 22

explain the advantages and disadvantages of 24-2

Answer 22

+: shorter testing time, improved reliability

nasal region 27 deg allow early detection of nasal step

reduced artefacts

-: only tests up to 24 deg except nasal region (27 deg)

Question 23

explain the advantages and disadvantages of 10-2

Answer 23

indicated for px with central scotoma e.g AMD or late stage glaucoma, allows for monitoring of any further progression

recently discovered that can be used to test for early glaucoma as well