HVF interpretations Flashcards
explain how fixation loss test runs.
what is the cut off value and the cause for fixation loss?
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
interpret the following fixation loss result.
fixation losses: 18/19 xx
18/19 times light flashed on blind spot, px detected
xx= FL > 20%
explain how false positive occurs.
what is the cut off value and the cause for FP?
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
explain how false negative occurs.
what is the cut off value and the cause for FN?
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
explain when gaze tracker is done? explain upward and downward deflection.
done throughout test
upward deflection: fixation instability
downward deflection: blinks, interference by lids/lashes
what can be done to improve test reliability?
instruct the px to fixate on the target tape lids (elderly) repeat test
explain glaucoma hemifield test (GHT)
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
what is the purpose of GHT?
detect any glaucomatous VFD
detect possible glaucoma
what are the possible outcomes of GHT?
- within normal limits
- outside normal limits: 1 pair zone differ, < 1% (abnormal)
- borderline: 1 pair zones differ, < 3% (abnormal)
- abnormally high sensitivity (trigger happy)
- general depression (cataract)
explain visual field index (VFI)
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.
what is the purpose of VFI
to get any average deviation from norm
what is the norm for VFI?
norm 100%
blind (abnormal): 0%
what is mean deviation?
average of all the deviation values of the TD numerical plot. has higher weightage for periphery
what is the purpose of MD?
to see how much better/worse px performs compared to norm.
what are the possible results for MD? what is the norm?
(+) 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
what is pattern standard deviation? what is its purpose?
the diff between expected data and px data
reflects irregularities in the field, such as those caused by localised field defects e.g glaucoma
what is the norm for PSD?
small, close to zero (both in norm and blindness)
what is abnormal for PSD
more (+) is highly abnormal, peaks at moderate levels of localized field loss
low=norm
explain what the first number in a test pattern refer to
e,g 30-2
it refers to thee degrees of the field tested
e.g 30-2 means the machine tests 30 deg around the fovea.
explain what the second number of the test pattern refers to
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
explain the advantages and disadvantages of 30-2
+:defects sometimes found earlier due to increased testing locations
-: more testing points= longertesting time and poorer reliability
higher chance of lid/rim artefacts
explain the advantages and disadvantages of 24-2
+: 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)
explain the advantages and disadvantages of 10-2
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
