GLAUCOMA 3- Automated Perimetry 1 and 2 Flashcards
What is the difference between kinetic and static?
Kinetic = the stimulus moves around (Goldmann)
Static = stimulus stays in same place (Humphrey/Henson)
What is threshold perimetry?
This gives us a depth of a VF. The depth of the scotoma
what spot sizes do we use?
Goldmann spot size 3
(research point = using larger spot sizes)
What is the DB scale?
0DB is the brightest DB
- Normal value is normally 33db.
This is a weird scale.
What is the Humphrey field analyser (HFA)?
- Full threshold and it is the gold standard
- Found in HES but also some optom clinics
Octopus
What are some advantages to the Humphrey field analyser 2?
- Compact size
- User friendly
- Gaze trackers
- “smart” data acquisition
What two programs can run on the Humphrey 2 analyser?
Central 30-2 :
- 30 degrees
- 76 test points
Central 24-2:
- 24 degrees
- 54 test points
Which one of the two is the gold standard and why?
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24-2 becasue of the speed time
What can be the down side to the 24-2?
It will neglect 80% of the feild
WHat can 24-2 be used to see?
Early Glaucoma
Why is one good thing about manual perimetry ?
You can go above 30 degrees of feild
when do we test binocular visual feild?
120 degrees, for DVLA
what are the seed/primary points?
4 points are assessed : representing the 4 quadrants. This will be used as a starting point for the rest of the feild
How do we reach the threshold?
and what is this technique called?
- The first point it is brighter then the px should see. (calculated on age)
- The machine then will go 4db higher to make it dimmer
- It will keep going 4db until they cannot see it : FIRST REVERSAL
- It will then go brighter by 2db.
- If the px cannot see this it make it brighter by 2 db until seen : SECOND REVERSAL.
STAIRCASE PROCEDURE!
what is the measured threshold?
the difference between the last unseen point and the second reversal.
What if the brightest stimulus was not seen?
This is the first reversal! The stimulus will then get bigger
What are the advanatges to automated perimetry?
- stimulus parameters standardised
- Exam stratategy is known and reproducible
- No observer bias
- computer records
- Non opthalmic qualified person can handle this
what is the bearing of the blind spot?
This blind spot can get bigger due to scotoma.
glaucomatous defect
What defect is more likely to occour first?
Superior
Which half of the field is more important on day to day?
Inferior, as we use this to walk about ect
What is a big issue with VF?
Measurement variablity.
Why might a VF have variability?
- artefacts
- pupil size
- media opacities (cat)
- poor fiaxtion
What can cause issues?
- Lens rim
- Refraction
- Pupil size
- Lid/brow
- Blinking (make sure they do blink)
What is the learning effect?
People get better at feilds the more they do the test this a pyschological thing that happens. We should consider the first two field sessions as training visits
What is the fatigue effect ?
This is when the px gets tired during the test
when is the fatigue effect more noticeable?
after 10 mins
what does the fatigue effect cause?
reduction in sensitivity and increased noise
How did we ddress the fatigue effect?
We made the test quicker by using the SITA test
What is the SITA test?
It a quick gold standard test used for tesing
How does SITA work?
It does one staircase and then uses that on a neighbouring test point
Does it present points closer to the threhold or away?
Closer
What are the advanatges to SITA?
- Faster and more intelligent
- Less fatigue
What are the disadvanatges to SITA?
- Black box method (does
- SITA fast is more quicker (uses bigger step sizes, so it reachs the threhold quicker)
Should we use SITA or SITA fast?
Crabbby boy found SITA fast is the same as using SITA
what do faster algirithms do?
- Speed up the efficiency for the px
- Increase the measurement variability (more noise)
What is short term fluctuation (SF) ?
- This is testing the same point twice on ten points
- Then seeing is there is a large SD.(large =variance/SD is large)
What is the disadvantage to Short term Fluc?
- extra testing = more time
- The variability depends on how much damage there is at a point!
- 10 points aren’t representative
What is fixation loss?
Seeing if the px can see in the blind spot - using the Heijl-Krakau technique : placing a very bright stimuli at the blind spot.
What is the disadvanatge to Heijl-Krakau technique?
- It will rely on how well the blind spot has been mapped out
- The blind spot is large! but the spot size used it small. So there might be a fixation loss but we wont pick it up
- Time consuming
- How many times do we do it? this is a q in this field
What is the eye movmeent recorder?
It is a real time monitor which will track the movement of the eyes.
How does the eye tracker present data?
It will produce a manhatten plot. The more spikes the more FL. We want a smooth line. (not quanititative)
What is the problem with the eye tracker?
- Struggles with small pupils and mascara
- Does not monitor head movments
what is the false positive response?
Trigger happy bredrin
How do false positives work?
No stimulus is presented but then then the px wil press
What is the problem?
- time consuming
- How many times do we do it?
What is the listening window in the SITA FP test?
False Positive rate is estimated based on px reaction time.
If your responses are always in the listening window = good !! If you responses are lower = too quick
If your responses are higher = too slow
On SITA why is the False postive a good way to see reliability?
It will use every point for this anaylsis! (Listening window)
What is a false negative?
- This is going back to a point where we have a DB value.
- Then presenting a bright stimulus - 9db above
- Then seeing if the press the button or not
What is the disadvanatge to false neg?
- Extra catch trials. How many do we do?
- Most px will not have any
- Depends on the VF loss in that point (scotoma extent)
- small samples mean it’s imprecise
What are the guidelines for a unreliable VF test ?
FL >20%
FP and FN > 33%
FP is the most informative!!! (remeber this for exam)
What is quanitificaion?
Taking all the information and then presenting it as numerical data
What is the total devation plot?
- This is based on an age - matched normal refernce
- This is a statistcal comparison between the px plots and the age plots
Negative values really far away from zero is showing it is bad.
What is the pattern devation?
This is measuring the subtle defects (focal losses) - especially seen in glaucoma plots
Why might a px have a big total devation loss?
Becasue of media opacities (cataract) / px not good at doing the test
WHat is the mean devation global indices?
This is the mean of the total deviation. The more negative the value the worse the VF.
This is a reporting of the overall depression in sensaivity of the feild
What is the pattern standard devation global indicies?
This is the average of pattern deviation values. “lumpiness of the VF”. The bigger the number the worse!
Why do we need to be aware of lumpiness? (local scotomas)
This is a sign of early glaucoma
What is the glaucoma hemifeild test?
This will detect glaucomatous defects.
How does it work?
- It will take the pattern deviations in the inferior and superior hemi-fields.
- it will compare them and then if it is irreuglar it indicates glaucoma
- It is insensitive to diffuse loss (not total devation, it is pattern devation)
what is the least useful reliability indicator?
false negatives
what is the most useful reliability indicator?
false positives
