GLAUCOMA 4 - VF Progression and Newer techniques Flashcards
what is the main goal of management in glauc px?
lowering IOP
list 3 basic ways of controlling glaucoma?
DROPS, LASER OR SURGERY- imp to consider in vf progression but also when making clinical trials - eg SLT treatment at moorfields
what are some clinical methods to monitor glauc?
-clinical management- px worsening? px stable?
-clinical trials
-benchmark has to be function
what is one limitation of using vf progression as a way to quanitfy glauc?
very difficult to detect changes
how can we improve visual field testing?
- explain to px- as results can be confusing
- supervise
- environment-quiet+noise free
what is ‘noise’ in relation to vf plots?
things that can interfere with the vf plot results
list 6 examples of ‘noise’ (variability)?
- Pupil size
- Refractive error, cataract
- Response reliability
- Poor fixation
- Learning effects
- Fatigue effects
is there a gold std method to check for glauc progression?
nope
why is it difficult to detect change?
Slow process
No natural history-ethically- control needed but that means some ppl wont get tx
typical methods of assessing glauc px?
- optic nerve head
- oct
- iops
- field plots
disadv of vf tests to assess glauc progression? 4 points
- Difficult to do
- Subjective
- Not quantitative
- Based off experience and judgement
what did a study done looking at 5 glauc specialists observing the same vf plots? (interobserver)
not 100% agreed with one other- poor interobserver reliability
what are global indices on a vf plot?
Mean Defect (MD)- zero means defect is normal for their age, the more negative the worst the VF is
Average of all deviations
Rate of loss (dB/year)
what does a mean defect of zero mean?
-means defect normal for age- it is when its negative that the vf is abnormal or worse
disadv of global indices?
- data reduction
-Poor sensitivity - low number - small md number-might not be sensitive to that tiny change at one or two locations - which might be more important than depression visual field (eg MD: -5db can look different in diff vf plots) md can be stable- and px could still be losing imp vision
what does ‘data reduction mean’?
reducing all data down into numbers
what does data reduction lead to?
loss of spatial information
i.e. we don’t know WHERE the VF defect is, just that there is one somewhere
why might be any reason MD gets worse (besides glauc)?
increase in media opacities- eg cataract
what is a newer way to measure mean defect at central location
visual field index
what is a pointwise or point by point method?- detailed diag in lecture
- ANALYSIS done at each location of central field
- looking at change over time
- sensitive tests ideal for a clinical trial-picking up small changes
what type of software is ‘point by point’ used in?
GPA- Glauc progression analysis
on a GPA, what does a dot indicate?
no change from baseline
on a GPA, what does an open triangle indicate?
significant change
on a GPA what does a black triangle indicate?
Change confirmed
- it is a “true change” therefore suspicious
- fallen below baseline on three occasions
on a GPA what does half a black triangle indicate?
change will be confirmed at next visit
how many VFs are needed to detect a ‘true change’?
5 VFs!
(baseline is avg of 2 VFs, + 3 follow up visits)
on a gpa what does X indicate?
‘Too much’ variability
or defect at baseline
(no decision)
how many black triangles do you need to be able to say there is likely progression?
3!
roughly how long after baseline does it take to detect a VF change?
2 years (6 month recall and need 5 VFs for a true change to be detected)
what is an advantages of GPA and where is it used?
very sensitive= used in clinical trials
disadvantages of GPA?
- Dependent on Baseline
- Database?
- Does not use all the fields
Why is it imp to have good software?
to help clinical decisions
name some vf glaucoma software
- progressor(medisoft)
- new software- OPEN eyes
- GPA on Humphrey
main things to consider when using vf software for glauc
Detecting progression to see if treatment works
Pointwise methods more sensitive
Good software available – Should be used!
why is it important to create functional tests or have novel perimetry?
Optic nerve will already start damaging itself before symtpoms seen or signs noticed - so structural change before impact on visual function
what axons are lost first in glauc and which pathway does this affect
Larger axons- first loss to glac- these larger axons belong to magnocellular pathway- can be probed by flickr, colour and emotion
what does magnocellular pathway correspond to?
High amounts of flicker
Achromatic stimuli
Moving stimuli
Low spatial frequencies
as glauc affects magnocellular pathway, what is a proposed method of novel perimetry + state some limitations?
-blue on yellow perimetry (SWAP)
-Longer Test! + Adaptation required
-More variability
-Poor response in elderly as yellowing of crystalline lens with age
another novel proposed test?
frequency doubling test
is frequency doubling test more effect at early detection of glauc?
No good evidence that the stimuli offers ‘earlier’ detection
But a well-designed instrument- so plus is it takes up less space
