Visual Field Analysis ? Flashcards
what personal details should you?
..Is it the correct patient ..Record ID number ..name ..DOB (Age) ..Refractive Error
Is the data correct
..Date of test
..correct eye
How is the reliability criteria classified?
False positive
False negatives
Fixation losses
When is the data unreliable?
False positive >33%
False Negative >33%
Fixation losses >20%
What does False positive mean?
Patient says they can see a light when no light is shown or responds faster than usual humanly possible
What does False negative mean?
Patient says they cant see a light when they are shown a brighter light in a location where they said they could see it before
What does fixation loss mean?
Patient responds to a light which is shown in their blind spot
What does data representation have?
Numeric printout Greyscale Global visual field indices Total and pattern deviation maps Probability analysis Glaucoma analysis
What does the numeric printout show?
Numeric representation of the threshold sensitivity. Higher the number the higher the threshold sensitivity
what does 0dB mean?
Just able to see the perimeters brightest max light
What does <0dB mean ?
Not able to see detect the perimeters brightest light cannot see anything then
what do the brackets mean in numeric printout?
Threshold measured twice
What does the grey scale show?
the grey scale is a graphical representation of the numeric printout ?
what does threshold sensitivity change with?
age
what happens as we get older?
decline in sensitivity?
how much sensitivity changes with age?
0.7 dB per decade
What is relative visual field sensitivity?
The difference between the measured visual field sensitivity and the age-corrected normal visual field sensitivity. This is also called the Total Deviation Decibel map
What does the Total deviation decibel map mean?
Total deviation decibel map= patients measured threshold sensitivity - the normal threshold sensitivity for their age at each test location
what does the negative numbers mean?
the number of dB less than they should have seen for their age
what are confidence intervals?
If the measured sensitivity is outside the confidence interval it is registered as abnormal and a probability level is assigned.
what does grey probability symbols mean?
the darker the more genuine pathology there is
what does localised visual field loss do?
Age matched normal field
measured field
what does cataract show?
a cataract of 20dB will register with the darkest probability symbol and mask any localised loss.
what does the diffuse lost do?
diffuse loss hides the localised lost and hides the pathology
what does the pattern deviation probability map show in cataract?
Pattern deviation plots exposes localised loss by adjusting the general height of the hill
What does the global visual field indices do?
Global visual field indices summarises the information about one aspect of the entire test.
what type of three global indices are there?
Diffuse loss
Focal loss
variability
What is Mean Deviation (MD)?
average of the total deviation values?
When is MD abnormal?
if the mean deviation is greater than -2.00dB
when do you increase MD?
in the presence of cataract and or large areas of focal loss
What is pattern standard deviation PSD?
the standard deviation around the mean of the total deviation
What are PSD sensitive to?
non uniformity in the visual field
when is PSD abnormal ?
abnormal when value greater than +2.00dB
what is advantage of global indices?
Give a single measure about the state of the visual field
can be used to monitor visual field change over time(Progression)
What is the disadvantage of global indices?
There is loss in spatial information
What is glaucoma hemifield test?
visual field sectors corresponding to the retinal nerve fibre arrangement in the upper hemifield are comp[ared for asymmetry with their mirror image sectors in lower hemifield
how does glaucoma hemifield classify pathology?
within normal limits outside normal limits borderline general reduction in sensitivity abnormally high sensitivity
what might artificially affect visual field plot?
mistakes are often made on the first examination
repeat fields at a later date
repeat at least once before considering referral
repeating on the same day would be affected by fatigue
what is the affect of fatique on VF ?
Clover leaf pattern on grey scale resulting from fatigue
fixation losses
increase in false negative
what might happen in fatigue effect?
increase in false +ve and false -ve responses
- fixation losses
- contraction opf the visual field due to droopy eyelids
How can you reduce the fatigue affect?
talk to the patient
encourage the patient
what happens to fatigue effect in pathology?
effects maybe exaggerated in patients with pathology
what other contraction due to external factors are there?
- droopy eyelids-maybe fatigue related
- heavy facial features
- spectacle rim
- lens holder
- hair
- poor positioning occluder
what happens in functional or hysterical field loss?
Failure of the patient to respond to visible stimuli
typically produces variable responses
Kinetic perimetry- peripheral isopter tends to decrease in size throughout testing
-spiral or star shaped isopter
Give examples of functional loss?
> Produce falsely low sensitive values at various location
>high false negative rate
>High spatial frequency value
>High no at the primary seed points give distinct clover shaped pattern
>long test duration particularly with SITA
What is true pathology of cataract?
General reduction in sensitivity
>HIGH mean deviation
>LOW pattern standard deviation/CPSD
>large no of significant pionts on Total deviation map
What is true pathology of early Glaucoma?
> nasal step is an early vf defect in glaucoma
note that MD and PSD are low
significant total and pattern deviation maps
what is true pathology of cataract and glaucoma ?
> cataract and glaucoma often co- exist
note general reduction in sensitivity on the total deviation map
the pattern deviation reveals the focal loss
