visual fields lec 4: visual field analysis Flashcards
what four things must you check in order to see if you are carrying out visual fields on the correct patient
- record ID number
- name
- DOB (age)
- refractive error
must check these things with patient and not just the record card
how must you make sure that the data is correct and why, name two things
- date of test: to be able to follow up progress of the visual field
- correct eye
what 3 things classes a visual field test as unreliable
check the reliability criteria: - false positives: >33% - false negatives: >33% - fixation losses: >20% so you need less than these values in order to have reliable data
what does false positive mean
patient says they can see a light when no light is shown or responds faster than usual or humanly possible
- desperate to finish the test
- trigger happy
- not reliable
how much % of false positive data is required for a px to have to repeat the visual field test
15%
what does false negative mean
patient says they can’t see a light when they are shown a brighter light in a location where they said they could see it before
- px is getting tired
- can’t see light as they are fatigued
- or they might have a significant visual field loss, so they will just have high false negatives
what can you do to avoid a px getting too many false negatives
ask them to come back on a day where they are less tired
what does fixation loss mean
patient responds to a light which is shown in their blind spot
- so px must be moving their eye around
- or we haven’t plotted the blind spot properly (so must plot it properly)
list the 6 different data representations found on a visual field analysis
- numeric print out
- greyscale
- global visual field indice
- total and pattern deviation maps
- probability analysis
- glaucoma analysis
what is a numerical printout of a visual field analysis
the numerical representation of the threshold sensitivity
what do high numbers is a numeric printout mean
high numbers = high sensitivity to light (able to detect dim light)
what does 0db mean on a numeric printout
just able to see the perimeters brightest light
what does
not able to see the perimeters brightest light
what do the bracketed numbers mean on a numeric printout
thresholds measured twice
what is the greyscale of a visual field analysis
a graphical representation of the numeric printout
what do the darker patches on the greyscale of a visual field analysis mean
the smaller the numerical threshold was = the worse that they can see the darker it gets
what declines as we age and by how much on average
threshold sensitivity, by 0.7db per decade on average (i.e. doesn’t drop by the same amount at every location in the visual field)
which part of the visual field drops more in sensitivity as we age, and by how much
sensitivity in the periphery drops more, by 0.8db per decade
which part of the visual field drops but less that in the peripheral visual field, as we age, and by how much
sensitivity in the central vf also drops but less that periphery, by 0.6db per decade
how can you calculate the exact amount that a person has dropped in sensitivity as they have aged and what map in the visual field analysis is this represented in
need to take away threshold of the patient, at every single location away from an age match norm (what they should have seen), location by location
located in the total/pattern deviation decibel map
what is the name of the calculation where the difference between the measured visual field sensitivity and the age corrected norm visual field sensitivity is calculated
relative visual field sensitivity
also called total deviation decibel map
what does it mean when a patient has a +ve value from their relative visual field sensitivity/total deviation decibel map
they can see better than their age matched norm
and if a -ve value = px saw less than what they should see for their age
what does it mean when a patient has a 0 value from their relative visual field sensitivity/total deviation decibel map
they saw what they should see for their age in that location
if their is a big difference in the value of total deviation decibel/probability map compared to the age norm, what can it indicate
a pathology (if its a high value)