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)
how much % of the confidence interval should a patient’s measured sensitivity fall in to be regarded as normal
95% (most people fall in this range)
if a patient’s measured sensitivity falls out of the 95% confidence interval, what is their sensitivity registered as
abnormal and a probability level assigned
if a patient’s measured sensitivity falls out of the 95% confidence interval, what is the chances of their measured sensitivity to be regarded as normal, and what can this indicate
5% chance of their measured sensitivity as being regarded as being normal
indicates that the px is likely to have a pathology
but e.g. not all 20 year olds see the same, so doesn’t necessarily mean they have a pathology
if someone’s measured sensitivity falls outside a 98% confidence interval, what can it mean
they only have a 2% of their threshold sensitivity being normal, i.e. anything outside 98% means you are most likely to have a pathology and only a small (2%) chance of actually being normal
what is a total deviation map sensitive to
diffuse loss
what does the darker square in a total deviation map indicate
it is more likely to be a pathology (the darker the square)
list the %’s found in a total deviation probability map, of if someone falls outside the confidence interval of them not having a pathology, from the lightest to the darkest squares
lightest to darkest squares:
- 5%
- 2%
- 1%
- 0.05%
what does light a patch on a total deviation probability map corresponding to
that the scotoma is not very deep
i.e. the threshold sensitivity in db is not too much lower than the age matched norm in that region
what threshold sensitivity is typical of someone who has a cataract to glaucoma
20db - registers with the darkest probability symbol
what problem can someone with a cataract who has reduced points of 20db in their total deviation probability map cause
it can mask any localised loss that can be underneath the cataract which shows 0.5% loss e.g. incase a px has glaucoma as well
as the cataract causes a diffuse vf loss all over, therefore hides any pathology that can be underneath and px will just be diagnosed with cataract, until it is removed and something like glaucoma can be revealed
how does a pattern deviation plot combat the problem where a cataract which causes a reduction in threshold sensitivity by 20db, causing 0.5% probability symbol across the whole of a total deviation probability map which can cover any other underlying pathology such as glaucoma
the machine will mathematically increase each point by 20db i.e. producing more greys than black probably symbols, and this will show is there is any other pathology underneath
i.e. the pattern deviation plots exposes localised loss by adjusting the general height of the hill (which is not done in a total deviation probability map)
when for example a general height of a hill is increased by 5 db in a pattern deviation probability map, if the value falls outside a given confidence interval, what is assigned
a probability symbol is assigned
when a total deviation probability map where one point is -7db is converted into a pattern deviation probability map where the height of the hill in increased by 5db, how does that value show as in a pattern deviation probability map
as -2 db
what is a pattern deviation probability map sensitive to
focal loss
what di global visual field indices summarise about a vf test
summarises the information about one aspect/thing of the entire visual field test
what are the two types of global indices i.e. two things it looks for to summarise about the entire visual field test
- diffuse loss
- total loss
what is diffuse loss measured by
the mean deviation (MD) - is the average of the total deviation values (and says how far that person is from a normal age matched patient)
what mean deviation value is considered to be abnormal from a total deviation map
values > -2.00db
what does the more -ve mean deviation value from a total deviation map indicate
the worse the visual field results are to a normal age matched individual i.e. higher risk of having a pathology, due to the abnormality
what type of pathology causes a global diffuse loss
a cataract - as it causes a large loss in the visual field
what is increased in the presence of a cataract
mean deviation - i.e. increased in the presence of large areas of focal loss
what is focal loss measured by
a pattern standard deviation (PSD) - which is the standard deviation around the mean of the total deviations
what are pattern standard deviations sensitive to and what is this good for
non uniformity in the visual field, good for detecting a small scotoma as the non uniformity throughout the mean total deviations will be detected, indicating a pathology
what pattern standard deviation value is considered to be abnormal from a pattern deviation map
> +2.00db
which two circumstances will you not get a total pattern standard deviation
if you are completely normal or completely abnormal, because PSD picks up on non-uniformity
give an example of a pathology which will have a low pattern standard deviations value and why
cataract - as they will have a mostly uniform visual field loss/total deviation values
give an example of a pathology with will have a high pattern standard deviation value and why
glaucoma - as they will have non-uniformity in their visual field loss/total deviation values
what is 2 advantages of mean deviation and pattern standard deviation
- gives a single measure about the state of the visual field
- can be used to monitor visual field change over time (progression)
e.g. from a -4 one year, to a -8 the next year mean deviation, indicates a pathology
(but make sure to analyse the whole of the visual field as vf does not progress equally)
what is a disadvantage of mean deviation and pattern standard deviation
there is a loss in spatial information
what is a glaucoma hemifield test
visual field sectors corresponding to the retinal nerve fibre arrangement in the upper hemifield which are compared for asymmetry with their mirror image sectors in the lower hemifield
what 5 things can a glaucoma hemifield test results pick up on
whether a patient is:
- within normal limits = don’t have glaucoma
- outside normal limits = has glaucoma
- borderline
- general reduction in sensitivity
- abnormally high sensitivity
list the 7 things a new humphrey visual field analyser print out for progression has
- baseline exams
- visual field index (VFI) percentage of normal age-adjusted visual field
- VFI rate of progression analysis of patients’ overall history
- regression analysis of VFI values and 3-5 year projection
- VFI bar graphical description of patient’s remaining vision and a 3-5 year projection of VFI if trend continues
- current report including, VFI, MD, PSD, progression analysis
- guided progression analysis alert (GPA) a message stating whether statistically significant deterioration noted in consecutive tests
what does a visual field index on a new humphrey visual field analyser print out for progression tell you
visual field index (VFI) percentage of normal age-adjusted visual field
tells you how much visual field is left that matches the normal age-adjusted visual field in %
what does a solid dot indicate in a guided progression analysis (GPA) indicator of a, new humphrey visual field analyser print out for progression
a point not changing by a significant amount
what does a small open triangle identify in a guided progression analysis (GPA) indicator of a, new humphrey visual field analyser print out for progression
a degree of deterioration expected less than 5% of the time at that location in stable glaucoma patients, that is, deterioration significant at the 5% level (p
what do half filled triangles indicate in a guided progression analysis (GPA) indicator of a, new humphrey visual field analyser print out for progression
significant deterioration at that point in two consecutive tests/visits
what do solid triangles indicate in a guided progression analysis (GPA) indicator of a, new humphrey visual field analyser print out for progression
significant deterioration of that point in three consecutive tests/visits
what does an X signify in a guided progression analysis (GPA) indicator of a, new humphrey visual field analyser print out for progression
that the data at that point was out of range for analysis. for data that is out of range. GPA cannot determine whether or not the encountered deviation at that point is significant. this occurs mainly with deepening field defects that were already quite deep at baseline, such that even the maximum available stimulus brightness is within the range of normal variability
list 4 main things that can artificially affect a visual field plot
- the learning effect
- the fatigue effect
- contraction due to external factors
- functional or hysterical field loss (malingerers)
what is meant by the ‘learning effect’ as a cause that can artificially affect a visual field plot
mistakes are often made of the first examination i.e. not very good at it the first time around
what is a resolution to the ‘learning affect’ as a cause that can artificially affect a visual field plot
repeat fields at a later date
- repeat at least once before referring
- repeating on the same day would be affected by fatigue
what 3 things occurs in the ‘fatigue affect’ as a cause that can artificially affect a visual field plot
- increase in false +ve and false -ve responses
- fixation losses increase
- contraction of the visual field due to droopy eyelids (and pupil miosis)
what 3 ways can you reduce the fatigue affect as a cause that can artificially affect a visual field plot
- talk to the patient
- give encouragement
- allow the px to stop the test for a minute and have a break
in which type of patient can the effects of fatigue be exaggerated
in patients with a pathology
what three things are characteristic of the fatigue affect on a visual field plot analysis
- clover leaf pattern of grey scale, resulting from fatigue
- fixation losses
- increase false negative
list 5 things that can contribute to a ‘contraction due to external factors’ as a cause that can artificially affect a visual field plot
- droopy lids (maybe fatigue related)
- heavy facial features
- spectacle rim
- lens holder
- hair
- poor positioning of occluder
what type of visual field defect does a spectacle or a lens holder not close enough to the patient cause
a ring defect
what causes a ‘functional or hysterical field loss’ as a cause that can artificially affect a visual field plot
failure of patient to respond to visual stimuli e.g. malingering
what type of responses does ‘functional or hysterical field loss’ as a cause that can artificially affect a visual field plot, produce
produced variable responses
which type of patients are the most common to have ‘functional or hysterical field loss’ as a cause that can artificially affect a visual field plot
usually women, 11-20 years old (malingerers)
what type of results in a goldmann kinetic perimeter that are characteristic of a ‘functional or hysterical field loss’ i.e. malingerer
- peripheral isopter tends to decrease in size throughout testing
- spiral or star shaped isopter
what 5 things show up on a visual field plot of a functional loss example e.g. malingerer
- produce falsely low sensitivity values at various locations
- high false negative rate (they say they can’t see a brighter light afterwards at the same spot)
- high SF value
- higher numbers at the primary seed points, give a distant clover shaped pattern
- long test duration particularly with SITA (which is modelled on normal or glaucoma patients, not ones who make it up)
list 4 things that will show up in a visual field analysis of a true pathology such as cataract
- general reduction in sensitivity
- high mean deviation (MD)
- low pattern standard deviation (PSD)/CPSD - as its affects are uniform
- large numbers of significant points on total deviation map i.e. lots of -ve numbers in db, as they will be higher than -2db
list 4 things that will show up in a visual field analysis of a true pathology such as early glaucoma
- nasal step: early visual field defect in glaucoma
- mean deviation (MD) is low
- pattern standard deviation (PSD) is low
- significant total and pattern deviation maps
what are the two main things that will show up in a visual field analysis of someone who has both cataract and glaucoma
- general reduction in sensitivity on the total deviation map (as cataract causes a diffuse loss)
- pattern deviation map reveals the focal loss i.e. glaucoma (once you elevate the threshold sensitivity in db, the height of the hill)
