visual fields lec 2: static perimetry Flashcards
what is kinetic perimetry
when a stimulus of a fixed size/luminance is moved from non-seeing to seeing until it is detected by the patient
what is static visual field analysis/perimetry
the visual field is probed at specific static points and threshold sensitivity is recorded
what does every point on the retina have
a certain threshold sensitivity
what is threshold sensitivity recorded as in static perimetry
decibels or log units
what does it mean if the decibel or log unit is higher
the higher the threshold sensitivity i.e. the dimmer the light detected (as can see more)
what is 0 DB
the maximum stimulus luminance of a perimeter i.e. the maximum possible brightness
which part of the retina is higher threshold sensitivities recorded
central retina
which part of the retina are lower sensitivity thresholds recorded
peripheral locations of the retina
what does static visual field analysis compensate for, and how does it achieve this
compensates for the change in sensitivity across the visual field, achieved by
- varying stimulus luminance e.g. brighter
- varying stimulus size e.g. bigger
name the two types of measuring static perimetry
- supra threshold screening
- threshold
how does supra threshold work
- can see a stimuli above a certain threshold, so presents a stimulus a couple of DB/threshold higher than the patient can actually see at each point of the visual field
- it screens for whether a px is either normal or has a pathology
how does threshold work
measures the precise threshold sensitivity by varying stimuli intensities at every single location
what is indicated if a px does not see the stimulus when using supra threshold
chances are they have a pathology if they can’t see the stimulus
what happens to a stimuli that falls in a scotoma on supra threshold screening
the stimuli will not be seen
what is supra threshold two zone
points that are missed twice are marked as a black on the printout i.e. the stimuli is shown twice just incase the px accidentally missed it the first time
the circles mean the px has seen the stimulus
what is supra threshold three zone
points that are missed twice are shown a stimulus of maximal luminance
if it is seen with maximal luminance (third time) then it is marked with an x (relative defect)
if not seen, then it is marked as black (absolute defect)
if can see stimulus the first or second time then it is marked with circle
what does the x stand for in a supra threshold three zone visual field plot
relative defect - the stimulus has been seen with maximal luminance
what does a black patch stand for in supra threshold three zone visual field plot
absolute defect - the stimulus has not been seen, even with maximum luminance
what do some supra threshold screening tests do, since age is a primary factor of visual field analysis
some instruments base their supra threshold setting on normative data for various age groups
the stimuli is set at a certain number of decibels higher than the age matched normal
how does threshold related supra threshold strategy work
determines the threshold for four points within the visual field and sets the supra threshold level a certain number of decibels above the 2nd most sensitive point (2nd highest point)
whats the advantage of supra threshold strategy
it is more accurate
how does supra threshold no quantification technique work
the examiner notes the stimuli that are not seen, there is no attempt to quantify the depth of the scotoma, the patient can either see it or not see it
how are the points missed recorded on a supra threshold no quantification technique
points missed twice are recorded as black on the printout
points seen first or second time are marked as circles
how does supra threshold screening with quantification work
if any supra threshold stimulus are missed, then the depth of the scotoma is assessed by establishing the threshold
this is done by going back to when the px can see the stimuli to quantify and measure it to see how deep the defect becomes
how does a supra threshold with quantification technique see how deep a defect becomes
it establishes the threshold by going back to when the px can see the stimuli to quantify and measure
in supra threshold with quantification technique, what does a higher number in the visual field plot mean
higher threshold sensitivity in DB and this indicates the depth of scotoma
what does the supra threshold with quantification technique visual field plot show for seen stimuli
circle
how is the single stimulus supra threshold strategy set up
the test is full automatic and requires no intervention by the perimetrist other than setting the patient up and giving the instructions
explain how the single stimulus supra threshold strategy works
- stimuli is presented at one time 5 db above the measurement of the px threshold sensitivity
- if the stimuli is not seen, then present a second time at the same intensity
- if the stimuli has been missed on both occasions, then the stimuli is presented at 8 db then at 12db above the threshold estimate
- the grey scale indicates the depth of the defect, whether its at 5db, 8db or 12db
what are the two different versions of supra threshold strategy provided with the henson software
- single stimulus
- multiple stimulus
what does multiple stimulus require more of that single stimulus test strategy with the henson
more perimetrist involvement than single stimulus
how is examination time reduced with multiple stimulus test strategy with the henson
by presenting multiple stimuli 2-4 simultaneously
explain how multiple stimulus test strategy with the henson is done
- at the start, the perimetrist determines the px’s threshold and stimuli presented 5 db above this threshold estimate
- px is then asked to report how many lights they saw
- if the stimulus is missed of both occasions, it is then presented at 8db and then 12db above threshold estimate
- if any are not seen, the positions of unseen stimulus is deduced and recorded
- a grey scale indicates the depth of the defect (5db, 8db or 12db)
although multiple stimulus test strategy with the henson is quicker, what is a disadvantage of this technique
it can be harder for the perimetrist and patient
up to how many points can a henson supra threshold programme be extended to
from 26, to 68 or 136
which extended programme of supra threshold with the henson if best to detect a very small scotoma
136 points
list 3 advantages of supra threshold used in perimetry
- rapid/quick examination time
- easier for the patient
- probability of detection of glaucoma is 90% or better, assuming the stimulus sampling density is great enough ~136 point screening
list 2 supra threshold disadvantages
- not as accurate as full threshold perimetry
- less information
how is the threshold technique in perimetry carried out
it is measured at every location in the visual field
uses algorithm: staircase procedure are used to estimate the threshold according to a pre-determined set of rules based upon a knowledge of normal age-related thresholds
what are the three types of threshold programmes
- full threshold (not used anymore)
- SITA for the humphrey
- ZATA for the henson
how does the standard threshold staircase procedure work
- starting stimulus is selected from the px’s age
- then theres a double crossing of the threshold (e.g. from non seeing, then make the stimuli 4db higher, then 4 more db higher, once px can see stimuli, reduce by 2db dimmer and a further 2db dimmer until px can’t see it again etc)
- threshold recorded as last seen stimulus
- termed a 4-2db staircase
- abbreviated staircase procedure exhibits low threshold variability “gold standard” in perimetry
which perimetry machines is the standard threshold staircase procedure available in
- henson
- humphrey
- octopus
- dicon
what three properties should the ideal full threshold algorithm possess
- accuracy
- reproducibility
- offer rapid examination time (however full threshold is not quick, it takes about 15min each eye)
the standard full threshold algorithm does not fulfil all of these criteria
what are the two new generation algorithms which are used instead
- humphrey: swedish interactive threshold algorithms (SITA)
- henson: zippy adaptive threshold algorithms (ZATA)
what are the two SITA programmes available on the humphrey
- SITA standard
- SITA fast
how much more faster is SITA standard, than the standard full threshold algorithm
50% faster (takes about 5-7 min)
how much more faster is SITA fast, than the standard full threshold algorithm
75% faster (takes about 2-5 min)
which threshold programme is more accurate and which one is less accurate than the standard full threshold programme and why
- SITA standard is more accurate than full threshold algorithm as the px is less susceptible to the fatigue affect
- SITA fast is not as accurate as the standard full threshold algorithm
how does the SITA threshold programme save time? state 3 points
based on models of normal and abnormal (glaucomatous) visual fields:
- it is used to predict future responses and speed up testing time, so the speed of the stimulus is adjusted to that of the patient (if press button faster, the programme goes faster)
- post test analysis
- reduction in number of catch trials
what two types of ZATA programmes are there
- ZATA standard (accurate)
- ZATA fast (speed)
how is the ZATA threshold programme compared to the full threshold programme
it is faster and more accurate
what data does the ZATA programme use and what advantage does this have
uses data from any previous visual field result or age dependent normal values, making it faster
how is the ZATA fast compared to ZATA standard
ZATA fast has a lower terminating criteria than ZATA standard, making it faster but less accurate
what are the three different central measurements that threshold can measure
- 10-2 central: 10 degrees
- 24-2 central: 24 degrees
- 30-2 central: 30 degrees
based on where the pathology is
which central measurement, measures further out in the visual field
30-2 central: 30 degrees
which central measurements can full threshold measure
10-2
24-2
30-2
which central measurements can SITA measure
10-2
24-2
30-2
which central measurements can ZATA measure
10-2
24-2
list 4 advantages of threshold
- enables statistical analysis
- provides diagnostic information
- can monitor visual field progression (glaucoma)
- provides information about reliability of the data
list 2 disadvantages of threshold
- more time consuming that supra threshold
- it is easier to supra threshold
although newer threshold procedures offer a comparable examination time
when is the estermann visual field test in the humphrey used
used for ascertaining whether fit to drive
how is the estermann visual field test in the humphrey carried out
- binocular (both eyes) field test
- no trial lenses
- if requires rx to function daily then use actual glasses (because px may use a chunky frame, but do with both specs and trial lenses in order to see if a scotoma is due to the px’s frames)
- if do not require rx to function daily to drive then do not use an rx during test
at what eccentricity is an ambler chart used to measure
central 10 degrees i.e. testing the macula
what is the ambler chart used for
it is valuable in testing a suspicious macula, or if unable to see the macula
what do you ask the patient when using an amasser chart on them
ask if any lines are missing or distorted
what should the patient be corrected for when using the amasser chart and why
patient should be corrected for near distance as the test is designed for 28-32 cm
which visual field test will you use on a 80 year old patient with senile dementia in whom an eye examination revealed nil pathology and state why
supra threshold single stimulus
as single stimulus is easier for someone with dementia and nil pathology use supra threshold
which visual field tests are most commonly used in an ophthalmology clinic and state why
- SITA standard
- SITA fast
(either as the px will have a pathology if they’re at a ophthalmology clinic, but SITA standard is longer so the px can lose accuracy)
which visual field test will you carry out on a 60 year old in whom an eye examination revealed nil pathology, however they have family history of glaucoma
SITA fast 24-2
which visual field test will you use on a 60 year old with advanced glaucoma and why
SITA standard 10-2
they have lost a lot of peripheral visual field, so cannot see whats left
what rx will you use in a 60 year old patient carrying out a 30-2 full threshold?
Distance correction: RE: -4.50/+1.50x80 LE: -4.50/+3.00x90
Reading addition: +1.50 either eye
RE: -3.00/+1.50x80
LE: -3.00/+3.00x90
use distance rx + reading add, and keep cyl in as it is above 1D
list the programmes you will use on a patient with nil pathology
supra threshold
- multiple stimulus 68 points (henson)
- single stimulus 68 points (henson)
- c-76 quantify (humphrey)
when will you use less points on a patient
if they struggle concentrating
when will you use more points on a patient
if they have a suspect small scotoma
which settings will you use on a patient who has a pathology
- SITA 24-2 (fast) (henson)
- ZATA 24-2 (fast) (humphrey)
smaller or larger field size based on pathology
which settings will you use on a patient with nil pathology however they have a risk factor (disc, IOP, FOH)
SITA or ZATA
