Visual Fields part 2 Flashcards
what is static perimetry?
a stimulus in fixed size and stimulus is moved from a non seeing area to a seeing area until it is detected by px
what is static perimetry?
the visual field is probed at a specific static point and threshold sensitivity is recorded
what does the retina have?
every point in the retina has a certain threshold sensitivity
what is static perimetry recorded ?
decibels or log unit
what does a high number mean?
high number means the higher the threshold sensitivity the dimmer the light detected
What is the max luminance?
max luminance is 0 dB
where are high and lower threshold sensitivity recorded?
higher threshold sensitivity are recorded in central locations
lower threshold sensitivity are recorded in peripheral locations
How do you compensate change in sensitivity across the visual field?
Varying the stimulus luminance
varying stimulus size
What types of static perimetry are there?
supra threshold screening
Full threshold
what is supra threshold screening?
a stimulus is seen above a certain threshold
What is full threshold?
measures precise threshold sensitivity by varying stimuli intensities
How does supra threshold screening work?
stimuli presented a certain number of dB av
above threshold at each point within visual field
any stimuli falling within a scotoma will not be seen
what is suprathreshold TWO ZONE?
show stimuli, px reports cant see
show stimuli again, if px sees it then mark with circle if px can see again mark black
= two responses
How many responses does suprathreshold TWO ZONE have?
two responses
what is suprathreshold THREE ZONE?
points missed twice are shown a stimulus of max luminance, if seen marked with an X (relaive defect ) if not seen marked as black (absolute defect )
How is supra threshold related?
Age related Supra-threshold
Threshold related supra-threshold
how does the age related supra-threshold strategy work?
since age is the primary factor, some instruments base the suprathreshold on normative data for various age groups
e.g 70 years old will compare with normal 70 year old
what is the stimuli in age related supra threshold?
stimuli is set at certain number of dB higher that age matched normal
how does the threshold related supra threshold strategy work?
determines the threshold for 4 points within the visual field. show stimulus cant see it, make it 4dB bright can see it make it 2dB dimmer until they cant see it
what is the stimuli in age related threshold related supra threshold?
set supra threshold testing level at a certain number of dB above the 2nd most sensitive point of 4 measurement is their threshold sensitivity and makes it couple dB brighter thats how they know what you should see
supra threshold screening can be measured by ?
No quantification
with quantification
what is no quantification?
examiner simply notes the stimuli that are not seen
no attempt to quantify the depth of scotoma
what is quantification?
if any suprathreshold stimuli is missed the depth of the scotoma is assessed by establishing threshold
which software provides supra threshold strategy?
Henson software
what two versions of henson supra threshold are there ?
multiple stimulus supra threshold strategy
Single stimulus supra threshold strategy
How does Single stimulus supra threshold strategy work?
> stimulus presented on at a time 5dB above a measurement of px threshold
stimuli not seen presented a second time at same intensity
if missed on both ocasions the stimuli is presented 8dB the 12dB above threshold estimate
a grey scale indicates the depth of defect
5dB 8dB 12dB
How does multiple stimulus supra threshold strategy work?
> multiple stimulus presented simultaneously
patient report how many lights seen
if any not seen, position of unseen stimulus is deduced and recorded
2, 3 or 4 stimulus patterns shown
at the start determine px threshold and stimuli presented 5dB above threshold
How far does multiple stimuli supra threshold work?
26 to 68 or 136 locations
when do you use 136 location?
if you have small scotoma
What is the advantage of supra threshold?
–Rapid examination time
–Easier for patient
–90% higher chance in detecting glaucoma
stimuli sampling density to 136 point screening
What is the disadvantage of supra threshold?
not as accurate as full threshold perimetry less information
What is full threshold?
a staircase procedure used to estimate the threshold according to a pre determined set of rules based upon a knowledge of normal age related thresholds
what softwares measure full threshold?
SITA
ZATA
Which software is SITA used for?
SITA for the humphrey
Which software is ZATA used for?
ZATA for henson
what does the staircase procedure involve?
> starting stimulus selected from age
double crossing of threshold
threshold recorded as last seen stimulus
termed 4-2dB staircase
shows light px cannot see then makes it 4dB brighter.
What should an ideal threshold algorithm have?
properties such as:
accuracy
reproducibility
offer rapid examination time
Does the standard full threshold algrithm fulfil all of these criterias?
No
What does SITA stand for?
swedish interactive threshold algorithms
What does ZATA stand for?
Zippy adaptive threshold algorithms
What is good about SITA?
sita standard is approx 50% faster than standard full threshold algorith
sita fast is approx 75% faster than the standarad full threshold algorithm
which accuracy is better for SITA?
Accuracy of SITA standard is slightly better than standard full threshold algorithm and is less susceptible to fatigue effect (5-7 mins)
accuracy of SITA fast not as good as standrad full threshold algorithm
what is good about ZATA ?
test is much faster than full threshold programs and also more accurate
Zata program uses data from prev visual field result or age dependent normal values making it faster
what is good about ZATA fast?
ZATA fast has looser terminating criteria than ZATA standard making it faster but less accurate
How does SITA save time?
- speed of stimulus adjusted to the patient
- post test analysis
- reduction in number of catch trails
- based on models normal and abnormal visual fields
- used to predict future responses and speed up testing times
what does 10-2 central visual field mean?
central 10 degrees
what does 24-2 central visual field mean?
24 degrees
what does 30-2 central mean ?
central 30 degrees
which degrees does full threshold measure?
10-2
24-2
30-2
which degree does SITA measure?
SITA ( 10-2, 24-2. 30-2)
which degree does ZATA measure?
ZATA ( 10-2, 24-2)
which full threshold can measure centre and peripheral visual field?
SITA
which full threshold can not measure peripheral visual field?
ZATA
what is the advantage of FULL threshold?
:enables statistical analysis
: provides diagnostic information
: can monitor visual field progression
: provides information about the reliability of the data
what is the disadvantage of FULL threshold?
: generally more time consuming than supra threshold
: although newer threshold procedures offer a comparable examination time
Which test can be used for driving?
Estermann visual field test
How does Estermann VF work>?
binocular both eyes
no trail lenses required. if px has glasses can wear them
what does the estermann VF test do?
used to ascertain whether fit to drive
what does amsler chart test used for?
used to measure central ten degrees of macula
how do you use amsler chart?
ask px if any of the lines are missing or distored
what distance do you use the amsler chart?
test isdesigned for 28-32cm so the patient should be corrected for the distance
which visual field test do you think you might choose for a 80 year old px who has senile dementia and nil pathology?
Supra threshold single stimulus
which visual field tests are more commonly used in an ophthalmology clinic?
SITA standard
SITA fast
which visual field test might you suggest to carry out on a 60 year old in whom and eye examination revealed nil pathology however they have a family history of glaucoma?
supra threshold multiple stimulus
which visual field test might you suggest to use on a 60 year old with advanced glaucoma ?
full threshold 24-2
if you have nil pathology which test should you use?
suprathreshold
: multiple stimulus 68 points ( henson )
: single stimulus 68 points ( henson )
: c-76 quantify (Humphrey )
if you have pathology what do you use?
SITA 24-2 fast - henson
ZATA 24-4 fast -humphrey
smaller or larger field size based on pathology
if px have nil pathology however risk factor ( Disc , IOP, FOH)
consider SITA ZATA
What would you do to see macula problem?
Amsler test chart
