Flashcards in Visual Field 3 Deck (34)
what is the FASTPC strategy to get threshold?
what is the threshold
how many transitions does it make from seeing to nonseeing or vice versa?
machine uses technique to figure out threshold (using points based off 25 db initially)
-shows a stimulus 2 dB dimmer than the expected threshold
-then travels down in dB (up in brightness) in intervals of 3 until pt switches from not seeing to seeing.
-point of seeing = threshold
ex. if machine things pt should have threshold of 28 dB at a given point
30 dB => 27 dB seen.
-27 = threshold
ex. 30 dB not seen => 27 dB not seen => 24 dB seen
-24 = threshold
what does SITA stand for
swedish interactive threshold algorithm
what does SITA compute threshold based on
computes threshold based on points w/ 50% probability of being seen
how does SITA estimate false positive responses
does not test directly
uses response time to estimate false + responses
when does SITA retest threshold
if the values are 12 dB off
(others retest at 7dB)
SITA programs are about ____% faster than the programs they resplace
ex. SITA standard is 40% faster than full threshold
SITA Fast is 40% faster than FASTPAC
what does short wavelenght automated perimetry (SWAP) use?
uses blue target and yellow background
what technique is used for a full threshold test
4-2-2 staircase used w/ the last seen value taken as the pt's threshold
-goes in 2 dB steps once it has crossed the line from seeing to non seeing or vice versa
what is the full threshold 4-2 algorithm
transition is crossed at least twice (from seeing to non seeing or vice versa)
ex. 27 seen => 31 not seen => 29 seen
-threshold is 29
we lose a decibel a decade after age ____
the hill of vision changes roughly ____dB every ____ degrees throughout the field
at fixation, how many dB should it be
what is the mean deviation (MD)
avg elevation/depression of pts field compared to a normal/reference visual field
ex. if the class avg is 80 and you scored a 75 your MD would be -5.00
what is total deviation
shows what the difference/deviation is at each individual spot, when compared to corrected normal for pts age
ex. a spot with +3 means pt has 3 more dBs than "normal"
-they are at a 29 rather than a 26
what does P < 2 mean
less than 2% of the normal pop shows an MD larger than the value found in this test
what is pattern deviation
similar to TD except the results are adjusted for the overall changes in the height of the measured hill of vision
what is pattern standard deviation (PSD)
a measurement of the degree to which the shape of the pts measured field departs from the normal corrected reference field
what does low PSD equal?
what is an abnormal PSD?
low PSD equals a smooth hill
high PSD indicates an irregular hill
usually a PSD of over 3 is considered abnormal
what is visual field index (VFI)
enhanced MD designed to be less effected by cataract, and more sensitive to changes near the center of the visual field to correlate better w/ ganglion cell loss
what does a VFI of 90% mean
90% of visual field is normal
VFI is plotted against _____
____% of fibers can be lost and a pt can still have a normal field.
-need ____% of fibers to be lost to get only a 5dB defect
what is a change analysis box plot
modified histogram, shows what is happening to the field over time
what is a guided progression analysis (GPA)
pick 2 previous fields, avg them, compare to today's test
what is likely progression in GPA?
what is possible progression
likely: where 3 or more points show deterioration in at least 2 consecutives tests
possible: in cases wehre 3 or more points show deterioration on at least 3 consecutvie tests
what are the different screening modes on the humphrey
2 zone strategy
3 zone strat
what are the 2 different ways a screening field forms a hill output?
1. four primary points, one in each quadrant are thresholded.
-2nd most sensitiv value is used to calculate the expected heigh of the hill of vision
2. machine sets an age-corrected hill. could be diff correction but age related is the most common
what is the 2 zone strategy
from expected height, theoretical hill of vision is calculated
-targets then presented 6dB brighter than the theoretical hill of vision
-if the point isn't seen at 6dB it is tested again.
-points missed twice at the 6dB brigher level are recorded as defects and a solid block is recorded
what is the 3 zone strategy
get a theoretical hill (either 4 primary points or age related hill)
-targets then presented 6dB brigher than theoretical hill of vision
-points missed twice at 6dB level are retested w/ brightest stimulus for the machine
-if see at brightest level an "x" is recorded
-if not seen, a solid block is recorded
-usful for pts who have had strokes