Visual Fields 1 Flashcards
general VF screening has ____ specificity and ___ sensitivity?
high specificity and good sensitivity
why does general VF screening have high specificity?
high ability to show a normal VF in normal patients, few false field defects
compromised specificity could cause:
many false field defects (missed points that are not due to true VF loss)
compromised sensitivity could cause:
many true defects missed
sensitivity is the ability to:
detect a VF defect when present
specificity is the ability to:
identify a normal VF as normal
100% sensitivity would mean:
all VF defects are detected
100% specificity would mean:
all normal VFs are identified as normal, no false field defects
what test do you run for Humphrey Field Analyzer (HFA)?
central 40 test
what tests do you run for the FDT?
C20 or N30 (N30 better)
what tests do you run for the Matrix?
C20 or N30 (N30 better)
incidence of visual field loss in the general population is about
3-6% (incidence increases with age)
code for problem specific VF screening
92081
code for diagnostic perimetry
92082
for diagnostic perimetry testing strategy, what is often needed?
some quantification of VF defects is needed-quantify defect or 3 zone strategy
for diagnostic perimetry, what kind of test points are best?
best to use more test points to define the defect size, shape, borders, etc. (Full Field 120 example)
code for quantitative perimetry
93083
what is the purpose of quantitative perimetry?
to quantify the VF of a patient at higher risk of VF loss in order to detect the onset of VF loss as early as possible
what is the typical testing strategy and point pattern for quantitative perimetry?
threshold (all points tested)- SITA standard or SITA fast with usually 50-76 points in the central field
in quantitative perimetry, the thresholds (dB values) allow the ability to:
determine if the VF loss if getting deeper (lower dB values) with time
quantitative perimetry has high sensitivity, which can result in what disadvantages?
- many more false defects with threshold perimetry and more difficult to interpret
- much longer testing time than screening VFs
what type of perimetry (and code) for the highest reimbursement but most limited acceptable diagnoses?
quantitative perimetry (92083)
normal monocular vision field, absolute limits for: superior
60
-highly variable
normal monocular vision field, absolute limits for:
inferior
75
normal monocular vision field, absolute limits for:
nasal
60
normal monocular vision field, absolute limits for:
temporal
100
normal monocular vision field, absolute limits for:
total lateral extent
160
normal monocular vision field, absolute limits for:
total vertical extent
135
total lateral extend for normal binocular vision field?
200
central ___ to each side of fixation is binocular overlap
central 60
the temporal ___ on each side of the binocular field is the monocular, temporal crescent
30-40
what type of alternative perimetry is used in SWAP?
blue stimulus on yellow background for SWAP (short wavelength automated perimetry)
what type of alternative perimetry is used in FDT (and Matrix)?
low spatial frequency grating undergoing rapid phase shift (frequency doubling illusion)
where is the peak of the HOV and what does it mean?
sensitivity at the fovea is highest to white stimuli on a white background under photopic conditions
where is the hole in the HOV?
15 degrees temporal to fixation (normal physiological blindspot)
size of the physiological blindspot (BS)?
7.5 degrees vertical and 5.5 degrees horizontal (vertical oval shape)
possible blind spot (BS) changes in glaucoma
BS may enlarge vertically in glaucoma but it is not a consistent early sign in glaucoma
possible blind spot (BS) changes in papilledema
BS enlarges in all directions
ONH is swelling due to increased intracranial pressure
how is BS used for perimetry?
BS used to check fixation quality in automated perimetry but its size/shape is not plotted for diagnostic purposes in modern automated perimetry
in the HOV, the greater the height, the greater the:
sensitivity
sensitivity at the peak of the HOV is the highest of all points and is about ___ dB higher than points just outside the fovea
3 or 4
what is the sensitivity at the BS?
0 dB (absolute scotoma)
sensitivity declines gradually from fixation to absolute limits of HOV, the slope is roughly:
3 dB per 10 degrees (in central 30 degrees)
in the HOV, there is a steeper and more variable slope in ___ field
superior VF
in the HOV, there is a flatter slope in the ___ field
temporal
when does the variability occur in short term fluctuation?
during a test
when does variability occur in long term fluctuation?
from test to test
short term fluctuation, or variability of sensitivity or threshold during a test, can average about ____ dB
1 to 2.5 dB in central field
short term fluctuation can be up to ___ dB in a single point in normals
6 dB
where does short term fluctuation tend to be greater in the field?
tends to be greater further from fixation, greater in peripheral VF (outside of central 30)
2 causes for increased short term fluctuation in central VF:
- abnormal VF- VF loss especially in early glaucomatous VF loss
- reduced patient reliability and consistency of responses
how is the decibel, unit of current perimetry, a relative unit?
relative to the brightest stimulus available on the instrument- therefore dB values vary from brand to brand and cannot be compared between different brands and instruments
on a decibel scale, what is the brightest stimulus available for that perimeter?
0 dB
10 dB would be what brightness compared to the brightest stimulus?
1/10 of the brightness of the brightest stimulus available on that perimeter
how are dB directly related to sensitivity?
the higher the sensitivity, the higher the dB value
highest dB value is normally at the:
fovea (the fixation point of the VF)
