2. • Short wavelength Automated Perimetry
• Frequency Doubling Perimetry
• High Pass Resolution Perimetry
• Flicker Perimetry
• Motion Perimetry
• Rarebit perimetry
• Acuity and resolution Perimetry
3. CONCEPT :
• There are several major retinal ganglion cells that project to different
portion of Lateral geniculate nucleus .
P cells : parvo cellular
layers of LG .
-CENTRAL VISION
-RESPONSIVE TO HIGH
SPATIAL FREQUENCIES
& LOW TEMPORAL
FREQUENCIES
-COLOR INFORMATION
-FORM INFORMATION
-SPATIAL RESOLUTION
K cells :
Koniocellular layers
of LG Nucleus
-BLUE SENSITIVE
RETINAL GANGLION
PROJECT TO K CELLS
-PROCESS BLUE
YELLOW COLOR
OPPONENT
INFORMATION
M cells : Magnocellular layers
of LG nucleus .
-HAVE FAST CONDUCTION
VELOCITIES
-RESPONSIVE TO LOW SPATIAL
FREQUENCIES
-PRIMARILY INVOLVED IN
PROCESSING OF RAPID
FLICKER , MOTION AND HIGH
TEMPORAL FREQUENCIES
4. • The ability to test different subsets of retinal ganglion cells underlying
specific visual function provides a more targeted means of
glaucomatous damage .
• Short wavelength automated primetry responses mediated by KCELLS
• HRP and ACUITY ( resolution/detection ) perimetry functions are
primarily determined by P cells .
• Frequency Double Perimetry mediated by a subset of Mcells
• Motion and Flicker perimetry responses are primarily determined by
a larger group of M cells
5.
6. SHORT WAVELENGTH AUTOMATED PERIMETRY
• Short wavelength sensitive pathways is the basis of blue on yellow or
short wavelength automated perimetry
• Short wavelength sensitive blue color vision mechanisms can be
isolated by using bright yellow background to adapt the middle (green
) and long(red) wavelength sensitive mechanisms and a large blue
target to stimulate the short wavelength sensitive mechanisms
• The bright yellow background suppress the sensitivity of middle –
green and long –red wavelength mechanisms and permits the
sensitivity of short wavelength sensitive mechanisms to be evaluated
7. • Detection of short wavelength stimulus at threshold is mediated by
the blue yellow opponent chromatic mechanisms .
• Blue yellow opponent chromatic pathways are responsible for
detecting the blue stimulus even in areas with extensive
glaucomatous visual field loss .
• In patients at risk of developing glaucoma , SWAP Losses appear
earlier than standard visual field defects and are predictive of future
glaucomatous loss of visual field .
• In addition to its utility in glaucoma patients and glaucoma suspects ,
SWAP has been useful in various types of retinal diseases , optic nerve
diseases , chiasmal and post chiasmal lesions
8. • Requirements :
The optimum stimulus condition for SWAP (on HFA) : a 100 cd/m2
yellow background , size V stimulus , a 200 ms stimulus duration and a
narrow band blue stimulus .
These conditions provide the best isolation of short wavelength
sensitive pathways .
9. • An example of r/e ocular
hypertensive patient of standard
automated perimetry and SWAP
• In year 1 standard automated visual
field is normal although superior
nasal step is present in SWAP
• By year 5 , the superior nasal step
for SWAP has progressed and
standard automated perimetry
begins to reveal the superior nasal
step
10. Drawbacks :
• SWAP has traditionally been indicated as a test to evaluate visual function in glaucoma
suspects, especially younger ones.
• The yellow tone of some initial nuclear cataracts may act as a blue filter and cause a
significant diffuse depression of sensitivity.
• Therefore, any diffuse depression of sensitivity seen on SWAP testing should be
interpreted with caution.
• Another important limitation of the SWAP Full-threshold strategy is the longer duration
of the test and the limited dynamic range.
• Although these limitations have largely been overcome with the introduction of the
SWAP SITA, the yellow background and the blue spot target of SWAP are still relatively
more difficult to recognize than the white-on-white test, which increase patient fatigue
and discomfort during the test.
• In addition, in advanced cases, the patient may not recognize even the brightest target;
therefore, because of the narrow dynamic range, the test may not be sensitive enough to
monitor progression in more advanced cases.
11. Frequency doubling technology (FDT)
• The FDT perimetry determines the contrast
sensitivity for detecting the frequency
doubling stimulus.
• The frequency doubling illusion
phenomenon was thought to be mediated
by a subset of magnocellular RGCs.
• FDT perimeter is portable and considerably
easier to use for both the technician and the
patient; the exam is faster than SAP and is
more resistant to blurring effects.
12. • When a LOW SPATIAL SINOSIDAL
GRATING ---- UNDERGOES HIGHER
FREQUENCY COUNTERPHASE FLICKER -
---- GRATINGS APPEARS to have twice
as many light and dark bars as actually
present .
• My subset of M cells have larger
diameter axons responsible for
generating the frequency doubling
effect .
• The rationale is that if there is damage
to my type cells more contrast will be
required to detect the frequency
double stimulus i.e. contrast sensitivity
for this stimulus will be reduced
13. • Two threshold test and two screening
tests are available for FDT perimetry
• Original thrashold test C-20 : 17 target
locations with 16 square target that are
10X10 degrees and a central target 5
degrees in diameter
• Second Thrashold ( N-30) has two
additional squares above and below the
horizontal line between 20 and 30
degrees . In this manner it is possible to
check for superior and inferior nasal
steps .
• Reliability indicies :
False positive error : blank stimulus of zero
contrast
False negative error : failing to respond to
100% stimulus
Fixation loss : responding to small stimulus
presented to location of blind spot
14. • Two Screening procedures in FDT both of which utilises the C-20
stimulus presentation pattern .
• First screening C-20-1 stimulus with contrast level 99% of normal
population is able to see ( 1% probability level stimulus )
Mild sensitivity loss ( failure to see 1% probability stimulus )
Moderate sensitivity loss ( failure to see 0.5% probability stimulus )
Sever sensitivity loss ( unable to detect 100 % contrast stimulus )
• Second screening C-20-5 : 5% stimulus presented followed by 2 %
probability level followed by 1 % probability level .
15. • The FDT Matrix (Carl-Zeiss Meditec) is the latest commercially available
version and offers a new additional testing program along with the same
tests provided by the previous versions of this technology.
• In the new testing protocol, the FDT Matrix utilizes grating targets smaller
than the original FDT to enable standard 24-2 and 30-2 test patterns, which
look identical to those in SAP.
• Similar to conventional perimetry, the test gives both raw sensitivity values
and probability plots .
• After comparing the results with age-matched normal individuals from the
internal database, a statistical analysis package provides the total and
pattern deviation plots, and the global indices MD and PSD
16.
17. High-Pass Resolution (HPR) or Ring
Perimetry
• The intent of HPR perimetry is to achieve
detection and resolution (identification) of
stimuli simultaneously.
• It consists of Ring targets of varying size
that are generated on a video monitor by
performing a high spatial frequency filtering
of a target incorporating a LIGHT CIRCULAR
CENTER AND A DARK ANNULAR SURROUND
• The underlying basis of HRP stimulus design
is that it corresponds to centre surround
arrangement of retinal ganglion cell
receptive fields and it may therefore be
better than conventional automated
perimetry in revelling glaucomatous
damage
18. • In HRP the stimulus contrast is
held constant and the target size
is varied to determine the
smallest ring stimulus that can be
detected at different visual field
locations .
• A total of 14 Target in equal 1 Db
steps are available giving
instrument optimal range of 14
Db.
. HPR stimuli
19. • HPR perimetry tests 50 locations
inside the 30° central visual field.
The locations are distributed in a
pattern resembling a normal
isopters.
• Results are plotted as threshold
target sizes, showing precisely
what the patient could see in
each location (Figure 3).
• Multiple studies have shown the
effectiveness of HR perimetry in
detecting glaucomatous visual
field loss and also determining
glaucomatous visual field
progression earlier than
conventional SAP
Figure 3. HPR perimetry
20. Flicker Perimetry
• The ability to detect a periodic intermittent flashing stimulus that is superimposed on a uniform background forms the basis
of flicker perimetry.
• Flicker perimetry is believed to primarily assess the magnocellular visual pathway.
• There are three types of flicker perimetry tests that have been developed:
CRITICAL FLICKER FUSION, CFF
PERIMETRY:
determination of the highest rate of
flicker that can be detected at high
contrast
-procedure employs Light emitting
diodes of matched luminance to a
uniform background . --- stimuli are
briefly flickered at 100 % contrast and
patient is asked to press response if
detected
TEMPORAL FREQUENCIES of the flicker
is varied to determine the highest rate
at which flicker is detected
TEMPORAL MODULATION PERIMETRY,
TMP:
evaluation of the amplitude of contrast
needed to detect a flickering stimulus of
fixed flicker rate
- Fixed rate of flickering stimuli is used
. The contrast is varied
- Employs stimuli that are matched to
background luminance . Stimulus
undergoes flicker above and below
the background but maintains an
average luminance equal to
background
LUMINANCE PEDESTAL
FLICKER : . detection of a
flickering stimulus that is
superimposed on a
luminance increment above
the background
- Stimuli has fixed rate and
contrast of flicker but
luminance varies .
21. • Flicker perimetry can be performed with commercially available
perimeters like Octopus and Medmont.
• Each of the flicker perimetry procedures has been shown to be
sensitive for detecting early visual field losses in glaucoma and retinal
diseases.
• One advantage of flicker perimetry method is that is relatively
unaffected by variations in blur (media opacities).
22. • An example of results of
critical flicker fusion and
temporal contrast
modulation forms of
flicker perimetry in
comparison to Humphrey
field analyser
• Lightly stippled circles
indicate locations within
normal limits
• Checkered circles indicate
location that are worse
than the normal 5%
probability level
• Black circles indicate
locations that are worse
than the normal 1%
PROBABILITY LEVEL
23. Motion Perimetry
The ability to detect motion has been a visual function of interest for
detection of glaucoma because of reports that Mcells and large
diameter fibres may be preferentially damaged early in glaucoma
• Because motion sensitivity is mediated by M cell mechanisms , early
glaucoma losses may be reflected in degradation of motion
perception .
• Motion detection perimetry is a method that measures a subject's
ability to detect a coherent shift in position of dots in a circular area
(stimulus) against a background of non-moving dots.
• The test background is composed of 10,000 randomly positioned
white dots with 3.26% of pixels illuminated .
24. • METHODS :
1. Detection of a single small dot or line stimulus . This procedure
determines the minimum displacement of the stimulus necessary to detect
movement .Motion displacement thresholds are elevated in glaucoma
patients often in visual field locations with normal sensitivity for
conventional automated perimetry
2. Another method of performing motion perimetry uses a random pattern
of light and dark dots , similar to snow pattern .A small portion of this
display is then moved in a particular direction .
The patient task is to determine the direction of motion of the dot subgroup
and the minimum percentage of dots ( coherence ) needed to accurately
detect the direction of motion is determined .
100 % COHERENCE STIMULUS WILL HAVE ALL DOTS MOVING IN SAME DIRECTION
50% COHERENCE STIMULUS WILL HAVE HALF OF THE DOTS MOVING IN SAME DIRECTION AND HALF
MOVING IN RANDOM DIRECTIONS
25. Figure 1. Stimuli in motion detection perimetry. A
magnified view of the target shows that 50% of the
dots are moving in random directions (open circles)
and 50% are moving coherently (solid circles). X is
the fixation target.
26. Advantage :
• Many studies have reported that motion perimetry is able to detect
early visual field deficits in glaucoma and other ocular and neurologic
disorders
• Motion is a very salient stimulus for peripheral vision , thereby
making this test easy for patients to perform
• Like flicker perimetry is highly resistant to changes in many different
stimulus conditions (contrast, size, background illumination, blur,
etc.).
• Large changes in pupil size donot appear to have much effect
At present a commercial version of motion perimetry is not available
27. Rarebit Perimetry (RBP)
• RBP works on the premise that sensitivity of visual field examination
to detect early damage improves with the use of test stimuli that are
small relative to receptive fields of the neural elements
• By using very small stimuli (rarebits or microdots), this procedure
presents 0, 1, or 2 suprathreshold dots at various local visual field
regions and requests the patient to indicate the number of dots that
they were able to detect.
28. • RBP uses 24 rectangular test areas in the central 30o field and
probes for the presence of vision within each area .
• By evaluating a number of combinations of dots in small
localized regions, it determines visual performance (detection
or “hit” rate) in these areas.
• Nearly all rarebits are seen with a normal retina (close to
100% "hit rate"), while disorders of the visual system result in
losses from missing or dysfunctional receptive fields which
appear as gaps in the receptive field matrix.
• The spatial density of gaps causes a proportionate reduction
in hit rates. For example, a 10% loss of receptive fields is
theoretically reported to produce a 10% reduction in rarebit
hit rate, to 90%.
29.
30. Acuity and resolution Perimetry
• Detection acuity : ability to distinguish a patterned stimulus from a
uniform field
• Resolution Acuity : ability to distinguish one patterned stimulus from
another example whether a grating stimulus is oriented horizontally
or vertically
• At present the sensitivity and specificity in relation to conventional
perimetry is not determined . Also the redundancy in the p Cell
system may make this test less sensitive than other techniques .
