Blue-Yellow (Swap) Testing; Advantages Of Testing With Blue-Yellow Perimetry; How Blue-Yellow Perimetry Works; Established Standards For Blue-Yellow Testing - Zeiss HUMPHREY 720i User Manual

TEST PARAMETERS AND STRATEGIES
BLUE -YELLOW
(SWAP) PERIMETRY
Advantages of testing
with blue-yellow perimetry
How blue-yellow perimetry
works
Established standards for
blue-yellow testing
REV. B 02/03 PN 51680-1
Blue-Yellow perimetry, also known as Short Wavelength Automated Perimetry, or SWAP, differs
from standard automated static perimetry only in that a carefully chosen wavelength of blue
light is used as the stimulus, and a specific color and brightness of yellow light is used for the
background illumination. Except for these differences, SWAP is still a basic static threshold
perimetry test in which standard Goldmann stimuli are presented in the standard way.
Blue-Yellow perimetry has performed much better than standard computerized perimetry in
several published longitudinal studies. Working independently, researchers from U.C.
Davis 1 , and U.C. San Diego 2 have found that Blue-Yellow perimetry identified early
glaucomatous visual field defects years before they could be detected using standard white-on-
white perimetry. In separate work, the Davis and San Diego teams also found that Blue-Yellow
perimetry detected progression in glaucomatous field loss significantly earlier than did white-
3,4
on-white perimetry . Other papers have found Blue-Yellow perimetry to be superior in
managing ocular hypertensives and in detecting neurological disease
Blue-Yellow perimetry isolates and measures Blue-Yellow ganglion cell function. The carefully
chosen bright yellow background desensitizes the green and red cones, while having little
effect on blue cone function. The narrow band 440 nanometer blue stimulus falls right on the
peak sensitivity of blue cones. Thus, Blue-Yellow perimetry tests the blue cones and their
ganglion cell connections.
There are at least two theories as to why Blue-Yellow perimetry provides earlier diagnosis. One
theory suggests that the Blue-Yellow ganglion cells are selectively damaged in early glaucoma,
and thus earlier Blue-Yellow perimetry diagnosis is just a function of testing the part of the
visual system which is damaged first. A second theory suggests that early diagnosis is achieved
simply because Blue-Yellow perimetry tests one of several pathways of the visual system; if only
a small part of the system is tested, then there is less redundancy, and loss will be discovered
earlier.
In the beginning of Blue-Yellow perimetry development, there was little agreement on exactly
how testing should best be done. The wavelength of the blue stimulus, the wavelength and
brightness of the yellow background, and what stimulus size should be used were all
considered. Teams at U.C. Davis, U.C. Berkeley, and U.C. San Diego began working together
under the sponsorship of Carl Zeiss Meditec to resolve the differences in their approaches and
to define an optimized common standard. They presented their recommendations to a larger
group from North America and Europe for peer review, criticism, and finally, acceptance. Out
of this process has come an internationally accepted standard for Short Wavelength Automated
7
Perimetry . The Blue-Yellow perimetry system now being offered on the Humphrey perimeter
adheres to this standard.
Note: References are listed in Appendix D along with a Blue-Yellow conversion table and
Blue -Yellow specifications. Additional information on Blue-Yellow test interpretation
can be found in Section 7.
HUMPHREY FIELD ANALYZER II - i series
4-11
5,6
.