Diagnostics are a key factor in disease management, especially in glaucoma. Although tremendous advances have been made in ophthalmic imaging during the past few years, visual field testing remains essential to the diagnosis and management of glaucoma.
The Humphrey Field Analyzer (Carl Zeiss Meditec, Inc., Dublin, CA) has been widely recognized as the gold standard in automated visual field testing for more than 25 years, and it has provided clinicians with a widely accepted and broadly available language of perimetry that most doctors understand. All major glaucoma clinical trials have relied upon Humphrey perimetry, including the Advanced Glaucoma Intervention Study (AGIS), the Collaborative Initial Glaucoma Treatment Study (CIGTS), the Early Manifest Glaucoma Trial (EMGT), the Normal Tension Glaucoma Study (NTGS), and the Ocular Hypertension Treatment Study (OHTS).1-5
This article briefly reviews some of the reasons why the Humphrey perimeter has come to enjoy this status.
STANDARDIZATION
Among the many contributions to ophthalmology
made by Hans Goldmann was the first universally standardized
method for manual visual field testing:
Goldmann perimetry. Goldmann perimeters all over the
world used the same standardized stimuli and background
level, allowing doctors to communicate in a common
perimetric language. The Humphrey automated
perimeter can be considered to be the modern day
extension of Goldmann's standardization efforts in terms
of availability and worldwide acceptance. The Humphrey
Field Analyzer is further enhanced by widely accepted
standardized testing strategies, normative data, and analytical
methods, all of which provides doctors not only
with an international standard for visual field testing but
also a standard language for communicating results. Such
uniformity has provided universally accepted criteria for
glaucoma staging and diagnosis that were not widely
available even 20 years ago.
TESTING ALGORITHMS
Standardization by itself is insufficient if the methods
used are not sensitive, reproducible, and efficient. In the
early 1980s, automated threshold testing strategies could
take as long as half an hour per eye, making them neither
clinically practical nor well accepted by patients. While it
was simple to reduce testing time by sacrificing precision
and reproducibility, it was not until the late 1990s that
strategies emerged that successfully reduced testing time
while maintaining diagnostic performance.6 These new
strategies came to be known as the Swedish Interactive
Threshold Algorithm (SITA) and now include the SITA
Standard, SITA Fast, and SITA SWAP (short-wavelength
automated perimetry). The SITA methods effectively cut
testing time in half without giving up reproducibility or
diagnostic performance.7,8
The SITA strategies have provided clinicians with a broad set of testing options that can be tailored to specific patient needs. SITA Standard 24-2 testing can run in as little as 4 minutes and is usually the most reliable option. SITA Fast 24-2 testing can be performed in as little as 2 minutes and provides a reasonable alternative in situations that demand the briefest of true threshold tests.
Some threshold testing methods save time by assuming that responses obtained at nearby test-point locations also apply to the point being tested. This shortcut blurs test points together, effectively decreasing the number of truly tested points. It is important to note that SITA is a true threshold test, which is to say that SITA methods still determine threshold at each tested location in the visual field by finding at least one brightness that can be seen and one that cannot be seen.
STANDARDIZED ANALYSIS
Once test data have been acquired, the next immediate
task is to interpret the results. If the Humphrey
perimeter is the gold standard of visual field testing, then
STATPAC (Carl Zeiss Meditec, Inc.) is the universal language of perimetry. STATPAC software compares results
to clinically validated, world-class, proprietary agenormative
and glaucoma databases. Data analyses not
only include simple plain language interpretations relative
to normal or to baseline, but they also provide specific
quantitative information that can help doctors make difficult
treatment decisions. STATPAC analysis software is
universally available, simple to use, and well documented
in the peer-reviewed literature. In a world where simplicity
is valued but details are often necessary, the inventors
of STATPAC have made consistently practical and useful
design decisions, and they continue to do so a quarter of
a century after the initial introduction of the product.
HUMPHREY PERIMETRY—PAST AND FUTURE
With the recent—and in many ways stunning—
improvements in ophthalmic imaging, it is easy to lose
track of the continuing role of standardized automated
visual field testing in glaucoma management. Continuing
advances in this field, however, confirm the role of
Humphrey perimetry as the gold standard in the diagnosis
and management of glaucoma.
