technology
New
Technology Allows for Earlier Detection of Pre-CNV
Next-generation
PHP offers more comprehensive reporting for reliable test results.
ROCHELLE NATALONI, CONTRIBUTING
WRITER
Preferential
hyperacuity perimetry is less familiar to retinal specialists than to their general
ophthalmology counterparts — but not for long. Users say the technology, which
monitors progression in age-related macular degeneration (AMD) patients and detects
recent-onset choroidal neovascularization (CNV), will likely become integral to
the management and comanagement of AMD.
Preferential
hyperacuity perimetry (PHP) uses a form of perimetry that is similar to Humphrey
visual fields testing, but instead of using white-on-white stimuli, it is based
on Vernier hyperacuity — or the ability to perceive minute differences in the
relative spatial localization of 2 objects in space.
"Regular monitoring with PHP affords more accurate and timely
referrals and identifies those patients who can best be helped by treatment," says
retinal specialist Nalin Mehta, MD, of the Colorado Retina Center in Denver. Dr.
Mehta, who has worked with the device in his practice since its early developmental
phase, says, "It enables intervention when treatment is most effective in preserving
vision."
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The new Foresee PHP from Notal Vision/MSS.
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WHAT DOES PHP DO?
Preferential hyperacuity perimetry maps
and quantifies visual field defects consistent with the progression of intermediate
dry AMD to the wet stage of the disease. By overcoming the brain's ability to compensate
for small visual field defects, PHP can identify CNV lesions while in development
and the patient still has good vision, allowing intervention when treatment is most
effective. A study of 185 patients, by the Preferential Hyperacuity Perimetry Research
Group, found that PHP testing can both detect recent-onset CNV resulting from AMD
and differentiate it from intermediate AMD with high sensitivity and specificity.
The group reported that monitoring with PHP should detect most
recent-onset CNV with few false-positive results at a stage when treatment usually
would be beneficial and concluded that this monitoring should be considered in the
management of the intermediate stage of AMD. Furthermore, the researchers added
that the use of baseline and serial PHP testing may obviate the need for fluorescein
angiography (FA) in some patients who have persistent symptoms suggestive of neovascular
AMD, such as metamorphopsia, even when the clinical examination shows no obvious
features of neovascular AMD.1
BENEFITS OF PHP
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A
screenshot of Foresee PHP results.
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Dr. Mehta says PHP fills a niche. "There's
nothing like it out there. Before this technology, the average size lesion that
could be picked up was about 3000 μm — or almost the size of a disc area
— before the general ophthalmologists would become aware of it and refer the
patient to a retina specialist for treatment. This instrument has the ability to
pick up abnormalities in the patient's distortion field that come from lesions that
are probably 60% to 70% smaller than what the norm had been up until now," says
Dr. Mehta. "We're finding that with more frequent monitoring we're identifying these
patients with better vision and that the lesions are less likely to be subfoveal.
If we pick them up early enough, we may be able to treat effectively with thermal
hot laser rather than doing damage control much further down the line."
INCREASED USE OF PHP
As the AMD population has grown in recent
years, so has the use of PHP among general ophthalmologists — particularly
those whose practices are comprised heavily of seniors. The PHP system, formerly
known as the Preview PHP (Carl Zeiss Meditec, Dublin, Calif), was recently revamped,
renamed, and reintroduced as the Foresee PHP (Notal Vision/MSS, Bloomington, Minn).
The new version has improved ergonomics, which makes testing easier for both the
patient and technician, but perhaps more importantly, the updated model provides
a more comprehensive patient report.
The Foresee PHP report features data on the history of examinations,
whether the visual field map is outside normal limits (and its p-value), test reliability,
relative location of defects in the macular area, and the likelihood of each visual
field defect being a true defect vs noise.
"The additional data give users a better idea of whether the pathology
is true CNV," says Dr. Mehta. The report also includes recommendations for further
actions. General ophthalmologists who use the Foresee PHP say this feature is particularly
helpful in the efficient comanagement of patients with their retinal specialist
colleagues.
Users say the test is patient-friendly and efficient. The patient
is seated at a computer and with the help of a technician is guided through the
process of responding via touchscreen technology to visual stimuli presented on
the computer screen. A chin rest helps hold the patient's head in place. If a patient
has unencumbered eye-hand coordination and is comfortable enough interfacing with
the computer to respond in a timely fashion, they are considered a reliable candidate
for the test, says Sara Sirkin, MD, a general ophthalmologist and PHP user.
Dr. Sirkin, of Sirkin Eyecare Center, Buffalo, NY, points to several
instances when a patient's vision was saved because the test enabled her to detect
macular changes more quickly [See sidebar: "Saving Viable Vision"]. "This device
allows me to follow my AMD patients more closely and to identify changes more quickly
so I can get them to the retina specialist and get them treated sooner, which is
of course a big advantage," she says.
"If the PHP indicates a definite increase in the macular scotoma
and I have some corroborating information from fundus photographs or OCT, I send
the patient to one of several retinal specialists to whom I refer," says Dr. Sirkin.
"They generally know that if I've seen changes on the PHP, odds are that FA will
confirm those changes and then they can simply proceed with what's going to be the
best treatment for the patient." Once treated, patients are referred back to Dr.
Sirkin for continued monitoring.
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Case Studies: Saving Viable Vision |
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Below are several instances
when viable vision was saved in AMD patients who might otherwise not have been as
fortunate. Buffalo, NY, general ophthalmologist Sara Sirkin, MD, discusses her use
of PHP visual field testing.
Case 1.
This
male patient had 2 PHPs several months apart. Four months after the second test,
he presented with vague complaints of not seeing things quite as clearly as he once
had. This patient had previous cataract surgery and was a reliable patient. When
Dr. Sirkin did the third PHP, a very subtle but definite change in pattern was identified.
Dr. Sirkin did an OCT and saw an area slightly temporal to the foveal area that
was suspiciously elevated.
"I had enough suspicion that
I sent him to a retina specialist," she says. Further testing identified a leak,
and the patient was treated first with pegaptanib sodium (Macugen, OSI/Pfizer) and
more recently with bevacizumab (Avastin, Genentech) and/or ranibizumab (Lucentis,
Genentech). "He has maintained his vision, which had previously dropped from 20/30
to 20/50 and is now back to 20/30."
Case 2:
This
female patient was a bilateral pseudophake who had macular drusen. She had 2 PHPs
several months apart at Dr. Sirkin's practice. A third PHP revealed a definite suspicion
of increase in scotoma. "After the test, I was actually able to see a minimal retinal
change of a little hemorrhage," says Dr. Sirkin. The patient has been undergoing
treatment since her pathology was identified and her vision has been maintained
at 20/40.
Case 3:
A
male patient (now deceased) who lost 1 eye to disease "long before the treatments
and technology that we have today" began to have complaints following cataract surgery.
Dr. Sirkin did a PHP, which showed increased scotoma. The patient was referred
to a retina specialist who treated with pegaptanib sodium and/or bevacizumab and
the patient maintained his 20/50 vision until his death. |
EARLY DETECTION
An
estimated 80% of wet AMD patients are diagnosed too late for effective treatment.
While a patient is asymptomatic and the Amsler grid is negative, the disease is
already active and causing irreversible damage to the retina. With PHP testing,
extrafoveal lesions can be identified at a stage when they can be effectively treated.
Foresee PHP users agree that the Amsler grid personifies the too-little,
too-late cliché and a study comparing PHP to Amsler grid found that PHP had
greater sensitivity.2
"You can put someone on high-dose antioxidants and give them an
Amsler grid to take home and consider checking them every 6 months, but the problem
with that is that the Amsler grid is a pretty lousy way of detecting progress to
CNV," says ophthalmologist John M. Weston, MD. "There are so many problems with
it. Compliance is a big issue, but even when patients follow through, they don't
know how to use it properly no matter how many times you go over it.
On top
of all that, there's really no way to control fixation."
PROBLEMS WITH THE AMSLER
GRID
Dr. Mehta points out that the Amsler grid
is apt to fail in detecting visual field defects until they are relatively large
and subfoveal due to several reasons. First, there's the natural tendency to scan
the world with the fovea and the fact that the Amsler grid does not force fixation.
This causes patients to scan the grid with the fovea, ignoring nonfoveal lesions.
Probably the main reason for failure of the Amsler grid to serve
as a tool for early detection of AMD lies in the ability of the human cortex to
compensate for visual field defects, namely "'cortical completion." Furthermore,
the interaction between neighboring lines in the periphery of the grid causes reduced
detectability of visual fields, also known as "crowding."
Dr. Mehta says he and his retina colleagues are often referred
AMD patients in the too early or too late stage. "This technology could help generalists
refer patients at the appropriate stage when treatment by a retina specialist can
best help save viable vision," he points out.
"By the time it shows up on an Amsler grid, a lesion is 1000 μm
to 2000 μm and that's tougher to treat. Even with our new treatment modalities,
we know that the less damage that has occurred: the smaller the lesion, the better
the patient is likely to respond. With PHP, we can catch these patients at a much
earlier stage," says Dr. Weston, a general ophthalmologist in private practice at
the Weston Eye Center in Roseburg, Ore.
EARLY AND GOOD REFERRALS
Early referral before widespread changes
occur throughout the macula is key. Dr. Weston says he relies on the Foresee PHP
to narrow down — in an automated fashion — the patients who can gain the
most by being referred to a retinologist.
"This system automates the process for me," he says. "We're monitoring
patients in a maximal fashion, catching changes at the earliest possible time when
treatment is likely to result in even better vision. It's much less of a guessing
game for me now."
Retina specialists appreciate good referrals — meaning patients
who are ripe for treatment — and Dr. Weston says the Foresee helps him oblige.
"PHP improves good referrals by pinpointing high-risk individuals who have characteristics
indicating that they are going from dry to wet AMD. Studies have shown that to be
the case, and our experience in my practice has shown that as well," he says.
The ideal time for patients to undergo PHP testing is at the stage
when National Eye Institute's Age-Related Eye Disease Study (AREDS) guidelines recommend
high-dose antioxidants, according to Dr. Weston. "The intermediate drusen patient
is the classic patient," he points out.
WHO SHOULD USE PHP
Dr. Mehta says he thinks the generalist's
practice is the best place for this instrument, but he adds that, "given that we
see so many AMD patients early in the progression of their disease, it can be very
useful in a retina practice as well." Another reason for this, he says, is that
often generalists are not comfortable following patients once they get more than
a few drusen. "If these physicians don't have this technology available — and
a lot of them don't — then we retina specialists may be the next best place
for the technology because we probably understand its potential more than most generalists
anyway."
There is some debate regarding the ideal frequency of PHP testing.
The manufacturer recommends that once a patient is deemed an appropriate candidate
for PHP, thenthe
test should be performed quarterly. Dr. Mehta suggests that the decision should
be that of the treating ophthalmologist and based on how frequently the patient
is seen. "General ophthalmologists will be using this as a clinical screening tool;
however, patient selection is very important. If they used it to get a baseline
on every patient, they'd risk overutilization for something that's going to have
very low yield. I use the same threshold as the AREDS, offering the test to patients
with moderate to severe macular degeneration and then repeating it every 3 to 4
months," he says.
NON-NEOVASCULAR POSITIVES
Early PHP clinical research indicated a
relatively high rate of false-positive results for healthy individuals, which appeared
to be a limitation of the device.3
Dr. Mehta clarified this by explaining that those "false positives" were actually
non-neovascular positives and may actually be another of PHP's features as opposed
to a limitation.
"These really weren't 'false positives' because every one was
positive for a reason. If it wasn't because the patient had wet AMD, it was because
they fell into one of several other categories that apparently trigger this 'positive'
outcome. For instance, having a large area of geographic atrophy can trigger the
instrument to show a defect that looks suspicious for wet AMD, but one that does
not show anything leaking. Also, if a patient has a large pigment epithelial detachment,
this will also distort the macula in a similar way that a wet macular degeneration
would," he explains. "If a patient has an RP detachment they should be sent to a
retina specialist anyway, because they could be harboring new vessel growth."
Dr. Mehta says if the Foresee PHP is used correctly and regularly,
and if the generalist is comfortable with the instrument, it is likely that the
yield of patients who are referred for FA and OCT will have a better likelihood
of having high-risk pathology that will need intervention. "Intuition and data tells
me that PHP can help with earlier diagnosis, earlier intervention, and ultimately
better prognosis. So the implications are huge in terms of maintaining usable viable
vision for a longer period of time," he says.
REFERENCES
1. Alster Y, Bressler NM, Bressler SB, et
al. Preferential Hyperacuity Perimeter (PreView PHP) for detecting choroidal neovascularization
study. Ophthalmology. 2005;112:1758–1765.
2. Loewenstein A, Malach R, Goldstein M, et al. Replacing the
Amsler grid: a new method for monitoring patients with age-related macular degeneration.
Ophthalmology. 2003;110:966–970.
3. Goldstein M, Loewenstein A, Barak A, et al. Results of a multicenter
clinical trial to evaluate the Preferential Hyperacuity Perimeter for detection
of age related macular degeneration. Retina. 2005; 25:296–303.
Rochelle Nataloni
is a freelance writer based in the Philadelphia area.
Retinal Physician, Issue: November 2006