Front-line Power Against AMD

Early detection of wet AMD is more important than ever, and preferential hyperacuity perimetry brings this capability to general ophthalmology practices.

BY ERIN MURPHY, CONTRIBUTING EDITOR

We can halt and sometimes even reverse vision loss from age-related macular degeneration (AMD).^1,2 It's been nearly a year since ranibizumab (Lucentis) changed the landscape of AMD treatment, but the words still carry a thrill. The drug improves vision for up to 40% of patients and retains vision for 95% of patients at 1 year.^1,2 With ranibizumab taking center stage because of its potential to restore vision, the importance of early detection has never been greater. The sooner patients begin treatment, the better their chances are to regain or retain their eyesight.

Preferential hyperacuity perimetry with the Foresee PHP (MSS) plays an important role in early detection.

"I've saved patients' sight with the PHP from very early on," says Sara R. Sirkin, M.D., a private practitioner in Tonawanda, N.Y. "When the PHP technology first became available, we could detect AMD early, but the only treatments available were laser or verteporfin (Visudyne). With the advent of effective treatments for wet AMD, the PHP allows me to refer patients to a retinal specialist early in the course of their disease process — very likely saving or preserving their vision. We can catch AMD early and actually stop the disease."

The Foresee PHP is a noninvasive visual field analyzer indicated for detecting conversion to wet AMD. The easy-to-use device detects the conversion to wet AMD with 82% sensitivity. This giant leap in efficacy from previous testing methods means practitioners can detect visual distortions consistent with AMD progression and refer patients to a retinal specialist sooner to ensure the best possible outcome.

Moving Away From the Old Way

Before the PHP arrived, general eyecare practitioners' methods for screening and tracking AMD were less than ideal. Jon-Marc Weston, M.D., F.A.C.S., a private practitioner in Roseburg, Ore., remembers it well.

"Before PHP testing, the standard of care for high-risk patients included recommending high-dose antioxidants, performing dilated examination of the macula twice a year and depending on home testing with an Amsler grid,"³ he recalls. "We'd ask patients to view and identify areas of irregularity on the grid, with the goal of identifying early warning signs of damage or progression to neovascularization between exams. But most patients didn't use the Amsler grid regularly. Even when they did, the lack of a standardized focal distance, the completion phenomena and other neurological processing errors made it a very poor test for detecting the onset of neovascularization."

The Foresee PHP records patients' responses and produces a report based on a predesigned algorithm. The report includes a hyperacuity deviation map, hyperacuity defect zones table, result (including normative database comparison), reliability index, examination history chart and comments (including recommendations for next steps).

Of course, at the same time, treatments for AMD were not nearly as promising as they are today. "Now that we have increasingly effective treatments for wet AMD, it's even more imperative that we make early diagnoses to optimize the chances of vision recovery and protection," Dr. Weston says. "If we detect AMD early, we can preserve or improve vision for 4 out of 5 patients."

The Foresee PHP has helped Dr. Weston attain this goal. He observes, "Studies have shown that compared to the Amsler grid testing,³ PHP's capabilities allow us to catch AMD at a point when treatment results will be superior for about 80% of patients."

How Foresee PHP Works

The Foresee PHP measures patients' hyperacuity, or Vernier acuity — that is, the ability to detect a small difference in the location of two or more visual stimuli. As the name indicates, hyperacuity is far more sensitive than visual acuity. While resolution ability might be 30 to 60 seconds of arc, hyperacuity may be as low as 3 to 6 seconds of arc. The idea is that testing hyperacuity will enable earlier detection of choroidal neovascularization (CNV), before retinal function is permanently lost. This is done while bypassing the brain's compensation mechanisms.

The Foresee PHP's visual stimuli are relatively resistant to media opacities, so the test is suitable for patients with clear or opaque media. The Foresee PHP maps defects within a patient's visual field by analyzing responses to "dot deviation signals" flashing on a computer screen. A signal, consisting of a series of closely spaced dots in a single straight line with several dots out of alignment creating a hump, or distortion, is displayed on the screen for 160 milliseconds. The patient uses a stylus pen to touch the screen to identify the most prominent distortion in the line. By utilizing a phenomenon called "preferential looking," the Foresee PHP can determine abnormalities that may indicate retinal pigment epithelium elevation. The patient's attention will always be drawn to the greatest distortion they see, so if a visual defect causes the patient to see a bend in the line that appears greater than the one presented by the instrument, the patient will select the physiological distortion. The dot deviation signals show differing magnitudes and locations of distortions to measure the extent and location of defects consistent with CNV.

The Foresee PHP is easy for technicians to operate. Patients sit in front of the machine and actually direct much of the test:

• A series of white dots on a dark background flash at predefined intervals across the central 14° of the macular visual field.
• The technician tells patients that if they see any abnormalities in the dot-deviation signal, they should touch the screen with the stylus at the approximate location of the abnormality.
• The test flashes artificial distortions that look like those seen by patients with AMD-related macular lesions.
• The system records patients' responses and produces a report based on a predesigned algorithm, which indicates if AMD progression is likely.

The Foresee PHP is a noninvasive visual field analyzer indicated for detecting conversion to wet AMD. The device can detect conversion to wet AMD with 82% sensitivity, according to MSS.

Dr. Sirkin, who has been using the Foresee PHP since it first entered the marketplace, has seen changes over time. "In the few years that I've had PHP technology, the manufacturer has improved it four or five times. They're continually improving the software and enhancing the normative databases," she says. "My staff finds it easier to use the newest software, which makes the testing procedure more self-directed by the patient. My results have improved, too. The tests are easier to interpret than those from earlier versions because of a new direct-comparison capability."

The Foresee PHP report includes a hyperacuity deviation map, hyperacuity defect zones table, result (including normative database comparison), reliability index, examination history chart and comments (including recommendations for next steps).

A New Standard

Like Dr. Sirkin, Dr. Weston has been using the Foresee PHP for several years. In fact, his practice was a beta test site for the current model.

"Our general ophthalmology practice sees a great deal of AMD. The testing algorithm developed along with this technology is designed to pick up neovascular membranes much earlier than before," Dr. Weston explains. "Currently, we're watching about 100 patients who meet the AREDS criteria in our practice. In addition to twice-yearly dilated eye exams, we perform PHP testing quarterly. Conversion from dry to wet AMD can happen fast, so it's medically necessary to monitor these patients four times a year. In four out of five eyes, this will find changes sooner than twice annual dilated exams with Amsler home testing."^4,5

Dr. Sirkin takes a similar approach. "I use PHP testing on most of my patients who've been diagnosed with some form of dry AMD and in all patients who have lost vision in one eye to wet AMD," she says. "For patients who can be tested with ease and consistency, the PHP is capable of detecting early conversion from dry to wet AMD." The manufacturer of the device recommends quarterly testing of patients with intermediate AMD, recognizing that each physician can choose his or her own testing regimen.

Both physicians say the Foresee PHP helps them identify AMD or progression to wet AMD that could have gone unnoticed without the new technology. "When I find progression in a patient's PHP pattern, it typically happens after I've examined the patient with the ophthalmoscope and seen no definite changes. Sometimes, I've seen some changes in the macular area beforehand that correlate with the PHP," Dr. Sirkin says.

The PHP's analyses contribute to its value as a diagnostic tool. "Serial monitoring is aided by the current software, which reports both reliability and progression probability indices," Dr. Weston says. "When it detects a significant change, we need to do further testing with OCT, angiography or both to determine the best course of treatment."

Dr. Weston is very satisfied with the results from the Foresee PHP. "Our results with the PHP are similar to those reported in major studies. Each year, we've verified a significant change for about 5% of our patients."

The Foresee PHP is helping doctors detect conversion to wet AMD earlier in the disease process, when ocular changes are less developed. Paired with new treatment capabilities, the device has the potential to help doctors save the sight of patients. Dr. Weston says the PHP is becoming indispensable for his practice. "Earlier diagnosis, earlier treatment and preserving vision — these are our goals," he says. "I think the PHP has the potential to become the standard of care for diagnosing and monitoring AMD patients in the comprehensive setting."

REFERENCES

1. Brown DM, Kaiser PK, Michels M, et al. Ranibizumab versus verteporfin for neovascular age-related macular degeneration. N Engl J Med. 2006;355:1432-1444.

2. Rosenfeld PJ, Brown DM, Heier JS, et al. Ranibizumab for neovascular age-related macular degeneration. N Engl J Med. 2006;355:1419-1431.

3. Loewenstein A, Malach R, Goldstein M, et al. Replacing the Amsler grid: a new method for monitoring patients with age-related macular degeneration. Ophthalmol. 2003;110:966-970.

4. Alster Y, Bressler NM, Bressler SB, et al. Preferential hyperacuity perimeter (Preview PHP) for detecting choroidal neovascularization study. Ophthalmol. 2005;112:1758-1765.

5. 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.