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The use of preferential hyperacuity perimetry (PHP) is expanding beyond general optometry to retinal specialists, who recognize its value in managing age-related macular degeneration. PHP testing allows for crucial detection of extrafoveal lesions in their earliest stage, when they can be treated most effectively.
With the latest advances in treating AMD, such as the anti-vascular endothelial growth factor antibodies that have the potential to retain or even improve vision, early detection of conversion to wet AMD has become critical. Choroidal neovascularization (CNV) typically occurs before the patient has symptoms or an abnormal Amsler grid test result. PHP testing allows for detection of extrafoveal lesions in a patient's earliest stage, when they can be treated most effectively.
Against the backdrop of new treatments for early AMD, PHP's ability to detect early indicators of conversion is critical, said Leo Semes, OD, professor, University of Alabama at Birmingham School of Optometry. "There are some good treatments now, but the window of opportunity to be successful is very brief," he said. "PHP is the most useful tool we have for discerning the earliest indictors of conversion."
A noninvasive visual field analyzer for monitoring AMD and detecting conversion to CNV (Foresee PHP, Sightpath Medical) can detect visual field distortions caused by lesions as small as 1,200 μm. The device has 82% sensitivity for early-stage CNV.
The device combines patient interactive software with an algorithm that measures relative photoreceptor field location as an indicator of early CNV. By testing the patient's ability to detect the misalignment of visual stimuli in space, the technology homes in on visual hyperacuity-a more sensitive indicator of retinal changes than normal visual acuity.
Visual hyperacuity is unaffected by contrast sensitivity and is highly resistant to retinal image degradation, making the device usable across a wide spectrum of ages and co-morbidities. The test is simple to administer and easy for patients to understand, according to Dr. Semes. The patent places his or her chin in the support in front of the screen and uses a stylus to identify misalignments in patterns of dots displayed on the screen.
The device analyzes the patient's responses to detect retinal abnormalities that may indicate retinal pigment epithelium (RPE) elevation. By varying the locations and size of the dot distortions, the device tests the site and degree of retinal defects indicative of CNV.
Enhanced screening, monitoring
To date, Dr. Semes has used the device in more than 75 patients. He conducts the first PHP test when a patient still has good visual acuity but has characteristics such as large or confluent drusen and pigmentary changes that suggest a high risk for conversion. Those patients who have an abnormal PHP test result subsequently undergo optical coherence tomography (OCT). "Our approach is to use PHP to monitor for function on patients at high risk for conversion, then test for structural changes as needed," Dr. Semes explained.
He reported the case of a man with 20/25 vision in one eye and 20/200 in the other whom he follows quarterly. "Our goal, of course, was to preserve vision in the 20/25 eye," Dr. Semes said. "In clinical photos, the RPE appears to be intact in the 20/25 eye, both eyes show pigmentary changes, and both eyes have large drusen present," he added.