Preferential Hyperacuity Perimetry (PHP)
A Method of Early Detection of AMD Progression
by Dan Roberts
Carl Zeiss Meditec, Inc. has developed a device that is proving to be an effective tool for early detection of age-related macular degeneration (AMD). Called the PreView PHP (Preferential Hyperacuity Perimetry), it identifies deviations in the retina using a vision test based upon the hyperacuity phenomenon.
Hyperacuity (also called Vernier acuity) is defined as the ability to identify a subtle misalignment of one object compared to another. The PHP allows distortions or scotomata (blind spots) to be mapped by flashing a dot deviation signal across different areas of the macula. Once this mapping is complete, the doctor can use the information as a baseline to monitor future changes in the visual field.
Until now, the most common diagnostic technique has been examination of the retina with a slit lamp followed by documentation and drawings of the problem areas (locations of drusen, swelling, presence of neovascularization, etc.) The Amsler grid and ERGs have also been useful for detecting changes. A study (Preferential Hyperacuity Perimeter (PreView PHP) for detecting choroidal neovascularization study (Alster Y, et al; Preferential Hyperacuity Perimetry Research Group. Clin Reg Consulting Services Inc., Irvine, California) showed that PHP testing yielded high percentages (over 80%) of sensitivity in detecting new choroidal neovascularization (CNV) in 122 patients presenting with intermediate-through-advanced AMD. This is an improvement over previous methods of early diagnosis, which supports the researchers' conclusion that the PHP should be considered as a useful adjunct to the management of the intermediate stage of AMD.
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