Macular degeneration can decrease acuity and cause central metamorphopsia and scotomas which further reduce visual function. Hyper acuity, or vernier acuity, is the human ability to perceive minute differences in the relative spatial localization of two objects in space. During a php test, stimuli are successively flashed in various locations of the visual field. A typical stimulus consists of a series of dots, the majority of which are aligned with respect to each other. A few dots are misaligned, creating the perception of a wave or distortion in an otherwise straight line. This test allows us to monitor changes within the visual field.
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