Preferential hyperacuity perimetry (PHP) is a psychophysical test used to identify and quantify visual abnormalities such as metamorphopsia and scotoma.
[1] Because of complex brain mechanisms such as filling-in, patients with small and peripheral defects in their vision are often unaware of such changes until late stages in the disease.
[4] Therefore, in retinal diseases such as macular degeneration responses to hyperacuity stimuli may be abnormal long before any changes in visual acuity are observed.
In a PHP test, the macula (central area of the retina) is scanned with a succession of stimuli, each stimulus consisting of a series of dots arranged along a vertical or horizontal axis.
When a stimulus is projected on a healthy portion of the retina, the examinee identifies the artificial distortion and is likely to mark a correct location.