Glossary

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Page Magnification(also: Page Zoom, Web Page Magnification)

An accessibility feature that enlarges the entire visual presentation of a web page, including text, images, and layout elements, to make content easier to see for people with low vision or visual fatigue. Unlike text-only size increases, page magnification scales all page…

Panning(also: Screen Panning, Viewport Panning)

The act of moving the visible area of a screen magnifier or viewport across a webpage or application to view content that extends beyond the currently displayed portion. For screen-magnifier users, panning is a fundamental but often arduous interaction technique, requiring…

Pelli-Robson Chart(also: Pelli-Robson Contrast Sensitivity Chart)

The Pelli-Robson chart is a clinical tool used to measure contrast sensitivity — the ability to detect objects at low-to-moderate contrast levels. The chart consists of a series of letter-charts composed of different contrasts, mapping a contrast-sensitivity function for the…

Peripheral Vision(also: Side Vision)

Vision that occurs outside the center of gaze, encompassing the ability to see objects and movement to the sides, above, and below the point of fixation. Peripheral vision is important for spatial awareness, navigation, and detecting motion. Musicians with low vision may rely on…

Point Spread Function(also: PSF)

A mathematical description of how a single point of light is spread or blurred by an optical system such as the human eye. The point spread function characterizes the degree and pattern of distortion introduced by optical aberrations. In accessibility research, PSFs are used to…

Pre-compensation(also: Display Pre-compensation, Image Pre-compensation)

A technique in which images displayed on a computer screen are mathematically modified in advance to counteract the visual aberrations of the viewer's eye. Rather than relying on corrective lenses or magnification, pre-compensation transforms the source image so that when it…

Precompensation(also: Display Precompensation, Image Precompensation)

A technique in visual accessibility that pre-modifies displayed images in a way that is opposite to the optical distortion introduced by a user's eye, so that the image arriving at the retina more closely resembles the intended original. Precompensation works analogously to an…

Preferred Retinal Locus(also: PRL, Preferred Retinal Location)

A specific area of the retina outside the damaged macula that a person with central vision loss adopts as their primary fixation point for viewing. When the central fovea is damaged (as in macular degeneration), individuals naturally or through training develop one or more PRLs…

Presbyopia(also: Age-Related Farsightedness, Loss of Accommodation)

An age-related vision condition in which the eye gradually loses the ability to focus on nearby objects, typically becoming noticeable after age 40. Presbyopia affects the vast majority of older adults and is caused by the hardening of the eye's lens, reducing its flexibility.…

Proliferative Diabetic Retinopathy(also: PDR)

An advanced stage of diabetic retinopathy in which abnormal new blood vessels grow on the retina, causing bleeding, scarring, and progressive vision loss that can include blurred vision, floaters, dark spots, and partial or complete blindness. A major cause of acquired low…

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