Glossary

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Text Scaling Assistive Service(also: TSAS, Font Size Scaling)

An Android platform service that allows users to increase or decrease the size of text displayed across applications. Text Scaling Assistive Service is critical for users with low vision who need larger text to read content comfortably. Apps that fail to support TSAS properly…

Tritanomaly(also: Tritan Anomalous Trichromacy)

A rare type of colour vision deficiency where the short-wavelength (blue) cone cells have a shifted sensitivity range. Tritanomaly results in reduced ability to distinguish blue from yellow. It is the rarest form of anomalous trichromacy and is less commonly addressed in…

Tritanopia(also: Tritan Dichromacy, Blue-Blind)

A rare type of colour vision deficiency caused by the complete absence of short-wavelength (blue) cone cells in the retina. People with tritanopia have difficulty distinguishing blue from yellow and blue from green. Tritanopia is much less common than protan or deutan CVD types…

Typography(also: Typographic Design)

The art and technique of arranging type to make written language legible, readable, and visually appealing. In accessibility contexts, typography encompasses font selection, size, weight, spacing (letter spacing, word spacing, line height), alignment, and contrast. Research has…

Useful Field of View(also: UFOV, Functional Visual Field)

The useful field of view (UFOV) is the area of the visual field from which a person can extract information in a single glance without moving their eyes or head. Unlike the anatomical visual field, the UFOV is a measure of functional vision that depends on cognitive processing…

Visual Affordance(also: Visual Affordances)

A visually conveyed cue that signals how an object can be used or what it represents - for example, a handle suggesting 'grasp', a button suggesting 'press', or color and labeling suggesting product identity. Many visual affordances are inaccessible through touch alone: blind…

Visual Dialogue(also: Visual Dialog, VisDial)

Visual dialogue is an AI task that involves holding a multi-turn natural language conversation about visual content such as an image or video frame. Unlike single-turn visual question answering (VQA), visual dialogue systems maintain context across multiple exchanges, using…

Visual Interpreter(also: Visual Interpreter Service, Visual Description Service, VIDS)

A visual interpreter or description service (VIDS) is a technology or human-powered service that provides people who are blind or have low vision with descriptions of their visual surroundings, typically by receiving camera feeds from the user's smartphone or smart glasses.…

Visual Presentation(also: Text Presentation)

The way text and content are visually rendered on screen or in print, encompassing typography, layout, color, spacing, and formatting choices. Visual presentation significantly affects readability and accessibility for all users but is especially critical for people with…

Visual Processing(also: Visual Processing Disorder, Visual Perception)

The brain's ability to interpret and make sense of visual information received through the eyes. Visual processing difficulties can affect reading, spatial awareness, figure-ground discrimination, and the ability to process complex visual layouts, even when visual acuity is…

Zernike Polynomials(also: Zernike Coefficients, Zernike Modes)

A set of mathematical functions used to describe the shape of optical wavefronts, commonly employed in ophthalmology and optometry to characterise the optical aberrations of the human eye. Each Zernike polynomial represents a specific type of optical distortion — for example,…

ZoomText

A commercial screen magnification and screen reading software for Windows, developed by Freedom Scientific (formerly Ai Squared). ZoomText provides up to 60x magnification along with features like smooth font display, cursor enhancements, focus tracking, and a built-in screen…