Glossary

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Nystagmus(also: Involuntary eye movement, Dancing eyes)

A condition characterized by involuntary, repetitive, rhythmic movements of the eyes, which may move side to side (horizontal), up and down (vertical), or in a circular pattern (rotary). Nystagmus can be congenital (present from birth) or acquired later in life due to…

Nystagmus(also: Involuntary Eye Movement, Dancing Eyes)

A condition involving involuntary, repetitive, and rhythmic movements of the eyes, which can be horizontal, vertical, or rotary. Nystagmus can be congenital (present from birth) or acquired later in life due to neurological conditions, medications, or other causes. It often…

Opportunistic Accessibility(also: Opportunistic Accessibility Improvement)

Opportunistic accessibility is an approach to improving digital accessibility in which enhancements are automatically applied to the maximum extent possible without causing negative side effects. Rather than treating accessibility as an all-or-nothing goal, opportunistic…

Optic Neuropathy(also: Optic Nerve Disease)

Damage to the optic nerve that can result in vision loss, including reduced visual acuity, impaired color vision, and visual field defects. Optic neuropathy can be caused by various conditions including glaucoma, inflammation, ischemia, trauma, or toxic exposure. The pattern and…

Optic atrophy(also: Optic nerve atrophy)

A condition involving damage to the optic nerve that results in partial or complete loss of vision. The optic nerve carries visual information from the eye to the brain, and when its fibers degenerate, visual acuity, color perception, and peripheral vision can all be affected.…

Overview+Detail(also: Overview and Detail)

A visualization interaction paradigm that presents a smaller overview view alongside a larger detail view, letting users navigate the whole while inspecting a part. Common in maps, document readers, and data dashboards. For low-vision users, overview+detail can support spatial…

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…

RNIB(also: Royal National Institute of Blind People, Royal National Institute for the Blind)

The largest charity supporting blind and partially sighted people in the United Kingdom, providing services including accessible format transcription, assistive technology advice, employment support, and advocacy. The RNIB operates one of the world's leading music transcription…

Residual Vision(also: Remaining Vision, Useful Vision)

The vision that remains after an eye condition has caused partial vision loss. Most people classified as having low vision retain some useful residual vision and prefer to use it for observing and interacting with their environment. Low-vision rehabilitation adopts an…

Restricted Field of View(also: Tunnel Vision, Peripheral Vision Loss, Visual Field Loss)

A condition in which the area of the visual environment that a person can see at any given moment is significantly reduced, often described as looking through a tunnel or a narrow tube. Restricted field of view can result from conditions such as glaucoma, retinitis pigmentosa,…

Retinitis Pigmentosa(also: RP)

A group of inherited genetic disorders that cause progressive degeneration of the retina, typically beginning with loss of night vision and peripheral vision and potentially leading to tunnel vision or complete blindness. RP affects the rod photoreceptor cells first, then may…

Retinitis pigmentosa(also: RP)

A group of inherited genetic disorders that cause progressive degeneration of the retina, typically beginning with loss of night vision and peripheral vision and gradually narrowing the visual field (tunnel vision) over years or decades. Some people with RP eventually lose most…

Saccade(also: Saccadic Eye Movement)

A rapid, ballistic eye movement that shifts the point of fixation from one location to another. Saccades are essential for visual search, reading, and scanning the environment. In low-vision rehabilitation, training saccadic eye movements helps individuals develop efficient…

Scotoma(also: Blind Spot, Visual Field Defect)

An area of partial or complete loss of vision within the visual field, surrounded by areas of relatively normal or less affected vision. Scotomas can result from conditions such as macular degeneration (central scotoma), glaucoma (peripheral scotomas), or retinal damage. People…

Scotoma(also: Blind Spot, Visual Field Defect)

An area of partial or complete loss of vision within an otherwise normal visual field. Scotomas can be central (affecting the area of sharpest vision) or peripheral, and may be caused by conditions such as macular degeneration, glaucoma, optic neuritis, or retinal damage. In the…

Screen Magnification(also: Screen Magnifier, Zoom)

Software or built-in operating system features that enlarge a portion of the screen display to make content more readable for people with low vision. Screen magnification tools are available on all major platforms, including the Zoom function on macOS and iOS, Magnifier on…

Screen Magnification(also: Screen Magnifier, Display Magnification)

Software or operating system features that enlarge a portion of the screen content to make it readable for people with low vision. Common modalities include full-screen magnification (which expands the entire display around a movable center point) and lens magnification (which…

Screen Magnifier(also: Screen Magnification Software, Magnification Software)

An assistive technology application that enlarges a portion of the screen display to make content more readable for people with low vision. Screen magnifiers work by rendering a zoomed-in view of the area around the cursor or focus point, often providing additional features such…

Skilled Vision(also: Vernacular Vision, Professional Vision)

Skilled vision is a concept from visual culture and anthropology that describes the process of learning to see and interpret visual information in specialized ways within a particular community of practice. Originally applied to professional fields (e.g., radiologists learning…

Space compaction(also: Horizontal compaction, White space reduction)

An accessibility technique used in screen magnification software and browser extensions that reduces excessive white space and adjusts column widths to minimize horizontal scrolling. For low-vision users who rely on high magnification levels (often 3x-16x), horizontal scrolling…

Stargardt Disease(also: Stargardt Macular Dystrophy, Juvenile Macular Degeneration)

An inherited eye disease that causes progressive damage to the macula, leading to central vision loss typically beginning in childhood or adolescence. Stargardt disease is the most common form of inherited macular degeneration. It may also affect color vision. Unlike age-related…

Teacher of the Visually Impaired(also: TVI, Vision Teacher, Teacher of Students with Visual Impairments)

A specialized educator trained to work with students who are blind or have low vision, providing instruction in skills such as Braille, use of assistive technology, orientation and mobility, and adapting educational materials for visual accessibility. In music education, TVIs…

Telescopic Magnifier(also: Bioptic Telescope, Telescopic Glasses)

A small telescope mounted in or attached to eyeglasses that provides magnification for viewing distant or intermediate-distance objects. Telescopic magnifiers are used by people with low vision for tasks like reading sheet music, watching performances, or reading signs. While…

Tiresias(also: Tiresias Screenfont, Tiresias Font Family)

A family of typefaces developed in 1998 by the Royal National Institute of Blind People (RNIB) specifically designed for legibility on screen displays, particularly television subtitling. Named after the blind prophet of Greek mythology, Tiresias became one of the most widely…

Tunnel Vision(also: Peripheral Vision Loss, PVL)

A visual impairment characterized by the loss of peripheral vision while central vision may remain intact, resulting in a narrow field of view as if looking through a tunnel. Tunnel vision can be caused by conditions such as retinitis pigmentosa, glaucoma, or stroke. It…

Video Magnifier(also: CCTV Magnifier, Electronic Magnifier, Desktop Video Magnifier)

An assistive device that uses a camera to capture and display magnified images of printed material, objects, or other visual content on a screen. Video magnifiers range from portable handheld units to desktop models with large monitors. For musicians with low vision, handheld…

Vision Multiplexing(also: Visual Multiplexing)

An optical engineering concept for low-vision aids that involves presenting multiple views or visual channels simultaneously to compensate for reduced visual function. In the context of assistive technology, vision multiplexing allows users to see both a wide field of view and a…

Vision Rehabilitation(also: Visual Rehabilitation)

See Low-Vision Rehabilitation. A comprehensive set of services and interventions designed to help people with vision loss maximize their remaining vision and develop adaptive strategies for independent living. Vision rehabilitation encompasses assessment, training, assistive…

Visual Aberration(also: Optical Aberration, Refractive Error)

A deviation from ideal optical performance in the eye that causes images to appear blurred, distorted, or otherwise degraded on the retina. Visual aberrations include both lower-order aberrations (such as myopia, hyperopia, and astigmatism) and higher-order aberrations (such as…

Visual Acuity(also: VA, Sharpness of Vision)

A measure of the eye's ability to distinguish fine details and shapes at a given distance. Visual acuity is commonly expressed as a Snellen fraction (e.g., 20/20, 20/200) or in logMAR units used in clinical research. It is the primary metric for classifying levels of vision…

Visual Crowding(also: Crowding)

A perceptual phenomenon in which the presence of nearby flanking characters or objects makes it harder to recognise a target character, especially in peripheral vision or when the target is small, low-contrast, or briefly viewed. Crowding jointly with limited visual span sets an…

Visual Fatigue(also: Eye Strain, Asthenopia, Visual Strain)

Discomfort, tiredness, or reduced visual performance resulting from prolonged or intensive visual tasks. For people with low vision, visual fatigue can occur more quickly because they must exert greater effort to see, often using non-optimal parts of their retina (eccentric…

Visual Field(also: Field of Vision)

The total area visible to a person when their eyes are fixated on a central point, including both central and peripheral vision. Visual field can be measured in degrees and is assessed through perimetry testing. Various eye conditions affect the visual field differently:…

Visual Profile(also: Visual Function Profile)

A visual profile is a comprehensive characterization of an individual's visual capabilities across multiple dimensions, typically including visual acuity, contrast sensitivity, visual field, and color perception. In accessibility, understanding a user's visual profile is…

Visual Search Strategy(also: Scanning Strategy, Visual Scanning)

Systematic approaches to visually exploring an environment or scene to locate specific objects, patterns, or information. In low-vision rehabilitation, therapists train clients in efficient search strategies such as systematic scanning patterns (horizontal, vertical, spiral),…

Visual acuity(also: VA, LogMAR acuity, Snellen acuity)

A measure of the sharpness or clarity of vision, typically expressed as a Snellen fraction (e.g., 20/20, 20/200) or LogMAR value. A person with 20/200 vision must be 20 feet away to see what someone with normal vision sees at 200 feet. Visual acuity of 20/200 or worse in the…

Visual field loss(also: Peripheral vision loss, Scotoma, Tunnel vision)

A reduction in the area of vision that a person can see, either in the periphery (peripheral vision loss or tunnel vision) or in the center (central vision loss or central scotoma). Visual field loss is caused by conditions such as glaucoma, retinitis pigmentosa, stroke, and…

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…