Glossary

Search results

Prelingual Deafness(also: Prelingually Deaf, Congenital Deafness)

Deafness present at birth or acquired before a child has developed spoken language, typically before around age three. Prelingually deaf individuals commonly learn a signed language as a first language and may have different literacy trajectories in the surrounding…

Presbyopia(also: Age-Related Farsightedness)

An age-related vision condition where the eye gradually loses its ability to focus on nearby objects, typically becoming noticeable in the early to mid-40s. Presbyopia affects virtually everyone as they age and significantly impacts web accessibility, making small text difficult…

Profound and Multiple Learning Disabilities(also: PMLD, Profound Intellectual and Multiple Disabilities, PIMD)

Profound and multiple learning disabilities (PMLD) refers to a combination of profound intellectual disability with additional physical, sensory, or health impairments that together create extremely complex support needs. Individuals with PMLD typically require high levels of…

Progressive Disability(also: Degenerative Condition, Progressive Condition)

A disability or condition that worsens over time, requiring adaptive strategies and technologies that can evolve with changing abilities. Progressive disabilities such as dementia, multiple sclerosis, and muscular dystrophy pose unique design challenges because assistive…

Protanomaly(also: Protan Anomalous Trichromacy)

A type of colour vision deficiency where the long-wavelength (red) cone cells have a shifted sensitivity range rather than being absent entirely. Protanomaly is a milder form of protan CVD compared to protanopia, resulting in reduced but not absent ability to distinguish reds…

Protanopia(also: Protan Dichromacy, Red-Blind)

A type of colour vision deficiency caused by the complete absence of long-wavelength (red) cone cells in the retina. People with protanopia cannot distinguish between red and green and perceive reds as significantly darker than people with typical colour vision. This darkening…

Pseudobulbar Affect(also: PBA, Emotional Incontinence, Involuntary Emotional Expression Disorder)

A neurological condition characterized by episodes of involuntary, exaggerated, or inappropriate emotional expression — such as uncontrollable laughing or crying — that may not match the person's actual emotional state. Pseudobulbar affect occurs after damage to the neural…

Reminiscence therapy(also: Reminiscence, Life review therapy, Memory sharing)

A therapeutic intervention widely used with older adults and people with dementia that involves the structured recall and sharing of personal memories and life experiences, often supported by prompts such as photographs, music, objects, or — increasingly — digital technologies.…

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…

Rett Syndrome(also: RTT)

A rare, X-linked neurodevelopmental disorder caused in most cases by mutations in the MECP2 gene, affecting almost exclusively females. After typical early development, children with Rett syndrome lose purposeful hand use and acquired speech between 6-18 months, develop…

Scoliosis

A structural condition in which the spine develops a sideways curvature, often in an 'S' or 'C' shape. Scoliosis ranges from mild curves requiring only monitoring to severe cases that can affect posture, breathing, mobility, and chronic pain, and it is sometimes associated with…

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…

Scotopic Sensitivity Syndrome(also: Irlen Syndrome, Visual Stress, Meares-Irlen Syndrome)

A perceptual processing condition in which the brain has difficulty handling certain visual information, particularly high-contrast patterns like black text on a bright white background. People with scotopic sensitivity may experience text appearing to move, shimmer, or blur on…

Sensorineural Hearing Loss(also: SNHL, Nerve Deafness)

Sensorineural hearing loss is hearing loss caused by damage to the hair cells of the inner ear (cochlea) or the auditory nerve, in contrast to conductive hearing loss, which involves the outer or middle ear. SNHL is the most common type of permanent hearing loss in adults and is…

Sensory Based Motor Disorder(also: SBMD)

A subtype of Sensory Processing Disorder in which the brain has difficulty using sensory information to plan and execute motor actions. SBMD encompasses two sub-types: postural disorder, which affects balance and core stability, and dyspraxia, which impacts motor planning and…

Sensory Processing(also: Sensory Integration, Sensory Processing Differences)

Sensory processing refers to the way the nervous system receives, organizes, and responds to sensory input from the environment, including sound, light, touch, smell, taste, and movement. When sensory processing works differently — as is common in autistic individuals and people…

Sensory Processing Disorder(also: SPD, Sensory Integration Disorder, Sensory Integration Dysfunction)

A condition in which the brain has difficulty receiving, organizing, and responding to sensory information from the environment and the body. People with Sensory Processing Disorder may be oversensitive or undersensitive to sensory input — including touch, sound, light,…

Sensory Processing Sensitivity(also: SPS, Sensory Processing Differences)

Sensory Processing Sensitivity refers to differences in how an individual perceives, filters, and responds to sensory input across modalities such as vision, sound, touch, taste, and proprioception. It is commonly elevated in autistic people, but also occurs in people with ADHD,…

Sloping Hearing Loss(also: High-frequency Hearing Loss, Sloping SNHL)

Sloping hearing loss is a common audiogram shape in which hearing thresholds are relatively preserved at low frequencies and progressively worse at higher frequencies, producing a downward slope on the audiogram. It is the typical presentation of age-related hearing loss…

Social Anxiety(also: Social Anxiety Disorder, Social Phobia)

Social anxiety (social anxiety disorder, SAD) is a mental-health condition characterised by persistent and intense fear of being judged, rejected or humiliated in social or performance situations, leading to avoidance of interactions that most people experience as routine. It is…

Spasmodic Dysphonia(also: Laryngeal Dystonia, SD)

Spasmodic dysphonia is a neurological voice disorder characterized by involuntary spasms of the laryngeal muscles during speech, causing interruptions in voice production. The most common form, adductor spasmodic dysphonia, causes the vocal folds to close too tightly, producing…

Speech Disfluency(also: Disfluent Speech, Non-Fluent Speech)

Any interruption to the normal flow of speech, including repetitions of sounds or words, prolongations of sounds, blocks (involuntary pauses), interjections, and revisions. While everyone experiences occasional disfluency, persistent speech disfluency conditions such as…

Speech disorder(also: Speech impairment, Communication disorder)

A condition that affects an individual's ability to produce speech sounds correctly or fluently, encompassing articulation disorders, fluency disorders, and voice disorders. Speech disorders are significant for digital accessibility because voice-controlled interfaces,…

Spinal Cord Injury(also: SCI)

Damage to the spinal cord that results in temporary or permanent changes in motor function, sensation, or autonomic function below the level of injury. Depending on the location and severity, spinal cord injuries can cause paraplegia (lower body paralysis) or…

Spinal Cord Injury(also: SCI)

Damage to the spinal cord that results in partial or complete loss of motor function, sensation, or both below the level of injury. The location of injury along the spine determines which abilities are affected: injuries at higher vertebrae (e.g., C4-C5) affect more of the body,…

Stammering(also: Stuttering, Stammer, Stutter)

A neurological condition that affects the rhythmic flow of speech, causing involuntary repetitions, prolongations, or blocks of sounds, syllables, or words. Blocking describes audible or silent moments when a person is unable to produce a specific sound despite intending to.…

Strabismus(also: Crossed eyes, Squint, Eye misalignment)

A condition in which the eyes do not align properly, causing one eye to point in a different direction from the other — inward (esotropia), outward (exotropia or exophoria), upward, or downward. Strabismus disrupts binocular coordination and can lead to double vision, amblyopia,…

Tinnitus(also: Ringing in the Ears)

Tinnitus is the perception of sound - most commonly ringing, buzzing, or hissing - without a corresponding external source. It can be continuous or intermittent, uni- or bilateral, and ranges from mild background nuisance to severely disabling. Tinnitus is often associated with…

Traumatic Brain Injury(also: TBI, Acquired Brain Injury, Head Injury)

An injury to the brain caused by an external bodily force, typically from road traffic accidents, falls, or other impacts. TBI severity is classified using the Glasgow Coma Scale (GCS): mild (GCS 13-15), moderate (GCS 9-12), and severe (GCS 3-8), with additional factors…

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…

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…

Upper Body Motor Impairment(also: Upper Limb Impairment, Upper Extremity Disability)

A condition affecting the motor function of the arms, hands, or upper body that limits or prevents the use of standard input devices such as keyboards, mice, and touchscreens. Upper body motor impairments can result from conditions including amputation, cerebral palsy, spinal…

Upper-Body Motor Impairment(also: Upper Extremity Impairment, Upper Limb Impairment)

Motor impairments affecting the upper extremities — including the arms, hands, fingers, shoulders, and neck — that limit a person's ability to perform tasks requiring fine motor control, gross motor movements, or upper-body strength. Common causes include spinal cord injury,…

Vascular Dementia(also: Multi-Infarct Dementia, Post-Stroke Dementia)

A type of dementia caused by reduced blood flow to the brain, often resulting from stroke or small vessel disease. Vascular dementia is the second most common form of dementia and typically affects processing speed, attention, and executive function rather than memory in its…

Vision Impairment(also: Visual Impairment, VI)

An umbrella term for any reduction in visual function — including low vision, blindness, and functional limitations that affect everyday tasks — regardless of cause. The World Health Organization distinguishes between distance and near vision impairment and further classifies…

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 Impairment(also: Vision Impairment, Low Vision, Sight Loss)

A reduction in the ability to see that cannot be fully corrected with standard glasses, contact lenses, or medical treatment. Visual impairments range from low vision (partial sight) to total blindness and include conditions like macular degeneration, glaucoma, diabetic…

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…

Vitiligo

A chronic skin condition in which patches of skin lose their pigment, resulting in irregular white or light areas on the body. Vitiligo can affect people of any skin tone but is more visually apparent on darker skin. The World Health Organization includes vitiligo under the…