Accessibility Quick Guide

Visual disabilities include:

• A complete absence of vision
• Partial sight
• Colour perception differences.

Each condition has distinct access implications.

Blindness

A person who is blind receives no functional visual information. They rely on non-visual means to access content and navigate the environment.

A blind person using a computer depends on a screen reader to convert text into speech or Braille output. Any visual information must have a text alternative for the assistive tools to be useful.

Legal and medical definitions of blindness vary. "Legally blind" often includes people with some residual vision. In accessibility practice, assume that a screen reader user may have no usable vision.

Low Vision

A person with low vision has partial sight that cannot be fully corrected by glasses or surgery. They may use their vision alongside assistive tools, often with significant magnification.

Someone with low vision might enlarge the text in their browser to 300%. They might also use high contrast mode or rely on a screen magnifier. They often use both vision and technology simultaneously, making layout and spacing critical.

Many low vision users do not use screen readers at all. Visual presentation matters more for this group.

Colour Vision Deficiency

Colour vision deficiency reduces the ability to distinguish between certain colours. The most common form impacts red-green discrimination. But this condition exists on a spectrum.

A chart with only red and green lines is hard to read for those with red-green colour vision deficiency. Adding distinct line patterns or labels solves the problem.

Colour vision deficiency is far more prevalent than most designers assume. It affects approximately 8% of men of Northern European descent. It is not the same as seeing only in grey tones. Most people with CVD see colour, but not as someone without the deficiency does.

Auditory disabilities include:

• Total deafness
• Partial hearing loss
• Differences in auditory processing

Each of these conditions requires different access strategies.

Deafness

A person who is deaf has no functional hearing. They can only understand audio content through visual options, such as captions, transcripts, or sign language interpretation.

A deaf person watching a video without captions receives no audio. Dialogue, sound effects, and tone of voice are all inaccessible unless provided in text or visual form.

Many Deaf people (with a capital D) identify with Deaf culture. They may prefer sign language over written text. For some, reading in a written language is a second-language skill, so captions alone may not be enough.

Hard of Hearing

A person who is hard of hearing has some degree of hearing loss. They may use residual hearing combined with hearing aids, captions, or other strategies.

In a meeting room with poor acoustics, a person with hearing aids may miss critical dialogue. A loop system or real-time captions gives them equal access to the conversation.

Central Auditory Processing Disorder

Central auditory processing disorder (CAPD) affects how the brain interprets sound. While the ear works normally, the person struggles to discern speech. This is especially true in noisy environments.

A person with CAPD in a busy café may hear someone talking but be unable to decode what is being said.

CAPD is easily overlooked because the person "passes" a standard audiological test. Their difficulty is neurological, not peripheral. They are often misunderstood as being inattentive or having a language difficulty.

Deaf-blindness is the combination of both hearing and vision loss. But it is more than the sum of its parts. Since neither sense fully compensates for the loss of the other, unique barriers to communication arise. People who are deaf-blind need tactile communication and other accessible channels.

A person who is deaf-blind may use a refreshable Braille display connected to a screen reader. Text is the only format that reaches them. So, alt text, captions, and transcripts are all essential, not supplementary.

Most people identified as deaf-blind have some residual vision or hearing. Complete absence of both senses is uncommon. Further, deaf-blindness exists on two separate spectra. So, the degree of loss in each sense determines the specific access needs.

Speech and language disabilities affect the ability to produce or process spoken language — they range from articulation differences to complete absence of speech, and they create barriers in voice-reliant systems and communication contexts.

Organic Speech Sound Disorders

Organic speech sound disorders have a physical cause — structural differences, neurological conditions, or sensory impairments that affect how speech sounds are produced.

A person with dysarthria caused by cerebral palsy may have speech that is difficult to understand — voice recognition software trained on typical speech patterns will fail to recognise their input reliably.

⚠️ "Organic" indicates there is an identifiable physical cause — this distinguishes these disorders from functional speech sound disorders where no structural cause is found.

Functional Speech Sound Disorders

Functional speech sound disorders affect articulation or phonological processing without an identifiable organic cause — speech sounds are substituted, omitted, or distorted in ways that may or may not resolve over time.

A child who consistently substitutes "w" for "r" (saying "wabbit" for "rabbit") has a functional articulation disorder — their speech mechanism is intact but the learned production pattern differs from the target.

No Speech (Mutism)

Mutism is the absence of speech — it may be selective (speech occurs in some contexts but not others) or total, and may have psychological, neurological, or other origins.

A child with selective mutism speaks freely at home but produces no speech at school — augmentative and alternative communication tools, such as a tablet with symbol-based output, can give them a way to participate.

⚠️ Selective mutism is an anxiety-based condition, not a choice or defiance — people with selective mutism are often fully capable of speech in other contexts and should never be assumed to have cognitive or language difficulties.

Aphasia

Aphasia is an acquired language disorder — typically from stroke or brain injury — that can affect speaking, understanding, reading, and writing in any combination.

A person with Broca's aphasia knows what they want to say but cannot produce fluent speech — they may communicate in single words or short phrases while their comprehension remains relatively intact.

⚠️ Aphasia affects language, not intelligence — a person with severe aphasia may have full cognitive capacity but be unable to express it through speech or writing. This distinction matters enormously for how people are treated and supported.

Mobility and body function disabilities affect movement, physical control, and bodily function — they create barriers in environments and interfaces designed for a standard range of physical ability.

Manual Dexterity and Fine Motor Control

Difficulties with manual dexterity and fine motor control affect the precise hand and finger movements needed to use a standard keyboard, mouse, touchscreen, or small physical controls.

A person with Parkinson's disease may find it impossible to accurately click small interface targets or type reliably with a standard keyboard — switch access, voice control, or larger touch targets restore independent access.

⚠️ Fine motor difficulties are often invisible — a person may appear unimpaired until they attempt a task requiring precision. Many users of keyboard navigation and switch access have fine motor, not visual, disabilities.

Ambulation

Ambulation disabilities affect the ability to walk or move through space — they range from conditions requiring mobility aids to complete inability to walk.

A wheelchair user approaching a building entrance blocked by steps cannot enter — a ramped or level entrance gives everyone the same access without requiring a detour or assistance.

Muscle Fatigue

Muscle fatigue disabilities cause the muscles to tire rapidly or unpredictably — the person may be able to perform a task initially but becomes unable to sustain it.

A person with multiple sclerosis may be able to type for short periods but experiences increasing weakness with sustained use — keyboard shortcuts, voice input, and tasks requiring fewer keystrokes reduce the physical load.

⚠️ Fatigue-related disabilities are episodic and variable — a person's ability on one day may not reflect their ability on another. Designing for efficiency and reducing repetitive actions benefits this group significantly.

Body Size or Shape

Body size or shape differences — including very short stature, limb differences, or atypical body proportions — create barriers in environments and products designed around a narrow assumed body range.

An ATM positioned at a height accessible to standing adults is unreachable from a seated position or for someone of very short stature — height-adjustable or lower-mounted controls address this.

⚠️ Body size and shape are often overlooked in discussions of disability and accessibility — the principles of universal design address this explicitly, particularly through the "Size and Space for Approach and Use" principle.

Cognitive disabilities affect how people process, understand, remember, and communicate information — they are among the most diverse category of disability and among the most underserved by mainstream accessibility practice.

Intellectual Disabilities

Intellectual disabilities involve significant limitations in cognitive functioning and adaptive behaviour — they affect learning, reasoning, problem-solving, and the ability to manage everyday tasks independently.

A person with an intellectual disability using a government benefits portal may struggle with complex sentence structures, abstract terminology, or multi-step processes — plain language, clear instructions, and simplified workflows directly expand their access.

⚠️ "Intellectual disability" is the preferred current terminology over older terms such as "mental retardation" — terminology in this area has changed significantly and precision matters professionally.

Reading and Dyslexia

Dyslexia is a specific learning disability that affects accurate and fluent word reading and spelling — it is neurological in origin, unrelated to intelligence, and affects people across the full cognitive spectrum.

A highly intelligent adult with dyslexia may read slowly, lose their place frequently, or confuse visually similar letters — text-to-speech, adjustable line spacing, and dyslexia-friendly fonts reduce the cognitive load of reading.

⚠️ Dyslexia is not a vision problem — the letters are not literally moving or reversed. It is a phonological processing difference that makes it harder to decode written symbols into spoken language units.

Math and Computation (Dyscalculia)

Dyscalculia is a specific learning disability affecting the ability to understand numbers, perform calculations, and process mathematical concepts — it is the numerical equivalent of dyslexia.

A person with dyscalculia may be unable to reliably tell which of two prices is larger, or struggle to count change at a checkout — presenting totals clearly and avoiding reliance on mental arithmetic improves access.

Attention Deficit Hyperactivity Disorder (ADHD)

ADHD is characterised by persistent patterns of inattention, hyperactivity, and impulsivity that interfere with functioning — it affects the ability to sustain focus, organise tasks, and regulate behaviour.

A person with ADHD trying to complete a long online form may lose focus partway through, miss required fields, or be distracted by animations and moving content — reducing distractions and saving progress automatically supports task completion.

⚠️ ADHD presents differently across individuals and contexts — inattentive presentations (without hyperactivity) are often missed, particularly in women and girls, and may be mistaken for disengagement or low motivation.

Autism Spectrum Disorders

Autism spectrum disorders affect social communication, sensory processing, and behavioural flexibility — the presentation varies enormously, and access barriers are as likely to be sensory or communicative as cognitive.

An autistic person may be overwhelmed by autoplay audio, flashing animations, or unpredictable interface changes — consistent, predictable design with user control over sensory elements reduces distress and supports access.

⚠️ Autism is a spectrum — some autistic people have high support needs, others are fully independent. "High-functioning" as a term is contested within the autistic community because it tends to dismiss support needs while masking ability.

Non-Verbal Learning Disability

Non-verbal learning disability (NVLD) affects the ability to interpret non-verbal information — spatial reasoning, patterns, facial expressions, tone of voice, and visual-spatial tasks are characteristically difficult.

A person with NVLD may excel at reading and verbal tasks while struggling with maps, diagrams, or inferring meaning from charts — replacing or supplementing visual-spatial content with clear verbal explanations improves access.

⚠️ NVLD is often described as the "inverse of dyslexia" — strong verbal skills can mask the disability, leading to it being underidentified, especially when academic success in verbal subjects suggests no difficulty.

Seizure disorders involve episodes of abnormal electrical activity in the brain — the type and trigger of seizures determine what access barriers are relevant in digital and physical environments.

General Seizure Disorders

General seizure disorders can produce a range of episodes — from brief absences to convulsions — without necessarily being triggered by environmental stimuli.

A person with generalised epilepsy may experience a tonic-clonic seizure without any warning or specific trigger — their access needs relate more to physical safety, reliable communication, and avoiding cognitive overload than to specific content restrictions.

Photosensitive Epilepsy

Photosensitive epilepsy is triggered by flashing or flickering visual stimuli — content that flashes more than three times per second can provoke a seizure in susceptible individuals.

An animated advertisement flashing rapidly on a news website could trigger a seizure in a person with photosensitive epilepsy — this is why accessibility guidelines set specific thresholds for flash frequency and restrict certain patterns.

⚠️ Photosensitive epilepsy affects a small percentage of people with epilepsy — but when it does trigger a seizure, the consequence is immediate and serious. This is one of the few accessibility failures that can cause direct physical harm.

Psychological disabilities affect mental health and behaviour in ways that can create barriers to participation — they are often episodic, variable, and invisible, and are frequently underrepresented in accessibility discussions.

Anxiety Disorders

Anxiety disorders involve persistent, disproportionate fear or worry that interferes with daily functioning — they can make unfamiliar, complex, or high-stakes digital tasks significantly more difficult.

A person with severe social anxiety may be unable to complete a task that requires real-time interaction or phone contact — offering asynchronous or text-based alternatives reduces the barrier without requiring the person to disclose their condition.

⚠️ Anxiety disorders are the most prevalent mental health conditions globally — design decisions that create uncertainty, unclear error recovery, or high-stakes irreversible actions disproportionately affect people with anxiety.

Mood Disorders

Mood disorders — including depression and bipolar disorder — affect motivation, energy, concentration, and the ability to sustain tasks over time.

During a depressive episode, a person may struggle to complete multi-step processes, retain information between sessions, or engage with dense text — saving progress, reducing cognitive load, and allowing tasks to be resumed easily all help.

⚠️ The episodic nature of mood disorders means a person's functional capacity varies — a design that works for them during a period of wellness may not work during an episode. Progressive disclosure and low-effort pathways provide resilient access.

Psychotic Disorders

Psychotic disorders — including schizophrenia — can affect perception, thinking, and the ability to distinguish reality from internal experience, with significant impacts on the ability to navigate complex or confusing environments.

A person experiencing a psychotic episode may misinterpret unclear interface messages, have difficulty filtering relevant from irrelevant content, or struggle to follow multi-step instructions — clear, literal language and predictable interfaces reduce cognitive confusion.

⚠️ Psychotic disorders are among the most stigmatised disability categories — accessibility discussions rarely include them explicitly, yet the same cognitive accessibility principles that support people with intellectual disabilities and dementia also benefit this group.

Many people live with more than one disability simultaneously — when conditions co-occur, the combined access barriers can be greater and more complex than either disability alone would suggest.