References

From Low Vision Accessibility Task Force

About these References

This page lists references and sources for the information in Accessibility Requirements for People with Low Vision.

This page is an in-progress draft. Not all references and sources are listed yet.

Introduction

Overview of Low Vision

Scope of Low Vision

  • WHO Visual impairment and blindness World Health Organization (WHO), Fact Sheet N°282, Updated August 2014.

    There are 4 levels of visual function, according to the International Classification of Diseases -10 (Update and Revision 2006): normal vision; moderate visual impairment; severe visual impairment; blindness. Moderate visual impairment combined with severe visual impairment are grouped under the term “low vision”: low vision taken together with blindness represents all visual impairment.

Incidence

  • Revision of visual impairment definitions in the International Statistical Classification of Diseases

    According to these revised definitions, the number of blind persons in the world defined as presenting visual acuity less than 6/60 in the better eye would be about 57 million as compared with the World Health Organization estimate of 37 million using the existing International Statistical Classification of Diseases definition of best-corrected visual acuity less than 3/60 in the better eye, and the number of persons in the world with moderate visual impairment defined as presenting visual acuity less than 6/18 to 6/60 in the better eye would be about 202 million as compared with the World Health Organization estimate of 124 million persons with low vision defined as best-corrected visual acuity less than 6/18 to 3/60 in the better eye.

    [emphasis added]
    • OPEN: In the Note, might we want to mention the higher numbers from Dandona? (We would probably want to find additional sources to confirm validity)

Cause and Progression of Low Vision

  • What You Should Know | National Eye Institute

    Low vision is usually caused by eye diseases or health conditions. Some of these include age-related macular degeneration (AMD), cataract, diabetes, and glaucoma. Eye injuries and birth defects are some other causes.

  • Vision Impairment and Blindness

    The leading causes of low vision and blindness in the United States are age-related eye diseases: macular degeneration, cataract and glaucoma. Other eye disorders, eye injuries and birth defects can also cause vision loss.

  • Facts About Diabetic Eye Disease

    Diabetic eye disease comprises a group of eye conditions that affect people with diabetes. These conditions include diabetic retinopathy, diabetic macular edema (DME), cataract, and glaucoma.

  • Vision decline with ageing in Web Accessibility for Older Users: A Literature Review

    ...declining vision conditions that most older adults naturally experience, from the yellowing of the eye’s lens and presbyopia (loss of elasticity of the lens) to pupil shrinkage. These conditions result in a variety of vision changes: Decreasing ability to focus on near tasks, including a computer screen; Colour perception and sensitivity; less violet light is registered, making it easier to see red and yellows than blues and greens and often making darker blues and black indistinguishable; Pupil shrinkage; resulting in the need for more light and a diminished capacity to adjust to changing light levels. For example, 60 year old retinas receive only 40% of the light that 20 year old retinas receive [Lighthouse ILE] while 80 year old retinas only receive around 15% [Eye Digest]; Contrast sensitivity; from the age of 40, contrast sensitivity at higher spatial frequencies starts to decline until at the age of 80 it has been reduced by up to 83% (See Figure 2); Reduction in visual field

Visual Impairments

Visual Acuity (Clarity)

  • Visual acuity Science Daily

    Visual acuity (VA) is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye, the sensitivity of the nervous elements, and the interpretative faculty of the brain.

Light and Glare Sensitivity

  • Photophobia

    Photophobia is eye discomfort in bright light. ...
    Photophobia is common. For many people, the problem is not due to any disease. Severe photophobia may occur with eye problems. It can cause bad eye pain, even in low light.

  • User Experiences | TAdER Project

    I need inverse contrast; white backgrounds create blinding glare that is very painful. ...
    Stark contrast of black on white is difficult for me for longer than a sentence. I really need to be able to set the colours myself, presets don't work. Someone else's idea is useless. ...
    I need light text on a dark background.

  • Normal Vision Changes

    The most common age-related vision changes and their effects on everyday activities can include the following: Increased sensitivity to glare. ...

Contrast Sensitivity

<a id="#Contrast-Tools">[Contrast-Tools]</a> Insert with for tools link

Field of Vision

[@@TO DO - add references]

  • “The visual field is a map of the extent of visual space seen without moving the eye” (Cassi, Fundamentals for Ophthalmic Technical Personnel, p.219)
  • "Visual field: The entire area that can be seen when the eye is directed forward, including that which is seen with peripheral vision." MedicineNet

Color Vision

OPEN: Determine the best resource to use in the Note. Do we use 8% or 10%?

  • Facts About Color Blindness

    As many as 8 percent of men and 0.5 percent of women with Northern European ancestry have the common form of red-green color blindness.

  • colourblindawareness.org

    Colour (color) blindness (colour vision deficiency, or CVD) affects approximately 1 in 12 men (8%) and 1 in 200 women in the world.

  • Color Blindness

    In most Caucasian societies up to 1 in 10 men...
    Red-green (Overall) Men 7 to 10%

Functional Vision

[@@TO DO add other authoritative reference for macular degeneration effects]

  • Specific Eye Conditions, Corresponding Impact on Vision, And Related Educational Considerations Texas School for the Blind and Visually Impaired
    Many of the eye conditions have multiple "effects on vision" or visual impairments.
    Macular Degeneration - effects on vision:

    Reduced central acuity; Peripheral vision is not affected; Central scotomas; Distorted vision; Blurred vision; Decreased color vision; Slow recovery from changes in light; Loss of contrast sensitivity; Visual fatigue.

  • When Text is Not Displayed Well | TAdER Project

    Both eyes getting tired - visual fatigue - and generalised fatigue because I have to concentrate quite hard. ...
    Because of my nystagmus (involuntary eye movement) and weaker eye muscles, it takes a lot of concentration and control to read normal text, therefore I get worn out easily.

    This resource also includes data for "I get tired" and additional quotes.

User Needs

Luminance and Color

Luminance Overall

Text Contrast

Not Relying on Color

Tracking

Rewrap for One Direction Scrolling

Reflow to Single Column

Line Length

Hyphenation

Perceiving

Text Size

Font

than Times New Roman, a serif font, for all grades."

Style

Capitalization

Size of All Elements

Spacing for Reading

Leading

Leading/line spacing recommendations for people with low vision, dyslexia, or who are older, range from 1.25 to 2.0 in the resources below. Some of these are for print, and likely apply online as well.

  1. 1.25 ("Space 1.25 between lines") — Kitchel, J.E. APH Guidelines for Print Document Design http://www.aph.org/research/design-guidelines/
  2. 1.25 or 1.3 ("at least 25 to 30 percent of the point size") — Arditi, Aries. Making Text Legible: Designing for People with Partial Sight. New York: Lighthouse International. (1999, 2002)
  3. 1.5 ("spacing between lines of text is 1.5") — AFB American Foundation for the Blind. Tips for Making Print More Readable. http://www.afb.org/info/reading-and-writing/making-print-more-readable/35
  4. ≥1.5 ("line spacing (leading) of at least 1.5") — CCLVI. Best Practices and Guidelines for Large Print Documents used by the Low Vision Community authored by the Council of Citizens with Low Vision International An Affiliate of the American Council of the Blind Arlington, VA. http://www.acb.org/large-print-guidelines
  5. 1.5 ("Line spacing of 1.5") — British Dyslexia Association. Dyslexia Style Guide http://www.bdadyslexia.org.uk/common/ckeditor/filemanager/userfiles/About_Us/policies/Dyslexia_Style_Guide.pdf
  6. 2.0 ("Double space body text") — National Institute on Aging. Making Your Printed Health Materials Senior Friendly. https://www.nia.nih.gov/health/publication/making-your-printed-health-materials-senior-friendly
  7. 2.0 ("Double-space the lines, if possible.") — The Center for the Partially Sighted. Print Guidelines http://web.archive.org/web/20110128083726/http://low-vision.org/en/Print_Guidelines
  8. (not specific) — Bix, L. The Elements of Text and Message Design and Their Impact on Message Legibility: A Literature Review. Journal of Design Communication, No. 4. http://scholar.lib.vt.edu/ejournals/JDC/Spring-2002/bix (2002)
  9. Calabrèse A, Bernard JB, Hoffart L, Faure G, Barouch F, Conrath J, Castet E. Small effect of interline spacing on maximal reading speed in low-vision patients with central field loss irrespective of scotoma size. Invest Ophthalmol Vis Sci. 2010 Feb;51(2):1247-54. (2010) "Increasing interline spacing is advisable only for very slow readers (<20 words/min) who want to read a few words (spot reading). Vertical crowding does not seem to be a major determinant of maximal reading speed for patients with central scotomas."
  10. Hartley, J. What does it say? Text design, medical information, and older readers. In D.C. Park, R.W. Morrell, and K. Shifren, eds. Processing of Medical Information in Aging Patients, 233-48. Mahwah, NJ: Lawrence Erlbaum Associates. (1999)
  11. Morrell, R. W., Dailey, S. R., Feldman, C., Mayhorn, C. G., & Echt, K. V. 2002. Older adults and information technology: A compendium of scientific research and Web site accessibility guidelines. Bethesda, MD: National Institute on Aging. (2002)
  12. Holt, Barbara. Creating Senior-Friendly Web Sites. Center For Medicare Education Issue Brief 1(4):1-8. (2000)

Letter Spacing

  • McLeish, Eve. “A Study of the Effect of Letter Spacing On Reading Speed of Young Readers With Low Vision.” The British Journal of Visual Impairment 25.2 (2007): 133–43. Print.
    • McLeish ran from .04 to .25 em tests (Wayne E. Dick PhD analyzed the McLeish study and translated from points). McLeish found an increasing curve in reading speed of actual materials up to .25, but it really started to flatten at .20. Previous studies that reported no improvement started at .5em. Right at the flat point. Hence Wayne recommends letter spacing be 0.12em, and word spacing be 0.16em for the Ability to Override SC.
  • Legge, Gordon E. Reading Digital with Low Vision (Aug 2016): 103-125.
    • "Overall, the evidence indicates that increasing spacing between letters is not helpful..."
  • Jo, Eunice. "Crowding affects reading in peripheral vision." (2000)
    • "It is suspected that reading in the periphery is difficult because crowding occurs when the letters within a word are too close to each other."
  • Chung, Susana T. L. "Dependence of Reading Speed on Letter Spacing in Central Vision Loss" Optom Vis Sci. 2012 Sep; 89(9): 1288–1298.
    • "In conclusion, by measuring reading speed as a function of letter spacing, we found that the optimal letter spacing for reading for observers with central vision loss is the standard spacing found in standard printed text. Increased letter spacing beyond the standard size, which presumably reduces crowding among letters, does not improve reading speed. "
  • Chung, Susana T. L. The Effect of Letter Spacing on Reading Speed in Central and Peripheral Vision " 2002, IOVS ARVO Journals.
    • "Increased letter spacing beyond the standard size, which presumably decreases the adverse effect of crowding, does not lead to an increase in reading speed in central or peripheral vision."

Word Spacing

Justification

Margins and Borders

Spacing Between Elements

Identifying Elements

Element-level Customization

Point of Regard and Proximity

Maintain Point of Regard

Proximity of Related Information

Work with User Settings

Seeing All Interface Elements

Printing Customized Text

Using User Settings

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