Academic journal article Visible Language

Reading Digital with Low Vision

Academic journal article Visible Language

Reading Digital with Low Vision

Article excerpt

1 Introduction

The term low vision was coined in the 1950s by eye-care clinicians to convey the idea that vision can vary between the extremes of Sighted and Blind. Low vision refers to any chronic form of vision impairment not correctable by glasses or contact lenses that adversely affects everyday function. The boundary between normal vision and low vision is sometimes based on the inability to read newsprint at a standard viewing distance of 40 cm (16 inches) with best optical correction. This definition is used because most people with low vision have problems with reading texts designed for people with normal vision (Elliott et al., 1997; Owsley et al., 2009).

Letter acuity is the traditional clinical measure of vision, dating from the eye chart introduced by the Dutch ophthalmologist Herman Snellen in 1862. Four notable values on the Snellen scale of print size illustrate the range of reading vision. A Snellen acuity of 20/20 is the conventional standard for normal vision, and refers to letter sizes at the acuity limit subtending 5 minutes of arc (min-arc) of visual angle.

At a reading distance of 40 cm, an x-height of 0.58 mm subtends 5 min-arc. Typical newspaper print has an x-height of about 1.45 mm, just 2.5 times larger than acuity letters, the font size that a person with 20/20 vision can just barely see. One criterion for low vision is an acuity less than 20/60, meaning the acuity letters for 20/60 vision are more than three times larger than the standard for normal vision, and larger than typical newspaper print. The criterion for legal blindness is 20/200 or less (acuity letters at least 10 times larger than the normal limit). With high magnification, people with acuities as low as 20/2000 (acuity letters 100 times larger than 20/20 letters) can read. This wide range of reading acuities emphasizes that low vision, even very low vision, is compatible with reading, provided that adequate magnification is available.

The World Health Organization (2014) estimated that there are 285 million people worldwide with vision impairment, 39 million blind1 and 246 million with low vision.1 These figures include many people in less developed countries whose impaired vision is due to uncorrected refractive errors or untreated cataracts. According to the National Eye Institute (2014), there are between 3.5 and 5 million Americans with low vision, and the number is rising as the U.S. population ages. Because the leading causes of visual impairment in the United States are age-related eye diseases-macular degeneration, glaucoma, diabetic retinopathy and cataract-the prevalence of impaired vision rises steeply with age. Reading poses problems for almost everyone with low vision because the print size in everyday text is too small.

Traditional hard copy reading is not inclusive of people who are blind or have low vision. Marshall McLuhan (1962) in his famous essay The Gutenberg Galaxy referred to the invention of movable type as bringing about the "tyranny of the visual.''2 After Gutenberg's invention, hard-copy printed materials became increasingly available and literacy increased. Success in society became highly dependent on the ability to read, requiring good visual acuity. The "tyranny of the visual' has persisted for centuries, and has excluded many people with impaired vision from the literate mainstream. Since not much could be done to make print accessible, low-vision reading received little attention.

In the early 20th century, the concept of "sight saving' was an additional deterrent to reading with low vision. It was thought that use of the eyes would accelerate eye disease; sight should be "saved' and used sparingly. This concept may have originated with the Myope School in London. Children with myopia were thought to be at risk because high myopia could lead to retinal detachment. It was believed that this risk could be avoided by not reading. The sight-saving philosophy held sway in the United States during the first half of the 20th century, and generalized from myopia to low vision (Jackson, 1983). …

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