WebAIM - Web Accessibility In Mind

视觉障碍
低视力

Types of Low Vision

While visual acuity of people with low vision varies widely, low vision is generally defined as a condition in which a person's vision cannot be fully corrected by glasses and interferes with daily activities such as reading and driving. Low vision is more common among the elderly, but it can occur in at any age as a result of conditions such as macular degeneration, glaucoma, diabetic retinopathy, or cataracts. Each of these conditions affects a person's vision in different ways; however, some general principles apply:

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低愿景人员的网络可访问性的关键原理是:

  1. Perceivable:小的内容不良好地放大,或者具有低对比度可能难以感知。

黄斑变性

黄斑位于视网膜的中心,这是眼睛后面的区域。“干燥”黄斑变性发生作为黄斑的组织随着时间的推移而变薄,导致逐渐丧失视力。当眼睛背面的血管开始泄漏液体或血液的血管开始漏液或常见的血液且经常导致视力快速丧失的血管,发生较少的常见。在任何一种情况下,该人的中心视线都受到影响最大。下面的图像有助于说明黄斑变性的影响..

An photograph of a boy, but the central area of vision is darkened and blurred, making it almost impossible to see the boy's face text can appear broken
Experience it for yourself

drawing of a woman covering her eyesTo get a better idea of what macular degeneration is like, hold up your hand about 12 inches (about 30 cm) from your eyes, so that you can't see straight in front of you, but you can see around the edges of your hand. Now, without looking to the sides, try to read something in your peripheral vision. Keep your vision focused on your hand! This illustrates how a person with advanced macular degeneration sees things. The problem isn't so pronounced for people with lesser degrees of macular degeneration, but the basic idea is the same.

青光眼

青光眼is caused by an increase in pressure inside the eye, which causes damage to the optic nerve. The end result is often the inverse of the effect of macular degeneration: the loss of peripheral vision and a blurry central area of vision. Text will appear faded and blurry. Some people have compared the effects of glaucoma to looking at everything through a straw.

photo of a boy that is blurred in the center and the edges are completely blacked out due to loss of peripheral vision text can be seen in the middle of this image, but it is blurry, and the sides are completely dark due to loss of peripheral vision

糖尿病性视网膜病变

One potential effect of long-term diabetes is the leaking of retinal blood vessels, which can cause dark patches in the field of vision where the leaks occur. Text may appear blurred or distorted in where these dark patches occur.

一个男孩的照片有黑暗的斑点区域 具有暗斑区域的文本,有些扭曲的区域

Cataract

Individuals with a cataract have areas of opacity in the lens of their eyes which results in a blurred or hazy effect, especially in bright light. Text may be difficult to distinguish from the background. High contrast is especially important for people with an advanced cataract.

photograph of a boy that is blurred and very light, making it difficult to see details 模糊和非常浅的文本反对明亮的背景,这很难阅读

Screen Magnifiers and Zoom

屏幕倍率或变焦是最常见的技术,人们具有显着低视力使用。软件或操作系统设置可用于放大屏幕的整个屏幕或部分,允许具有低视觉的人更清楚地看到它。用户还可以使用浏览器设置来缩放网页或增加其默认文本大小。

某些内容难以在扩大或放大时解释。例如,在放大时,包含文本的图形可能变得截然且像素,使得难以读取的文本。考虑下面的两个图像。左侧的那个是被放大的文本的屏幕截图。右侧的图像是已放大的图形中的文本的屏幕截图。

enlarged text with the word 'Helen' which is clear and easy to read enlarged graphic of the word 'Keller' which is very blocky and pixelated
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在放大时使文本更清晰,尽可能使用真实文本,而不是图形中的文本。

Web pages should be designed so that there is no loss of content or functionality when it is enlarged/zoomed or when the text size is increased. When possible, horizontal scrolling should be avoided—it is especially difficult to read page content when the user must scroll or pan to read lines of text that extend off the screen. Implementing responsive/adaptive design to support small screen and mobile devices will also better ensure that content adapts to a screen when it is zoomed or enlarged.

High Contrast and Customized Colors

Web content with low contrast, meaning the brightness difference between text or a graphic and its background, can be difficult to read, especially for people with low vision. Some color combinations are not easy on the eyes for anyone, especially for people with low vision. Color contrast can be checked usingWebaim对比检查员确保它符合WCAG 2.0 AA指南。

While authors should ensure their content has sufficient contrast, some users with low vision may need even more contrast. Some may benefit from specific color combinations, such as blue text on a yellow background. Users with low vision may enable high contrast modes or may override default colors via settings in their operating system or web browsers. When these are enabled, users may not see the author-defined web page colors.

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尽可能大,最大化您的网页的对比度,包括图形,字体和背景。确保颜色不用为指示或区分含义或内容的唯一手段。