Between 12 and 16 percent of all adults (in America and Canada) are not blind but have difficulty seeing small objects especailly type. They are the readers of the large type book editions. The great majority of the people who have visual accessiblity problems with computers are NOT blind. The majority simply have what the medical profession describes as "low vision" or "limited vision." This is typically the situation where the individual has sight, but cannot discern small details or discriminate between letters of small fonts. The signtless person uses readers which is the reason that Alt Tags are so important, but the low vision person generally uses the computer visually. He/she uses a large screen, uses larger fonts, uses "magnifiers" such as those built in to Windows, uses brighter screens, uses high contrast, or a combination of the above.
However, all of the above "solutions" have their problems. This is especially true with computers in general and web sites in particular. There is much that can be done by the computer user, but the self help methods are more or less effective depending on how the web site is designed artistically and developmentally. Drupal can do much to allow websites to be easier for the low vision users. This post describes sone of the parameters so that those designing Drupal for future accessiblity can take these factors into account. Much can be done with not much developmental and/or design limitiation.
Size is the Key Variable
There are a number of variables that affect readability for low vision readers. Low vision is a continuous (analog) variable which not only can be from almost unnoticable to legally blind even though the eye sees the image. The degree of low vision is not static either. It tends to worsen as we get older and a large number of you reading this perfectly easily will find this cabability only temporary. There are many other factors that also alter the vision ranging from tiredness at a particualr time to recreational style. Underwater divers for example will have changes in vision after extended high pressure exposure or with medical treatment in a hyperbaric chamber. Stress and other factors affect the vision.
Corrective lenses (eye glasses) at first is the best solution, as it is for people who have difficulty focusing on near objects (farsightedness). But as we get older (or have other problems) the range of correction narrows. For example, I have corrective lenses which work fine at 22 inches between my eyes and the screen. However, in an airplane coach seat I am only 14-16 inches from my laptop, and it is hard to see with the corrective lenses. Likewise, if I stand behind a colleague and we are viewing his/her screen, I am 30 inches away and have great difficulty. Of course in the early morning my "computer glasses" do not work as well as they do at midday. Further, what are my "computer glasses" make be almost blind walking around a room or going outside and driving with them is impossible. Many resort to bi and tri-focals, but this is akward and change is constant.
If you cannot correct the eye optically, the best solution is size. If the image is large enough corrective lenses have a much larger range and may not even be needed by many. I can do about 80 percent of my computer work without the corrective glasses, by using digital solutions. So can most people theoretically, but few know how to manage the digital variables. High contrast and brightness also help. Even if your eyes are normal, recall trying to read a menu in small type in a candle-lit restaurent. (The eye is like the auto focus on a digital camera. If the scene is poorly lit the auto-focus cannot do its thing.) However, the brightless and contrast produce small assistance compared with size. With fonts, san serif are a little easier that the serif fonts. More imporatant in fact is the interletter spacing and the leading between lines. There is even a specially designed font, that has been developed for the low vision reader that is freely usable, but the benefit is small compared with bumping up the font size.
It would seem that websites would produce the least problems for the low vision reader in that all the browsers enable the fonts to be enlarged. That will do it for most low vision readers. The problem is of course that there are many different algorithms for enlarging the font on a website--especially one where the fonts are controlled by one or more CSS. Do we just enlarge the body text, or all fonts proportionally? What about shapes--blocks, graphics, regions. How do the sidebars fuction? It is actually an incredibly complex problem, which is not easy to resolve in the general case, but I have found that there is a relatively simple solution within a reasonable range. And in general, Drupal fares as well or better than most other frameworks and web systems.
Specifically, start with IE8. Consider the Drupal.org site. In the bottom right hand corner of IE there is a "percentage" zoom adjustment. I have found that almost all Drupal developed websites display on a wide screen laptop with the IE zoom set to 150%. In almost all cases all components of the site will properly display and do so relative to the graphic elements. A horizontal scroll is needed occasionally, but for most themes even that is not required. I have not found a Drupal site where the 125% IE zoom would not do the trick. Most low vision users can function well with the 150% zoom. Only about half can manage with 125%. This of course assumes that the user is viewing a large laptop, at least 15-17 inches. This will not work with an 9 or 10 inch notebook. Iffy at 12-14 inches. But any low vision user is so aware and will be using a larger screen laptop.
One of the reasons that Drupal themes tend to work so well when enlarged is that there appears to be a fair amount of space with most Drupal themes between the left and right margins of the sidbars (assuming left and right) and the edge of the screen. An IE 150% zoom seems to be just the right size to eliminate these side margins and still show the entire design, side bars and all.
While the Zoom functions well, the "Text Size" option does not in many web pages and particularly so in Drupal. The Other non Microsoft Browsers also zoom, via and , but the algorithm does not seem to be as easy for the low site readers. I usually develop with IE8 and often shift to Firefox when I need Firebug or want to view some of the CSS3 features that Microsoft seems to be slow in adopting.
The best advice I can give all web designers and devlopers to give the low vision users a good shot is to:
Keep body fonts 16 pixels or larger if possible.
Avoid using subtle color differentials between the font and the background colors. A blue font on a green background mught be cool for some, but it makes it harder for the low vision reader to discriminate the shape of the font. Save that for headlines where size makes up for the low contrast.
When using reverse type (light color font on dark background), use bold font if you can.
For body fonts, stay with san sefif styles.
View the site yourself at a zoom of 150 and be sure that the blocks and graphics place correctly.
If you do these things, your site will not look any better, but more people will be able to use it!