Vision gives a person the ability to scan in two dimensions: up-down and left-right. This is a very useful capability because it enables the use of two-dimensional design elements in an HTML document.
Two-dimensional design elements include tables, frames and panes. A table, by its very nature is a two-dimensional construct. With the rare exception of single-dimensional (a single row, or a a single column), most tables are two dimensional.
To a person with vision, look up an item in a table is relatively easy. Starting with the column header, a vision-enabled person can select the right row. Then, the same person can follow the column header to select the correct column. The intersection of the select row and column is the item to be chosen.
For example, assume that in a particular table, columns represent day-of-week, and rows represent half-hour periods of activities. A vision-capable person can look up the activities from 15:00 to 15:30 on Thursday by looking for the intersection of the column representing Thursday and the row representing the time period 15:00 to 15:30.
A table can also be used in a reversed manner. Let’s say a particular activity “Science experiment” is found in the table of our example. A vision-capable person can then look up the row and column, and identify which day of the week and which time period the activity is scheduled.
A vision-impaired person, however, will have difficulties interpreting contents of a table because the table cannot be seen. A screen-reader program can read the content of a table, but usually in a particular order. In our example, the table can be read by-row-first, or by-column-first. But neither method is easy to interpret.
Using the by-row-first method, this is what the reader will sound like: “time, Monday, Tuesday,... Friday, (new row), 8:00, English, Mathematics, P.E.,... 8:30, Art, Reading, ...”
The problem is that a person relying on a screen reader needs to do the following:
The problem gets even more difficult when cells are merged across columns and rows.
Another design element that makes a web page difficult to navigate for visually impaired people is the <frame> element. While it is easy for a vision-capable person to move a mouse across different frames, it is much more difficult for a non-visual user. Relying only on a screen reader, it is easy to lose track of what content is in which frame because each frame is read in its entirety before the reader moves on to the next one.