Food for serious thought.

 Practicality of Very Large Print and a Responsive User Interface for
People with Low Vision

A lot of literature places a cap of approximately 200% on the practical
magnification size for large print.  Larger than that and many contend that
extreme methods like changing to Braille or use of screen magnification are
the only possible solutions. For example, "Students who need print 28
points or larger should probably be considered as candidates for Braille
education.", American Printing House for the Blind
<http://www.aph.org/research/lpguide.htm>).  This set of calculations shows
that a very satisfying reading experience can be obtained with up to 900%
enlargement of 12 point font when normal word wrapping is employed.  Since
word wrapping is one of the oldest technologies of the personal computing
and web era, the technology to obtain this user interface is well known and
well within the means of any web author, media producer or browser
provider.

For many people with low vision it is very possible to read on a laptop
with a standard screen of 13.3 inches. Now a good print size for normal
readers is 12 point, where we use the Adobe standard point size of 1/72
inch.  Thus 24 point is 200% normal, 36 point is 300% normal, 48 is 400%
normal, 72 point is 600% normal and 108 point is 900% times normal.  This
range should be sufficient to address the needs of people with mild low
vision (20/40-20/60) and moderate low vision (worse than 20/60 and better
than 20/200).
Now the list bellow gives the screen capacity in characters. This is
calculated as follows: If we break the screen into an grid where each grid
square has an edge size in points: 24, 36,...108. Now for line length there
are between 2 and 2.4 characters per square due to proportional packing and
character widths that are less than the actual square height. The line
height just equals the square height. Using 2.2 as the width multiplier and
rounding off fractional parts we get the following.

   - 13.3" monitor
      - 24 pt = 1/3 inch letters has 76 character lines and 19 lines per
      page.
      - 36 pt = 1/2 inch letters has 50 character lines and 13 lines per
      page.
      - 48 pt = 2/3 inch letters has 38 character lines and 9 lines per
      page.
      - 72 pt = 1 inch letters 25 character lines and 6 lines per page.
      - 108 pt = 1.5 inch letters 16 character lines and 4 lines per page.

For less visual acuity, a non-portable solution using 20-36 inch monitors
would include approximately the same screen capacities with nearly double
the magnification. *Note* that 16 characters per line would involve some
horizontal scrolling for words larger than 16 characters.  That would be
very infrequent in most languages.

If people with low vision were given a responsive interface, whether it is
obtained by a popular authoring technique like responsive web design (RWD)
or by some other means, they can benefit. The only real responsiveness
required is reversion to one column format with appropriate print size. In
the intermediate ranges 36 point to 72 point, use of a portable device like
a 13.3 inch laptop as a reading device is extremely practical.
Not everyone with low vision needs large print. For this group, line length
is often an issue. Again a single column format with narrow columns may
work, or a multi-column format depending on the user's need.

The main point is this. Responsive user interfaces are old in the world of
personal computing and the technology is well know. The first was automatic
word wrapping and WYSIWYG. That sold personal computing to the general
public.  It was followed by early Microsoft Windows systems that enabled
the user's choice of icon and font size, color and font face that
propagated through all Windows applications.  This was lost with Windows 7
and later, but the capability was established.  Any entity who cared to put
in a little effort could establish responsive user interfaces that would
work for people with low vision.  This article demonstrates that for most
people with low vision, there is even a portable solution. No new
technology needs to be invented. All that is needed is a user interface
that is built with responsiveness in mind.