DISCUSSION
Our results indicate that computer users with presbyopia
and multi focal lens correction chose to position displays lower
and with more screen tilt than computer users without
presbyopia. Multi focal lens wearers selected a display height
that induced a downward eye-to-screen angle at an average
21.4° below the horizontal line of sight. Prepresbyopes
selected a display height that induced a downward eye-to-screen angle at an average 13.7°below the HLS. The results
replicate previous field studyfindings (Allie et al. 2009 and
Jaschinski et al. 1999) that observed either one or the other
age group, but are differentiated as LCD flat panel,
widescreen display technology was utilized. These results
suggest that the common-practice statement instructing
computer users to position the top of the display near eye level
may be more acceptable for prepresbyopes but not for
presbyopes.
Gathering measures while using the same display and
adjustable support improves our confidence that observed
differences are not related to factors such as display illumi-nation technology and screen size. The results provide a
foundation for understanding how to design display supports
that respond to the needs of both young and aging computer
users. To support both groups, an adjustable display support
would minimally need to allow the center of the screen to
adjust between the group means, 8.8” to 11.8”. A more
inclusive display support design would adjust higher and
lower and respond to the total range observed in this study.
Our results indicate that 11.2” inches, or more, of display
height adjustment is necessary to satisfy the needs of both
groups of computer users observed. We should also note that
the prepresbyope male with the greatest sitting eye height sat
in a deep recline. If his preferred sitting posture had been
more upright, his selected display height may have been
higher than the highest display setting reported. The need for
a large screen tilt angle adjustment range is also revealed.
Some participants selected screen tilt angles equal to the
measured eye-to-screen angle. As the workforce ages and
computer users become presbyopic the low end of the
adjustment range (and concurrently more screen tilt) will be
used by more individuals.
When considering worker needs and work space design,
computer users with presbyopia should have enough clear
work surface so the display can be positioned low. A display
and stand resting on top of a CPU will make the screen too
high for many multi focal wearers.Our findings also suggest
that some multi focal wearers may need a work surface lower
than 28.5 inches in order to get the display in a preferred
position, especially if the display is larger than 18.5 inches.
Because many multi focal wearers position the display low and
tilted back, a lighting system that incorporates indirect
illumination may help reduce glare on the computer screen.
This may be the first study to report that arc angle was
routinely smaller than the minimum 16 arc min recommended
by ANSI/HFES 100-2007, and much less than the suggested
20 arc min. Most participants in this study, and perhaps a
majority of computer users, are content to view text on the
display at the size native to the display drivers or operating
system software. This raises a concern that the prevalence of
eye strain symptoms mentioned earlier may remain unchanged
due to viewing screen content at such small arc angles. The
topic of arc angles and their affect on eye comfort and
performance could be a beneficial addition to education and
training programs for computer users. Appropriate arc angle
can be achieved by making viewing distance shorter and/or
increasing character height on the screen.
For organizations interested in providing workers with
more display surface, the multi focal lens wearer preference for
low display placement may impact the size and number of
displays in a workstation. Since MF’s position the display
low they may prefer two wide aspect ratio displays placed
side-by-side compared to one larger 4:3 aspect ratio display.
The center of two wide aspect displays can be positioned
lower than a single 24” display. Further research is necessary
to understand display size and placement that best fits
presbyopic computer user needs.
The authors would like to acknowledge Herman Miller Inc.
and Steel case Inc. for participating in this study.