Allie et al. (2009) completed a field study that measured
self-selected display placement of 10 participants between the
ages of 45 and 64 (mean 55) who wore Progressive Addition
Lens (PAL) correction for presbyopia. Observed mean eye-to-center of screen angle was 19.6°below the HLS with a
range between 6°and 39°below the HLS (while viewing a 19
inch LCD display mounted on an adjustable arm).
Comparing the eye-to-screen viewing angles reported in
published studies suggests unique display placement needs for
each of the user groups. Previous field research results
suggest that multi focal lens wearers will place displays lower,
creating a more declined eye-to-screen angle with a screen
tilted more rearward of vertical compared to prepresbyopes.
Allie et al. (2009) reported a low display height for PAL users
and Jaschinski et al. (1999) suggested that wearing multi focal
vision correction may restrict display position.
An interest has been emerging (or perhaps re-emerging) in
display placement research regarding the influence of arc
angle subtended on the display viewers’ eye and resulting
visual comfort. Both the ANSI/HFES 100-2007 and ISO
9241-303-2008 guidelines address arc angle and performance
effects. ANSI/HFES 100 states the minimum character height
shall be 16 arc min and should be 20 to 30 arc min. For rapid
and accurate identification of individual characters 16 to 18
arc min is normally adequate, although reading speed
continues to increase until character height exceeds 22 arc
min. ISO 9241-303-2008 contains similar guidelines. Several
studies, Rempel et al. (2007) and Allie et al. (2009) reported
that subjects experienced more visual discomfort when
participants viewed text that subtended less than 14 arc min in
the eye compared to 16 arc min or larger.
To better understand the display placement and
adjust ability needs of computer workers, the current field
study was designed to determine the self-selected display
placement and character arc angles of two groups of users;
those younger than 39 years of age and those older than 45