Civil Engineering Reference
In-Depth Information
FIGURE 4.11
Changes in
accommodation of the eye with age.
The shaded area indicates that there is
a large variability between individuals
(Handbuch für Beleuchtung, 1975).
at infinity. The near point of accommodation is then 9 cm, which can be calculated using
the equation:
f
=
1/D
where
f
is the focusing distance (in meters), and
D
is the number of diopters of
accommodation.
Likewise, if the far point for a 50-year-old with 2 diopters of accommodation is at
infinity, then the near point is 50 cm (Figure 4.12). But assuming that the same 50-year-
old has 3 diopters of uncorrected short-sightedness (myopia), then the far point (without
glasses) is 33 cm and the near point is 20 cm. A person who is myopic at a young age
will typically find that with increasing age the far point moves closer and the near point
moves further away. For an individual with no refractive errors as a young person, the
near point moves further away, while the far point may stay at infinity.
The implication for industrial work is that the different ranges of vision not only affect
the visibility of the task but also the work posture. To compensate for poor vision, a
myopic (short-sighted) person will move closer, and a hyperopic (farsighted) individual
