Behavioural Lens Trials:
NEAR-ZONE PROGRESSIVE ADDITION LENSES
By Charles Boulet
> This is the second part of our series on behavioural lens trials
In the context of vision rehabilitation,
progressive addition lenses (PAL) are
used as palliative appliances for specific
tasking, for example computer work
for those with traumatic brain injury
(TBI), or as a support for daily living
for those with certain binocular vision
concerns. Typical examples of applications in the latter case would include
presbyopia, pseudophakia, but also
accommodative/vergence disturbances
in instances where vision rehabilitation
is not possible, including for school-aged
children. These applications might be
for varying periods, ranging from fulltime permanent wear for certain tasks,
to short durations as an assist while
therapy can take its course to a point
where the lenses are no longer required
or desired.
Near-zone PALs (nzPAL), aka ‘task’
lenses, are modified PAL designs
engineered specifically to sacrifice
distance clarity and function for a
better optical result in the near proximity. Given the significant distance
vision penalties, these lenses are never
recommended for ambulation,
regardless of the patient’s health status. Likewise, these lenses should be
selected after consultation with the
patient, including a good description
of what to expect – the pros as well
as the cons.
While there are a number of task/
computer lenses in the market place,
my lens trials were centred largely
around the IOT Office series of
40 Optical Prism | July 2016
nzPALs, what IOT refers to as their
PX EDUCATION TIP:
“Office Readers” from their Occupational Design Series. These lenses
come in three variants, the 1.3, 2.0,
and 4.0, each type corresponding
to the maximum distance viewable
through the top portion of the lens:
1.3m, 2.0m, and 4.0m, respectively.
This is depicted in the first illustration where the 1.3 is in the green
range, the 2.0 is the violet, and the 4.0
is the red. Bear in mind that as the
wearer sits erect, they will be viewing
through the lower add power, so the
distance will already appear blurred
even without lifting the nose.
There is no doubt the distant field is
disturbed with these lenses, but the
benefits far outweigh this artifact: We
are selecting these lenses specifically
because they sacrifice distance viewing in order to enhance the near field.
When first fitting these lenses to the
patient, avoid having them look off to
the distance as a first assessment.
Rather, have them observe a page
from a book or magazine, or a smart
phone first without the lenses in
place, then with the lenses on. Next,
tell them that when they look to the
distance, they will notice blur, and
this is by design.