Aging (Optical Factors)
we age, changes in the visual system begin to affect our
ability to carry out everyday tasks. For some individuals
the changes can be severe. Approximately half of the people
in North America who are legally blind (corrected acuity
worse than 20/200 and/or visual fields of 20 deg or less)
are 65 or over, as are about two-thirds of those with severe
visual impairment (inability to read newspaper print with
best correction). Fortunately, normal age-related visual
changes are much less dramatic.
in the optical media of the eye attenuate, scatter and alter
the spectral composition of the light reaching the retina.
The pupil decreases in size with aging, a change called
senile miosis. This reduces the light entering
the eye. The lens also hardens (lenticular sclerosis)
and yellows, further reducing the light reaching the retina,
especially from the blue end of the visible spectrum. Changes
in the lens also increase light scatter, which reduces light/dark
differences (i.e., contrast) in the image. By age 60, it
is estimated that the retina receives only about one-third
as much light as a 20-year old eye. About two-thirds of
this loss is due to a smaller pupil, the other one-third
to changes in the lens.
Does Aging Affect Visual Function?
Age-related optical changes
in the eye have several adverse effects on visual functioning.
Acuity, our ability to see fine details, declines. This
is especially true under conditions of low illumination.
In addition, generally we need more contrast to detect or
recognize stimuli, especially if they are small. Older persons
are also more disadvantaged by glare conditions. Hardening
of the lens reduces the eyes ability to accomodate,
that is, make the lens more spherical and thus increase
its refractive power for focusing on nearby objects. This
change, called presbyopia, (old eye),
results in an age-related recession of the near point,
the closest distance for clear vision. At age 20, the average
person can focus as close as 10 cm.; this increases to 22cm
at age 40 and to 100 cm by age 60. The visual effects of
this progressive change usually become noticeable by about
age 45, which explains why older people are often seen holding
their reading material at arms length.
photos (below) approximate a view of a traffic scene in
a young observer and an elderly observer. Notice the decreased
luminance and clarity in the second photo.
observers benefit from visual materials that are of high
contrast, larger size and presented in good non-glare lighting
conditions. Tasks involving low light levels or subtle discriminations
between different shades of blue should be avoided. Presbyopia
is treated using convex (positive sphere) corrective lenses
to compensate for the older eyes inability to increase
its refractive power for near stimuli. This can take the
form of reading glasses or by the addition of a positive
sphere component to the lower part of the persons
regular eyeglasses (i.e., bifocal, trifocal or multifocal
| Cézanne | Degas
| El Greco | Monet
| Renoir | Van