Defective
vision is a broad term that usually
refers to farsightedness (hyperopia)
and nearsightedness (myopia) but
color blindness, astigmatism,
and night blindness are also considered
to be categories of defective
vision.
Causes and Risk Factors
The causes and risk factors
of defective vision depend on
the type of vision defect that
the individual is suffering from.
Farsightedness
or hyperopia (hypermetropia)
Individuals
who are suffering from farsightedness
can see objects at a distance
fairly clearly but struggle to
see objects that are close. For
instance, a farsighted individual
may be able to see clearly enough
to drive while needing corrective
lenses to read a book.
Farsightedness
is a genetic trait that results
in a cornea that is flatter than
normal or with a very short distance
between the cornea and the retina.
These factors cause images to
be focused at a point that is
beyond the retina, which means
that the distance vision remains
clear but the objects that are
close appear to be blurry. Farsightedness
becomes a degenerative disorder
as age increases so most individuals
who are older than 40 years old
lose the ability to focus their
lenses. In some rare cases, diseases
such as retinopathy (degeneration
of the retina), eye tumors, and
lens dislocation may also lead
to farsightedness.
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