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Hyperopia
(ãFarsightednessä)
Far away things are
seen with less effort than near things. Consider this eye small. Small
amounts of hyperopia are normal for infants, children and young
adults. It is usually outgrown as they reach their twenties. Small
amounts are overcome with focusing effort. This is automatic and
requires no conscious effort. Spectacle correction may be
needed for moderate or large amounts of hyperopia or for focus related
crossing of the eyes (accommodative esotropia).
Myopia
(ãNearsightednessä)
Near things are seen
with less effort than far things. Consider this eye too long. Images
come into focus in front of the the retina (the ãseeingä part in the
back of the eye). Glasses (or contact lenses) are usually worn to
compensate for more than small amounts.
Astigmatism
This eye can be
considered ãout of roundä (for example, consider the shape of the back
side of a spoon). It is usually the result of unequal surface curves
of the clear, front part of the eye called the cornea. Small amounts
sometimes do not require glasses. Glasses (or toric contact lenses)
are usually worn to correct the image blur.
Presbyopia
Far away things are
seen clearly, but magnification is needed for near. This usually
begins to occur in patients over 40 years. The eye is normal size and
shape, with a ãfatiguedä near focus mechanism. It is the result of the
loss of elasticity in the lens of the eye.
Anisometropia
When the focusing power
is different between the two eyes it is called anisometropia. Small
amounts may not require correction. Larger amounts may need correction
to avoid amblyopia (lazy eye) in childhood and to avoid asthenopia
(eye fatigue) at a later age.
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