Patient Education - Refractive Conditions
Myopia, Nearsightedness, Farsightedness, Hyperopia, Astigmatism, etc. What Do They All Mean?
These are questions that eye doctors are frequently asked. It can be confusing when there are common terms for medical conditions.
Myopia or Nearsightedness
A
condition where a person’s uncorrected vision is only clear up
close. Instead of the light focusing on the retina, it focuses in
front of the retina. A myopic person can read a magazine, however
their distance vision is blurry and requires glasses or contact
lenses to make it clear.
Hyperopia or Farsightedness
Hyperopia,
commonly referred to as farsightedness, is when a person sees
better in the distance than at near. Light entering the eye focuses
behind the retina placing a blurry image on the retina. For a
hyperopic person to see clearly at any distance a muscle, inside the
eye
called the ciliary body, must focus an intra-ocular lens. As we get
older it becomes more difficult for the eye to accomplish this auto
focusing. Because of the eye’s ability to focus, farsighted people
often don’t need glasses until their 30s or 40s. Uncorrected
farsightedness, however, may cause a person to experience eyestrain
or an eye turn (strabismus), depending on the degree of
farsightedness and the patient’s age. The younger we are the easier
it is for the eye to compensate for farsightedness. Uncorrected
farsightedness can lead to amblyopia. Farsightedness and presbyopia
are often confused.
Presbyopia
A person is presbyopic when the crystalline lens in the eye can no longer focus well at near, making reading glasses or bifocals necessary. A person can be both farsighted and presbyopic or nearsighted and presbyopic. Presbyopia typically begins in our early 40s. The older we get the more difficult it is for our eyes to focus at near. The effects of presbyopia level off in our mid to late 60s.
Astigmatism
Many people
feel astigmatism is a bad, progressive disease. Actually
astigmatism is
caused
when light focuses in two points in the back of the eye because it
is not in the shape of a sphere. An eye with astigmatism has often
been described to be in the shape of an egg or football, to some
degree that is true, though an astigmatic eye is not exaggerated to
that degree. Most people have some astigmatism. Visually, a person
with uncorrected astigmatism will often see a faint shadow on
letters or objects.
Emmetropia
A person is emmetropic when an image focuses clearly on the retina. A person that is emmetropic has uncorrected “normal vision”.
Updated 7/12/06