|
How the Eye Functions:
The eye functions on much the same
principle as a camera. The iris, or colored portion of the eye,
acts as the shutter to regulate the amount of light admitted to the eye.
The cornea (the clear window at the front of the eye), and the lens
(located behind the pupil), serve to focus light rays, from the object
viewed, onto the retina at the back of the eye. The retina then
transmits the "picture" of the object viewed to the brain where the
object is "seen".
Refractive Error:
For the eye to present a clear image,
the light rays entering the eye need to come to focus on the back of the
eye. In 35% of people the rays of light do not focus on the back
of the eye, giving a blurred image at the brain. This is
correctable by glasses or contact lenses and is known as a refractive
error. Refractive errors can be the result of a number of factors,
which include:
- The curvature of your cornea
- The strength of your lens
- The length of your eye
The three categories of refractive
errors are: Myopia
(nearsightedness), Hyperopia
(farsightedness), and
Astigmatism
(distorted vision). All of these are usually able to be
corrected by laser surgery.
Back to the top
How do I tell which refractive error I have:
There are two ways to tell which form
of refractive error that you have. The first is to ask your eye
specialist or look at your prescription.
There are three main numbers on a
prescription. There is a sphere, a
cylinder and an axis. The cylinder and the axis is indicating
the presence of astigmatism. NOT
everybody has a cylinder correction, as not everybody has astigmatism.
The cylinder is the amount of astigmatism that you have, and the axis is
the orientation of the astigmatism.
The sphere, the first number on
the prescription tells you if you are far or near sighted. If the
sphere is a positive (+) number then you are Hyperopic
or farsighted. If the sphere is a negative (-) number then you are
Myopic
or nearsighted.
The cylinder
is the second number on the prescription, this can sometimes look like
the bottom number of a fraction.
If your prescription has an add,
written below the main numbers then this is the correction for your
Presbyopic or reading correction.
Back to the top
Myopia (Nearsightedness):
Myopia is caused by one or a
combination of the following:
- Steep cornea
- Long eyeball
- Powerful lens
Consequently light rays focus in front
of the retina, instead of directly on the retina.
Nearsighted people are able to see
close up objects clearly, but objects in the distance are blurry and
indistinct. People with moderate to high levels of myopia are
unable to see anything of real value without their glasses.
Laser surgery corrects myopia by making
the central cornea flatter, thereby refocusing light rays onto the
retina.
There are different degrees of myopia.
They are classified as:
* Low 0 to -4
* Moderate -4 to -8
* High -8 and above
All of the above can be improved, but
those in the higher range of myopia, may still need to wear a small
prescription for certain activities. The laser can successfully
treat up to 15 diopters of myopia.
Back to the top
Hyperopia
(Farsightedness):
Hypermetropia is caused by one or a
combination of the following:
- 1. Flat cornea
- 2. Short eyeball
Consequently light rays are focused behind
instead of on the retina.
Farsighted people are able to see
images in the distance more clearly than they can see images at close.
Though most hypermetropic people are unable to see at either distance
clearly without their glasses.
Laser surgery corrects hypermetropia by
making the cornea steeper so the rays of light are refocused on the back
of the eye.
There is a limit on the degree of
hyperopia that can be fully corrected, approximately 6 diopters.
If you are above the level of treatment it is still worth while coming
for a consultation. Laser treatment may be able to give you less
dependence on glasses and contact lenses, or outline other treatment
options available to you.
Back to the top
Astigmatism: (Distorted Vision)
Astigmatism means that the front of the eye is not
entirely spherical like a soccer ball, but shaped more like a football,
(ie. it is not equally curved in all places). This means that the
rays of light are bent unequally, therefore giving a distorted or
blurred image at all distances.
Astigmatism can be found either alone, or
in conjunction with myopia or hypermetropia. Laser surgery can treat
astigmatism alone, or when found in conjunction with myopia or
hypermetropia.
Back to the top
Presbyopia:
 Presbyopia
occurs in all adults approximately 45 years or older. Presbyopia
is a natural aging process of the lens inside the eye. This means
that distance vision will be unchanged, but near vision will become
blurry.
People who are mildly
nearsighted will be unaffected by the symptoms of presbyopia, but
people who have no prescription, are farsighted
or strongly short sighted will suffer from the symptoms of presbyopia.
Presbyopia is able to be treated by
Monovision.
Back to the top
Monovision:
Monovision is a form of treatment for
Presbyopia, when one eye is used for distance vision and the other is
used for short distance or near vision.
People with no refractive error will
have only one eye treated. This eye will be made mildly myopic
(farsighted), allowing this eye to be used for near or short distance
vision. People with
myopia
(nearsightedness) will have both eyes treated. One eye will be
fully corrected and the other will be under corrected. This will leave
one eye mildly myopic (nearsighted) for near vision.
People with
hyperopia
(farsightedness) will also have both eyes treated. One eye will be
fully corrected and the other eye will be over corrected. This
will leave the eye mildly myopic (nearsighted) for near vision.
95% of people will accept this
situation happily. It may take up to 2 to 3 weeks to fully adjust to the
situation but most people will find it a useful alternative to being
presbyopic and wearing reading glasses.
The disadvantages to Monovision are:
- Decreased depth perception
- Reading very fine print may still be
a problem
- Driving long distances at night may
not be comfortable. This can be overcome by wearing a
correction when driving long distances
|
