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Why vision defects?
In
the eye that refract the light correctly an object is projected on the retina,
which is a condition for a good acuteness of vision. The eye's refractive parts
are the lens and cornea.
When
nearsighted (myopia) you do not see well in long distances. The eye is
too long in proportion to the eye's refractive ability. The picture of a remote
subject is front of the retina. But with a concave lens you move the sharp picture
backwards to the retina. When
long-sighted (heperopia) you cannot see well in a close range. The eye
is too short in proportion to the eye's refractive ability. The picture of a remote
subject is front of the retina. But with a convex lens you move the sharp picture
forward to the retina. Astigmatism
can exist independently if you are nearsighted or long-sighted. The cornea is
when not symmetrically, which makes the light refracting asymmetrically. Therefor
a sharp picture is not created on the retina. Regular astigmatism can be corrected
by a cylinder lens. By
presbyopia you cannot see sharply in the close range. In old age the eye's
ability to accommodate decrease. Presbyopia usually starts in the 40's. Reading
glasses helps against presbyopia.
Read more about Monovision
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There
are today tree ways of correcting refraction error 1.
Glasses
2. Lenses
3. Surgery
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1. Glasses
For many years, vision defects have been corrected by glasses with lenses that
either weaken the optical system of the eye - "minuses" for shortsighted persons
- or strengthen it - "pluses" for farsighted persons. This simplest way of correcting
vision defects is not sufficient for all patients, though. Glasses meant for big
defects are thick and inconvenient. Even the best-fitted ones distort images and
reduce the field of vision. For
patients with different refractive errors of the two eyes (anisometropy) or with
complex defects, it is not always possible to select glasses that will assure
vision acuity. Glasses can limit professional or life activities such as sports.
In their search to find correction methods that would allow them to live a life
without glasses, many patients are also motivated by cosmetic reasons.
How you read your glass prescription
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| Convex lens |
concave
lens |
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Lenses
Contact lenses have been widely used as an optical method
of correcting vision defects. They successfully replace glasses and in many cases
offer the best way to improve the quality of vision. Wearing contact lenses, shortsighted
persons normally get a better eyesight acuity, which sometimes comes as a surprise
that they can see the world in its true, not reduced dimensions.
There
are, however, a number of medical contraindications to wearing contact lenses.
Among them are: skin diseases, allergies, general disorders, e.g. diabetes, chronic
eye diseases and use of certain medications. People
who have been wearing contacts for a long time can develop intolerance symptoms:
a sensation of a foreign matter, changes in the conjunctiva, allergies, hyperemia,
which force them to resign from this method. Many
patients find wearing contact lenses inconvenient, for it requires discipline
in following hygiene, doctor's instructions and care procedures for storage and
disinfection.
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3. Surgical methods of
correction vision defects
Surgical
methods offer a chance to see better to patients for whom optical methods failed
to produce expected results, who cannot accept wearing glasses or cannot wear
contact lenses.
Surgical procedures are performed for the following reasons: Medical
- when neither glasses nor contacts offer sufficient improvement in the quality
of vision Professional
- when glasses hinder a patient's professional career or full vision acuity is
required without optical correction e.g. for pilots Cosmetic
- the most frequent around the world, considered by people who do not want to
wear glasses or contacts in their everyday lives. |
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