LASIK
>Refractive Errors
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Direct telephone 040 5551 0366
Ms Sheetal 93463 19982/040 3061 2131
Shaik Yousuf Arfath 040 3061 2101
Email: lasik@lvpei.org
Fax: 040 2354 8339 |
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What are
refractive errors?
The eye functions like a camera. Light rays entering the eye
are focused by the cornea and the lens of the eye onto the
light sensitive retina (which is like the film of a camera)
at the back of the eye. The retina then transmits a clear
image, or photo, to the brain. In people with refractive error
(or poor vision, such as nearsightedness or farsightedness),
the light rays do not get focused on to the retina and blurred
images are formed. These can be measured as aberration patterns.
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Myopia
and treatment options
Myopia, commonly known as near-sightedness or short-sightedness,
refers to a condition where the patient is unable to see distant
objects. The word 'myopia' is derived from the Greek root
myein - meaning 'to close', and ops - meaning 'eye', probably
referring to the tendency of near-sighted individuals of partially
closing the eye or squinting to improve the sharpness of distant
objects.
Myopia is rare before the school-going
age, gradually increasing during school life and reaching
its peak during the intense study years of college. Its etiology
is multi-factorial, with both genes and environment playing
important roles. Though it is believed that prolonged reading
harms the eyes, attempts to reduce accommodative fatigue (like
introducing pauses during reading and teaching, eye exercises,
etc.) have not helped to reduce myopia among children.
Myopia is classified into low
(-3 diopters), moderate (-3 to -6 diopters), and high (more
than -6 diopters). Persons with severe myopia are liable to
have vision-threatening complications and should have a dilated
eye examination at least once a year. (A diopter is the power
of a lens for focussing light rays.)
The treatment options for myopia
are spectacles, contact lenses, and refractive surgery. Spectacles
are inexpensive and safe and offer clear vision, relief from
eyestrain and headaches, and reduced risk of developing a
squint. Patients with high power are advised to use high index
glasses, which are not very thick. Plastic glasses are lighter,
but get scratched easily.
Those who do not want to wear
spectacles can opt for contact lenses, which are mainly of
two types: soft and semi-soft or rigid gas permeable. Soft
contact lenses may be conventional or disposable. Soft lenses
do not allow enough oxygen to reach the eye and, on a long-term
basis, may lead to complications like blood vessels on the
cornea, inflammation and dry eyes. Semi-soft lenses or rigid
gas permeable lenses are better, because they correct more
astigmatism as compared to soft lenses. For high errors of
astigmatism, surgeons may suggest toric contact lenses, or
soft and semi-soft lenses.
Disposable lenses (daily or
weekly) are discarded as indicated, while extended wear lenses
can be worn while sleeping also, though this is not recommended.
Sleeping or swimming with the lenses on increases the risk
of corneal ulcers and infections, which are sight-threatening
complications. All types of lenses should be removed at the
end of the day, cleaned and soaked in the specified solution.
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Hyperopia
and treatment options
Hyperopia refers to the condition known commonly as long-sightedness,
wherein the patient has difficulty seeing objects or reading
at close distances without the aid of glasses.
In general, LASIK is recommended
for patients with up to +4 to +5 diopters spherical of hyperopia
or far-sightedness. It is relatively easier to flatten the
cornea for myopia patients, but it is more difficult to steepen
the cornea in hyperopia. If we steepen the cornea too much,
there will be a gradual regression of the power and a risk
of the patient losing the best corrected vision. If the error
is more than +5 diopters, in young patients contact lenses
are preferable to surgery. For patients above the age of 40,
refractive lens exchange (along with the removal of the clear
lens) with a regular monofocal/multifocal lens is recommended.
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