When you are myopic (short-sighted), close-up objects seem
clear but images in the distance will seem blurry. Here, your
eye is too long and/or the cornea
is too curved. Images are focused in-front of the retina,
so your brain interprets it as a blurred image.
When you are hypermaetropic (long-sighted), objects in the
distance are slightly blurred while objects that are near
seem more blurred. Here, your eye is too short and/or the
cornea is too flat. Images are focused behind the retina,
so your brain interprets it as a blurred image.
When you have astigmatism all objects seem blurry, whether
near or far. Here, the shape of the cornea is distorted. Images
are focused on more than one point in-front of, or behind
the retina, so your brain interprets it as a “doubled”
image.
LASIK can correct myopia, hypermaetropia
and astigmatism by changing the curvature of the cornea.
Presbyopia (old
age long sightedness or “Lau Hwa Yan”)
When you have presbyopia, usually in middle age (between
40-45 yrs old), distant objects appear clear but you need
reading glasses to see near objects clearly. As you age, your
eye’s lens loses elasticity and cannot fine-tune the
focus of light on the retina properly.
LASIK cannot correct
presbyopia because the procedure cannot change the elasticity
of the lens.
Presbyopia Correction
Every year, claims of a cure for presbyopia are made all
over the world. Unfortunately, none has been able to completely
cure presbyopia. Laser Thermokeratoplasty, Conductive Keratoplasty,
scleral expansion plugs, accommodative intraocular lens, multifocal
intraocular lenses and presbyopic LASIK surgery all have had
limited success.
Even so, presbyopic LASIK surgery has recently received intense
publicity. This surgery is designed to change the shape of
the cornea to a multifocal and more prolate (conical) shape.
This increases the depth of focus, but cannot eliminate the
basic problem of stiffening in an ageing human lens.
The final cure will be an artificial lens with the ability
to change its shape by entirely mimicking
the way the human lens focuses. Billions of dollars have been
invested to design and test various lenses but presently,
none are able to focus as effectively as the natural human
lens.
Confusion Over The Term “Long-Sightedness”
“Long-sightedness” is used to describe two
different and distinct conditions – Hypermaetropia and
Presbyopia – both of which cause blurred vision at close
range. The term “long sightedness” has led to
much confusion amongst patients, and even doctors.
Hypermaetropia
Presbyopia
Also known as:
Far-sightedness;
Youthful long-sightedness.
Also known as:
“Lau Hwa Yan”;
Old age long-sightedness.
Vision problem:
Objects in the distance are slightly blurry.
Objects at close range are more blurry.
The young patient can strongly focus and compensate
partially or totally their hypermaetropia (see animation
below)
Patient has ‘tired’ eyes due to constant
re-focusing.
Vision problem:
Objects in the distance are clear.
Objects at close range are blurry.
Patient needs reading glasses to see close-up objects
clearly.
No amount of effort in focusing will make near objects
appear clear.
Cause:
The eye is too short and/or the cornea is too flat.
Cause:
Loss of lens elasticity due to natural aging process.
Age of occurrence:
Any age, but usually in the young;
Does not occur to everyone.
Age of occurrence:
Middle age, usually 40 years and above;
Occurs to everyone.
Correction by LASIK:
Yes
Correction by LASIK:
No
Before you proceed with LASIK, it is important to determine
whether you are hypermaetropic or presbyopic.
