Over
half of all adults in the UK wear glasses or contact lenses
to correct short-sightedness, long-sightedness, or astigmatism.
These vision disorders are known as refractive errors. Although
many people are happy with their glasses or contact lenses,
advances in surgical techniques are now proving a popular alternative.
The
refractive process in your eye is similar to the way a camera
takes a picture. The cornea and lens in your eye act as the
camera lens focusing rays of light. The retina is similar
to the photographic film. The image your retina "sees" is
transmitted to your brain, which interprets the image. If
the image is not focused, the film (or retina) receives a
blurred image.
Myopia (Shortsightedness)
Myopic or shortsighted people have
an eye which is too long relative to the refractive powers
of the cornea and lens. This results in distant objects appearing
blurred because they are focused in front of the retina. However
close objects are seen clearly and myopes can read without
glasses. Myopia affects about a third of the adult population.
At present, the majority of all refractive surgery patients
are myopic.
Hyperopia
(Longsightedness)
Hyperopia, or long-sightedness, is the opposite of myopia. Distant
objects are relatively clear, but close-up objects appear blurred.
Hyperopia results from an eyeball that is too short relative
to the refractive powers of the eye causing the images to focus
on a point behind the retina. Some hyperopes are able to benefit
from LASIK or other refractive surgery procedures.
Astigmatism
Astigmatism is a condition in which uneven
curvature of the cornea blurs and distorts both distant and
near objects. A normal cornea is round, with even curves on
all sides, like a football. The astigmatic cornea is shaped
more like a rugby ball, curved more in one direction than in
another. This causes light rays to have more than one focal
point and focus on two separate areas of the retina, distorting
the visual image. Most people have very slight astigmatism,
but a significant number require spectacle or contact lens
correction to see clearly. Advances in laser techniques, and
in complex cases the use of wavefront technology, allow astigmatism
to be corrected with LASIK.
Presbyopia
Presbyopia is part of the normal ageing process
and results in blurring of near vision. As we age the muscles
supporting the lens of our eye become less able to focus
the lens for near vision. This is why most people find
that in their 40s they require reading glasses. New surgical
techniques such as PRELEX have been highly successful
in treating people with presbyopia.
