One of the most common types of eye surgery
done all over the world today is laser surgery to correct common eyesight
defects. Short sight (myopia), long sight (hyperopia) and astigmatism can all
be improved by using a laser to change the shape of the cornea. This allows
light to focus directly on the retina, rather than in front of, or behind it.
The first type of laser eye surgery
developed for visual correction was PRK – photorefractive keractectomy.
What is PRK?
Photorefractive keractectomy can be a
permanent solution to eyesight defects. The laser techniques involved were
developed during the 1970s and 1980s but PRK as a form of surgery was not
approved until 1995. Since then, probably millions of PRK procedures have taken
During PRK, the eye surgeon removes the
surface layer of the cornea using alcohol or a physical technique to scrape
away the cells. This reveals the layers of the cornea that can be modified by
Today, complex 3D mapping techniques using
scanning and computer technology produce a contour map of each individual
cornea so that the surgeon can use the laser with great accuracy and precision.
Afterwards, a disposable contact lens is
placed over the eye to protect it until new cells grow to replace the outer
layer removed at the start of surgery.
Disadvantages of PRK
Healing can take a few days and people
often find those days quite uncomfortable. For some people, PRK is still the
ideal solution and this type of laser eye surgery is still used. It has been
superceded to some extent by newer techniques.
LASEK is a variation of PRK. The acronym
stands for laser-assisted sub-epithelial keratectomy.
LASEK differs from PRK because the surface
layer of the cornea is not destroyed either chemically or physically at the
start of surgery. It is gently pushed out of the way and then put back onto the
cornea after reshaping with the laser is complete. The cells within the surface
layer don’t survive, but placing them over the sculpted cornea is easier on the
eye during the few days in which a new surface layer grows.
As the technique is damaging to the cornea,
recovery can be faster. People report less pain in their eyes after surgery,
clearer vision with no haze and less time to having improved vision.
LASEK has been used successfully on
probably hundreds of thousands of people in the world but it is currently less
popular than the newer LASIK technique.
LASIK was developed at the end of the
1990s. The surface layer of the cornea is not removed or scraped away, or
pushed to one side. Removal is done very precisely using microsurgery to create
a flap, which remains attached at one side.
The laser is then used to make the required
shape changes to the cornea underneath, and then the flap is closed. The eye
then recovers with its surface layer in tact.
As you would expect, recovery is much
faster and easier than after PRK or LASEK. When the flap of tissue is laid back
over the cornea, surface tension sucks it into place and cell regenerate at the
edges of the flap, usually within a few hours.
Combination laser eye surgery
The different techniques have their own
subtle variations and successful laser eye surgery often depends on the skill
of the surgeon in matching the patient with the most suitable technique for
them, not just in his or her skill in the operating theatre.
Techniques are also
evolving and people who have very severe sight problems, abnormal corneas or
other complications may be treatable using a combination of laser surgery and
lens implants. Bioptics is a new area of ophthalmology that could expand a
great deal in the next few years.