الفهرس 
Photorefractive keratectomyOnly 14 pages are availabe for public view
 |  | from | 264 |  |  |
| | | from | 264 | | |
Abstract
Refractive errors as myopia are naturally occurring defects and
have required the use of external aids like spectacles or contact
lenses. These devices have their own inherent flaws as regard to
cosmesis and comfort. Refractive surgery has emerged as a new
subspecialty in ophthalmology designed to develop an ideal surgical
technique to help people reduce their dependency on their external
visual aids.
Radial Keratotomy (RK) is one of the early surgical techniques
that were used to correct myopia. During the procedure, radial
incisions are made in the cornea of the eye with a highly precise
diamond blade set to a particular depth. These incisions allow the
sides of the cornea to bugle outward and thereby flatten the central
portion of the cornea. This brings the focal point of the eye closer to
the retina and improves one’s distance vision. RK for myopia was the
most commonly performed refractive procedure in the late 1970s
and 1980s. Ten years later it was realized that there are many
complications occurred with RK and the procedure not safe as it is
initially appeared.
Excimer laser surface ablation has been used since 1987 to treat
myopia, the original procedure was termed photorefractive
keratectomy (PRK) in which the epithelium is scraped prior to laser
refractive surgical correction, major disadvantage is the great and
Summary
181
persistent postoperative pain associated with de-epithelialization.,
slow visual recovery, and stromal haze, these complications drove to
the appearance of LASIK.
Laser in situ keratomileusis (LASIK) is the most commonly
performed refractive surgery. LASIK is a relatively new procedure
that is technically a variation of PRK. The Lasik procedure involves
the use of microkeratome to create a hinged flap in the cornea
underneath which an excimer laser is used to remove micro amounts
of stromal tissue to correct the particular refractive error.
The visual rehabilitation, after LASIK is rapid; it’s major
limitations include ectasia, flap wrinkles, free caps, incomplete pass
of the microkeratome, epithelial ingrowth, flap melt, interface debris,
and diffuse lamellar keratitis.
Laser subepithelial keratomileusis (LASEK) is a surgical
procedure which may reduce the complications of LASIK and PRK.
The early results seem promising especially for the potential
applications in thin corneas. Alcohol is often used to facilitate
removal of the corneal epithelium as a sheet. A hinged epithelial flap
is created by peeling the loosened epithelium as a sheet using one of
several recently developed surgical techniques. After laser ablation,
the flap is repositioned over the ablated stroma. This provides
coverage of the lasered stromal bed, and reduces epithelial migration
in those patients where the flap adheres to the stroma.
Summary
182
LASEK is safe and effective in treating low and moderate
degrees of myopia, and eliminates LASIK related flap
complications; however there is concern about the probable toxic
effects of alcohol on epithelium and underlying corneal stroma.
In 2003, Pallikaris described an alternative method for epithelial
separation using an instrument called epikeratome, with the use of
this device the corneal epithelium can be separated from the
underlying stroma without previous preparation with alcohol, the
epithelial sheet is then repositioned on the stroma after ablation is
complete. This procedure is known as (Epi-LASIK)
Epi-LASIK incorporates the advantages of LASIK and LASEK
and avoids the potential risk posed by the creation of the LASIK
flap, therefore it is possible that the quality of vision would be better
in Epi-LASIK treated patients than in LASIK treated patients,
meanwhile Epi-LASIK avoids the alcohol related side effects of
LASEK, which believes to be associated with less postoperative
pain, faster visual recovery and less haze.
Femtosecond (fs) laser may offer new possibilities in the field of
refractive surgery especially when using the laser as microkeratome.
By generating microplasmas inside corneal stroma with femtosecond
pulses, it is possible to achieve a cutting effect inside tissue while
leaving the anterior layer intact.
FS laser is the first bladeless and most accurate modality for
corneal flap creation available today.
Summary
183
Compared with mechanical microkeratome, fs lasers offer more
options for customizing the flap position, shape, diameter &
orientation during refractive surgery. In addition, it may be better for
creating thin flaps, because it leaves stronger corneas & is likely to
cause less denervation kertopathy.
Femtosecond Lenticule Extraction (FLEX) is a new form of
refractive eye surgery that creates a lenticule from the cornea for
removal and a corneal flap, all with a femtosecond laser.
In 1708, Herman Boerhaave suggested clear lens extraction
(CLE) as means of treating high myopia.
A refractive lens exchange (or “clear lens extraction”) refers to
the situation where a healthy crystalline lens is removed and
replaced by a corrective lens. Accommodative or multifocal IOL can
also be used but have varying refractive success.
Phakic intraocular surgery is now considered a promising
treatment option for patients who suffer from high and extreme.
myopia Implantable lenses are similar to the intraocular lenses
(IOLs) used in cataract surgery. However, implantable lenses are
placed in eyes that retain their natural lens, unlike in cataract surgery
where IOLs replace a natural lens that has turned cloudy. The phakic
IOL that are used are classified into anterior chamber and posterior
chamber pIOL. The anterior chamber can also be classified into
angle supported and iris fixated IOL. Phakic intraocular surgery has
the advantage of reversibility and the ability to correct high myopia
Summary
184
unlike corneal refractive surgery which is limited by corneal
thickness. Possible complications include increased chance of a
detached retina, loss of endothelial cells, inflammation, infection and
cataract.
Intrastromal corneal ring (ICR) segment are now an exciting
addition to the refractive surgeons. In 1978 Reynolds hypothesized
that a ring shaped implants could be introduced through a single,
peripheral radial incision in the cornea. Reynolds reasoned that this
implant would alter the anterior corneal curvature through expansion
or constriction in the diameter of the device, so it can treat myopia.