Use of Lasik Surgery for Astigmatic Correction – Dr. Kevin Niksarli May 2014

Use of Lasik Surgery for Astigmatic Correction – Dr. Kevin Niksarli
LASIK surgery is used for astigmatic correction as well as simple myopia by the use of the excimer laser.
An excimer laser corrects simple myopia by restructuring the Cornea. Greater laser energy is applied to
the central cornea as compared to the peripheral cornea usually accomplished by closing or opening a
circular aperture or alternatively by using a scanning laser to focus the pulses on the central region. The
final result is a convex surface caused by the central stroma of the Cornea getting more laser energy
than the peripheral region.

On the other hand Hyperopic correction is achieved by focusing more laser energy on the peripheral
regions of the cornea as compared to the stromal region. This creates a concave surface caused by the
central stroma of the Cornea getting less laser energy than the peripheral region. Myopic Astigmatism is
corrected by applying the laser energy in an elliptical pattern in the central region of the flat meridian.
This enables the flattening of the steep axis. In the same way hyperopic astigmatism is corrected by
applying the laser beam in the peripheral region, thus steepening the flat axis.

The most common type of laser, which is used for effecting the restructuring process is one with a
wavelength of 193 nm, which removes approximately 0.25 µm of stromal tissue with each pulse. If
greater correction is needed more tissues are removed.

There are some basic differences between LASEK or laser epithelial keratomileusis and LASIK surgery.
Even though the calculations and the ablation methods are the same, the main difference between the
two techniques is the depth within the cornea where the laser energy is applied.

In LASIK surgery the Laser energy is sent in the midstromal layer after the LASIK flap is created and the
stromal layers are exposed. In PRK, the removal of tissue occurs in the Bowman layer and anterior
stroma rather than in the midstromal region. IN LASEK surgery the epithelium is retained as a sheet and
then placed over the ablated area after the process has been completed.

The last few years has seen the development of quite a few advances in LASIK surgery. Techniques have
been perfected to collect refractive data, which enables correction of not only myopia, hyperopia, and
astigmatism but also higher order refractive anomalies. One such technology is the Wavescan Digital
technology, which was originally developed for astrophysics to correct distortion of images by
atmospheric interference. The same technique is now used to correct higher order spherical aberration,
and astigmatism.