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ones. A recent addition in this field is the area of customized correction, by lasers using
wave front technology. Even though the customized correction procedures are becoming

popular by the day, controversies still surround many of its presumed theoretical
advantages. Since conventional LASIK surgery by itself is a highly accurate procedure, it
becomes all the more difficult to establish the superiority of the customized correction
over the conventional one.

Conventional
By varying the ablation pattern, the excimer laser can alter the anterior corneal curvature
to modify a particular refractive error described by sphere and cylinder. The laser delivery
methods currently being utilized to achieve the ablation pattern are broad beam, scanning
slit, or flying spot systems. Eye-tracking technology is integrated into the current
commercially available excimer laser systems and permits the ablation to remain centered
on the pupil in the presence of small ocular movements.

Potential advantages of customized treatment
Wave front based aberrometry has certain theoretical advantages, the notable one being
the evaluation of whole eye optics. In certain instances, visual symptoms can be correlated
with certain higher order aberrations. However the measurements of these aberrations are

not reproducible. For example, it has been shown that Postoperative wavefront
.
aberrations do not always correlate with contrast sensitivity measurements The magnitude
of higher order aberrations have been documented to increase with increasing papillary
size. Hence there is a theoretical beneficial effect of correcting higher order aberrations in
people with large pupils, who have to work mainly in dim light conditions.

Potential disadvantages of customized treatment
1. All aberrations are not treated: The aberrometer generates a lot of data from a human
eye. Not all of these are treatable using customized LASIK procedure. In fact,
customized LASIK has been demonstrated to induce additional higher order aberrations
as well. This again brings us to the notion that the significance of these aberrations is
still not well understood at this point of time and further refinements are yet to be
done in this field.

2. All aberrations are not reproducible: The aberrations generated from a human eye are
not reproducible and this is one of the major draw backs. Daily fluctuations in wave
front aberrations have been noted in several studies and are attributed to
accommodation, tone of the pupil and tear film distribution.
3. Wave front changes with age: The wave front measurements of the eye alter with age,
because of changes that occur in the lens and cornea with age. Hence even if one
performs customized corneal ablation, it will be interesting to watch whether these
changes would be permanent.

4. Pupillary size: Pupillary alterations happen almost on a continuing basis in our day to
day routine. The output of the wave front images changes with minute changes in the

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