EW Chicago 2012
Advances
in cataract and refractive surgery: A clinical update
7
Figure 1. As the amount of astigmatism increases, the uncorrected
visual acuity decreases
Figure 3. Intended cylinder correction at month 3
Figure 2. Nomogram parameters to date
Limbal marks with a sterile pen
were placed at the 3 o'clock and 9
o'clock positions at the slit lamp just
prior to the procedure to ensure
proper alignment. The incision
details, including the depth, optical
zone, and arc length were pro-
grammed into the iFS. From that
point on, the procedure was similar
to using the laser to create a LASIK
flap.
Our nomogram was simple. The
optical zone was 7 mm and three arc
angles were used: 40 degrees for an
intended cylinder correction
between –0.50 and –1.25 D, 50
degrees for –1.50 and –1.75 D, and
60-75 degrees between –2.00 and
–3.50 D (see Figure 2). The initial
lessons we learned are that (1) ISAK
can safely correct low to moderate
astigmatism, (2) there is an overall
undercorrection (see Figure 3), (3) a
nomogram can titrate the amount of
correction (the correction ratio was
similar over the range of treated
astigmatism), (4) the results seem
stable through 3 months of follow-
up in a consecutive cohort analysis,
and (5) there is still significant
variability in outcomes.
Our initial results are very
encouraging, but the procedure
needs additional refinement. This
can be accomplished through a
better understanding of the biome-
chanics of the intrastromal cut and
a detailed analysis of patient and
surgical factors that may influence
outcomes, such as different optical
zones and side cut angles. This will
undoubtedly result in a more refined
nomogram and better outcomes.
This procedure will evolve,
mature, and improve—we've barely
scratched the surface of what we can
achieve with femtosecond lasers.
Dr. Schallhorn is global medical director for
Optical Express. He can be contacted at
scschallhorn@yahoo.com.
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