Refractive%20Accuracy%20of%20LASIK%20Using%20the%20IntraLase%20and%20Zyoptix

1
Refractive Accuracy of LASIK Using the IntraLase
and Zyoptix
?
Jonathan M. Davidorf, MD (Davidorf Eye Group
Los Angeles, CA)
Entered vs. Achieved Spherical Equivalent
METHODS As part of an ongoing nonrandomized,
unmasked, prospective study of myopic eyes were
treated with Lasik using Zyoptix. The most
recent one hundred treated eyes with one month
follow-up are presented. Preoperatively,
patients had complete ophthalmologic
examinations, including manifest and cycloplegic
refractions, undilated and dilated wavefront
measurements (Zywave), corneal topography/pachymet
ry (Orbscan II-Z), and mesopic pupil size
measurement. Patients with a history of prior
ocular surgery or with poorly controlled medical
problems were excluded from the study.
Treatment plans were calculated preoperatively
using the Zylink software version 2.38. A
customized nomogram developed from previously
treated eyes was used. The nomogram is based on
a regression equation with the mean of the
manifest and cycloplegic spherical equivalent
refractions as the independent variable, and the
inputted spherical equivalent as the dependent
variable. All eyes were targeted for best
possible uncorrected distance vision. The
information from the Zyoptix workstation was
brought to the excimer laser on a floppy disk and
the data then transferred to the laser. Lamellar
flaps were created using the Intralase with an
intended flap thickness between 90 and 120
microns (depending on preoperative corneal
thickness and calculated maximum ablation depth).
When appropriate, bilateral simultaneous Lasik
was performed. The spot scanning excimer laser,
the Bausch Lomb Technolas 217-Z, was used in
all cases. Optical zone sizes from 5.50 to 6.70
mm were used depending on the amount of
correction, mesopic pupil size, and corneal
thickness. Postoperatively, patients
underwent additional Zywave testing at the one
month interval. Only undilated Zywave
measurements were performed postoperatively.
Uncorrected distance visual acuity, manifest
refraction, and loss of best spectacle corrected
visual acuity were evaluated. Data was entered
into an Excel spreadsheet for evaluation.
RESULTS

• BACKGROUND
• Wavefront guided customized lasik procedures are
  designed to correct both lower order (sphere and
  cylinder) and higher order optical aberrations
  (HOAs). Zyoptix is the customized, wavefront
  guided platform for the Bausch Lomb Technolas
  217-Z excimer laser. The system incorporates a
  Hartmann-Shack aberometer (Zywave) and topography
  data (Orbscan II-z). The Hartmann-Shack
  aberrometry data from the Zywave is combined with
  the Orbscan data to generate the custom treatment
  plans. The IntraLase femtosecond laser (AMO)
  uses pulsed infrared light to photodisrupt
  corneal tissue at a preset depth in order to
  construct the lamellar flap for LASIK. LASIK
  with the IntraLase has been demonstrated to
  improve refractive outcomes compared to LASIK
  with mechanical microkeratomes1.
• While there are factors extraneous to the excimer
  laser ablation profile (such as flap creation,
  wound healing, laser centration, and ocular
  surface abnormalities) in LASIK that influence
  postoperative HOAs and refractive accuracy,
  wavefront guided custom treatments attempt to
  minimize the induction of laser induced HOAs.2
  Perhaps more important, is the accuracy of the
  wavefront guided treatments in correcting the
  lower order aberrations. The purpose of this
  study is evaluate the refractive efficacy and
  predictability in myopic eyes undergoing Lasik
  with Zyoptix software version 2.38 using the
  IntraLase femtosecond laser for flap creation.

Higher Order Aberrations (RMS - m)
Graph of the spherical equivalent
entered into the Zyoptix treatment versus the
postoperatively achieved spherical equivalent
(mean of preoperative manifest and cyloplegic
spherical equivalent refraction minus
postoperative spherical equivalent refraction)
Discussion Wavefront guided custom lasik with
Zyoptix and Intralase demonstrated excellent
efficacy and predictability regarding lower order
aberrations as manifest by 74 of eyes realizing
20/20 or better uncorrected visual acuity and
over 1/3 of eyes attaining 20/15 or better
uncorrected visual acuity. All eyes had best
spectacle corrected visual acuity of 20/20 or
better preoperatively and postoperatively. The
Entered vs. Achieved graph of spherical
equivalent shows a tight data series with an R2
of 0.97. Continued nomogram refinements may
further improve subsequent data. The main
limitation of this study is the lack of
comparison of the effects (using similar nomogram
adjustments) of Zyoptix Lasik treatments with
Intralase compared to either conventional
treatments or to Zyoptix treatments using a
standard microkeratome.
Pre-op (m) Post-op (m)
5 mm 0.23 0.09 0.31 0.15 D
6 mm 0.36 0.14 0.47 0.23
OBJECTIVE
Mean optical zone diameter 6.06 0.34 mm (5.50
to 6.70 mm)
Intraoperative Flap Complications
No visually significant flap complications
occurred in this series of treated eyes. Of
note, two eyes demonstrated a faint horizontal
ridge in the stromal bed upon flap elevation.
Both cases occurred inferiorly (superior hinged
flaps), outside the visual axis, and did not
affect the excimer laser treatments nor the
visual outcomes. One patient with a small
horizontal corneal diameter (white-to-white)
had three small air bubbles identified in the
anterior chamber following flap creation. The
bubbles were within the pupil margin and did
inhibit eye tracker acquisition, and there were
no visual sequelae. The bubbles were gone by the
first postoperative day.
The Bausch Lomb Technolas 217-Z Excimer
Laser

• CONCLUSIONS
• Lasik with Zyoptix and IntraLase demonstrated
• Excellent efficacy and safety
• Excellent predictability

To study the refractive predictability in myopic
eyes undergoing wavefront guided LASIK with the
Intralase and Bausch Lombs 217-Z excimer laser
using software version 2.38 (Zyoptix).
Postoperative Uncorrected Visual Acuity
Sample preoperative Zywave maps
Demographics

eyes (pts) 100 eyes (55 pts)
Gender 63 F, 37 M
Mean age 34 yrs (17 56)
Mean Pre-op SE -4.27 2.08 D (-0.50 to -9.63D)
Mean Pre-op Cyl Mean Pupil Size -0.68 0.54 D (0 to -2.75 D) 6.1 0.9 mm (4.0 to 8.3 mm)

• References
• Dezirian GM, Stonecipher KG. Comparison of the
  IntraLase femtosecond laser and mechanical
  keratomes for laser in situ keratomileusis. J
  Cataract Refract Surg. 200430804-811.
• Bühren J, Kohnen T. Factors affecting the change
  in lower-order and higher-order aberrations after
  wavefront-guided laser in situ keratomileusis for
  myopia with the Zyoptix 3.1 system. J Cataract
  Refract Surg. 2006321166-1174.

For additional information please
contact Jonathan M. Davidorf, MD Davidorf Eye
Group www.davidorf.com
The Zyoptix Dual Workstation (Zywave and Orbscan
II-Z)