Refractive Accuracy of LASIK Using the IntraLase and Zyoptix

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.

Jonathan M. Davidorf, MD (Davidorf Eye Group; Los Angeles, CA)

OBJECTIVE

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/pachymetry (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

CONCLUSIONS

Lasik with Zyoptix and IntraLase demonstrated:

• Excellent efficacy and safety

• Excellent predictability



For additional information please contact:

Jonathan M. Davidorf, MDDavidorf Eye Groupwww.davidorf.com

# 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)

Demographics

0.23

0.31

0.36

0.47

5 mm 6 mm

Pre-op

Post-op

Higher Order Aberrations (RMS - )

Pre-op () Post-op ()

5 mm 0.23 + 0.09 0.31 + 0.15 D

6 mm 0.36 + 0.14 0.47 + 0.23

Postoperative Uncorrected Visual Acuity

34%

74%87% 99%

20/15+ 20/20+ 20/25+ 20/40+

DiscussionWavefront 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.

Entered vs. Achieved Spherical Equivalent

To study the refractive predictability in myopic eyes undergoing wavefront guided LASIK with the Intralase and Bausch & Lomb’s 217-Z excimer laser using software version 2.38 (Zyoptix).

Sample preoperative Zywave maps

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)

References

1. Dezirian GM, Stonecipher KG. Comparison of the IntraLase femtosecond laser and mechanical keratomes for laser in situ keratomileusis. J Cataract Refract Surg. 2004;30:804-811.

2. 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. 2006;32:1166-1174.

The Bausch & Lomb Technolas 217-Z Excimer Laser

The Zyoptix Dual Workstation (Zywave and Orbscan II-Z)

Mean optical zone diameter: 6.06 + 0.34 mm (5.50 to 6.70 mm)

Ent v. Ach Avg MRCR M-Zx Last 100 3/31/08

y = 0.9362x - 0.4877

R2 = 0.9653

-10.00

-8.00

-6.00

-4.00

-2.00

0.00

-12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00

ach Avg MRCRSE

En

t S

E

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.