Ординатура / Офтальмология / Английские материалы / LASIK and Beyond LASIK Wavefront Analysis and Customized Ablation_Boyd_2001

Chapter 34

Case 8. Status Post Hyperopic Lasik

This forty year-old female underwent uneventful lasik for + 4.75 – 0.75 x 090 which was followed by enhancement for a residual refractive error of + 2.75 – 1.25 x 065. Her best spectacle corrected vision preoperatively was 20/20-0. Manifest refraction at time of wavefront analysis was +0.75 – 0.5 x 105 for 20/30+1 best spectacle corrected vision. Autorefraction was + 3.0 – 0.5 x 100. Wavefront refraction was + 2.7 – 0.3 x 104.

Autokeratometry was 46.0 @ 154 / 48.0 @ 064. The patient felt her vision in the left eye was not as “ crisp “ as she would desire. Note the eccentricity of the left contour image and its significant large scaling range of 19 microns and the aberration on the higher order map with a scaling range of 5 microns. There is significant higher order aberration for this eye. The Humphrey Atlas topography map is displayed for comparison.

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Case 9. Status Post Myopic Lasik

Fifty-one year-old male optometrist who underwent bilateral myopic astigmatic lasik. He has no unwanted subjective visual symptoms and is very happy with his postoperative status monocularly and binocularly. Preoperative refraction of the left eye was – 4.0 – 2.0 x 176 for 20/15 best spectacle corrected vision. Target refraction was –1.87 – 0.25 x 176 for monovision. Uncorrected distance vision in the left eye was 20/80 and near vision was J-1+. Manifest refraction was – 1.63 – 0.5 x 160 for 20/15 best spectacle corrected

WAVEFRONT ANALYSIS

acuity. Autorefraction was –2.25 – 1.0 x 177 and wavefront refraction was –1.7 – 1.1 x 011. Manual keratometry was 38.25 @ 005 / 39.12 @ 095 and autokeratometry was 38.25 @ 174 / 39.75 @ 084. The left visual acuity map has a scaling range of 28 microns and the higher order map has a scaling range of 3 microns. Note on the left acuity map what appears to be with-the-rule astigmatism.

Thibos and Hong 7 have shown an increase in higher order aberrations specifically spherical aberration after myopic lasik. The following comparison below nicely displays this finding.(Cont. in next page)

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Normal eye the day before and the day after myopic lasik. Upper row shows pupil phase maps (contour maps analogous to Visx 20/10 Perfect Vision Acuity Maps), lower row shows the distribution of wavefront error by Zernike order. To emphasize the change in higher order aberrations, the residual spherocylindrical refractive er-

rors were omitted from the analysis. Note the significant increase of 3rd, 4th orders along with increase in 5th –10 th orders. (Figure courtesy American Academy of Optometry - Thibos LN, Hong X. Clinical applications of the Shack-Hartmann Aberrometer. Optom Vis Sci 1999;76:817-825.)7

Thirty-one year-old female with no subjective complaints and no ocular or surgical history. She has no contact lens history. Uncorrected acuities were 20/20- O.D. and 20/20 O.S. Manifest refraction was +0.25 – 1.25 x 105 O.D. for 20/15 best spectacle corrected vision and – 1.0 sphere for 20/20+ best spectacle corrected vision O.S. Wavefront refraction was + 0.7 – 1.8 x 101 O.D. and –0.7 sphere O.S. Manual keratometry

was 41.37 @ 000 / 42.12 @ 090 O.D. and 41.37 @ 000 / 41.50 @ 090 O.S. and autokeratometry was 41.25 @ 090 / 41.37 @ 180 O.D. and 41.00 @ 022 / 41.50 @ 112 O.S. The acuity map of the right eye shows the againstthe- rule astigmatism pattern nicely corresponding with the plus cylinder manifest steep axis of 015. This can be appreciated by knowing the red color scheme peripherally at 015

(Cont. in next page)

and 195 meridia reflects the wavefront being ahead of the reference plane and the 105 and 285 meridia wavefront shaded in blue lagging behind the reference plane. This accurately describes the wavefront emerging sooner from the steep or recessed horizontal axis peripherally and emerging latter from the flat or protruding vertical axis peripherally. The acuity map of the left eye reveals a relatively spheri-

cal eye. The higher order map has a relatively narrow scaling of 3 microns with the contour changes noted between 0 and – 1.5 microns inferiorly. No clinical correlate could be made to this except for the outside possibility of tear film abnormality at the time of the test. No SH data image was available for assessment. Humphrey topographies provided for comparison.

REFERENCES

1.Liang J, Grimm B, Goelz S, Bille JF. Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor. J Opt Soc Am A 1994;11:1949-57.

2.Optics, Refraction, and Contact Lenses, Basic and

Clinical Science Course, American Academy of Ophthalmology, 1993-4,

p.p. 94-7.

3. Records RE, Brown JL. Visual Acuity, Contour Resolution, and Temporal Charachteristics of the Visual System. In Biomedical Foundation of Ophthalmology, Vol. 2, Chapter 17.

Wave Front Analysis - Clinical Primer

John F. Doane, M.D.1

Scot Morris, O.D.1

Andrea D. Border, O.D. 1

Lon S. EuDaly, O.D.1

James A. Denning, B.A., B.S.1

Louis E. Probst MD2

1Discover Vision Centers

Kansas City, Missouri, U.S.A.

2Medical Director

TLC The Laser Eye Centers, USA

4.Dougherty PJ, Wellish KL, Maloney RK. Excimer laser ablation rate and corneal hydration. Am J Ophthalmol. 1994;118:169-76.

5.Customized Ablations: The Future is Close. Medical Laser Report 2000; January;3-6.

6.Webb R, Penny CM, Thompson K. Measurement of ocular local wavefront distortion with a spatially resolved refractometer. Appl Opt 1992;31:3678-86.

7.Thibos LN, Hong X. Clinical applications of the Shack Hartmann Aberrometer. Optom Vis Sci 1999; 76:817-825.

8.Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA. Comparison of Corneal Wavefront Aberrations after Photorefractive Keratectomy and Laser

in situ Keratomileusis. Am J Ophthalmol 1999; 127:1-7.

The authors would like to thank Greg Halstead, Thomas McKay and Kevin Tausend of Visx, Inc., Santa Clara, California, for their technical support and encouragement in this manuscript.

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To date, LASIK surgery is accomplished through a set of algorithms or mathematic formulas that are pre-programmed into the laser’s computer. These formulas are based on the standard refractive errors usually originate in patients undergoing LASIK surgery. They have been provided in a non-custom- ized approach. Laser surgery using these standard formulas produce remarkable results in a large number of patients. Pre-operative diagnostics, including topography, are routinely performed, but an analysis of the eye’s entire optical system was not available.

The Bausch & Lomb Zyoptix system for the Technolas 217 laser can customize LASIK for each patient. Like matching a fingerprint, it provides a distinctive laser treatment plan for each eye to potentially reach better visual results than before in a safer process.

Zywave is a distinct approach of looking at the eye. The information collect by this system is shared with that of corneal mapping system Orbscan II. With this entire information of the eye’s optical system, surgeons could plan personalized treatments for their patients rather than rely upon the basic laser algorithms or mathematic formulas.

PERFORMING ZYOPTIX

TREATMENT

For Zyoptix treatment to be performed, there are several hardware and software requirements (Table 1).

A- Orbscan II multidimensional diagnostic system that collect 9000 data points in 1.5 seconds and bring corneal mapping technologies (Figure 35-1).

B- Zywave diagnostic device designed to identify abnormalities throughout the entire optical system with the use of wavefront technology (Figure 35-2).

C- Zylink is use to generate an optimal treatment (Figure 35-3).

TABLE 1.

REQUIREMENT FOR ZYOPTIX

TREATMENT

Orbscan IIz

Zywave aberrometer

Zylink

Technolas 217z

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Figure 35-1: Orbscan II multidimensional diagnostic system.

D- Bausch & Lomb Technolas 217z laser with an active eye tracking system utilizes a 2-mm and 1-mm flying spot beam. The Soft spot system allow the surgeon to eliminate most of the tissue with 2 mm laser beam, and then use the 1 mm beam to treat higher-order aberration and “polish up” the ablation (Figure 35-4).

Orbscan II

The Orbscan II is a multi-dimensional diagnostic system that enables eye surgeons to map both the anterior and posterior surface of the cornea. By mapping the entire corneal surface, the surgeon can detect any corneal imperfections in elevation or curvature that might impact the expected surgical results.

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Figure 35-2: Zywave diagnostic device. Section 4

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