Visual outcomes of wavefront-guided laser in situ keratomileusis in eyes with moderate or high myopia and compound myopic astigmatism

Article Outline

• Abstract
• Patients and methods
  • Study Design
  • Enrollment Criteria
  • Clinical Outcome Measures
  • Statistical Analysis
• Results
  • Demographics and Refractive Error
  • Predictability
  • Stability
  • Safety
  • Efficacy
  • Higher-Order Wavefront Aberrations
  • Complications
• Discussion
• References
• Biography
• Copyright

Purpose

To evaluate the safety, efficacy, and clinical outcomes of wavefront-guided laser in situ keratomileusis (LASIK) surgery for the treatment of moderate to high myopia and compound myopic astigmatism.

Setting

Stanford University School of Medicine, Department of Ophthalmology, Stanford, California, USA.

Methods

This retrospective study included patients with moderate (−6.0 to −8.0 diopters [D]) and high (greater than −8.00) myopia treated with wavefront-guided LASIK using the WaveScan linked to the CustomVue system (AMO USA, Inc.). Eyes were analyzed preoperatively and 1, 3, and 12 months postoperatively.

Results

The mean patient age was 38.4 years ± 7.14 (SD). Eighty-nine eyes of 45 patients were evaluated at 3 months and 50 eyes of 25 patients at 12 months. No eye was retreated during the study. The mean manifest refraction spherical equivalent was −8.10 ± 0.98 D (range −6.00 to −10.63 D) preoperatively and −0.33 ± 0.55 D (range −1.625 to 1.375 D) 12 months postoperatively. Ninety percent of the eyes were within ±1.00 D of the intended correction and 64.0%, within ±0.50 D. For all eyes, the safety index was 1.00 and the efficacy index, 1.18.

Conclusion

The data support the safety and efficacy of correcting moderate to high myopia and compound myopic astigmatism using wavefront-guided LASIK.

In recent years, wavefront-guided laser in situ keratomileusis (LASIK) has become the dominant procedure used in correcting refractive errors.¹ This new technology is thought to have the potential to provide better postoperative quality of vision in patients, especially in contrast sensitive conditions such as scotopic and mesopic vision, than older conventional excimer laser technology.² With the technological discovery of wavefront measurements, ophthalmologists were able to quantify and potentially treat ocular higher-order aberrations (HOAs) by excimer laser surgery.³ Hence, the concept of wavefront-guided ablation should improve the image and quality of the eye, improving patients' visual acuity, as can be observed with adaptive optics.⁴

Recent studies report excellent clinical outcomes, safety, and efficacy of various wavefront-guided and wavefront-optimized LASIK platforms (Visx Star S4, AMO; LADARVision 4000, Alcon Laboratories; WaveLight Allegretto, WaveLight; Zyoptix, Bausch & Lomb) in low to moderate myopia, although data in cases of high myopia are scarce.⁵, ⁶, ⁷, ⁸, ⁹, ¹⁰, ¹¹ Unfortunately, LASIK has risks, especially in eyes with high myopia. Eyes with high myopia are at increased risk for ectasia, may have decreased visual and refractive outcomes, and have increased reoperation rates. In addition, wavefront-guided ablations consume greater amounts of corneal tissue than conventional lasers for a given refractive error. With proper preoperative screening and intraoperative pachymetry evaluations, such complications can be reduced.¹²

The purpose of this study was to evaluate the predictability, safety, efficacy, complications, and change in ocular aberrations after wavefront-guided LASIK in patients with moderate or high myopia and compound myopic astigmatism.

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Patients and methods 

Study Design 

This retrospective single-surgeon study examined 89 eyes of 45 healthy patients who were treated with wavefront-guided LASIK surgery using the Visx Star S4 excimer laser with software version 5.18 and the Visx WaveScan aberrometer with software version 3.67 (AMO USA, Inc.).

Enrollment Criteria 

A group of patients with moderate to high myopia was retrospectively selected from a large group of myopic eyes consecutively treated with the wavefront-guided platform. The inclusion criterion for patient selection was myopia of −6.0 diopters [D] or more. Patients with myopia less than −6.0 D were excluded. The patient population was further divided in 2 groups: moderate myopia (−6.0 to −8.0 D) and high myopia (greater than −8.0 D).

Clinical Outcome Measures 

In addition to general medical and ophthalmic histories, preoperative measures included uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), manifest spherical refraction, cycloplegic refraction, ultrasonic pachymetry (Advent Pachymeter, Mentor O & O, Inc.), corneal topography (Orbscan, Bausch & Lomb), slitlamp examination of the anterior segment, and fundoscopy. Analysis of HOAs was performed using the Visx WaveScan aberrometer. The safety index was defined as the mean postoperative BCVA divided by the mean preoperative BCVA and the efficacy index, as the mean postoperative UCVA divided by the mean preoperative BCVA.¹³

Wavefront aberrations were measured with an undilated pupil (larger than 6.0 mm) in scotopic conditions at all preoperative and postoperative visits. To assess aberrometry readings, 3 readings of each eye were taken on each visit before and after surgery. The best acquisition of the 3 readings was determined by the clearest centroid image. The aberrometry image that closely matched the manifest refraction was selected. The best-acquired image was used as a standard study analysis for the aberrometry data before and after LASIK. The maximum allowed ablation depth was calculated as follows: [(total corneal thickness) − (planned flap thickness) − (minimum allowed residual bed thickness)]. The diameter treatment zone was set as wide as possible for the maximum allowed ablation depth in reference to corneal thickness and pupil diameter.

After topical anesthesia was administered, a flap of approximately 110 μm was created with a femtosecond laser (IntraLase, Inc.). The laser operated at a 15 kHz treatment rate. A superior hinge location with a flap diameter of 9.2 mm was used in all cases. Wavefront-based excimer laser treatment with the Visx WaveScan aberrometer was used (AMO USA Inc.). The WaveScan uses a Hartmann-Shack aberrometer for wavefront capture, in which light rays are projected into the eye and data are analyzed to measure aberrations. Data are then imported into the Visx Star S4 machine, and the corresponding laser ablation is performed by a variable size and shape beam (1.0 to 6.0 mm) using a 60 Hz eye tracker with a built-in iris registration platform. A minimum post-LASIK stromal bed of 300 μm was left in all cases, which was confirmed by intraoperative pachymetry testing. The flap and stromal bed were then irrigated with a balanced salt solution and dried for approximately 2 minutes.

Postoperatively, patients were instructed to instill gatifloxacin 4 times daily for 4 days and prednisolone acetate 1% 4 times daily for 7 days. Postoperative follow-up examinations were at 1 day, 1 week, and 1, 3, and 12 months. The 1-, 3-, and 12-month data are presented here.

Statistical Analysis 

Patient data were compiled in Microsoft Excel. Statistical significance was calculated using the Student t test (P<.05). Data are expressed as means ± standard deviation and ranges (minimum to maximum). For safety and efficacy, visual acuity was calculated using the logMAR scale for each individual eye and subsequently reconverted to the respective Snellen fraction.

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Results 

Demographics and Refractive Error 

The moderate myopia group comprised 44 eyes (49.4% of patient population) and the high myopia group, 45 eyes (50.6%). Eighty-nine eyes of 45 patients were followed for 3 months and 50 eyes of 25 patients, for 12 months. The mean age of patients was 38.4 ± 7.14 years (range 26 to 58 years). Table 1 shows the preoperative demographic and refractive data for all 89 eyes.

Table 1. Preoperative demographic and refractive information.

Demographic	Eyes at 3 Months (n = 89)	Eyes at 12 Months (n = 50)
Sex, n (%)
Male	19 (42.2)	10 (40.0)
Female	26 (57.8)	15 (60.0)
Eye, n (%)
Right	44 (49.4)	25 (50.0)
Left	45 (50.6)	25 (50.0)
Age (y)
Mean ± SD	38.4 ± 7.14	39.6 ± 8.47
Range	26–58	26–58
Preoperative refractive data
Spherical correction (D)
Mean ± SD	−8.48 ± 1.11	−8.33 ± 0.97
Range	−6.50 to −12.25	−6.50 to −10.00
Cylinder (D)
Mean ± SD	0.76 ± 0.71	0.75 ± 0.56
Range	0.00 to 3.50	0.00 to 2.75
MRSE (D)
Mean ± SD	−8.10 ± 0.98	−7.95 ± 0.96
Range	−6.00 to −10.63	−6.00 to −9.85
Postoperative refractive data
Spherical correction (D)
Mean ± SD	0.38 ± 0.54	−0.51 ± 0.58
Range	−2.00 to 1.75	−1.75 to 1.00
Cylinder (D)
Mean ± SD	0.34 ± 0.38	0.34 ± 0.38
Range	0.00 to 1.25	−0.25 to 2.25
MRSE (D)
Mean ± SD	−0.24 ± 0.38	−0.34 ± 0.55
Range	−1.87 to 1.75	−1.62 to 1.37

MRSE = mean refractive spherical equivalent

Table 2 shows the preoperative refractive error by sphere and cylinder. Preoperatively, the mean spherical correction in all 89 eyes was −8.48 ± 1.11 D (range −6.50 to −12.25 D), the mean cylinder was 0.76 ± 0.71 D (range 0.0 to 3.5 D), and the mean manifest refraction spherical equivalent (MRSE) was −8.10 ± 0.98 D (range −6.00 to −10.63 D).

Table 2. Preoperative refractive error stratified by sphere and cylinder, all eyes (N = 89).

Predictability 

Twelve months postoperatively, the mean spherical correction in 50 eyes was −0.51 ± 0.58 D (range −1.75 to 1.00 D) and the mean cylinder was 0.34 ± 0.38 D (range −0.25 to 2.25 D). The mean MRSE was −0.33 ± 0.55 D (range −1.625 to 1.375 D) (Figure 1).

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• Figure 1 

  Attempted vs achieved change in MRSE (Δ MRSE) 12 months after wavefront-guided LASIK (predictability).

Stability 

Figure 2 shows the stability outcomes. Between 1 month and 3 months, the change in MRSE from emmetropia was within ±1.00 D of the intended correction in 39 (88.6%) of the 44 eyes in the moderate myopia group and all 45 eyes in the high myopia group. Of all eyes at 3 months, 94.4% were within ±1.00 D of the intended correction and 74.2% were within ±0.50 D. Between 3 months and 12 months, the change in MRSE from emmetropia was within ±1.00 D of the intended correction in 20 (83.3%) of 24 eyes in the moderate myopia group and 25 (96.2%) of 26 in the high myopia group. Of all eyes at 12 months, 90% were within ±1.00 D of the intended correction and 64.0% were within ±0.50 D.

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• Figure 2 

  Change in MRSE over time. Error bars indicate 1 standard deviation (stability).

Safety 

Twelve months after surgery, 11 (45.8%) of 24 eyes in the moderate myopia group had improved BCVA and 13 (54.2%) had BCVA similar to the preoperative BCVA. No eye in the moderate myopia group lost 1 or more lines of visual acuity. Sixteen (61.5%) of 26 eyes in the high myopia group had improved BCVA, and 7 (26.9%) had BCVA similar to the preoperative BCVA (Figure 3 and Table 3). Three eyes (11.5%) in the high myopia group lost 1 line of acuity; no eye lost 2 or more lines. The safety index (ratio of postoperative and preoperative BCVA) in all eyes at 12 months was 1.00.

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• Figure 3 

  Distribution of the BCVA 12 months postoperatively after wavefront-guided LASIK in both moderate and high myopia (safety).

Table 3. Change in postoperative BCVA in the moderate and high myopia groups at 12 months.

Efficacy 

Figure 4 compares the UCVA preoperatively and 12 months postoperatively. At 12 months, 17 (70.8%) of 24 eyes in the moderate myopia group had a UCVA better than or equal to 20/20, and 24 eyes (100%) had a UCVA better than or equal to 20/40. In the high myopia group, 15 (57.7%) of 26 eyes had a UCVA better than or equal to 20/20 and all 26 eyes (100%) had a UCVA better than or equal to 20/40. Furthermore, 27 of the total 50 eyes (54.0%) had a postoperative UCVA that was equal to or better than the preoperative BCVA. The efficacy index (ratio of postoperative UCVA and preoperative BCVA) in all eyes at 3 months was 1.18.

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• Figure 4 

  Distribution of the UCVA preoperatively and 12 months after wavefront-guided LASIK in both moderate and high myopia (efficacy).

Higher-Order Wavefront Aberrations 

Table 4 shows the HOA parameters, including total HOA root mean square (RMS), coma, trefoil, spherical aberration, and axis of astigmatism in the moderate and high myopia groups preoperatively and 3 months postoperatively. Table 5 shows the same parameters preoperatively and at 12 months. Measurements were taken at the 6.0 mm optical zone without dilation. The mean preoperative total HOA RMS error in all eyes was 0.34 ± 0.17 μm. The error was increased by a factor of 1.55 to 0.53 ± 0.20 μm after 3 months (P<.001) and by a factor of 1.59 to 0.54 ± 0.25 μm after 12 months (P<.001). A small but significant increase in coma and spherical aberration was observed in the moderate myopia and high myopia groups at 3 months and 12 months (Table 4, Table 5, respectively). Trefoil and axis of astigmatism values decreased in both the moderate and high myopia groups at 3 months and 12 months.

Table 4. Root mean square parameters before and after surgery in the moderate myopia and high myopia groups at 3 months.

HOA = higher-order aberration; RMS = root mean square

Table 5. Root mean square parameters before and after surgery in the moderate myopia and high myopia groups at 12 months.

HOA = higher-order aberration; RMS = root mean square

Complications 

No flap complications (epithelial defects, microstriae, or macrostriae) were observed. No eye developed epithelial ingrowth. There was no topographic evidence of ectasia.

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Discussion 

Our retrospective review of patients supports that the new commercially available wavefront-guided LASIK procedure is predictable, safe, and effective. At 12 months, more than 92% of eyes with moderate myopia and more than 81% with high myopia had similar or better postoperative BCVA than preoperatively. Furthermore, 18 (75.0%) of 24 eyes with moderate myopia and 25 (96.2%) of 26 with high myopia were within ±1.00 D of the intended correction at 12 months.

Our postoperative results are consistent with the U.S. Food and Drug Administration's (FDA) summary of safety and effectiveness data for the Visx ophthalmic excimer laser system (http://www.fda.gov/cdrh/pdf/P930016s021b.pdf. Accessed October 3, 2007). In that report, 184 eyes had a preoperative MRSE ranging between −5.0 D and −12.0 D. Twelve months postoperatively, 95.3% of eyes (102 of 107) in the FDA report were within ±1.0 D of the intended spherical correction compared with 90.0% (45 of 50) in our study. Furthermore, 12 months postoperatively, the FDA report showed that 86.0% of all eyes had a UCVA better than or equal to 20/20 and all had a UCVA better than or equal to 20/40, compared with 64.0% and 100% of total eyes, respectively, in our study. These comparisons show that the wavefront-guided LASIK procedure is predictable and effective in cases of moderate to high myopia.

Wavefront-guided LASIK ablations may yield superior results compared with the results of conventional LASIK ablations.⁶, ¹⁴, ¹⁵, ¹⁶ However, confounding variables prevent a true side-by-side comparison of the 2 technologies. One issue is the optical zone treatment diameter. Most conventional LASIK ablations use smaller ablation diameters than used in wavefront LASIK ablations. A larger ablation diameter can independently influence the effect of LASIK on HOAs. In addition, most conventional LASIK ablations do not use blend zones. The blend zones used in wavefront-guided ablations can also influence outcomes. A true comparison between wavefront-guided LASIK and conventional LASIK would have to control for these important variables.

Changes in HOAs, notably spherical aberrations, are observed postoperatively with conventional LASIK and photorefractive keratectomy (PRK).¹⁷, ¹⁸ Customized ablation such as wavefront-guided LASIK was designed to help minimize postoperative HOAs. Despite limited evidence that wavefront-guided laser ablation has notably better outcomes than conventional treatment,¹⁹ it is evident that wavefront-guided laser procedures induce fewer aberrations than conventional treatments, suggesting improved vision quality.²⁰, ²¹ Recent studies show that wavefront-guided LASIK induces increases in HOAs, especially spherical aberration, although the increases are minimal.²², ²³ Furthermore, increases in HOAs have been documented with various wavefront-guided or optimized LASIK platforms such as the Visx Star S4, LADARVision 4000, WaveLight Allegretto, and Zyoptix.⁸, ⁹, ¹⁰, ¹¹ It is also important to note that creating a LASIK flap has been shown to increase HOAs in previous studies,²⁴, ²⁵, ²⁶, ²⁷ but it is still unclear whether this translates into a good measure of visual performance.²³ Our study is consistent with the literature in that we reveal an increase in total HOA RMS, coma, and spherical aberration at 12 months postoperatively in both moderate and high myopia groups. Although the postoperative trefoil and axis of astigmatism values decreased in both the moderate and high myopia groups, the overall total HOA RMS increased.

A limitation to our HOA analysis is that we did not control for pupil size in preoperative and postoperative measurements. Spherical-like aberrations have been shown to increase significantly with increasing pupil size in unoperated corneas.²⁸ In our study, all eyes had pupils of at least 6.0 mm in diameter preoperatively and postoperatively, and the lighting conditions for aberrometry images were identical for all preoperative and postoperative measurements (3 lux). Based on the minimum pupil size and standardized lighting conditions, we believe our data are worth reporting in this study.

Our retrospective review supports the use of wavefront-guided LASIK procedures in selected patients with high myopia. However, not all patients, especially those with high myopia, are candidates for wavefront-guided LASIK. In these cases, surgeons can offer alternative procedures that may be suitable, such as wavefront-guided PRK, conventional LASIK or PRK, phakic intraocular lenses, or clear lens extraction. Surgeons should be aware of such alternatives to wavefront-guided LASIK, although further discussion of these procedures and their benefits to wavefront-guided LASIK in selected cases is outside the scope of our study.

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References 

1. Awwad ST, McCulley JP. Wavefront-guided LASIK: recent developments and results. Int Ophthalmol Clin. 2006;46(3):27–38
   • View In Article
   • MEDLINE
   • CrossRef
2. Kaiserman I, Hazarbassanov R, Varssano D, Grinbaum A. Contrast sensitivity after wave front-guided LASIK. Ophthalmology. 2004;111:454–457
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (111 KB)
   • CrossRef
3. 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 Opt Image Sci Vis. 1994;11:1949–1957
   • View In Article
   • MEDLINE
   • CrossRef
4. Liang J, Williams DR, Miller DT. Supernormal vision and high-resolution retinal imaging through adaptive optics. J Opt Soc Am A Opt Image Sci Vis. 1997;14:2884–2892
   • View In Article
   • MEDLINE
   • CrossRef
5. Mrochen M, Kaemmerer M, Seiler T. Clinical results of wavefront-guided laser in situ keratomileusis 3 months after surgery. J Cataract Refract Surg. 2001;27:201–207
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (219 KB)
   • CrossRef
6. Nuijts RMMA, Nabar VA, Hament WJ, Eggink FAGJ. Wavefront-guided versus standard laser in situ keratomileusis to correct low to moderate myopia. J Cataract Refract Surg. 2002;28:1907–1913
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (155 KB)
   • CrossRef
7. Aizawa D, Shimizu K, Komatsu M, et al. Clinical outcomes of wavefront-guided laser in situ keratomileusis: 6-month follow-up. J Cataract Refract Surg. 2003;29:1507–1513
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (344 KB)
   • CrossRef
8. Kohnen T, Bühren J, Kühne C, Mirshahi A. Wavefront-guided LASIK with the Zyoptix 3.1 system for the correction of myopia and compound myopic astigmatism with 1-year follow-up; clinical outcome and change in higher order aberrations. Ophthalmology. 2004;111:2175–2185
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (251 KB)
   • CrossRef
9. Binder PS, Rosenshein J. Retrospective comparison of 3 laser platforms to correct myopic spheres and spherocylinders using conventional and wavefront-guided treatments. J Cataract Refract Surg. 2007;33:1158–1176
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (1142 KB)
   • CrossRef
10. Brint SF. Higher order aberrations after LASIK for myopia with Alcon and WaveLight lasers: a prospective randomized trial. J Refract Surg. 2005;21:S799–S803
    • View In Article
    • MEDLINE
11. Tran DB, Shah V. Higher order aberrations comparison in fellow eyes following IntraLase LASIK with WaveLight Allegretto and CustomCornea LADARVision4000 systems. J Refract Surg. 2006;22:S961–S964
    • View In Article
    • MEDLINE
12. Condon PI, O'Keefe M, Binder PS. Long-term results of laser in situ keratomileusis for high myopia: risk for ectasia. J Cataract Refract Surg. 2007;33:583–590
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (453 KB)
    • CrossRef
13. Koch DD, Kohnen T, Obstbaum SA, Rosen ES. Format for reporting refractive surgical data. [editorial] J Cataract Refract Surg. 1998;24:285–287
    • View In Article
    • MEDLINE
14. Phusitphoykai N, Tungsiripat T, Siriboonkoom J, Vongthongsri A. Comparison of conventional versus wavefront-guided laser in situ keratomileusis in the same patient. J Refract Surg. 2003;19:S217–S220
    • View In Article
15. Vongthongsri A, Phusitphoykai N, Naripthapan P. Comparison of wavefront-guided customized ablation vs. conventional ablation in laser in situ keratomileusis. J Refract Surg. 2002;18:S332–S335
    • View In Article
    • MEDLINE
16. Sugar A, Rapuano CJ, Culbertson WW, et al. Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy (Ophthalmic Technology Assessment). A report by the American Academy of Ophthalmology. Ophthalmology. 2002;109:175–187
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (134 KB)
    • CrossRef
17. Moreno-Barriuso E, Merayo Lloves J, Marcos S, et al. Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing. Invest Ophthalmol Vis Sci. 2001;42:1396–1403
    • View In Article
    • MEDLINE
18. Oliver KM, Hemenger RP, Corbett MC, et al. Corneal optical aberrations induced by photorefractive keratectomy. J Refract Surg. 1997;13:246–254
    • View In Article
    • MEDLINE
19. Netto MV, Dupps W, Wilson SE. Wavefront-guided ablation: evidence for efficacy compared to traditional ablation. Am J Ophthalmol. 2006;141:360–368
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (171 KB)
    • CrossRef
20. Chalita MR, Chavala S, Xu M, Krueger RR. Wavefront analysis in post-LASIK eyes and its correlation with visual symptoms, refraction, and topography. Ophthalmology. 2004;111:447–453
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (136 KB)
    • CrossRef
21. Kim T-I, Yang S-J, Tchah H. Bilateral comparison of wavefront-guided versus conventional laser in situ keratomileusis with Bausch and Lomb Zyoptix. J Refract Surg. 2004;20:432–438
    • View In Article
    • MEDLINE
22. Chung S-H, Lee IS, Lee YG, et al. Comparison of higher-order aberrations after wavefront-guided laser in situ keratomileusis and laser-assisted subepithelial keratectomy. J Cataract Refract Surg. 2006;32:779–784
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (149 KB)
    • CrossRef
23. Applegate RA, Marsack JD, Ramos R, Sarver EJ. Interaction between aberrations to improve or reduce visual performance. J Cataract Refract Surg. 2003;29:1487–1495
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (310 KB)
    • CrossRef
24. Pallikaris IG, Kymionis GD, Panagopoulou SI, et al. Induced optical aberrations following formation of a laser in situ keratomileusis flap. J Cataract Refract Surg. 2002;28:1737–1741
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (117 KB)
    • CrossRef
25. Porter J, MacRae S, Yoon G, et al. Separate effects of the microkeratome incision and laser ablation on the eye's wave aberration. Am J Ophthalmol. 2003;136:327–337
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (649 KB)
    • CrossRef
26. Potgieter FJ, Roberts C, Cox IG, et al. Prediction of flap response. J Cataract Refract Surg. 2005;31:106–114
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (381 KB)
    • CrossRef
27. Waheed S, Chalita MR, Xu M, Krueger RR. Flap-induced and laser-induced ocular aberrations in a two-step LASIK procedure. J Refract Surg. 2005;21:346–352
    • View In Article
    • MEDLINE
28. Wang Y, Zhao K, Jin Y, et al. Changes of higher order aberration with various pupil sizes in the myopic eye. J Refract Surg. 2003;19:S270–S274
    • View In Article
    • MEDLINE

First author:

Simon R. Bababeygy

Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA