Purpose
To compare postoperative visual function after implantable collamer lens (ICL) implantation and after wavefront-guided laser in situ keratomileusis (LASIK) in eyes with low to moderate myopia.
Design
Retrospective observational case study.
Patients and Methods
We investigated 30 eyes of 20 patients undergoing ICL implantation and 64 eyes of 38 patients undergoing wavefront-guided LASIK for the correction of low to moderate myopia (manifest spherical equivalent: −3.00 to −5.88 diopters [D]). Ocular higher-order aberrations (HOAs) and contrast sensitivity (CS) function were measured by Hartmann-Shack aberrometry and a contrast sensitivity unit before and 3 months after surgery, respectively. From the contrast sensitivity, the area under the log contrast sensitivity function was calculated.
Results
For 4-mm and 6-mm pupils, the changes in ocular third-order aberrations, fourth-order aberrations, and total HOAs after ICL implantation were significantly less than those after wavefront-guided LASIK ( P < .05, Mann-Whitney U test). The postoperative area under the log contrast sensitivity function was significantly increased after ICL implantation ( P < .001), whereas, after wavefront-guided LASIK, it was not significantly changed ( P = .11).
Conclusions
ICL implantation induces significantly fewer ocular HOAs than wavefront-guided LASIK. Moreover, CS was significantly improved after ICL implantation but unchanged after wavefront-guided LASIK in eyes with low to moderate myopia. Thus, even in the correction of low to moderate myopia, ICL implantation appears to be superior in visual performance to wavefront-guided LASIK, suggesting that it may be a viable surgical option for the treatment of such eyes.
Wavefront-guided laser in situ keratomileusis (LASIK) is becoming widely accepted as an effective method for the correction of myopia. However, patients with thin corneas face some restrictions in avoiding the risk of developing keratectasia. Moreover, a large amount of laser ablation may lead to the deterioration of superior intrinsic corneal optical performance. The Visian Implantable Collamer Lens (ICL) (STAAR Surgical, Nidau, Switzerland), a posterior chamber phakic intraocular lens (IOL), has been reported to be effective for the correction of moderate to high ametropia. As LASIK requires more laser ablation, the cornea becomes more oblate, resulting in more surgically induced higher-order aberrations (HOAs), especially spherical aberrations. It has already been demonstrated that ICL implantation is better than LASIK in all measures of safety, efficacy, predictability, and stability, not only in eyes with moderate to high myopia but also in eyes with low myopia. Considering that ICL implantation does not require surgical tissue abstraction and leaves the central cornea untouched, ICL implantation may have advantages over LASIK with respect to HOA induction, which may compromise the contrast sensitivity (CS) function after surgery, even in low to moderate myopic eyes. Both HOAs and CS play an important role in the refractive outcomes and the patient satisfaction after these surgical procedures. The purpose of the present study is to compare HOAs and CS after ICL implantation and after wavefront-guided LASIK for the correction of low to moderate myopia.
Patients and Methods
Thirty eyes (13 of men and 17 of women) of 20 patients who underwent implantation of the posterior chamber phakic ICL (STAAR Surgical) and 64 eyes (26 of men and 38 of women) of 38 patients who underwent wavefront-guided LASIK for the correction of low to moderate myopia (manifest spherical equivalent: −3.00 to −5.88 diopters [D]) were included in this retrospective observational study. The sample size in this study offered 92% statistical power at the 5% level in order to detect a 0.15-μm difference in HOAs between the 2 groups when the standard deviation (SD) of the mean difference was 0.2 μm, and offered 85% statistical power at the 5% level in order to detect a 0.10-difference in the area under the log contrast sensitivity function between the 2 groups when the SD of the mean difference was 0.15. The patient ages at the time of surgery were 30.9 ± 7.6 years (mean age ± standard deviation; range, 19 to 46 years) in the ICL group and 31.9 ± 5.2 years (range, 17 to 43 years) in the wavefront-guided LASIK group. The preoperative manifest spherical equivalents were −4.79 ± 0.93 D (range, −3.00 to −5.88 D) in the ICL group and −4.65 ± 0.84 D (range, −3.00 to −5.88 D) in the wavefront-guided LASIK group. The preoperative manifest refractive cylinders were 1.11 ± 1.08 D (range: 0.00 to 3.00 D) in the ICL group and 0.98 ± 0.85 D (range, 0.00 to 3.25 D) in the wavefront-guided LASIK group. In the ICL group, we selected non-toric ICL in 20 eyes (67%) with the manifest cylinder of 1.25 D or less and toric ICL in 10 eyes (33%) with manifest cylinder of 1.5 D or more. Eyes with keratoconus were excluded from the study by using the keratoconus screening test of Placido disc videokeratography (TMS-2; Tomey, Nagoya, Japan).
Implantable Collamer Lens Power Calculation
ICL power calculations were performed by the manufacturer (STAAR Surgical) using a modified vertex formula. Toric ICL power calculation was performed by the manufacturer using the astigmatism decomposition method. The size of the ICL was also chosen by the manufacturer based on the horizontal corneal diameter and anterior chamber depth measured with scanning-slit topography (Orbscan IIz; Bausch & Lomb, Rochester, New York, USA).
Implantable Collamer Lens Surgical Procedure
The patients preoperatively underwent 2 peripheral iridectomies with a neodymium-yttrium-aluminum-garnet laser. On the day of surgery, the patients were given dilating and cycloplegic agents. After topical anesthesia, a model V4 ICL was inserted through a 3-mm clear corneal incision with the use of an injector cartridge (STAAR Surgical) after placement of a viscosurgical device (Opegan; Santen, Osaka, Japan) into the anterior chamber. The ICL was placed in the posterior chamber, the remaining viscosurgical device was completely washed out of the anterior chamber with balanced salt solution, and a miotic agent was instilled. For toric ICL implantation, to control for potential cyclotorsion in a supine position, the zero horizontal axis was marked preoperatively using a slit lamp. A Mendez ring was also used for measuring intraoperatively the required rotation from the horizontal axis. After the ICL had been placed in the posterior chamber, rotated by 22.5 degrees or less using the manipulator. After surgery, steroidal (0.1% betamethasone; Rinderon, Shionogi, Osaka, Japan) and antibiotic (levofloxacin, Cravit; Santen) medications were administered topically 4 times daily for 2 weeks, and the dose was steadily reduced thereafter.
Wavefront-Guided Laser in Situ Keratomileusis Surgical Procedure
Wavefront-guided LASIK was performed with the Technolas 217z excimer laser system (Bausch & Lomb) using a wavefront-guided ablation algorithm (Zyoptix, version 3.1) to apply a flying spot of 1.0 or 2.0 mm in diameter with a Gaussian profile and a 120-Hz active eye tracker. The LSK-1 microkeratome (Moria, Antony, France) was used for creating a hinged corneal flap of 130-μm thickness. After surgery, steroidal (0.1% fluorometholone, Flumetholone; Santen) and antibiotic (Cravit; Santen) medications were topically administered 4 times daily for 2 weeks.
Assessment of Visual Acuity, Ocular Higher-order Aberrations, and Contrast Sensitivity
We assessed logMAR (logarithm of the minimal angle of resolution) uncorrected visual acuity (UCVA), logMAR best spectacle-corrected visual acuity (BSCVA), wavefront aberrations, and CS function before and 3 months after surgery. Ocular HOAs for a 4-mm pupil were measured by Hartmann-Shack aberrometry (KR-9000, Topcon, Tokyo, Japan). The root mean square of the third-order Zernike coefficients was used to represent third-order aberrations, and the root mean square of the fourth-order coefficient to represent fourth-order aberrations. Total HOAs were calculated as the root mean square of the third- and fourth-order coefficients. CS function was also measured by contrast sensitivity unit (VCTS-6500; Vistech, Dayton, Ohio, USA) under photopic conditions. The test was performed with best spectacle correction at 2.5 m. From the contrast sensitivity, the area under the log contrast sensitivity function was determined as described previously. In brief, the log of contrast sensitivity was plotted as a function of log spatial frequency, and third-order polynomials were fitted to the data. The fitted function was integrated between the fixed limits of log spatial frequencies of 0.18 (corresponding to 1.5 cycles/degree) and 1.26 (corresponding to 18 cycles/degree), and the resultant value was defined as the area under the log contrast sensitivity function. All examinations were performed by 2 experienced ophthalmic technicians.
Statistical Analysis
All statistical analyses were performed using StatView software version 5.0 (SAS, Cary, North Carolina, USA). The Wilcoxon signed rank test was used for statistical analysis to compare the pre- and post-treatment data. The Mann-Whitney U test was used to compare the data between the 2 groups. The results are expressed as mean ± SD, and a value of P < .05 was considered statistically significant.
Results
Patient Population
Preoperative patient demographics are summarized in Table 1 . There were no significant differences between the 2 groups in terms of age ( P = .14, Mann-Whitney U test), sex ( P = .59), manifest spherical equivalent ( P = .34), manifest cylinder ( P = .83), logMAR UCVA ( P = .55), logMAR BSCVA ( P = .38), HOAs ( P = .12 for third-order aberrations, P = .27 for fourth-order aberrations, P = .12 for total HOAs for a 4-mm pupil), or area under the log contrast sensitivity function ( P = .09). All surgeries were uneventful, and no vision-threatening complications were seen throughout the observation period.
| ICL Group | Wavefront-Guided LASIK Group | P Value | |
|---|---|---|---|
| Age | 30.9 ± 7.6 years (range, 19 to 46 years) | 31.9 ± 5.2 years (range, 17 to 43 years) | .14 |
| Sex (% female) | 56.6% | 59.4% | .59 |
| Manifest spherical equivalent | −4.79 ± 0.93 D (range, −3.00 to −5.88 D) | −4.65 ± 0.84 D (range, −3.00 to −5.88 D) | .34 |
| Manifest cylinder | 1.11 ± 1.08 D (range, 0.00 to 3.00 D) | 0.98 ± 0.85 D (range, 0.00 to 3.25 D) | .83 |
| logMAR UCVA | 1.14 ± 0.16 (range, 0.70 to 1.40) | 1.17 ± 0.13 (range, 0.70 to 1.40) | .55 |
| logMAR BSCVA | −0.17 ± 0.07 (range, −0.30 to 0.00) | −0.18 ± 0.06 (range, −0.30 to 0.00) | .38 |
| Third-order aberrations (4 mm) | 0.09 ± 0.05 μm (range, 0.02 to 0.25 μm) | 0.10 ± 0.04 μm (range, 0.04 to 0.25 μm) | .12 |
| Fourth-order aberrations (4 mm) | 0.04 ± 0.02 μm (range, 0.01 to 0.08 μm) | 0.05 ± 0.03 μm (range, 0.01 to 0.15 μm) | .27 |
| Total HOAs (4 mm) | 0.10 ± 0.05 μm (range, 0.04 to 0.24 μm) | 0.11 ± 0.04 μm (range, 0.05 to 0.25 μm) | .12 |
| CS (area under the log CS function) | 1.44 ± 0.16 (range, 0.88 to 1.64) | 1.49 ± 0.12 (range, 1.14 to 1.68) | .09 |
Visual Acuity and Refraction
LogMAR UCVA improved significantly, from 1.14 ± 0.16 (range, 0.70 to 1.40) preoperatively to −0.16 ± 0.12 (range, −0.30 to 0.10) postoperatively, in the ICL group ( P < .001, Wilcoxon signed rank test). LogMAR UCVA also improved significantly, from 1.17 ± 0.13 (range, 0.70 to 1.40) preoperatively to −0.15 ± 0.08 (range, −0.30 to 0.10) postoperatively, in the wavefront-guided LASIK group ( P < .001). logMAR BSCVA was significantly improved, from −0.17 ± 0.07 (range, −0.30 to 0.00) preoperatively to −0.22 ± 0.07 (range, −0.30 to 0.00) postoperatively, in the ICL group ( P = .005). LogMAR BSCVA was changed, but not significantly, from −0.18 ± 0.06 (range, −0.30 to 0.00) preoperatively to −0.20 ± 0.06 (range, −0.30 to −0.08) postoperatively, in the wavefront-guided LASIK group ( P = .06). We found no significant differences in logMAR UCVA ( P = .32, Mann-Whitney U test) or logMAR BSCVA ( P = .07) 3 months postoperatively between the 2 groups. In the ICL group, 16 of 30 eyes (53%) showed no change in BSCVA, 11 eyes (37%) gained 1 line, 2 eyes (7%) gained 2 lines, 1 eye (3%) lost 1 line, and no eyes lost 2 lines or more, while in the wavefront-guided LASIK group, 43 of 64 eyes (67%) exhibited no change in BSCVA, 11 eyes (17%) gained 1 line, 1 eye (2%) gained 2 lines, 9 eyes (14%) lost 1 line, and no eyes lost 2 lines or more.
The manifest spherical equivalent changed significantly, from −4.79 ± 0.93 D (range, −3.00 to −5.88 D) preoperatively to −0.05 ± 0.24 D (range, −0.50 to 0.50 D) postoperatively, in the ICL group ( P < .001, Wilcoxon signed rank test). It also changed significantly, from −4.65 ± 0.84 D (range, −3.00 to −5.88 D) preoperatively to 0.13 ± 0.32 D (range, −0.75 to 1.00 D) postoperatively, in the wavefront-guided LASIK group ( P < .001). The manifest cylinder changed significantly, from 1.11 ± 1.08 D (range, 0.00 to 3.00 D) preoperatively to 0.39 ± 0.37 D (range, 0.00 to 1.00 D) postoperatively, in the ICL group ( P < .001). It also changed significantly, from 0.98 ± 0.85 D (range, 0.00 to 3.25 D) preoperatively to 0.34 ± 0.25 D (range, 0.00 to 0.75 D) postoperatively, in the wavefront-guided LASIK group ( P < .001).
Ocular Higher-order Aberrations
Preoperative and postoperative HOAs for 4-mm and 6-mm pupils are summarized in Table 2 . The inductions of third-order aberrations, fourth-order aberrations, and total HOAs were 0.02 ± 0.04 μm (range, −0.08 to 0.11 μm), 0.01 ± 0.01 μm (range, −0.03 to 0.03 μm), and 0.02 ± 0.04 μm (range, −0.10 to 0.11 μm) after ICL implantation, respectively ( Figure 1 ) . On the other hand, the inductions of third-order aberrations, fourth-order aberrations, and total HOAs were 0.14 ± 0.12 μm (range, −0.23 to 0.44 μm), 0.06 ± 0.05 μm (range, −0.07 to 0.17 μm), and 0.16 ± 0.11 μm (range, −0.24 to 0.44 μm) after wavefront-guided LASIK, respectively ( Figure 1 ). For a 4-mm pupil, the changes in third-order aberrations, fourth-order aberrations, and total HOAs after ICL implantation were significantly less than those after wavefront-guided LASIK ( P < .001, Mann-Whitney U test).
| ICL Group | Wavefront-Guided LASIK Group | |||
|---|---|---|---|---|
| Pre | Post | Pre | Post | |
| Third-order aberrations (4 mm, μm) | 0.09 ± 0.05 (range, 0.03 to 0.21) | 0.11 ± 0.06 (range, 0.03 to 0.28) | 0.10 ± 0.04 (range, 0.04 to 0.25) | 0.16 ± 0.07 (range, 0.08 to 0.46) |
| Fourth-order aberrations (4 mm, μm) | 0.04 ± 0.02 (range, 0.01 to 0.08) | 0.05 ± 0.02 (range, 0.02 to 0.09) | 0.05 ± 0.03 (range, 0.01 to 0.15) | 0.09 ± 0.04 (range, 0.03 to 0.19) |
| Total HOAs (4 mm, μm) | 0.10 ± 0.05 (range, 0.04 to 0.24) | 0.12 ± 0.06 (range, 0.05 to 0.29) | 0.11 ± 0.04 (range, 0.05 to 0.25) | 0.18 ± 0.07 (range, 0.10 to 0.47) |
| Third-order aberrations (6 mm, μm) | 0.25 ± 0.13 (range, 0.05 to 0.59) | 0.35 ± 0.17 (range, 0.15 to 0.82) | 0.32 ± 0.12 (range, 0.12 to 0.60) | 0.50 ± 0.20 (range, 0.21 to 1.54) |
| Fourth-order aberrations (6 mm, μm) | 0.16 ± 0.06 (range, 0.08 to 0.30) | 0.20 ± 0.09 (range, 0.06 to 0.37) | 0.20 ± 0.07 (range, 0.04 to 0.35) | 0.48 ± 0.16 (range, 0.19 to 0.95) |
| Total HOAs (6 mm, μm) | 0.30 ± 0.12 (range, 0.11 to 0.60) | 0.41 ± 0.17 (range, 0.19 to 0.86) | 0.38 ± 0.12 (range, 0.14 to 0.67) | 0.71 ± 0.21 (range, 0.37 to 1.63) |
The inductions of third-order aberrations, fourth-order aberrations, and total HOAs were 0.10 ± 0.11 μm (range, −0.09 to 0.38 μm), 0.04 ± 0.07 μm (range, −0.05 to 0.22 μm), and 0.11 ± 0.12 μm (range, −0.09 to 0.37 μm) after ICL implantation, respectively ( Figure 2 ) . On the other hand, the inductions of third-order aberrations, fourth-order aberrations, and total HOAs were 0.18 ± 0.22 μm (range, −0.09 to 0.96 μm), 0.28 ± 0.14 μm (range, 0.00 to 0.65 μm), and 0.33 ± 0.21 μm (range, −0.04 to 1.00 μm) after wavefront-guided LASIK, respectively ( Figure 2 ). For a 6-mm pupil, the changes in third-order aberrations ( P = .02, Mann-Whitney U test), fourth-order aberrations ( P < .001), and total HOAs ( P < .001) after ICL implantation are also significantly less than those after wavefront-guided LASIK.
There was no significant correlation between the induction of the fourth-order aberrations and the manifest spherical equivalent correction in eyes undergoing ICL implantation (Pearson correlation coefficient r = −0.04, P = .85 for a 4-mm pupil, r = −0.03, P = .88 for a 6-mm pupil). On the other hand, there was a significant correlation between the induction of the fourth-order aberrations and the spherical equivalent correction in eyes undergoing wavefront-guided LASIK (r = 0.27, P = .03 for a 4-mm pupil; r = 0.34, P = .006 for a 6-mm pupil).
Contrast Sensitivity
The area under the log contrast sensitivity function was significantly increased, from 1.44 ± 0.16 (range, 0.88 to 1.64) preoperatively to 1.52 ± 0.15 (range, 0.99 to 1.79) postoperatively, in eyes undergoing ICL implantation ( P < .001, Wilcoxon signed rank test). There was also a significant increase in CS at 4 of 5 spatial frequencies (but not at 3 cycles/degree) after ICL implantation ( Figure 3 ) . On the other hand, the area under the log contrast sensitivity function was changed, but not significantly, from 1.49 ± 0.12 (range, 1.14 to 1.68) preoperatively to 1.46 ± 0.16 (range, 1.12 to 1.77) postoperatively, in eyes undergoing wavefront-guided LASIK ( P = .11). There was no significant decrease in CS at any of 5 spatial frequencies after wavefront-guided LASIK ( Figure 4 ) .
