Surgically-induced Astigmatism After Laser in situ Keratomileusis for Spherical Myopia

Comparison of myopic astigmatic correction after cross-assisted SMILE, FS-LASIK, and transPRK

PURPOSE

To compare astigmatic correction among cross-assisted small-incision lenticule extraction (SMILE), femtosecond laser-assisted in situ keratomileusis (FS-LASIK), and transepithelial photorefractive keratectomy (transPRK).

SETTING

The Eye Hospital of Wenzhou Medical University, Zhejiang, China.

DESIGN

Prospective comparison study.

METHODS

154 right eyes of 154 patients with astigmatism of -1.00 to -2.75 diopters (D) were included in this study. 64 eyes, 42 eyes, and 48 eyes were receiving SMILE, FS-LASIK, and transPRK, respectively. The SMILE group used cross-axial alignment for head positioning for astigmatism correction. In the FS-LASIK and transPRK groups, static and dynamic cyclotorsion control were used. Changes in ocular parameters and vector analysis were assessed at 6 months postoperatively.

RESULTS

The safety and efficacy indices were comparable among the 3 groups at 6 months postoperatively. Residual astigmatism was smallest in the SMILE group (-0.23 ± 0.25 D) compared with that in FS-LASIK (-0.40 ± 0.28 D, P = .009) and transPRK groups (-0.42 ± 0.32 D, P = .001). 53 (82.8%), 36 (85.7%), and 37 (77.1%) eyes achieved an angle of error within ±5 degrees, respectively ( P = .55). Notably, vector analysis showed that the difference vector, the magnitude of the error, and its absolute value were significantly smaller in the SMILE group than those in the other groups ( P < .05). In addition, the higher-order aberrations, especially coma, were significantly induced postoperatively in each group ( P < .001).

CONCLUSIONS

Residual astigmatism magnitude was smallest by cross-assisted SMILE, followed by FS-LASIK and transPRK, and the astigmatism axial correction was comparable among groups.

Advantages of Small Incision Lenticule Extraction (SMILE) for Mass Eye and Ear Special Issue

This review summarizes the advantages of Small-incision lenticule extraction (SMILE), including improved patient intraoperative experience, improved postoperative ocular surface, low incidence of regression, low re-treatment rates, and advantageous biomechanical corneal stability. Visual and refractive outcomes are similar to those achieved with LASIK, notably in large population studies. Since the inception of SMILE almost 10 years ago, the procedure has been rapidly growing in popularity. With the implementation of the novel SMILE technology in their practice, refractive surgeons generate excitement and potential for expanding the refractive market. Other parts of the world, including Asia, Europe, and Russia, SMILE has become the most popular refractive procedure performed. It is speculated that as SMILE continues to grow in popularity in the US since FDA approval in 2016 and more refractive surgeons implement this technology into their practice, it will drive an increase in the refractive market similar to what is seen in other countries.

Enhancement after Small-Incision Lenticule Extraction: Incidence, Risk Factors, and Outcomes

PURPOSE

To report the incidence, risk factors, and outcomes of enhancement after small-incision lenticule extraction (SMILE).

DESIGN

Retrospective cohort study.

PARTICIPANTS

Five hundred twenty-four eyes of 307 patients who underwent SMILE at Singapore National Eye Center between February 2012 and March 2016.

METHODS

The data collected included patient age at primary SMILE, gender, race, preoperative and postoperative manifest refraction spherical equivalent (MRSE), preoperative and postoperative uncorrected distance visual acuity and corrected distance visual acuity, the occurrence of suction loss during the procedure, and the need for enhancement. All enhancements were carried out by performing an alcohol-assisted photorefractive keratectomy (PRK) procedure with application of mitomycin C (MMC).

MAIN OUTCOME MEASURES

Incidence, prevalence, preoperative and intraoperative risk factors for enhancement, and outcomes after enhancement.

RESULTS

The prevalence of enhancement was 2.7%, and 71.4% eyes had enhancement within 1 year of primary SMILE. The incidence of enhancement was 2.1% and 2.9% at 1 and 2 years, respectively. Age older than 35 years, preoperative MRSE more than -6.00 diopters (D), preoperative myopia more than 6.00 D, preoperative astigmatism more than 3.00 D, and intraoperative suction loss were significant risk factors for enhancement after SMILE after adjusting for all other covariates (odds ratios, 5.58, 4.80, 1.41, 3.06, and 2.14, respectively; P = 0.004, 0.021, 0.022, 0.002, and 0.020, respectively). In the patients who underwent bilateral SMILE, the first-operated eye had a marginal trend toward significance for enhancement (P = 0.054). There was no gender or racial difference. In the 14 eyes requiring enhancement, the uncorrected distance visual acuity before enhancement ranged from 20/80 to 20/25, and the mean attempted enhancement spherical equivalent was -0.50±0.86 D. The uncorrected distance visual acuity improved in most patients (92.9%) after enhancement.

CONCLUSIONS

The 2-year incidence of enhancement after SMILE was 2.9%. Risk factors associated with enhancement included older age at SMILE procedure, greater preoperative MRSE, greater preoperative myopia, greater preoperative astigmatism, and the occurrence of intraoperative suction loss. Clinical outcomes of using PRK with application of MMC for enhancement were good.

Comparison of astigmatic correction after femtosecond lenticule extraction and wavefront-guided LASIK for myopic astigmatism

PURPOSE

To compare postoperative astigmatic correction between femtosecond lenticule extraction (FLEx) and wavefront-guided LASIK in eyes with myopic astigmatism.

METHODS

Fifty-eight eyes of 41 patients undergoing FLEx and 49 eyes of 29 patients undergoing wavefront-guided LASIK to correct myopic astigmatism were examined. Visual acuity, cylindrical refraction, predictability of the astigmatic correction, and astigmatic vector components were compared between groups 6 months after surgery.

RESULTS

There was no statistically significant difference in manifest cylindrical refraction (P = .08) or percentage of eyes within ± 0.50 diopter (D) of its refraction (P = .11) between the surgical procedures. The index of success in FLEx was statistically significantly better than that of wavefront-guided LASIK (P = .02), although there was no significant difference between the groups in other indices (eg, surgically induced astigmatism, target-induced astigmatism, astigmatic correction index, angle of error, difference vector, and flattening index). Subgroup analysis showed that FLEx had a better index of success (P = .02) and difference vector (P = .04) than wavefront-guided LASIK in the low cylinder subgroup; the angle of error in FLEx was significantly smaller than that of wavefront-guided LASIK in the moderate cylinder subgroup (P = .03).

CONCLUSIONS

Both FLEx and wavefront-guided LASIK worked well for the correction of myopic astigmatism by the 6-month follow-up visit. Although FLEx had a better index of success than wavefront-guided LASIK when using vector analysis, it appears equivalent to wavefront-guided LASIK in terms of visual acuity and the correction of astigmatism.

Efficacy and predictability of laser in situ keratomileusis for low astigmatism of 0.75 diopter or less

PURPOSE

To examine the refractive and visual outcomes of wavefront-optimized laser in situ keratomileusis (LASIK) in myopic eyes with low astigmatism of 0.75 diopter (D) or less.

SETTING

University Medical Center Hamburg-Eppendorf, Germany, and Care Vision private clinics, Germany and Austria.

DESIGN

Retrospective cross-sectional data analysis.

METHODS

This study comprised consecutive myopic patients with a preoperative refractive cylinder of 0.75 D or less and a preoperative subjective sphere between -2.75 D and -11.50 D. Three subgroups were formed based on preoperative refractive cylinder magnitude (0.25 D, 0.50 D, and 0.75 D). Manifest refraction, uncorrected distance visual acuity (UDVA), and corrected distance visual acuity were assessed preoperatively and postoperatively. The astigmatic changes were determined using Alpins vector analysis.

RESULTS

This study enrolled 448 eyes of 448 patients (145 men, 303 women; mean age at surgery 37.8 years ± 9.4 [SD]). By 4 months (mean 116.8 ± 27.7 days) postoperatively, the mean UDVA was 0.10 ± 0.13 logMAR and the mean manifest refraction spherical equivalent (MRSE) -0.05 ± 0.68 D. There was no statistically significant difference in efficacy or safety between the preoperative cylinder groups. Astigmatic overcorrection for a preoperative cylinder of 0.25 D and 0.50 D was suggested by the correction index, the magnitude of error, the index of success, and the flattening index.

CONCLUSIONS

Although the mean UDVA and mean MRSE obtained by the 4-month follow-up were appropriate, a preoperative cylinder of 0.50 D or less was significantly overcorrected. Accordingly, caution should be used when considering full astigmatic correction for manifest cylinder of 0.50 D or less.

Astigmatism correction: Laser in situ keratomileusis versus posterior chamber collagen copolymer toric phakic intraocular lens implantation

PURPOSE

To compare the stability and predictability of astigmatism correction between toric phakic intraocular lens (pIOL) implantation and laser in situ keratomileusis (LASIK).

SETTING

Nagoya Eye Clinic, Nagoya, Japan.

DESIGN

Comparative case series.

METHODS

Consecutive patients who had Implantable Collamer Lens pIOL implantation or LASIK were divided into 3 subgroups according to the amount of refractive cylinder correction (low, 0.00 to 1.25 diopters [D]; moderate, 1.50 to 2.75 D; high, ≥ 3.00 D). Manifest refraction was measured preoperatively and 1, 3, 6, and 12 months postoperatively. Based on these data, the predictability and stability of the refractive cylinder correction, error of the refractive cylinder correction, and error of the refractive cylinder correction axis were evaluated.

RESULTS

The study comprised 338 eyes (196 patients) in the toric pIOL group and 351 eyes (202 patients) in the LASIK group. In the moderate cylinder subgroup, more eyes were corrected within ± 0.50 D of the postoperative refractive cylinder in the LASIK group (132 eyes [91%]) than in the toric pIOL group (111 eyes [79%]). In the high refractive cylinder subgroup, the error of the refractive cylinder correction in the LASIK group was significantly higher than in the toric pIOL group (P=.032). The postoperative manifest refractive cylinder did not change in either group during the follow-up period.

CONCLUSIONS

The stability of the refractive cylinder after toric pIOL implantation was as high as after LASIK. Although predictability in the LASIK group was higher than in the toric pIOL group in eyes with moderate refractive cylinder, the toric pIOL group had higher predictability than the LASIK group in eyes with high refractive cylinder.

Variables affecting refractive outcome following LASIK for myopia

AIM

To investigate factors affecting refractive outcome following LASIK for myopia.

METHOD

Six hundred and seventy-four consecutive uncomplicated myopic LASIK surgeries, performed by a single surgeon, either using the Technolas 217 planoscan (n=372) or the NIDEK EC 5000 (n=302), were evaluated. Stratified random sampling was used to match the groups for refractive error, patient age, and gender. The final analysis included 302 patients from each treatment group. Conditions were identical for both surgeries, and pre-operative refractive errors were between -1.00 and -14.00 DS and <-1.50 DC. Refractive success was defined as -0.50 to +0.50 DS of the targeted refraction measured 3 months after surgery. A stepwise logistical regression analysis was used to determine variables associated with refractive failure.

RESULTS

A successful refractive outcome was achieved in 78% (235/302) of surgeries using the Technolas laser and in 88% (266/302) using the NIDEK laser. Predictor variables for not achieving refractive success were pre-operative refractive error of above -5.00 DS, age more than 40 years, and surgery performed with the Technolas laser.

CONCLUSION

Both the Technolas 217 and the NIDEK EC-5000 excimer lasers achieve a successful refractive outcome in the majority of cases. However, patient and surgical factors can influence refractive outcome.

Corneal Hysteresis, Resistance Factor, Topography, and Pachymetry After Corneal Lamellar Flap

PURPOSE

To measure prospectively the early changes in corneal hysteresis, topography, and pachymetry after the creation of a stromal flap cut without laser photoablation.

METHODS

A 37-year-old man was referred for a bioptic procedure to correct for compound myopic astigmatism in the left eye. A 159-microm-thick 8x8.5-mm superior hinged flap was created with a mechanical microkeratome in the left cornea. Changes in the corneal hysteresis, corneal resistance factor, Goldmann correlated intraocular pressure (lOP), corneal compensated IOP, anterior and posterior topography, and optical and ultrasound pachymetry were monitored prospectively before and at 1 hour, 1 day, 5 days, and 25 days after flap creation. The right eye served as a control.

RESULTS

In the left eye, corneal hysteresis and corneal resistance factor decreased immediately after the flap cut and remained lower than preoperatively at 1 hour, 1 day, 5 days, and 25 days. Corneal compensated IOP varied significantly less than Goldmann correlated IOP in both eyes. Central flattening of the horizontal meridians was observed on the difference topography maps. The values of the left eye posterior best fit sphere increased after the flap cut. Increased central corneal thickness occurred immediately after the flap cut and decreased over time without returning to its preoperative value.

CONCLUSIONS

The creation of a stromal flap can modify the biomechanical properties of the cornea, including a reduction in corneal hysteresis. The topographic changes were consistent with previously reported cases of flap cut in normal corneas.

Risk factors for postoperative cylindrical prediction error after laser in situ keratomileusis for myopia and myopic astigmatism

PURPOSE

To study the risk factors for the occurrence of cylindrical prediction error (PE) after laser in situkeratomileusis (LASIK) for myopia and myopic astigmatism.

METHODS

The study was a nested case-control study. Five hundred eyes of 252 consecutive patients who underwent LASIK for myopia and myopic astigmatism on the Chiron Technolas 217C laser and completed 6 months of follow-up. There were 435 controls and 65 cases based on the postoperative refractive cylindrical PE. The probable risk factors studied included preoperative sphere and cylinder, keratometry, pachymetry, suction ring used, flap thickness, hinge centeration, optic zone, ablation depth, and intraoperative complications.

RESULTS

By univariate analysis, the cylindrical PE was found to be associated with preoperative spherical equivalent higher than -6 D (chi(2)=10.83; P=0.001), preoperative sphere higher than -6 D (chi(2)=6.15, P=0.013), preoperative cylinder more than -0.75 D (chi(2)=6.61; P-value=0.010), and an optic zone less than 5.5 mm (chi(2)=19.3; P=0.001). Risk factors for postoperative astigmatism by stepwise multivariate logistic regression analysis were an optic zone of less than 5.5 mm with an odds ratio (OR) of 2.81 (95% confidence interval (CI)=1.62-4.86) and preoperative cylinder more than -0.75 D with an OR of 1.60 (95% CI=0.92-2.77).

CONCLUSION

Postoperative astigmatism (as indicated by the cylindrical PE) is more likely to occur with an optic zone of less than 5.5 mm and a higher preoperative cylindrical error.

A Comparison of Induced Astigmatism in Conventional and Wavefront-guided Myopic LASIK Using LADARVision4000 and VISX S4 Platforms

PURPOSE

To evaluate and compare the surgically induced astigmatism in myopic eyes undergoing conventional and wavefront-guided LASIK.

METHODS

A retrospective review was performed of the charts of 200 myopic eyes of 121 patients who underwent either custom or conventional treatments via the VISX S4 or LADARVision4000 platforms (50 consecutive eyes in each of the four groups). The primary outcome measure was manifest refraction, which was evaluated preoperatively and at 3 months postoperatively. The magnitude and axis of the unintended surgically induced astigmatism were calculated using vector analysis. The Student t test was used to compare the magnitudes of the surgically induced astigmatism and the absolute angle of error.

RESULTS

The mean preoperative manifest cylinder was 0.66 +/- 0.38 diopters (D) for conventional VISX S4 and 0.68 +/- 0.39 D for VISX CustomVue (P = .795), and 0.76 +/- 0.56 D for LADARVision and 0.61 +/- 0.36 D for LADAR CustomCornea (P = .114). The success index was 0.19 +/- 0.41 for VISX S4 and 0.49 +/- 0.49 for VISX CustomVue (P = .0013), and 0.25 +/- 0.47 for LADARVision and 0.20 +/- 0.39 for LADAR CustomCornea (P = .5721). The absolute mean angle of error was 4.4 +/- 13.9 degrees for VISX S4 versus 14.9 +/- 23.9 degrees for VISX CustomVue (P = .0085), and 6.1 +/- 12.30 for LADARVision versus 3.9 +/- 11.1 degrees for LADAR CustomCornea (P = .3501). Of the VISX CustomVue eyes, 32% had an absolute angle of error > 10 degrees, as compared to 10% for both the VISX S4 and LADAR CustomCornea eyes (P = .013), and 16% for the LADARVision group (P = .056).

CONCLUSIONS

Wavefront-guided ablation is associated with higher surgically induced astigmatism and larger astigmatic axis shift on the VISX platform as compared to the LADAR CustomCornea and the LADAR and VISX conventional platforms. Care should be emphasized mainly during registration/alignment to minimize surgically induced astigmatism in wavefront-guided LASIK.

Refractive outcomes of laser in situ keratomileusis after flap complications

PURPOSE

To study the refractive and visual outcomes, including surgically induced astigmatism, of laser in situ keratomileusis (LASIK) after flap buttonholes and incomplete flaps.

SETTING

Rajendra Prasad Center for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India.

METHODS

This was a retrospective case series of 15 patients (15 eyes) who had LASIK after flap complications (6 eyes with buttonholes and 9 with incomplete flaps). The second surgery was performed after the refraction was stable for 2 months. The refractive and visual outcomes were studied.

RESULTS

After the flap complication, the spheroequivalent did not change significantly (P = .78) but the mean pachymetry changed from 523.6 microm +/- 23.14 (SD) to 530.4 +/- 23.96 microm (P = .04) and the mean absolute cylinder changed from 0.63 +/- 1.01 diopter (D) to 0.88 +/- 0.87 D (P = .026). The second surgery was performed at a mean interval of 6.2 months (range 3 to 17 months). Two eyes had flap complications (irregular flaps) again after the second surgery. At the 6-month follow-up, the mean spheroequivalent was -0.34 +/- 0.65 D and the mean cylinder was 0.15 +/- 0.19 D x 83.6. Thirteen eyes (86.66%) were within 0.5 D of the attempted correction. Post-LASIK complications included diffuse lamellar keratitis (1 eye), epithelial ingrowth (1 eye), and flap striae (2 eyes). After the flap complication, no eye lost 2 or more lines of best spectacle-corrected visual acuity (BSCVA); but after the second surgery at 6 months, 1 eye had lost 2 lines of BSCVA. Six months postoperatively, all eyes had a BSCVA of 20/40 or better.

CONCLUSION

Laser in situ keratomileusis after flap complications is associated with good refractive and visual outcomes; however, there is a higher risk for intraoperative and postoperative complications after the second surgery.

Wavefront-guided Ablation With Bausch and Lomb Zyoptix for Retreatments After Laser in situ Keratomileusis for Myopia

PURPOSE

To evaluate the efficacy of wavefront-guided ablation for treatment of residual refractive error and higher order aberrations after laser in situ keratomileusis (LASIK) for myopia.

METHODS

Twenty-one eyes of 13 patients with residual refractive error after myopic LASIK were treated with a wavefront-guided ablation with the Zyoptix technique. In 13 eyes of 8 patients (Group A) we lifted the flap with an epitheliorhexis technique; in 8 eyes of 5 patients (Group B) we cut a new flap with a Hansatome microkeratome.

RESULTS

Preoperative root mean square (RMS) values were 1.370 for second order aberrations, 0.382 for total higher order aberrations, 0.273 for third order, 0.243 for fourth order, and 0.052 for fifth order aberrations. Three months postoperatively, RMS values decreased significantly to 0.278 (second order), 0.189 (total higher order), 0.138 (third order), 0.107 (fourth order), and 0.038 (fifth order). Ablation depth was two times greater than needed with a standard Planoscan treatment. Patients in the microkeratome recut group showed a trend toward overcorrection, and residual astigmatism was higher (-0.75 +/- 0.58 D) than in the flap lift group (-0.25 +/- 0.29 D).

CONCLUSIONS

Wavefront-guided ablation was an effective method to correct residual refractive error and higher order aberrations after myopic LASIK. Functional and refractive outcomes were better when we lifted the flap than when we recut the flap.

Induced optical aberrations following formation of a laser in situ keratomileusis flap

PURPOSE

To determine how refractive error, visual acuity, and high-order aberrations (3rd- and 4th-order) are affected by the formation of a lamellar corneal flap during laser in situ keratomileusis (LASIK).

SETTING

University refractive surgery center.

METHODS

The effect of lamellar corneal flap formation was analyzed in 15 myopic eyes (mean preoperative refraction -4.72 diopters [D] [range -1.25 to -7.25 D]). The flap was created using a 2-step procedure: (1). a nasally hinged lamellar corneal flap was created; (2). the flap was lifted and stromal ablation performed 2 months after the flap was made. A Hartmann-Shack aberrometer was used to measure the aberrations.

RESULTS

There was no significant change in the refractive error (spherical equivalent pre-flap -4.72 +/- 1.99 D and post-flap -4.62 +/- 1.99 D [P =.28]) or visual acuity (pre-flap uncorrected visual acuity [UCVA] 0.07 and best corrected visual acuity [BCVA] 0.96; post-flap UCVA 0.08 and BCVA 0.95 [P =.16 and P =.33, respectively]). A statistically significant increase in total higher-order wavefront aberrations was observed following flap formation (root mean square pre-flap 0.344 +/- 0.125 and post-flap 0.440 +/- 0.221 [P =.04]).

CONCLUSION

Flap formation during LASIK can modify the eye's existing natural higher-order aberrations (especially spherical and coma-like aberrations along the axis of the flap's hinge), while visual acuity and refractive error remain unaffected.

Astigmatism and LASIK

Although laser in situ keratomileusis (LASIK) enjoys a high success rate, postoperative residual or induced astigmatism may limit uncorrected visual acuity and cause starbursts and glare at night. Irregular astigmatism can also cause loss of best-corrected visual acuity, monocular diplopia, and ghosting of images. Astigmatism may be measured by keratometry and refraction, while corneal topographic techniques help to define irregular astigmatism, in particular. Further information may be obtained regarding induced higher-order aberrations with aberrometry. Because astigmatism has both direction and magnitude, its analysis is more complex than that of the spherical component of the treatment. There are multiple approaches to the analysis of surgically induced astigmatism, including vector analysis, conversion to a Cartesian coordinate system, matrix formalism, and linear optics. Both excimer laser and incisional techniques may be used to correct astigmatism after LASIK, but the treatment of irregular astigmatism requires selective zonal ablation techniques or customized corneal ablations, using topographic or wavefront derived data.

Surgically Induced Astigmatism After Laser in situ Keratomileusis for Spherical Myopia

PURPOSE

To study risk factors for surgically induced astigmatism (SIA) after laser in situ keratomileusis (LASIK).

METHODS

In a retrospective case control study of 104 eyes (52 patients) that underwent LASIK for myopia (spherical ablation alone), two groups were studied: 42/104 eyes with SIA, and controls (62/104 eyes). The main variables studied were preoperative refraction, corneal thickness, preoperative keratometric power, amount of ablation, ablation zone diameter, flap thickness, flap size, and the presence of complications. The effect of SIA on visual performance was also evaluated.

RESULTS

The mean myopia for which LASIK was undertaken was -4.50 +/- 2.04 D. Mean scalar astigmatism induced was 0.35 +/- 0.50 D at 1 month, 0.33 +/- 0.40 D at 3 months, and 0.16 +/- 0.60 D at 6 months. SIA based on refractive cylinder was 0.66 +/- 0.29 D at 1 month, 0.54 +/- 0.32 D at 3 months, and 0.49 +/- 0.34 D at 6 months. Mean axis of vector induced astigmatism was 82.5 degrees +/- 57 degrees at 1 month, 98.86 degrees +/- 52.4 degrees at 3 months, and 113.9 degrees +/- 62.6 degrees at 6 months. Risk factors associated with the occurrence of SIA were preoperative keratometric power of >44 D [OR (95% CI); 1.97 (0.62 to 6.26)], ablation zone diameter of <6 mm [OR (95 % CI) 2.76; (0.6 to 12.6)], and suction ring diameter of 8.5 mm [OR (95% CI) 12.46; (2.0 to 77.38)]. The occurrence of SIA had no significant effect on uncorrected Snellen high contrast visual acuity, contrast sensitivity, and glare in comparison with controls.

CONCLUSION

Surgically induced astigmatism was more likely to occur with the use of smaller suction rings of 8.5 mm and in ablation zones less than 6 mm. Parameters for visual performance were not affected by the presence of surgically induced astigmatism.

Laser Epithelial Keratomileusis for Myopia With the Autonomous Laser

PURPOSE

To describe the refractive outcome, objective clinical data, and subjective patient experiences after laser epithelial keratomileusis (LASEK) at 1, 3, and 6 months after surgery.

METHODS

This was a retrospective, nonrandomized, comparative study of 58 LASEK-treated eyes (36 patients) with myopia (with and without astigmatism) between -1.50 and -14.75 D (mean -7.80 +/- 2.90 D, median -7.90 D). Refractive surgery was performed using the Alcon Summit Autonomous LADAR Vision excimer laser. Manifest refraction, best-spectacle and uncorrected Snellen visual acuity, stability of refraction, and corneal haze were evaluated before surgery and up to 6 months after surgery. A group of randomly selected LASIK-treated eyes were compared at each time point.

RESULTS

Patients who opted for monovision (n=12) were excluded. In the emmetropia targeted eyes (n=46), 45%, 83%, 85%, and 89% achieved 20/40 or better uncorrected Snellen visual acuity (UCVA) at 1 day, 1 week, 2 weeks, and 1 month respectively. At 6 months, 73% (n=28) of eyes treated achieved UCVA 20/20 with 97% achieving 20/40 or better (mean, -0.51 D). At 3 and 6 months, 71% (n=46) and 68% (n=28) were within +/- 0.50 D of emmetropia. The percentage of eyes that achieved UCVA 20/40 or better at 6 months was 97% (n=28). Visually significant corneal haze was evident in two LASEK-treated patients (four eyes) at 6 months. No eyes lost two or more lines of best spectacle-corrected Snellen visual acuity.

CONCLUSIONS

Preliminary data suggest that LASEK appears to be a safe, effective, and comparable alternative to LASIK, even for higher amounts of myopia. A prospective, randomized clinical trial is needed to better define the role of LASEK as it compares to other refractive procedures, specifically LASIK and PRK.

Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy: a report by the American Academy of Ophthalmology

OBJECTIVE

This document describes laser in situ keratomileusis (LASIK) for myopia and astigmatism and examines the evidence to answer key questions about the efficacy and safety of the procedure.

METHODS

A literature search conducted for the years 1968 to 2000 retrieved 486 citations and an update search conducted in June 2001 yielded an additional 243 articles. The panel members reviewed 160 of these articles and selected 47 for the panel methodologist to review and rate according to the strength of evidence. A Level I rating is assigned to properly conducted, well-designed, randomized clinical trials; a Level II rating is assigned to well-designed cohort and case-control studies; and a Level III rating is assigned to case series and poorly designed prospective and retrospective studies, including case-control studies.

RESULTS

The assessment describes randomized controlled trials published in 1997 or later (Level I evidence) and more recent comparative and noncomparative case series (Level II and Level III evidence), focusing on results for safety and effectiveness. It is difficult to extrapolate results from these studies that are comparable to current practices with the most recent generation lasers because of the rapid evolution of LASIK technology and techniques. It is also difficult to compare studies because of variations in the range of preoperative myopia, follow-up periods, lasers, nomograms, microkeratomes and techniques, the time frame of the study, and the investigators' experience.

CONCLUSIONS

For low to moderate myopia, results from studies in the literature have shown that LASIK is effective and predictable in terms of obtaining very good to excellent uncorrected visual acuity and that it is safe in terms of minimal loss of visual acuity. For moderate to high myopia (>6.0 D), the results are more variable, given the wide range of preoperative myopia. The results are similar for treated eyes with mild to moderate degrees of astigmatism (<2.0 D). Serious adverse complications leading to significant permanent visual loss such as infections and corneal ectasia probably occur rarely in LASIK procedures; however, side effects such as dry eyes, night time starbursts, and reduced contrast sensitivity occur relatively frequently. There were insufficient data in prospective, comparative trials to describe the relative advantages and disadvantages of different lasers or nomograms.