Topographical analysis of ablation centration after excimer laser photorefractive keratectomy and laser in situ keratomileusis for high myopia

Methods of Corneal Vertex Centration and Evaluation of Effective Optical Zone in Small Incision Lenticule Extraction

Inappropriate small incision lenticule extraction (SMILE) centration methods can affect the decentration of the effective optical zone (EOZ) after operation, which can subsequently lead to the decline of postoperative visual quality. We aimed to provide an overview of corneal vertex (CV) centration methods and an evaluation of the size and decentration of the EOZ in SMILE. We described the CV centration methods for patients with myopia, myopic astigmatism, hyperopia, and large kappa angle. The measurement methods of the EOZ were evaluated from the aspects of corneal morphology and corneal refractive power. Additionally, we summarized the advantages and disadvantages of measuring decentration based on topographic mapping and intraoperative video-captured images. Finally, we discussed the relationship between the EOZ and visual quality. Based on our review, clinicians should consider the following when choosing CV centration methods and evaluating EOZ postoperatively. First, the tear film mark center or topographic map comparison method is preferred for the correction of myopia, low myopic astigmatism, hyperopia, and large kappa angle (>0.2 mm). Triple marking centration is recommended for high myopic astigmatism (-3.5 diopters). Second, the total corneal power better reflects the change in refractive power than the topographic method. The measurement of the area rather than the diameter of the total corneal refractive power is more suitable for the evaluation of noncircular EOZs after high myopia astigmatism (<-2.0 diopters). Third, for the evaluation of decentration, the tangential curvature difference map method is preferred as it is not influenced by offset pupils. Finally, a large EOZ after SMILE may improve patient tolerance to decentration.

Main Complications of Photorefractive Keratectomy and their Management

Photorefractive keratectomy (PRK) was the first surface ablation procedure introduced for the treatment of refractive errors and has been proven to be effective and safe. In some cases, however, the patient may not be totally satisfied with the final result and retreatment may be necessary. We performed a literature review to describe the main conditions that may arise following PRK that may require retreatment and new promising techniques to allow customized and effective treatments for patients. There is currently no gold standard for retreatment of residual refractive error after PRK. The surgeon must take into account the patient's history and type of problem when choosing the most appropriate technique. LASIK and PRK are the main options. Haze can be treated with good results with phototherapeutic keratectomy and mytomicin C. High order aberrations and decentration may be addressed with topographically-guided excimer photoablation or with wavefront-guided PRK.

Functional Optical Zone and Centration Following SMILE and LASIK: A Prospective, Randomized, Contralateral Eye Study

PURPOSE

To compare centration and functional optical zone (FOZ) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (LASIK).

METHODS

In this prospective, randomized, single-masked, paired-eyed, clinical trial, 70 patients received SMILE in one eye and LASIK in the other eye for myopia and myopic astigmatism. FOZ was calculated using custom software on 3-month postoperative refractive power maps (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany). Programmed treatment area was defined as the total area of the programmed OZ plus the transition zone. Centration was evaluated by the linear distance between FOZ centroid and the pupil center and the corneal apex.

RESULTS

The average preoperative spherical equivalent (-5.38 ± 1.65 vs -5.45 ± 1.61 diopters [D]), postoperative spherical equivalent (0.05 ± 0.39 vs 0.06 ± 0.39 D), uncorrected distance visual acuity (0.01 ± 0.13 vs 0.00 ± 0.08 logMAR), and corrected distance visual acuity (-0.07 ± 0.10 vs -0.07 ± 0.10 logMAR) were comparable in SMILE- and LASIK-treated eyes of the 60 patients with complete datasets (P > .419). Postoperative increase in spherical aberration was lower in SMILE than in LASIK (0.08 ± 0.16 vs 0.17 ± 0.18 µm, P = .002). The FOZ area was significantly larger in SMILE than in LASIK (30.25 ± 3.60 vs 29.21 ± 3.72 mm²), despite the smaller programmed OZ diameter (6.48 ± 0.08 vs 6.52 ± 0.11 mm) and smaller programmed treatment area (33.87 ± 0.81 vs 46.30 ± 2.61 mm², P < .037). Pupil centration (0.43 ± 0.21 vs 0.41 ± 0.22 mm) and apex centration (0.48 ± 0.24 vs 0.48 ± 0.22 mm) were comparable between SMILE and LASIK (P > .694).

CONCLUSIONS

SMILE created a larger FOZ than LASIK, despite the smaller programmed OZ. This may be due to a difference in the biomechanical response between the two procedures. Visual outcome and centration were comparable between SMILE and LASIK. [J Refract Surg. 2019;35(4):230-237.].

Decentration following femtosecond laser small incision lenticule extraction (SMILE) in eyes with high astigmatism and its impact on visual quality

Background

To measure the decentration following SMILE in eyes with high myopic astigmatism and investigate its impact on visual quality.

Methods

The prospective study was conducted to analyze patients who underwent SMILE for correction of myopia and myopic astigmatism ≥2.5D (high astigmatism group, HA) at the ophthalmology department, Eye and ENT hospital, Shanghai, China.. Patients with myopic astigmatism < 1.5D served as controls (low astigmatism group, LA). Decentration was measured using a Scheimpflug camera with a difference map of the tangential curvature at 12 months postoperatively. Also the associations between decentration from the coaxial sighted corneal light reflex (CSCLR) and the visual outcomes, correction efficacy of astigmatism, wavefront aberrations and objective scatter index (OSI) were analyzed.

Results

No significant differences were observed in the decentered distance between HA and LA in either eyes (OD: HA: 0.18 ± 0.10 mm, LA: 0.20 ± 0.14 mm, P = 0.659; OS: HA: 0.22 ± 0.11 mm, LA: 0.20 ± 0.11 mm, P = 0.637). The analysis across the three levels of decentration (< 0.1 mm, 0.1–0.2 mm, and > 0.2 mm) showed no significant association between decentration and visual outcomes of predictability, efficiency, safety, MTF cutoff, OSI, SR and OVs in both groups. Also no significant association was observed between decentration and postoperative astigmatism in either group. A significant relationship between the magnitude of decentration and induced coma and spherical aberration was observed in HA.

Conclusions

The amount of decentration between HA and LA groups showed no differences. Decentration > 0.20 mm from CSCLR resulted in greater induction of coma and SA after SMILE in eyes with HA.

Intraoperative centration during small incision lenticule extraction (SMILE)

To evaluate intraoperative decentration from pupil center and kappa intercept during small incision lenticule extraction (SMILE) and its impact on visual outcomes.This was a retrospective noncomparative case series. A total of 164 eyes that underwent SMILE at the Singapore National Eye Center were included. Screen captures of intraoperative videos were analyzed. Preoperative and 3 month postoperative vision and refractive data were analyzed against decentration.The mean preoperative spherical equivalent (SE) was -5.84 ± 1.77. The mean decentration from the pupil center and from kappa intercept were 0.13 ± 0.06 mm and 0.47mm ± 0.25 mm, respectively. For efficacy and predictability, 69.6% and 95.0% of eyes achieved a visual acuity (VA) of 20/20 and 20/30, respectively, while 83.8% and 97.2% of eyes were within ±0.5D and ±1.0D of the targeted SE. When analyzed across 3 groups of decentration from the pupil center (<0.1 mm, 0.1-0.2 mm, and >0.2 mm), there was no statistically significant association between decentration, safety, efficacy, and predictability. When analyzed across 4 groups of decentration from kappa intercept (<0.2 mm, 0.2-<0.4 mm, 0.4-<0.6 mm, and ≥0.6 mm), there was a trend toward higher efficacy for eyes with decentration of kappa intercept between 0.4 and <0.6 mm (P = .097). A total of 85.4% of eyes in the 0.4 to <0.6 mm group had unaided distance VA of 20/20 or better, as compared to only 57.8% of eyes in ≥0.6 mm group.Decentration of 0.13 mm from the pupil center does not result in compromised visual outcomes. Decentration of greater than 0.6 mm from the kappa intercept may result in compromised visual outcomes. There was a trend toward better efficacy in eyes which had decentered treatment from 0.4 to <0.6 mm from the kappa intercept. Patients with a large kappa intercept (>0.6 mm) should have their lenticule created 0.4 to 0.6 mm from the kappa intercept and not close to the pupil.

Small-incision lenticule extraction in a patient with congenital nystagmus

We report a case of a 23-year-old woman with congenital nystagmus who had small-incision lenticule extraction (SMILE) procedure to correct refractive errors. The manifest refraction was -5.50 -1.75 × 180 in the right eye, -5.0 -2.50 × 180 in the left eye, and the patient presented with horizontal pendular nystagmus with an amplitude range of 5 to 10 degrees. Uneventful simultaneous bilateral small-incision lenticule extraction was performed. Six months postoperatively, the uncorrected distance visual acuity was 20/18 with -0.25, -0.25 × 80 in the right eye, and 20/20 with +0.25 -0.5 × 50 in the left eye. The case suggests that small-incision lenticule extraction can be an effective alternative for correcting myopic astigmatism in patients with nystagmus.

Impact of Treatment Decentration on Higher-Order Aberrations after SMILE

Purpose. To evaluate decentration following femtosecond laser small incision lenticule extraction (SMILE) and sub-Bowman keratomileusis (SBK) and its impact on higher-order aberrations (HOAs). Methods. Prospective, nonrandom, and comparison study. There were 96 eyes of 52 patients who received SMILE and 96 eyes of 49 patients who received SBK in this study. Decentration was calculated 6 months after surgery with Pentacam. HOAs and visual acuity after the surgery were examined for patients in both groups before and 6 months after surgery. Results. The mean decentration displacement in SMILE group was significantly less than SBK group (P = 0.020). 89 eyes were decentered within 0.50 mm after SMILE and SBK. The association between vertical decentration and the induced spherical aberration was insignificant in SMILE group (P = 0.035). There was an association between decentration and safety index, efficacy index, vertical coma, spherical aberration, and HOAs in root mean square (RMS, μm) after SBK (all P < 0.05). No difference was found in uncorrected and corrected distance visual acuity, safety index, efficacy index, and wavefront aberrations between the two subgroups at any delimited value after SMILE (all P > 0.05). Decentration exceeding 0.37 mm affected vertical coma and RMSh of SBK eyes (P = 0.002, 0.005). Conclusion. SMILE surgery achieved more accurate centration than SBK surgery. Vertical decentration is associated with the induced spherical aberration in SMILE.

Comparison of Visual Outcomes After Femtosecond LASIK, Wave Front-Guided Femtosecond LASIK, and Femtosecond Lenticule Extraction

PURPOSE

To compare the mesopic contrast sensitivity (CS) and higher order aberrations (HOAs) at 3 months after femtosecond-laser in situ keratomileusis (LASIK) (FS-LASIK), wave front-guided femtosecond LASIK (WF-LASIK), and femtosecond lenticule extraction (FLEx) for the correction of myopia and myopic astigmatism.

METHODS

In this prospective nonrandomized study, 332 right eyes of 332 patients were treated with FS-LASIK, WF-LASIK, or FLEx. The HOAs and mesopic CS were evaluated preoperatively and at 3 months postoperatively.

RESULTS

At 3 months of follow-up, 98 eyes (96.1%) of the FS-LASIK group, 92 eyes (98.9%) of the WF-LASIK group, and 133 eyes (96.4%) of the FLEx group had an uncorrected distance visual acuity of 20/20 or better. The HOAs improved from 0.34 μm during preoperative examination to 0.56 μm of the end of the follow-up in the FS-LASIK group, from 0.31 to 0.41 μm in the WF-LASIK group, and from 0.32 to 0.54 μm in the FLEx group (all P < 0.01). At a spatial frequency of 12 cycles per degree, a better mesopic CS was observed in the WF-LASIK group (1.47) than in the FS-LASIK (1.36) and FLEx (1.33) groups (P < 0.01); a better mesopic CS with glare was also noted in the WF-LASIK group (1.37) than in the FS-LASIK (1.25) and FLEx (1.29) groups (P < 0.01).

CONCLUSIONS

The FS-LASIK, WF-LASIK, and FLEx procedures result in comparable refractive results at 3 months postoperatively. However, there is improvement in the mesopic CS and HOAs after WF-LASIK.

Topographic analysis of the centration of the treatment zone after SMILE for myopia and comparison to FS-LASIK: subjective versus objective alignment

PURPOSE

To evaluate the centration of the treatment zone after small incision lenticule extraction (SMILE) and compare it to femtosecond laser-assisted LASIK (FS-LASIK).

METHODS

Sixty-nine myopic eyes of 36 patients who underwent SMILE were compared to 69 myopic eyes of 36 patients treated with FS-LASIK. All procedures were performed by a single surgeon using the VisuMax platform (Carl Zeiss Meditec, Jena, Germany). The Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) was used for preoperative and postoperative topography and pachymetry. The centration of the treatment zone was estimated pachymetrically by the distance of the thickest point on the corneal thickness differential map from the topographical center of the entrance pupil and the coaxial corneal light reflex.

RESULTS

In SMILE cases, the mean decentration of the lenticule from the center of the entrance pupil was 0.326 ± 0.196 mm (range: 0.014 to 1.062 mm), whereas the distribution of the lenticule centers demonstrated a nasalization pattern. In FS-LASIK cases, this value was 0.452 ± 0.224 mm (range: 0.02 to 1.040 mm), whereas the ablation centers were distributed randomly. In relation to the coaxial corneal light reflex, the decentration in SMILE was 0.315 ± 0.211 mm (range: 0.0 to 1.131 mm), whereas FS-LASIK eyes demonstrated a mean decentration of 0.516 ± 0.254 mm (range: 0.103 to 1.265 mm). The decentration from the reference point of its technique (coaxial corneal light reflex in SMILE, the entrance pupil center in FS-LASIK) was significantly more extended in the FS-LASIK group (P < .001).

CONCLUSIONS

The centration of the treatment zone as measured by the Pentacam was better for patient-controlled fixation during SMILE than active eye tracker-assisted FS-LASIK.

Pupil size and LASIK: a review

PURPOSE

To provide a literature review on the evidence both for and against pupil size as an independent predictor of adverse visual outcomes after LASIK.

METHODS

Peer-reviewed publications on the effect of pupil size on LASIK outcomes since 2002 are reviewed. Particular attention was paid to the following attributes of each publication: type of study, number of patients or eyes, mean age, mean level of myopia, mean pupil size, testing conditions, ablation zone diameter, presence or absence of blend zones, and mean follow-up period.

RESULTS

Among the 19 studies examined, none correlates a persistent relationship between pupil size and night vision complaints (NVCs) beyond 3 months when LASIK was performed with a 6.0-mm optical zone or larger ablation. The studies that did explicitly determine a correlation either included some or all patients with ablation zones smaller than 6.0 mm or did not specify ablation diameter at all. Among the studies that had drawn more mixed conclusions, the studies either covered short follow-up intervals (1 to 3 months) or showed a progressive improvement in NVCs over time in a relatively small patient cohort.

CONCLUSIONS

As keratorefractive technology continues to evolve, the role of pupil size warrants further investigation; however, based on the literature reviewed herein, modern LASIK has negated the role of the low light pupil in predicting adverse visual outcomes after LASIK outside of the early postoperative period.

Causes of decentration after laser-assisted subepithelial keratectomy

BACKGROUND AND OBJECTIVE

To determine important factors causing decentration after laser-assisted subepithelial keratectomy (LASEK).

PATIENTS AND METHODS

A total of 223 cases (446 eyes) were evaluated after LASEK using corneal topography to determine the amount of decentration. Decentration and pupillary offset values and their components on the nasal, temporal, superior, and inferior axes were analyzed with the t test and the two-way repeated measures analysis of variance test in patients with myopia or hypermetropia. Correlation analysis between the amount of decentration and the possible determinative variables (age, gender, spherical refractive error, magnitude of astigmatism, spherical equivalent, average keratometry, mesopic pupil diameter, decentration, and pupillary offset) were performed.

RESULTS

Although decentration up to 0.99 mm was observed, mean decentration was 0.26 ± 0.16 mm. Alternatively, pupillary offset values were higher and the mean pupillary offset was 0.28 ± 0.16 mm. In myopia, mean total decentration was significantly less than hyperopia (P = .001). The inferior component of decentration was higher than the other locations in both myopia and hypermetropia. The nasal component of pupillary offset was highest among others. When all cases were included in the analysis, Pearson correlation analysis showed a statistically significant correlation between decentration and presence of hyperopia (r = 0.162 and P =.001) and amount of pupillary offset (r = 0.296 and P = .001).

CONCLUSION

Mean decentration was higher in hyperopia than in myopia. Most of the decentration may be attributed to inferior decentration. Pupillary offset values were the factor most significantly correlated to the amount of decentration in all cases.

Influence of induced decentered orthokeratology lens on ocular higher-order wavefront aberrations and contrast sensitivity function

PURPOSE

To quantitatively evaluate the effect of overnight orthokeratology lenses intentionally left decentered after 3 months of wear and assess the influence on clinical outcomes such as ocular higher-order wavefront aberrations and contrast sensitivity function.

SETTING

Department of Ophthalmology, Tsukuba University Hospital, Ibaraki, Japan.

METHODS

This prospective study assessed refraction, visual acuity, corneal topography, wavefront aberration, and contrast sensitivity function before and 3 months after overnight orthokeratology treatment. Decentration of the treatment zone from the center of the entrance pupil was determined using computerized videokeratography (TMS-4) and data-analysis software (MatLab). The relationship between decentration and the clinical parameters was analyzed.

RESULTS

The mean age of the 23 patients (46 eyes) was 24.2 years+/-3.3 (SD) and the mean spherical equivalent refraction before treatment, -2.38+/-0.98 diopters. The mean magnitude of decentration (0.85+/-0.51 mm) was statistically significantly correlated with the amount of myopic correction (P<.05), increases in coma-like aberration (P<.01), increases in spherical-like aberration (P<.01), and reductions in contrast sensitivity function (P<.0001). Changes in contrast sensitivity function were also statistically significantly correlated with the amount of myopic correction (P<.05), changes in coma-like aberration (P<.01), and changes in spherical-like aberration (P<.01). Stepwise multiple regression analysis showed that the magnitude of decentration was the only explanatory variable related to contrast sensitivity function (P<.0001).

CONCLUSION

Decentered treatment of orthokeratology resulted in decreased contrast sensitivity after treatment, showing that centration of the procedure is crucial to good outcomes.

Effects of decentration of photorefractive keratectomy on the induction of higher order wavefront aberrations

PURPOSE

To evaluate the effects of ablation decentration on the induction of higher order wavefront aberrations (HOAs) in active eye-tracker-assisted myopic photorefractive keratectomy (PRK) using the VISX STAR S4 laser with ActiveTrak (Abbott Medical Optics [AMO]).

METHODS

Ninety-four myopic eyes (53 patients) were divided into three groups according to ablation decentration (group 1, ≤0.15 mm, 20 eyes; group 2, >0.15 to ≤0.30 mm, 54 eyes; and group 3, >0.30 mm, 20 eyes). The distances of ablation centers from the centers of the entrance pupils were analyzed using corneal topography. Wavefront errors were measured preoperatively and at 6 months after PRK using a VISX WaveScan aberrometer (AMO). Statistical analysis was performed to assess the influence of ablation decentration on PRK-induced HOAs.

RESULTS

The mean decentration was 0.23±0.10 mm (range: 0.04 to 0.52 7 mm). The magnitude of all HOAs was significantly increased at 6 months postoperatively (P<.05). Increases in PRK-induced HOAs including total HOA, coma, and spherical aberration were significantly different among the three groups (P<.05). Statistically significant differences were noted between pairs of data in group 1 versus group 3 for total HOA (P=.015), coma (P=.038), and spherical aberration (P=.038), and group 2 versus group 3 for coma (P=.049).

CONCLUSIONS

Ablation decentration >0.30 mm from the center of the entrance pupil was associated with greater induction of total HOA, coma, and spherical aberration after PRK, as compared with ablation decentration <0.15 mm. In addition, ablation decentration has a more significant influence on coma-inducing effects.

Comparison of the topographic ablation zone after photorefractive keratectomy for myopia using two different excimer lasers

PURPOSE

To compare the topographic features of eyes treated with photorefractive keratectomy (PRK) for myopia using two different excimer lasers.

METHODS

A total of 65 eyes in 39 patients treated with PRK (6.0-mm optical zone) using Technolas 217C and VISX S4 excimer lasers were evaluated retrospectively to determine the size of the topographic ablation zone.

RESULTS

The zones ablated using the VISX S4 had shorter diameters in both axes (-0.89+/-0.73, -1.59+/-0.49 mm; both P=0.00), whereas those ablated using the Technolas 217C had a longer diameter in the major axis (0.96+/-0.63 mm; P=0.00) and a shorter diameter in the minor axis (-0.39+/-0.59 mm; P=0.00). The theoretical ablated zone was a circle with a diameter of 6.0 mm. The Technolas 217C group tended to have oval cuts in comparison with the VISX S4 group, and the difference between the programmed (6.0 mm) and topographic diameters was significant in both groups.

CONCLUSIONS

There was a difference between the programmed and postoperative topographic diameters of the ablation zone. The postoperative ablation zone differed in shape and size according to the type of excimer laser.

Wavefront aberrations in eyes with decentered ablations

PURPOSE

To compare the refractive and functional outcomes and wavefront profiles in eyes with decentered ablations and eyes with well-centered ablations.

SETTING

Medical Research Foundation, Chennai, Tamil Nadu, India.

METHODS

This retrospective analysis comprised eyes with topographically diagnosed decentered ablations after laser in situ keratomileusis (LASIK). Refraction, contrast sensitivity, and ocular wavefront aberrations were measured preoperatively and 1 month postoperatively. The induced aberrations in these eyes were compared with those in eyes with well-centered ablations.

RESULTS

Forty-six eyes (38 patients) had decentered ablations and 60 eyes (32 patients), well-centered ablations. The mean decentration in the study group was 0.86 mm +/- 0.29 (SD) (range 0.35 to 1.61 mm). There was no significant correlation between decentration and attempted refractive correction. There was, however, a statistically significant (P<.05) linear correlation between the distance of decentration and the magnitude of induced tilt (r = -0.31), coma (r = -0.41), and secondary astigmatism (r = 0.36). The induced changes in tilt, oblique astigmatism, vertical coma, and spherical aberration were statistically significantly higher in eyes with decentered ablations than in eyes with well-centered ablations. A statistically significantly higher percentage of eyes (87%) with well-centered ablations than eyes with decentered ablations (70%) had a postoperative uncorrected visual acuity (UCVA) of 20/20 or better. There was no significant difference in contrast sensitivity between groups.

CONCLUSION

Eyes with decentered ablations had a significantly higher magnitude of induced aberrations and lower UCVA than eyes with well-centered ablations.

Topography-guided treatment of decentered laser ablation using LaserSight's excimer laser

PURPOSE

To assess the efficacy of topography-guided laser ablation for correction of previously decentered laser ablation using LaserSight's excimer laser.

METHODS

Re-treatment was performed to correct decentered ablation using LaserSight's excimer laser for 18 patients who previously underwent LASIK surgery for myopia correction in both eyes. For each patient, only the decentered eye was re-treated while the other asymptomatic eye forms a control group for this study. Measurements were conducted on ablation center, best spectacle-corrected visual acuity (BSCVA), contrast sensitivity and corneal aberrations pre- and post-operatively.

RESULTS

For the retreated 18 eyes, the mean decentration was significantly reduced from 1.32+/-0.28mm to 0.61+/-0.23mm post-operatively (t=16.24, p<0.001), and with a significant improvement in mean BSCVA from 0.08+/-0.09 logMAR to 0.01+/-0.11 logMAR (t=4.58, p<0.001). The post-operative contrast sensitivity at the spatial frequencies (SF) of 1.00 and 0.70 was significantly improved (p<0.05 for both SFs). Corneal higher-order aberrations (HOAs), including the coma-like aberrations and spherical aberration, were decreased. In comparing the measurements for the retreated group to those for the control group, no significant differencewas found either in decentration or in BSCVA, but the contrast sensitivity at 0.70 was lower and the level of corneal aberrations was higher.

CONCLUSIONS

Topography-guided ablation with LaserSight excimer laser is effective to correct decentered ablation. However, the re-treated eye is still inferior to the eye with originally centered ablation in corneal optical quality or visual performance.

Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery

Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery today. The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. This way, we are able to change the refractive status of the patient, providing better unaided vision. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are the responsible for new surgical instrumentation, which makes the surgical procedure easier for the surgeon, and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. This article aims to describe the more relevant advances in LASIK that have played an important role in the spread and popularity of this technique.

Laser Ablation in Eyes With Congenital Nystagmus

PURPOSE

To report photorefractive keratectomy and LASIK for the correction of myopia in eyes with congenital nystagmus.

METHODS

Photorefractive keratectomy was performed in one eye and LASIK performed in eight eyes of five adult patients (three men and two women) with congenital nystagmus. Mean patient age was 34 years.

RESULTS

Preoperative refraction ranged between -1.50 and -22.00 diopters (D) sphere, and -0.50 and -3.25 D of astigmatism; best spectacle-corrected visual acuity (BSCVA) ranged between 2 m finger counting and 20/30. In all nine eyes, postoperative uncorrected visual acuity (UCVA) equaled or exceeded preoperative BSCVA. Postoperative topography showed central ablations. Results were stable at follow-up 18 months after surgery, except in one eye with follow-up of 4 months. Enhancement was not required in any eye.

CONCLUSIONS

Positive results were achieved for ablation performed with a broad beam laser in eyes with nystagmus.

Topographic Centration of Ablation After LASIK for Myopia Using the CustomVue VISX S4 Excimer Laser

PURPOSE

To determine the ablation centration, efficacy, predictability, and safety of CustomVue LASIK using the VISX S4 excimer laser for the treatment of myopia and myopic astigmatism.

METHODS

A retrospective review of 20 myopic eyes of 12 patients treated with LASIK CustomVue VISX S4 was conducted. Corneal topography was used to determine ablation centration. Primary outcome variables including manifest refraction, best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), and complications were evaluated at 3 months postoperatively.

RESULTS

Mean decentration (from ablation zone to entrance pupil) was 0.23 +/- 0.08 mm at 3 months postoperatively. No eyes were decentered > 0.5 mm. Preoperatively, the mean spherical equivalent refraction was -4.81 +/- 11.39 diopters (D) (range: -6.75 to -2.25 D). At 3 months postoperatively, mean spherical equivalent refraction was -0.63 +/- 0.25 D (range: -2.00 to 0.25 D). Nineteen (95%) of 20 eyes had UCVA of 20/40 and 16 (80%) of 20 eyes had UCVA of 20/20 at 3 months postoperatively. Fourteen (70%) eyes were within +/- 0.50 D and 18 (90%) eyes were within +/- 1.00 D of emmetropia. No eye lost > 1 line of BSCVA.

CONCLUSIONS

Wavefront-guided LASIK using the CustomVue VISX S4 for myopic eyes results in minimal decentration ablation and effective, predictable, and safe visual outcomes.

Effects of reference axes used during measurements of ocular and corneal higher-order aberrations in patients following LASIK

PURPOSE

To determine the effects of the reference axes used during the measurements of ocular and corneal higher-order aberrations (HOAs) in patients before and after laser in situ keratomileusis (LASIK).

METHODS

Wavefront sensing and corneal topography were determined for 29 eyes of 15 patients before and after LASIK. Ocular and corneal HOAs were calculated for 4-mm- and 6-mm-diameter pupils with the instrument aligned with the line of sight (LOS) or with the vertex normal (VN).

RESULTS

For ocular HOAs after surgery, the spherical-like aberration was significantly larger when the VN axis rather than the LOS axis was used for pupils of both diameters. For corneal HOAs before surgery, in addition to the larger spherical-like aberration for VN, coma-like aberrations were significantly larger with LOS than with VN for both pupil diameters. For corneal HOAs after surgery, the spherical-like aberrations and total HOAs for 4-mm-diameter pupils with VN were significantly larger than those with LOS.

CONCLUSIONS

The HOAs were significantly different depending on the axes used and should be described on the basis of a common axis. These results suggest that the anterior surface of the normal or post-LASIK cornea is more rotationally symmetrical along the VN than along the LOS.

Avoidance, recognition, and management of LASIK complications

PURPOSE

To provide important concepts of the latest developments in laser in situ keratomileusis (LASIK) complication avoidance, recognition, and management.

DESIGN

A perspective.

METHODS

A comprehensive literature search and review of a total of 816 publications that discussed LASIK complications from 1992 to 2005 was conducted.

RESULTS

The risk of visually threatening complications is inherent in any ophthalmologic surgical procedure. Not only does LASIK require the use of several complex medical devices, but there can be significant human variation in response to this surgical intervention. As a result, many potential complications can occur after LASIK. The risk of many complications can be mitigated by appropriate patient selection and preoperative, surgical, and postoperative care. Unforeseen complications will occur, despite meticulous planning, and must be managed. Important current developments in the avoidance, recognition, and management of LASIK complications are reviewed.

CONCLUSIONS

Complications as a result of LASIK can threaten vision and may cause debilitating symptoms in an otherwise healthy eye. Advancing our understanding of the prevention and management of the complications of LASIK is an endeavor that must be continued as long as refractive surgery is performed.

Laser in situ keratomileusis in myopic patients with congenital nystagmus

PURPOSE

To evaluate the results of laser in situ keratomileusis (LASIK) and IntraLASIK in the treatment of myopic patients with nystagmus.

METHODS

Eight patients with congenital nystagmus (16 eyes), aged 23 to 49 years, had LASIK surgery. Corneal flaps were created using the Bausch & Lomb Hansatome microkeratome or the IntraLase femtosecond laser. The ablations were performed with the Bausch & Lomb excimer laser with an active tracking system. In some patients, the eyes were fixated with forceps or a fixation ring during laser ablation.

RESULTS

The refractive errors were corrected in all cases. There was no decentration or loss of best corrected visual acuity greater than 1 line. In 56% of the eyes, the postoperative uncorrected visual acuity was better than the best spectacle-corrected visual acuity (BSCVA). The BSCVA improved in 62.5% of the eyes. The overall visual performance improved in all patients. One patient who did not drive before surgery became eligible for a driver's license after surgery.

CONCLUSIONS

Selected patients with myopia and congenital nystagmus may benefit from laser refractive surgery. Laser refractive surgery may be safely and accurately performed using the Hansatome microkeratome or the IntraLase femtosecond laser and an active tracking system with or without mechanical fixation. The BSCVA may improve in certain patients postoperatively.

Comparison of Ablation Centration After Bilateral Sequential Versus Simultaneous LASIK

PURPOSE

To compare ablation centration after bilateral sequential and simultaneous myopic LASIK.

METHODS

A retrospective randomized case series was performed of 670 eyes of 335 consecutive patients who had undergone either bilateral sequential (group 1) or simultaneous (group 2) myopic LASIK between July 2000 and July 2001 at the China Medical University Hospital, Taichung, Taiwan. The ablation centrations of the first and second eyes in the two groups were compared 3 months postoperatively.

RESULTS

Of 670 eyes, 274 eyes (137 patients) comprised the sequential group and 396 eyes (198 patients) comprised the simultaneous group. Three months post-operatively, 220 eyes of 110 patients (80%) in the sequential group and 236 eyes of 118 patients (60%) in the simultaneous group provided topographic data for centration analysis. For the first eyes, mean decentration was 0.39 +/- 0.26 mm in the sequential group and 0.41 +/- 0.19 mm in the simultaneous group (P = .30). For the second eyes, mean decentration was 0.28 +/- 0.23 mm in the sequential group and 0.30 +/- 0.21 mm in the simultaneous group (P = .36). Decentration in the second eyes significantly improved in both groups (group 1, P = .02; group 2, P < .01). The mean distance between the first and second eyes was 0.31 +/- 0.25 mm in the sequential group and 0.32 +/- 0.18 mm in the simultaneous group (P = .33). The difference of ablation center angles between the first and second eyes was 43.2 < or = 48.3 degrees in the sequential group and 45.1 +/- 50.8 degrees in the simultaneous group (P = .42).

CONCLUSIONS

Simultaneous bilateral LASIK is comparable to sequential surgery in ablation centration.

Comparison of ablation centration in initial and retreatment active eye-tracker-assisted laser in situ keratomileusis and the effect on visual outcome

PURPOSE

To evaluate the relationship between initial and retreatment ablation centers in active eye-tracker-assisted myopic laser in situ keratomileusis (LASIK) and determine whether the relationship between the 2 ablation centers influences the visual outcome after retreatment.

SETTING

Department of Ophthalmology, China Medical University Hospital, Taichung, Taiwan.

METHODS

This retrospective study comprised 21 eyes of 15 patients who had retreatment at least 3 months after primary myopic LASIK by lifting the initial flap. Corneal topography and best corrected visual acuity (BCVA) were evaluated preoperatively and 3 months postoperatively. The ablation centration was analyzed by corneal topography preoperatively and at 3 months.

RESULTS

The mean decentration of the primary treatment was 0.43 mm +/- 0.21 (SD) and of the retreatment, 0.34 +/- 0.15 mm. There was no significant difference between them (P =.07). The 2 ablation centers were close each other. The mean distance between the 2 ablation centers was 0.29 +/- 0.18 mm and the mean angle between them, 39.7 +/- 46.2 degrees. The BCVA was unchanged after retreatment regardless of the relationship between the 2 ablation centers.

CONCLUSIONS

With an active eye-tracking system, the retreatment center was not only close to the pupil center but also close to the primary ablation center. Regardless of the relationship between the 2 ablation centers, the BCVA did not change if the retreatment ablation was well centered.

Five-Year Follow-Up of Photorefractive Keratectomy for Myopia

PURPOSE

To analyze long-term results of photorefractive keratectomy (PRK) for myopia and myopic astigmatism.

METHODS

This retrospective study included 15 eyes of 8 patients who were examined annually for 5 years after PRK. The Nidek EC-5000 laser with an ablation zone of 5.0 mm was used. Evaluations included spherical equivalent manifest refraction, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), corneal haze, and corneal astigmatism calculated by Fourier analysis of videokeratography data.

RESULTS

A tendency toward myopic regression was most evident within the first postoperative year, with manifest refraction changing from +0.80 +/- 1.62 D at 1 week to -0.45 +/- 0.70 D at 1 year postoperatively (P = .007). Regression continued after the second postoperative year. There was a statistically significant difference between manifest refraction at 2 years (-0.36 +/- 0.75 D) and 5 years (-1.11 +/- 1.12 D) (P = .002). Postoperative UCVA stabilized from 3 months up to 3 years, but slightly deteriorated at 4 years and thereafter due to the myopic refractive shift. BSCVA remained stable throughout the 5-year follow-up period. Several eyes developed mild corneal haze after surgery, but haze was minimal in the majority of patients by 1 year and continued to fade over time. The asymmetry component of the cornea significantly increased after surgery, with all postoperative values significantly higher than before PRK (P < .05). Higher order irregularity increased after surgery, with a statistically significant difference between preoperative and 1 year postoperative (P < .05), but values after 2 years were not different from preoperative baseline.

CONCLUSION

Fifteen eyes with a baseline refraction of -3.00 to -9.00 D had PRK with the Nidek EC-5000 laser and a 5-mm-diameter ablation zone. Myopic regression occurred in the first year, with continued mild regression of approximately -0.75 D between 2 and 5 years. Nevertheless, the results show the procedure was relatively safe and effective in this group.

Maximum permissible torsional misalignment in aberration-sensing and wavefront-guided corneal ablation

PURPOSE

To determine the maximum permissible torsional misalignment in wavefront-guided refractive surgery.

SETTING

University of Zurich, Department of Ophthalmology, Zurich, Switzerland.

METHODS

The effect of torsionally misaligned ablations on the optical outcome was simulated using measured wavefront aberration patterns (2nd to 6th orders) in 130 normally aberrated eyes. The calculations were done for 3.0 mm, 5.0 mm, and 7.0 mm pupils. The optical quality of the simulated correction was rated by the root-mean-square residual wavefront error.

RESULTS

The required accuracy of torsional alignment is higher for the correction of higher-order aberrations than for cylindrical treatments only. To improve the optical performance to the level of the best 10% of a normal, untreated population, ablation would have to occur within a tolerance range of 4.0 degrees for 7.0 mm pupils.

CONCLUSIONS

The tolerance range for torisional alignment in wavefront-guided higher-order corrections depends on the amount of original optical error in each eye. Rough centration based on the surgeon's judgment may not be accurate enough to achieve significantly improved optical quality in a high percentage of treated eyes.

Correlation of Aberrations With Visual Symptoms Using Wavefront Analysis in Eyes After Laser in situ Keratomileusis

PURPOSE

To evaluate the information assessed with the Alcon LADARWave wavefront measurement device and correlate it with visual symptoms in eyes previously treated with laser in situ keratomileusis (LASIK), and to analyze the influence of scotopic pupil size on visual symptoms.

METHODS

One hundred and five eyes of 58 patients who underwent LASIK were evaluated. Wavefront measurements were assessed using the Alcon LADARWave device. Visual symptoms were correlated to higher order aberrations in three different pupil sizes (5 mm, 7 mm, and scotopic pupil size). Generalized estimating equations were used for statistical analysis.

RESULTS

In eyes after LASIK, visual symptoms analysis showed positive correlation of double vision with total coma and with horizontal coma for the 5-mm and 7-mm pupil sizes, negative correlation between starburst and total coma for the 7-mm pupil size, positive correlation of double vision with horizontal coma, and glare and starburst with spherical aberration and with total aberrations. Scotopic pupil size had a positive association with starburst and negative association with double vision.

CONCLUSION

The LADARWave wavefront measurement device is a valuable diagnostic tool in measuring ocular aberrations in eyes after LASIK. A strong correlation between visual symptoms and ocular aberrations, such as monocular diplopia with coma, and starburst and glare with spherical aberration, suggest this device is valuable in diagnosing symptomatic LASIK-induced aberrations. Horizontal coma was correlated with double vision, while vertical coma was not, demonstrating a greater sensitivity with horizontally oriented multifocality.

Ablation Centration in Laser in situ Keratomileusis for Hyperopia: Comparison of VISX S3 ActiveTrak and VISX S2

PURPOSE

To compare ablation centration and outcome measurements in laser in situ keratomileusis (LASIK) for hyperopia using the pupil-tracking VISX S3 ActiveTrak or the nontracking VISX S2 excimer laser.

METHODS

In a retrospective study, 49 consecutively treated hyperopic eyes (32 patients) that had LASIK by the VISX StarS3 ActiveTrak were compared to 49 control-matched eyes treated with the VISX StarS2 without pupil-tracking. Primary outcome variables including ablation centration, uncorrected visual acuity, best spectacle-corrected visual acuity, manifest refraction, complications, and induced cylinder analyzed by vector analysis were evaluated 3 months postoperatively.

RESULTS

Hyperopic sphere ranged between plano and +5.50 D and cylinder between 0 and +2.75 D. Ninety-five of 98 eyes (96.9%) were available for analysis at 3 months. Of these 95, 52 eyes could be used for analysis of ablation centration. Mean decentration of the ablation zone from the entrance pupil was 0.30 +/- 0.20 mm in tracked eyes (n=31) and 0.41 +/- 0.39 mm in nontracked eyes (n=21), P=.17. Two eyes (6.5%) in the tracked group were significantly decentered between 0.5 and 1 mm from the pupil center. In the nontracked group, decentration was between 0.5 and 1 mm in one eye (4.8%) and greater than 1 mm in two eyes (9.5%).

CONCLUSIONS

Comparable ablation centration in LASIK for hyperopia was achieved between actively-tracked and nontracked eyes. Decentrations (greater than 1 mm) were not seen with a tracking system in this study. Visual and refractive results were similar between the VISX StarS3 ActiveTrak and VISX StarS2 laser systems.

Ablation centration in myopic laser in situ keratomileusis. comparing the Visx S3 ActiveTrak and the Visx S2

PURPOSE

To compare ablation centration and outcome measurements in myopic laser in situ keratomileusis (LASIK) using the eye-tracking Visx S3 ActiveTrak and the nontracking Visx S2 excimer lasers.

SETTING

University-based refractive surgery practice.

METHODS

In a retrospective study, 71 consecutively treated myopic eyes that had LASIK with the Visx Star S3 ActiveTrak were compared to 71 control-matched eyes treated with the Visx Star S2 without pupil tracking. Primary outcome variables including ablation centration, uncorrected visual acuity, best spectacle-corrected visual acuity, manifest refraction, complications, and induced cylinder analyzed by vector analysis were evaluated 3 months postoperatively.

RESULTS

The myopia ranged from -1.50 to -11.25 diopters (D) and the cylinder, from +0.25 to +2.75 D. Ninety-four of 142 eyes (66%) were available for analysis at 3 months; 50 eyes could be used to analyze ablation centration. At 3 months, the mean decentration of the ablation zone from the entrance pupil was 0.22 mm +/- 0.20 (SD) in tracked eyes (n = 25) and 0.21 +/- 0.26 mm in nontracked eyes (n = 25) (P =.88). Three eyes (12%) in the tracked group were decentered 0.5 to 1.0 mm, and 1 eye (4%) in the nontracked group was decentered more than 1.0 mm. All other eyes were decentered less than 0.5 mm. There was an association in the tracked group between greater decentrations and higher levels of myopia (r = 0.67), but this association did not exist in the nontracked group (r = -0.03).

CONCLUSION

Comparable ablation centration as well as visual and refractive outcomes can be achieved with and without active eye tracking during myopic and astigmatic myopic LASIK.

Clinical results of laser in situ keratomileusis with superior and nasal hinges

PURPOSE

To compare the differences in the clinical results of LASIK with a nasal corneal flap and with a superior corneal flap.

SETTING

Department of Ophthalmology, Kangnam St. Mary's Hospital, Seoul, Korea.

METHODS

This randomized prospective study comprised 30 patients whose age and degrees of myopia were similar. In 1 group (25 eyes), a superior hinge was made and in the other group (25 eyes), a nasal hinge was made. Uncorrected visual acuity (UCVA), spherical equivalent (SE), astigmatism, and corneal topographical change before surgery and 1 week and 2 and 6 months after surgery were compared. The tear breakup time (BUT) and the Schirmer test before surgery and 2 months postoperatively were also compared.

RESULTS

At 6 months, there were no significant between-group differences in UCVA, SE, astigmatism, and corneal ablation decentration (P >.05). At 2 months, the results of BUT and the Schirmer tests were 6.80 seconds and 9.54 mm, respectively, in the nasal hinge group (P >.05) and 5.08 seconds and 6.05 mm, respectively, in the superior hinge group (P <.05).

CONCLUSIONS

There were no between-group differences in UCVA, SE, astigmatism, and corneal ablation decentration at 6 months, but the BUT and Schirmer test results were aggravated after LASIK in the superior hinge group.

Glare and halo phenomena after laser in situ keratomileusis

PURPOSE

To simulate and measure subjectively observed glare and halos after laser in situ keratomileusis (LASIK).

SETTING

University of Vienna, Medical School, Department of Ophthalmology, Vienna, Austria.

METHODS

In 16 eyes of 10 patients, the best corrected visual acuity (BCVA) and subjectively observed glare and halo size under mesopic conditions were measured before LASIK and 1, 3, and 6 months postoperatively. Infrared pupillography was used to ensure that all patients had a larger ablation zone than the measured pupil size under mesopic conditions.

RESULTS

Preoperatively, the mean Snellen BCVA was 0.88 +/- 0.17 (SD) and the mean glare and halo size was 1.97 +/- 1.20 square degrees (sqd) before the treatment. One month after LASIK, the BCVA was 0.83 +/- 0.29 and the mean glare and halo size, 2.61 +/- 3.14 sqd. Three months after LASIK, the mean values were 0.90 +/- 0.26 and 1.88 +/- 2.37 sqd, respectively. Six months after LASIK treatment, they were 0.85 +/- 0.28 and 1.30 +/- 1.63 sqd, respectively. The 95% confidence interval for the difference between preoperative glare and halo and glare and halo at 6 months was -1.56 to + 0.51 sqd.

CONCLUSIONS

Subjectively observed glare and halo size after LASIK reached a peak after 1 month and decreased in the following postoperative period.

Maximum permissible lateral decentration in aberration-sensing and wavefront-guided corneal ablation

PURPOSE

To investigate the lateral alignment accuracy needed in wavefront-guided refractive surgery to improve the ocular optics to a desired level in a percentage of normally aberrated eyes.

SETTING

Department of Ophthalmology, University of Zurich, Zurich, Switzerland.

METHODS

The effect of laterally misaligned ablations on the optical outcome was simulated using measured wavefront aberration patterns from 130 normal eyes. The calculations were done for 3.0 mm, 5.0 mm, and 7.0 mm pupils. The optical quality of the simulated correction was rated by means of the root-mean-square residual wavefront error.

RESULTS

To achieve the diffraction limit in 95% of the normal eyes with a 7.0 mm pupil, a lateral alignment accuracy of 0.07 mm or better was required. An accuracy of 0.2 mm was sufficient to reach the same goal with a 3.0 mm pupil.

CONCLUSION

Procedures must be developed to ensure that the ablation is within a tolerance range based on each eye's original optical error. Rough centration based on the surgeon's judgment might not be accurate enough to achieve significantly improved optical quality in a high percentage of treated eyes.

Corneal flap displacement and drift in LASIK: comparison of Hansatome and Automated Corneal Shaper microkeratomes

PURPOSE

To describe and compare the displacement of corneal flaps created during laser in situ keratomileusis (LASIK) procedures performed with two different microkeratomes and analyze parameters (for example, pupil-to-hinge distance, drift during suction) that might affect the flap displacement or be influenced by flap displacement.

DESIGN

This work was based on a cross-sectional study design.

METHODS

Images copied from video recordings of 206 consecutive LASIK surgeries were analyzed to determine the distance from pupil center to corneal flap hinge (pupil-to-hinge distance), the hinge size, the distance from the center of the pupil to the margins of the flap, and the positions of the suction ring before and after vacuum in corneal flaps created by the Hansatome and the Automated Corneal Shaper (ACS) microkeratomes. Accurate measurements of all these variables could be obtained in 121 eyes (Hansatome: n = 66, right eye (OD) = 27 eyes, left eye (OS) = 39 eyes; ACS: n = 55, OD = 25 eyes, OS = 30 eyes), which were included in the analysis. Formulas were derived to calculate from the measurements the magnitude and direction of the drift of the suction ring during vacuum and the final displacement of the corneal flap.

RESULTS

The mean +/- standard deviation (SD) drift of eyes during suction with the Hansatome was 0.27 +/- 0.02 mm and with the ACS was 0.12 +/- 0.02 mm (P <.001). The Hansatome induced, on average, more biased (temporal vs random) drift than did the ACS. The mean final displacement of the center of the flap from the center of the pupil was of equal magnitude for the two instruments (0.37 +/- 0.02 mm and 0.36 +/- 0.02 mm with the Hansatome and ACS, respectively).

CONCLUSION

The drift induced by the Hansatome contributes to the horizontal component of the final decentration of the corneal flaps. This tendency for drift and the resultant decrease in pupil-to-hinge distance should be considered to minimize flap displacements during LASIK.

Contrast sensitivity after laser in situ keratomileusis. one-year follow-up

PURPOSE

To determine whether contrast sensitivity measurement, a more sensitive test of visual function than visual acuity, better characterizes visual outcomes after laser in situ keratomileusis (LASIK).

SETTING

Hong Kong Laser Eye Centre, Hong Kong, China.

METHODS

Contrast sensitivity was monitored in 41 LASIK patients for 1 year. Seven spatial frequencies (0.3, 0.8, 1.5, 3.4, 6.9, 10.3, and 20.5 cpd) were tested with 15 sequences per spatial frequency, and a staircase technique was used for target presentation.

RESULTS

There was a general depression in the contrast sensitivity function after LASIK; 1.5 cpd and 3.4 cpd were the most affected frequencies. Recovery took at least 6 months. The reduction in contrast sensitivity was greater for higher amounts of myopia.

CONCLUSION

The post-LASIK nonpermanent depression in contrast sensitivity was probably due to optical factors.

Laser in situ Keratomileusis for Myopic Astigmatism With the Nidek EC-5000 Laser

PURPOSE

We studied the efficacy, predictability, and safety of laser in situ keratomileusis (LASIK) for moderate to high simple and compound myopic astigmatism.

METHODS

Ninety-two eyes of 46 consecutive patients who had LASIK for myopic astigmatism (64 eyes, astigmatism 3.00 to 9.00 D; myopia 0 to -20.00 D), or simple myopia (28 eyes, myopia -4.00 to -20.00 D; astigmatism 0 to 0.50 D) were retrospectively studied. Mean baseline spherical equivalent refraction (SE) in the myopia group was -8.11 +/- 3.94 D and in the astigmatism group, -8.55 +/- 4.49 D. All eyes underwent LASIK using the Nidek EC-5000 laser by the same surgeon.

RESULTS

At 6 months after LASIK in the myopia group versus the astigmatism group, 24 eyes (85%) vs. 54 eyes (84%) were available for follow-up, 12 eyes (50%) vs. 13 eyes (24%) had uncorrected visual acuity (UCVA) of 20/20, 19 eyes (79%) vs. 44 eyes (81%) had UCVA of 20/40, 8 eyes (33%) vs. 18 eyes (33%) had SE within +/- 0.50 D, 15 eyes (62%) vs. 39 eyes (72%) had SE within +/- 1.00 D, and mean SE was -1.22 +/- 1.17 D vs. -0.74 +/- 1.46 D. Mean astigmatism (vertexed to the corneal plane) in the astigmatism group was 2.77 D at 0 degrees before surgery and 0.32 D at 7 degrees at 6 months. None of the myopic eyes and three of the astigmatic eyes (5%) lost > or = 2 lines of best spectacle-corrected visual acuity.

CONCLUSION

LASIK with the Nidek EC-5000 laser for myopic astigmatism was reasonably effective, predictable, and safe. Astigmatism was under-corrected with the nomogram implemented in this study.

Laser in situ keratomileusis in a patient with congenital nystagmus

We report the results of laser in situ keratomileusis (LASIK) to correct myopia in a 47-year-old woman with congenital motor nystagmus and myopia. The patient had simultaneous bilateral LASIK using the Alcon-Summit-Autonomous LADARVision excimer laser. Her uncorrected visual acuity (UCVA) preoperatively was 20/600 in the right eye and 20/800 in the left eye; best corrected visual acuity was 20/40 in both eyes. Twelve months after bilateral LASIK, with an enhancement procedure in both eyes at 4 months, UCVA was 20/40 in both eyes. Corneal topography showed well-centered ablation zones.

Monocular Diplopia Related to Asymmetric Corneal Topography After Laser in situ Keratomileusis

PURPOSE

To show a specific relationship between monocular diplopia and corneal refractive asymmetry after laser in situ keratomileusis (LASIK).

METHODS

One hundred thirty-eight eyes of 98 patients who underwent LASIK for myopia between -2.12 and -17.75 D were examined under room-lighted conditions. We examined 51 eyes at 2 weeks, 46 eyes at 3 months, 32 eyes at 6 months, and 9 eyes at 1 year after LASIK. We attempted to correlate the presence of monocular diplopia with their corneal topographical features.

RESULTS

Eight eyes of five patients (five eyes at 2 weeks, three eyes at 3 months after LASIK) produced symptoms of monocular diplopia. These symptomatic patients had a common corneal topographical feature caused by decentralized or inhomogeneous ablation. Every pupillary area in the patients' topographies contained steeper and flatter areas. The range of refractive power variation in these asymmetric areas was at least 1.50 D. The location of the secondary image correlated with the direction of the steeper area in all eight eyes. Pinhole viewing eliminated or reduced the prominence of secondary images in every case.

CONCLUSION

Monocular diplopia following LASIK appears to correlate with postoperative corneal refractive power variation inside the pupillary area, caused by decentralized or inhomogeneous ablation.

Surgically induced topographical abnormalities after LASIK: management of central islands, corneal ectasia, decentration, and irregular astigmatism

Proper preoperative evaluation is critical for avoiding many postoperative complications associated with laser in-situ keratomileusis (LASIK). Proper nonsurgical management includes careful monitoring of patients during the recovery period using various testing procedures, including corneal topography. When surgical intervention is required, a stepwise approach often is used as a conservative treatment, allowing further treatment if necessary. Many complications after LASIK are amenable to further treatment. However, it often is advisable to monitor patients until improved instrumentation is developed. The authors review the etiology and management of several complications after LASIK by reviewing the literature and relaying their own clinical experiences.

200 Hz flying-spot technology of the LaserSight LSX excimer laser in the treatment of myopic astigmatism: six and 12 month outcomes of laser in situ keratomileusis and photorefractive keratectomy

PURPOSE

To evaluate safety, efficacy, predictability, and stability in the treatment of myopic astigmatism with laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) using the 200 Hz flying-spot technology of the LaserSight LSX excimer laser.

SETTING

SynsLaser Clinic, Tromsø, Norway.

METHODS

This retrospective study included 110 eyes treated with LASIK and 87 eyes treated with PRK that were available for evaluation at 6 and 12 months, respectively. The mean preoperative spherical equivalent (SE) was -5.35 diopters (D) +/- 2.50 (SD) (range -1.13 to -11.88 D) in the LASIK eyes and -4.72 +/- 2.82 D (range -1.00 to -15.50 D) in the PRK eyes. The treated cylinder was 4.00 D in both groups. Eleven (8.5%) LASIK eyes and 8 (7.4%) PRK eyes had secondary surgical procedures before 6 and 12 months, respectively, and were excluded when the 6 and 12 month outcomes were analyzed.

RESULTS

None of the eyes lost 2 or more lines of best spectacle-corrected visual acuity. Seventy-seven percent of the LASIK eyes and 78% of the PRK eyes achieved an uncorrected visual acuity of 20/20 or better; 98% in both groups achieved 20/40 or better. The SE was within +/-0.5 D of the desired refraction in 83% of the LASIK eyes and 77% of the PRK eyes; it was within +/-1.0 D in 97% and 98%, respectively. The cylinder correction had a mean magnitude of error of 0.04 +/- 0.31 D (range -0.96 to +0.85 D) in the LASIK eyes and 0.02 +/- 0.37 D (range -1.44 to +0.72 D) in the PRK eyes. Refractive stability was achieved at 1 month and beyond in the LASIK eyes and at 3 months and beyond in the PRK eyes.

CONCLUSION

The outcomes of this study are comparable to those achieved with lasers that use small-beam technology with a lower frequency, as well as with other types of delivery systems. They suggest that the 200 Hz technology used in the LaserSight LSX excimer laser is safe, effective, and predictable and that with LASIK and PRK the results are stable when treating low to moderate myopia and astigmatism up to 4.0 D.

Improvement in photorefractive corneal laser surgery results using an active eye-tracking system

PURPOSE

To study the advantage of modern eye-tracking systems for photorefractive surgery.

SETTING

Department of Ophthalmology, University of Zurich, Zurich, Switzerland.

METHODS

Photorefractive surgery (photorefractive keratectomy and laser in situ keratomileusis) for myopia and myopic astigmatism was performed in 40 eyes with a commercially available medical excimer laser system. The eyes were selected retrospectively from a larger group of patients treated at 1 clinic. In 20 eyes, the ablation was centered on the entrance pupil using the active, video-based, eye-tracking system (sampling frequency 50 Hz) of the laser. During laser treatment in the nontracker group (20 eyes), the active eye-tracking system was switched off and centration was done manually by the surgeon. Preoperatively and 1 and 3 months after surgery, the patients had a standard ophthalmic examination as well as wavefront analysis by means of a custom-designed wavefront analyzer.

RESULTS

After surgery, the visual acuity was significantly better (P <.05) in patients treated with the eye tracker. The increase in coma-like (relative increase factor 0.4) and spherical aberrations (relative increase factor 1.1) was significantly smaller in these patients than in those in the nontracker group (spherical equivalents of 3.9 and 5.1, respectively; P <.05). The refractive outcome, however, was not significantly different in sphere and cylinder.

CONCLUSION

The use of active eye tracking appeared to improve the optical and visual outcomes but did not affect the refractive outcome after photorefractive laser surgery.

Corneal irregular astigmatism after laser in situ keratomileusis for myopia

AIMS

To quantitatively evaluate the changes in corneal irregular astigmatism after laser in situ keratomileusis (LASIK) in relation to the amount of laser ablation.

METHODS

In 189 eyes of 116 patients undergoing LASIK for myopia, corneal topography was obtained before and 1 month after surgery. Using Fourier harmonic analysis of the topography data, corneal irregular astigmatism (asymmetry and higher order irregularity) was calculated.

RESULTS

By surgery, asymmetry component significantly increased (p < 0.0001, Wilcoxon signed rank test), while higher order irregularity did not (p = 0.767). The increases in the asymmetry component significantly correlated with ablation depth (Spearman rank correlation coefficient r(s) = 0.440, p < 0.0001). No significant correlation was found between changes in higher order irregularity and ablation depth (r(s) = 0.137, p = 0.074).

CONCLUSION

LASIK significantly increases the asymmetry component of the cornea which is dependent on the amount of laser ablation.