Topography-Guided Versus Wavefront-Optimized LASIK for Myopia With and Without Astigmatism: A Meta-analysis

PURPOSE

To evaluate the differences in efficacy, predictability, safety, and visual quality between topography-guided customized ablation treatment (TCAT) and wavefront-optimized (WFO) laser in situ keratomileusis (LASIK) for the treatment of myopia with and without astigmatism.

METHODS

A comprehensive literature search of PubMed, Embase, the Cochrane library, Web of Science, and ClinicalTrials was used to identify randomized controlled trials (RCTs) comparing TCAT-LASIK with WFO-LASIK for myopia with and without astigmatism up to September 2020. The references of all searched literature were checked as supplements. Literature was screened according to the inclusion and exclusion criteria and relative data were extracted. RevMan software version 5.3.0 (Cochrane Collaboration) was used for meta-analysis.

RESULTS

A total of seven RCTs (1,168 eyes) were included. There were no statistically significant differences in the ratio of uncorrected distance visual acuity of 20/20 or better (relative risk [RR] = 1.01, 95% CI [0.97 to 1.06], P = .64) and 20/16 or better (RR = 0.96, 95% CI [0.80 to 1.16], P = .69). Compared with WFO-LASIK, TCAT-LASIK achieved a higher proportion of postoperative manifest refractive spherical equivalent within ±0.50 diopters of the target (RR = 1.06, 95% CI [1.02 to 1.11], P = .003) and less surgically induced higher order aberrations (weighted mean difference [WMD] = -0.11, 95% CI [-0.15 to -0.0], P < .00001), spherical aberrations (WMD = -0.04, 95% CI [-0.05 to -0.03], P < .00001), and coma (WMD = -0.15, 95% CI [-0.28 to -0.01], P = .03). No patient lost two or more lines of distance-corrected visual acuity postoperatively in the two groups.

CONCLUSIONS

This meta-analysis suggests that both TCATLASIK and WFO-LASIK show excellent efficacy, predictability, and safety for myopia. TCAT-LASIK exhibited more accurate postoperative refraction predictability and less surgically induced higher order aberrations, spherical aberrations, and coma. More randomized, prospective, and large sample-sized studies are needed to confirm these conclusions in the long term. [J Refract Surg. 2021;37(10):707-714.].

Past and present of corneal refractive surgery: a retrospective study of long-term results after photorefractive keratectomy and a prospective study of refractive lenticule extraction

Surgical correction of refractive errors is becoming increasingly popular. In the 1990s, the excimer laser revolutionized the field of corneal refractive surgery with PRK and LASIK, and lately refractive lenticule extraction (ReLEx) of intracorneal tissue, using only a femtosecond laser, has become possible. Two new procedures were developed, ReLEx flex (FLEX) and ReLEx smile (SMILE). Until this thesis, only a few long-term studies of PRK with a relatively limited number of patients had been published; therefore, this thesis intended to retrospectively evaluate long-term outcomes after PRK for all degrees of myopia for a large number of patients. Furthermore, a prospective contralateral eye study comparing FLEX and SMILE, when treating high to moderate degrees of myopia, had not been performed prior to this study. This was the second aim of this thesis. In the first study, results from 160 PRK patients (289 eyes) were presented. Preoperative spherical equivalent ranged from -1.25 to -20.25 D, with 78% having low myopia (<-6 D). Average follow-up time was 16 years (range 13-19 years), making this the longest published follow-up study on PRK patients. Outcomes from eyes with low myopia were generally superior to outcomes from eyes with high myopia, at final follow-up. Seventy-two percent were within ± 1.00 D of target refraction, as compared to 47% of eyes with high myopia. However, results from a subgroup of unilateral treated PRK patients indicated that refraction at final follow-up was affected by myopic progression. Fifty percent of eyes with low myopia had uncorrected 20/20 distance visual acuity or better, as compared to 22% of eyes with high myopia. Haze did not occur if attempted corrections were <-4 D, and only eyes with high myopia lost two lines or more of CDVA (corrected distance visual acuity). Eighty-one per cent were satisfied or very satisfied with their surgery.

CONCLUSION

The results support the continued use of the excimer laser for corneal surface ablation as a treatment option for correction of low degrees of myopia, and as the treatment of choice for subgroups of refractive patients (thin corneas, etc.). The results also highlight that treatment of higher degrees of myopia with standard PRK should only be done today under special circumstances, due to low refractive predictability, and high risk of corneal haze. Technological advances since then should be taken into account when comparing these results with contemporary techniques. In the second study, 35 patients were randomized to receive FLEX in one eye and SMILE in the other. Preoperative spherical equivalent refraction ranged from -6 to -10 D with low degrees of astigmatism. A total of 34 patients completed the 6 month follow-up period. Refractive and visual outcomes were very similar for the two methods, as well as tear film measurements and changes in corneal biomechanics. Ninety-seven percent were within ± 1.00 D of target refraction, no eyes lost two lines or more of CDVA, and contrast sensitivity was unaffected after both procedures. The changes in higher-order aberrations were also very similar. There were also no differences in tear film parameters 6 months after surgery, although less postoperative foreign body sensation was reported within the first week after surgery in SMILE eyes. Corneal sublayer pachymetry measurements demonstrated equally increased epithelial thickness 6 months after surgery. Contrary to expectations, it was not possible to measure the theoretical biomechanical advantages of a small corneal incision in SMILE as compared to a corneal flap in FLEX. The main differences between FLEX and SMILE were found when the corneal nerves and intraoperative complications were evaluated. Thus, corneal sensitivity was better preserved and corneal nerve morphology was less affected after SMILE, but intraoperative complications occurred more frequently, although without visual sequela. Finally, 97% were satisfied or very satisfied with both their surgeries.

CONCLUSION

The results support the continued use of both FLEX and SMILE for treatment of up to high degrees of myopia. Overall, refractive and visual results for both procedures were good and similar, but from a biological point of view, the less invasive SMILE technique is more attractive, as demonstrated in this study, despite being slightly more surgically demanding than FLEX.

Precision of a commercial hartmann-shack aberrometer: limits of total wavefront laser vision correction

PURPOSE

To assess the intrasession and intersession precision of higher-order aberrations (HOAs) measured using a commercial Hartmann-Shack wavefront sensor (Zywave; Bausch & Lomb) in refractive surgery candidates.

DESIGN

Prospective, experimental study of a device.

METHODS

To analyze intrasession repeatability, 1 experienced examiner measured 30 healthy eyes 5 times successively. To study intersession reproducibility, the same clinician obtained measurements from another 30 eyes in 2 consecutive sessions at the same time of day 1 week apart.

RESULTS

For intrasession repeatability, excellent intraclass correlation coefficients (ICCs) were obtained for total ocular aberrations, total HOAs, and second-order terms (ICC, > 0.94). The ICCs for third-order terms also were high (ICCs, > 0.87); however, fourth-order ICCs varied from 0.71 to 0.90 (Z(4)(0) = 0.90); and fifth-order ICCs were less than 0.85. For intersession reproducibility, only total ocular aberrations, total ocular HOAs, second-order terms, Z(4)(0), Z(3)(1), and Z(3-)(3) had ICCs of 0.90 or more. Bland-Altman analysis showed that the limits of agreement (were clinically too wide for most higher-order Zernike terms, especially for the third-order terms (> 0.21 μm).

CONCLUSIONS

Total ocular aberrations, total HOAs, and second-order terms can be measured reliably by Zywave aberrometry without anatomic recognition. Third-order terms and Z(4)(0) are repeatable, but not as reproducible between visits. Fourth-order terms, except for Z(4)(0), and fifth-order terms are not sufficiently reliable for clinical decision making or treatment. Because the variability of Zywave can be a major limitation of a truly successful wavefront-guided excimer laser procedure, surgeons should consider treating HOA magnitudes that are more than the intrasession repeatability values (2.77 × S(w)) as those presented in this study.

Analysis of the effects of Eye-Tracker performance on the pulse positioning errors during refractive surgery☆

Purpose

To analyze the effects of Eye-Tracker performance on the pulse positioning errors during refractive surgery.

Methods

A comprehensive model, which directly considers eye movements, including saccades, vestibular, optokinetic, vergence, and miniature, as well as, eye-tracker acquisition rate, eye-tracker latency time, scanner positioning time, laser firing rate, and laser trigger delay have been developed.

Results

Eye-tracker acquisition rates below 100 Hz correspond to pulse positioning errors above 1.5 mm. Eye-tracker latency times to about 15 ms correspond to pulse positioning errors of up to 3.5 mm. Scanner positioning times to about 9 ms correspond to pulse positioning errors of up to 2 mm. Laser firing rates faster than eye-tracker acquisition rates basically duplicate pulse-positioning errors. Laser trigger delays to about 300 μs have minor to no impact on pulse-positioning errors.

Conclusions

The proposed model can be used for comparison of laser systems used for ablation processes. Due to the pseudo-random nature of eye movements, positioning errors of single pulses are much larger than observed decentrations in the clinical settings. There is no single parameter that ‘alone’ minimizes the positioning error. It is the optimal combination of the several parameters that minimizes the error. The results of this analysis are important to understand the limitations of correcting very irregular ablation patterns.

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.