Risk Factors for Sporadic Diffuse Lamellar Keratitis After Microkeratome Laser-Assisted In Situ Keratomileusis: A Retrospective Large Database Analysis

Factors Predicting Loss of Best-Corrected Visual Acuity After Hyperopic Laser-Assisted In Situ Keratomileusis

PURPOSE

The aim of this study was to identify risk factors for the loss of corrected distance visual acuity (CDVA) after uncomplicated hyperopic laser-assisted in situ keratomileusis (LASIK).

METHODS

A retrospective study including hyperopic patients who underwent microkeratome-assisted LASIK between January 2000 and December 2019 at Care-Vision Laser Centers, Tel-Aviv, Israel. Loss of CDVA was defined as ≥ 2 lines (0.20 logarithm of the minimum angle of resolution [logMAR] increase). Excluded were patients who had loss of CDVA because of intraoperative or postoperative complications or developed cataract at their final visit.

RESULTS

Overall, 1998 eyes of 1998 patients were included in the study, of which 35 eyes (1.75%) had CDVA loss at final follow-up (mean 387 days). The vision-loss group had a significantly greater spherical treatment (3.4 vs. 2.8 D, P = 0.02), ablation depth (69.4 vs. 53.8 μm, P = 0.01), a higher proportion of treatments with a smaller optic zone (6.0 mm) (31.4% vs. 13.4%, P = 0.002), treatment with the EX200 (Alcon) excimer rather than the EX500 (Alcon) (74.3% vs. 39.0%, P < 0.001), and treatment with the Moria M2-90 microkeratome rather than the Moria Sub-Bowman's keratomileusis (SBK) microkeratome (65.7% vs. 29.6%, P < 0.001). In multivariate binary logistic regression, factors that remained significant predictors of CDVA loss were a greater spherical treatment (per 1 D treatment, odds ratio = 1.42, 95% CI, 1.11-1.81, P = 0.004) and the use of the Moria M2-90 microkeratome (odds ratio = 4.66, 95% CI, 2.30-9.45, P < 0.001).

CONCLUSIONS

In patients undergoing uncomplicated hyperopic LASIK, a greater spherical hyperopic treatment is associated with a higher risk for vision loss. Transition to a newer microkeratome model significantly reduced vision loss rate.

Bibliometric and visualized analysis of myopic corneal refractive surgery research: from 1979 to 2022

Background

Myopic corneal refractive surgery is one of the most prevalent ophthalmic procedures for correcting ametropia. This study aimed to perform a bibliometric analysis of research in the field of corneal refractive surgery over the past 40 years in order to describe the current international status and to identify most influential factors, while highlighting research hotspots.

Methods

A bibliometric analysis based on the Web of Science Core Collection (WoSCC) was used to analyze the publication trends in research related to myopic corneal refractive surgery. VOSviewer v.1.6.10 was used to construct the knowledge map in order to visualize the publications, distribution of countries, international collaborations, author productivity, source journals, cited references, keywords, and research hotspots in this field.

Results

A total of 4,680 publications on myopic corneal refractive surgery published between 1979 and 2022 were retrieved. The United States has published the most papers, with Emory University contributing to the most citations. The Journal of Cataract and Refractive Surgery published the greatest number of articles, and the top 10 cited references mainly focused on outcomes and wound healing in refractive surgery. Previous research emphasized "radial keratotomy (RK)" and excimer laser-associated operation methods. The keywords containing femtosecond (FS) laser associated with "small incision lenticule extraction (SMILE)" and its "safety" had higher burst strength, indicating a shift of operation methods and coinciding with the global trends in refractive surgery. The document citation network was clustered into five groups: (1) outcomes of refractive surgery: (2) preoperative examinations for refractive surgery were as follows: (3) complications of myopic corneal refractive surgery; (4) corneal wound healing and cytobiology research related to photorefractive laser keratotomy; and (5) biomechanics of myopic corneal refractive surgery.

Conclusion

The bibliometric analysis in this study may provide scholars with valuable to information and help them better understand the global trends in myopic corneal refractive surgery research frontiers. Two stages of rapid development occurred around 1991 and 2013, shortly after the innovation of PRK and SMILE surgical techniques. The most cited articles mainly focused on corneal wound healing, clinical outcomes, ocular aberration, corneal ectasia, and corneal topography, representing the safety of the new techniques.

Femtosecond Laser-Assisted Ophthalmic Surgery: From Laser Fundamentals to Clinical Applications

Femtosecond laser (FSL) technology has created an evolution in ophthalmic surgery in the last few decades. With the advantage of high precision, accuracy, and safety, FSLs have helped surgeons overcome surgical limits in refractive surgery, corneal surgery, and cataract surgery. They also open new avenues in ophthalmic areas that are not yet explored. This review focuses on the fundamentals of FSLs, the advantages in interaction between FSLs and tissues, and typical clinical applications of FSLs in ophthalmology. With the rapid progress that has been made in the state of the art research on FSL technologies, their applications in ophthalmic surgery may soon undergo a booming development.

Complications of laser-assisted in situ keratomileusis

Laser-assisted in situ keratomileusis (LASIK) is one of the most commonly performed kerato-refractive surgery globally. Since its introduction in 1990, there has been a constant evolution in its technology to improve the visual outcome. The safety, efficacy, and predictability of LASIK are well known, but complications with this procedure, although rare, are not unknown. Literature review suggests that intraoperative complications include suction loss, free cap, flap tear, buttonhole flap, decentered ablation, central island, interface debris, femtosecond laser-related complications, and others. The postoperative complications include flap striae, flap dislocation, residual refractive error, diffuse lamellar keratitis, microbial keratitis, epithelial ingrowth, refractive regression, corneal ectasia, and others. This review aims to provide a comprehensive knowledge of risk factors, clinical features, and management protocol of all the reported complications of LASIK. This knowledge will help in prevention as well as early identification and timely intervention with the appropriate strategy for achieving optimal visual outcome even in the face of complications.

Incidence, Risk, and Visual Outcomes after Repositioning of Acute Non-Traumatic Flap Dislocations Following Femtosecond-Assisted LASIK

Although the use of femtosecond lasers instead of mechanical devices has decreased the incidence of flap complications following laser-assisted in situ keratomileusis (LASIK), dislocations and striae still occur. Flap repositioning is an effective intervention to improve visual outcomes after acute flap complications in both microkeratome-assisted and femtosecond-assisted LASIK. This retrospective case series included patients undergoing flap repositioning secondary to acute flap dislocation and/or visually significant striae within the first two weeks following femtosecond LASIK (FS-LASIK) from 2015 to 2020 at a single institution. Preoperative, intraoperative, and postoperative de-identified data were analyzed for incidence, risk factors, and visual acuity outcomes. The incidence of flap repositioning was 0.35% in 21,536 eyes (n = 70). Indications for repositioning included acute flap dislocation (35.7%) and visually significant striae (64.3%). High myopia (OR = 3.04, p = 0.001) and patient age over 50 years (OR = 3.69, p = 0.001) were the strongest risk factors for these complications. Prior to flap repositioning, uncorrected distance visual acuity (UDVA) of 20/20 or better and 20/40 or better occurred in 19% and 57% of eyes, respectively. After repositioning, a final UDVA of 20/20 or better and 20/40 or better occurred in 78% and 98% of eyes, respectively. After repositioning, one line of UDVA was lost in two eyes (2.8%) and two lines were lost in one eye (1.4%). Risk factors for acute flap dislocation included high myopia and age over 50 years. Flap repositioning was effective in salvaging visual outcomes.

Diffuse lamellar keratitis after LASIK with low-energy femtosecond laser

PURPOSE

To evaluate the incidence, evolution, and prognosis of diffuse lamellar keratitis (DLK) in a large series of laser in situ keratomileusis (LASIK) with low-energy femtosecond laser.

SETTING

Private practice, Siena, Italy.

DESIGN

Retrospective, consecutive, noncomparative case series study.

METHODS

Single-use instruments, powder-free gloves, and no corneal marking were used. Flap was created by a low-energy femtosecond laser (Ziemer Z2 and Z4).

RESULTS

A total of 37 315 eyes of 19 602 patients were reviewed. DLK was observed in 236 eyes (0.63%) of 149 patients (0.76%). Grade 1 DLK was observed in 231 eyes of 142 patients, grade 2 in 1 eye: when treated with topical steroids, they had no visual consequences. Three patients had bilateral grade 3 to 4 DLK: one of them, with bilateral grade 3, despite flap lifting and irrigation worsened to stage 4 (central stroma thinning and flattening), partially recovered in 2 years, and underwent repeat femtosecond laser-assisted LASIK for hyperopic shift in 1 eye. In all the 5 eyes that developed grade 4 DLK, corneal thickness decreased until the first month and then partially recovered; mean final tissue loss at 1 to 2 years was 35 µm. Compensatory epithelial thickening was observed.

CONCLUSIONS

DLK after low-energy femtosecond laser-assisted LASIK is rare; severe DLK (stages 3 and 4) was found in only 6 eyes (0.016%). Flap lifting and irrigation might not prevent progression. Spontaneous reformation of stromal tissue and epithelial thickening improve visual acuity in the long term; residual hyperopic shift can be corrected by repeat femtosecond laser-assisted LASIK.

Complications of small incision lenticule extraction

The procedure of small incision lenticule extraction (SMILE) was introduced in 2011, and since then there has been an increase in the number of cases undergoing this procedure worldwide. The surgery has a learning curve and may be associated with problems in the intraoperative and postoperative periods. The intraoperative problems during SMILE surgery include the loss of suction, the occurrence of altered or irregular opaque bubble layer and black spots, difficulty in lenticular dissection and extraction, cap perforation, incision-related problems, and decentered ablation. Most of the postoperative problems are similar as in other laser refractive procedures, but with decreased incidence. The identification of risk factors, clinical features, and management of complications of SMILE help to obtain optimum refractive outcomes.

Refractive surgery beyond 2020

Refractive surgery refers to any procedure that corrects or minimizes refractive errors. Today, refractive surgery has evolved beyond the traditional laser refractive surgery, embodied by the popular laser in situ keratomileusis or 'LASIK'. New keratorefractive techniques such as small incision lenticule extraction (SMILE) avoids corneal flap creation and uses a single laser device, while advances in surface ablation techniques have seen a resurgence in its popularity. Presbyopic treatment options have also expanded to include new ablation profiles, intracorneal implants, and phakic intraocular implants. With the improved safety and efficacy of refractive lens exchange, a wider variety of intraocular lens implants with advanced optics provide more options for refractive correction in carefully selected patients. In this review, we also discuss possible developments in refractive surgery beyond 2020, such as preoperative evaluation of refractive patients using machine learning and artificial intelligence, potential use of stromal lenticules harvested from SMILE for presbyopic treatments, and various advances in intraocular lens implants that may provide a closer to 'physiological correction' of refractive errors.

Refractive surgery

Refractive surgery has evolved beyond laser refractive techniques over the past decade. Laser refractive surgery procedures (such as laser in-situ keratomileusis), surface ablation techniques (such as laser epithelial keratomileusis), and photorefractive keratectomy have now been established as fairly safe procedures that produce excellent visual outcomes for patients with low-to-moderate amounts of ametropia. Additionally, a broader selection of options are now available to treat a wider range of refractive errors. Small incision lenticule extraction uses a femtosecond laser to shape a refractive lenticule, which is removed through a small wound. The potential advantages of this procedure include greater tectonic strength and less dry eye. In the future, intracorneal implants could be used to treat hyperopia or presbyopia. Phakic intraocular implants and refractive lens exchange might be useful options in carefully selected patients for correcting high degrees of ametropia. Thus, physicians are now able to provide patients with the appropriate refractive corrective option based on the individual's risk-benefit profile.

Incidence and Outcomes of Sterile Multifocal Inflammatory Keratitis and Diffuse Lamellar Keratitis After SMILE

PURPOSE

To report the incidence outcomes of sterile multifocal inflammatory keratitis and diffuse lamellar keratitis (DLK) after small incision lenticule extraction (SMILE) in a large population.

METHODS

This was a retrospective review of a population of 4,000 consecutive eyes treated by SMILE at the London Vision Clinic using the VisuMax femtosecond laser (Carl Zeiss Meditec, Jena, Germany). The inclusion criterion was to have presented with inflammatory keratitis after SMILE. In some cases after SMILE, the inflammatory keratitis presented as sterile multifocal interface keratitis uncharacteristic of classic DLK. The incidence was measured and categorized as primary or secondary by presenting appearance, grade, and time to presentation. Patients were observed for 1 year after surgery and standard outcomes analysis was performed.

RESULTS

Of the 4,000 eye population, there were 18 cases (0.45%) of DLK grade 1 or 2. All cases were managed and resolved with topical steroid therapy. Of these, 12 cases (67%) were of classic appearance and 6 cases (33%) presented as sterile multifocal inflammatory keratitis. DLK was primary in nature in 11 cases (61%) and secondary in 7 cases (39%). Postoperative uncorrected distance visual acuity was 20/20 or better in 93% of eyes. No patients lost any lines of corrected distance visual acuity and there was no change in contrast sensitivity.

CONCLUSIONS

DLK occurred after SMILE with an incidence of 0.45% in this population. Topical steroid therapy resolved the DLK in all cases with no sequelae and no adverse effect on refractive or visual outcome at 1 year postoperatively. A unique type of DLK presentation can occur after SMILE, characterized by multiple focal sterile inflammatory spots. Management is the same as for classic DLK, but with a lower threshold for performing an interface washout. [J Refract Surg. 2018;34(11):751-759.].