Histochemical and ultrastructural evaluation of myopic corneal lenticules based on refractive error.

BACKGROUND: This study aimed to investigate cell degeneration, apoptosis, and ultrastructural differences in refractive lenticules (RL) obtained using small incision lenticule extraction (SMILE) compared with spherical equivalence (SE) refraction values. METHODS: This study included 84 eyes from 42 patients. Patients were divided into two groups according to the SE values: those with values below 4 diopters (D) (Group 1) and above 4 diopters (D) (Group 2). Patients who did not belong to the same SE group were excluded from the study. One RL obtained from each patient was separated for light microscopy and immunohistochemical examinations, and another for transmission electron microscopy (TEM) examinations. Caspase-3 for apoptosis and alpha-smooth muscle actin (α-SMA) for cell degeneration were evaluated using immunohistochemical examinations. RESULTS: Histological analyses showed that the density of collagen fibres was greater in Group 1 than in Group 2. Glycoaminoglycan and glycoprotein staining intensities were also higher in Group 1. TEM observations showed that Group 1 had intact cell and nuclear membranes, peripheral heterochromatin, and large nuclei, while Group 2 showed heterochromatin condensation and fragmentation, increased intracellular vacuoles, and loss of cytoplasm. Immunohistochemical analyses revealed that α-SMA and caspase-3 were significantly higher in Group 2 than in Group 1 (p < 0.001 and p < 0.001, respectively). CONCLUSIONS: Cell degeneration and apoptosis were significantly more common in the RLs with high SE values after SMILE surgery. The tissue response induced by surgery was more severe in the RLs with high SE values. This should be considered when reusing RLs.

Femtosecond laser-assisted stromal keratophakia for keratoconus: A systemic review and meta-analysis.

PURPOSE: Femtosecond lasers have revived the possibility of stromal keratophakia or tissue additive keratoplasty, a technique originally introduced by Prof. Jose Ignacio Barraquer in the 1960s. The surgical technique offers a unique solution to treat keratoconus. In the current study, we reviewed and performed a meta-analysis of the clinical outcomes of the femtosecond laser-assisted stromal keratophakia in the treatment of keratoconus. METHODS: This is a systematic review and meta-analysis of the estimated outcome difference between pre- and post-lenticule implantations. RESULTS: A total of related 10 studies were found in the literature. No studies reported adverse events, such as persistent haze or graft rejection, at last patients' visits. We further narrowed down the article selection in accordance to our inclusion criteria to report the composite outcomes (9 studies) and meta-analysis (4 studies). In the composite analysis, we demonstrated that lenticule implantation in keratoconus and post-LASIK ectasia patients appeared to expand the stromal volume of the thin corneas, flattened the cones, and significantly improved uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA) and spherical equivalent (SE). The meta-analysis showed that the random estimated UCVA, BCVA, SE and mean keratometry (Km) differences following the lenticule implantation was -0.214 (95% CI: -0.367 to 0.060; p = 0.006), -0.169 (-0.246 to 0.091; p < 0.001), -2.294 D (-3.750 to -0.839 D; p = 0.002), and 2.909 D (0.805 to 5.012 D; p = 0.007), respectively. CONCLUSIONS: Femtosecond laser-assisted stromal keratophakia is a feasible technique to correct the refractive aberrations, expand corneal volume and regularize corneal curvature in patients with keratoconus. However, there is a need to standardize the technique (e.g., whether to crosslink or not or to use convex or concave lenticules) and to formulate a mathematical model that accounts for the long-term epithelial thickness changes and stromal remodeling to determine the shape or profile of the lenticules, in order to improve the efficacy of the keratophakia further.

Assessment of Changes in Cap and Residual Stromal Thickness Values during a 6-Month Observation after Refractive Lenticule Extraction Small Incision Lenticule Extraction.

Background: In this study, the changes in corneal cap and residual stromal thickness (RST) values during a 180-day observation period after refractive lenticule extraction small incision lenticule extraction (ReLEx SMILE) were assessed. Methods: Fifty patients underwent ReLEx SMILE using the VisuMax 500 femtosecond laser, with corneal imaging conducted pre and post procedure via anterior segment optical coherence tomography (AS-OCT). Cap thickness in the center and 1.5 mm from the center in four meridians was measured at various intervals. Results: The results showed a significant decrease in cap thickness 180 days post procedure compared to earlier intervals (p < 0.05). Similarly, RST decreased gradually and significantly post procedure (p < 0.05). Notably, changes in cap thickness within the central 1.5 mm area were more dynamic than RST changes during the 6-month observation period following SMILE. Conclusions: The corneal cap thickness measured with swept-source AS-OCT within the central 1.5 mm area underwent more dynamic changes than the residual stromal thickness during the 6-month observation following SMILE.

Electron beam-irradiated donor cornea for on-demand lenticule implantation to treat corneal diseases and refractive error.

The cornea is the major contributor to the refractive power of the eye, and corneal diseases are a leading cause of reversible blindness. The main treatment for advanced corneal disease is keratoplasty: allograft transplantation of the cornea. Examples include lenticule implantation to treat corneal disorders (e.g. keratoconus) or correct refractive errors. These procedures are limited by the shelf-life of the corneal tissue, which must be discarded within 2-4 weeks. Electron-beam irradiation is an emerging sterilisation technique, which extends this shelf life to 2 years. Here, we produced lenticules from fresh and electron-beam (E-beam) irradiated corneas to establish a new source of tissue for lenticule implantation. In vitro, in vivo, and ex vivo experiments were conducted to compare fresh and E-beam-irradiated lenticules. Results were similar in terms of cutting accuracy, ultrastructure, optical transparency, ease of extraction and transplantation, resilience to mechanical handling, biocompatibility, and post-transplant wound healing process. Two main differences were noted. First, ∼59% reduction of glycosaminoglycans resulted in greater compression of E-beam-irradiated lenticules post-transplant, likely due to reduced corneal hydration-this appeared to affect keratometry after implantation. Cutting a thicker lenticule would be required to ameliorate the difference in refraction. Second, E-beam-sterilised lenticules exhibited lower Young's modulus which may indicate greater care with handling, although no damage or perforation was caused in our procedures. In summary, E-beam-irradiated corneas are a viable source of tissue for stromal lenticules, and may facilitate on-demand lenticule implantation to treat a wide range of corneal diseases. Our study suggested that its applications in human patients are warranted. STATEMENT OF SIGNIFICANCE: Corneal blindness affects over six million patients worldwide. For patients requiring corneal transplantation, current cadaver-based procedures are limited by the short shelf-life of donor tissue. Electron-beam (E-beam) sterilisation extends this shelf-life from weeks to years but there are few published studies of its use. We demonstrated that E-beam-irradiated corneas are a viable source of lenticules for implantation. We conducted in vitro, in vivo, and ex vivo comparisons of E-beam and fresh corneal lenticules. The only differences exhibited by E-beam-treated lenticules were reduced expression of glycosaminoglycans, resulting in greater tissue compression and lower refraction suggesting that a thicker cut is required to achieve the same optical and refractive outcome; and lower Young's modulus indicating extra care with handling.

Incisional surface quality of electron-beam irradiated cornea-extracted lenticule for stromal keratophakia: high nJ-energy vs. low nJ-energy femtosecond laser.

Introduction: Corneal lenticules can be utilized as an additive material for stromal keratophakia. However, following extraction, they must be reimplanted almost immediately or cryopreserved in lenticule banks. Electron-beam (E-beam) irradiated corneas permit room-temperature storage for up to 2 years, enabling keratophakia to be performed on demand. This study aims to compare the performance of high nano Joule (nJ)-energy (VisuMax) and low nJ-energy (FEMTO LDV) femtosecond laser systems on the thickness consistency and surface quality and collagen morphology of lenticules produced from fresh and E-beamed corneas. Methods: A total of 24 lenticules with -6.00 dioptre power were cut in fresh human donor corneas and E-beamed corneas with VisuMax and FEMTO LDV. Before extraction, the thickness of the lenticules was measured with anterior segment-optical coherence tomography (AS-OCT). The incisional surface roughness of extracted lenticules was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Multiphoton microscopy was then used to assess the surface collagen morphometry. Results: The E-beamed lenticules that were cut using FEMTO LDV were significantly thicker than the fresh specimens as opposed to those created with VisuMax, which had a similar thickness as the fresh lenticules. On the vertex, they were ∼11% thicker than the fresh lenticules. The surface roughness (Rq) of E-beamed lenticules incised with FEMTO LDV did not differ significantly from the fresh lenticules. This contrasted with the VisuMax-fashioned lenticules, which showed notably smoother surfaces (∼36 and ∼20% lower Rq on anterior and posterior surfaces, respectively) on the E-beamed than the fresh lenticules. The FEMTO LDV induced less cumulative changes to the collagen morphology on the surfaces of both fresh and E-beamed lenticules than the VisuMax. Conclusion: It has been previously demonstrated that the low nJ-energy FEMTO LDV produced a smoother cutting surface compared to high nJ-energy VisuMax in fresh lenticules. Here, we showed that this effect was also seen in the E-beamed lenticules. In addition, lower laser energy conferred fewer changes to the lenticular surface collagen morphology. The smaller disparity in surface cutting quality and collagen disturbances on the E-beamed lenticules could be beneficial for the early visual recovery of patients who undergo stromal keratophakia.

Experiment-Based Validation of Corneal Lenticule Banking in a Health Authority-Licensed Facility.

With the expected rise in patients undergoing refractive lenticule extraction worldwide, the number of discarded corneal stromal lenticules will increase. Therefore, establishing a lenticule bank to collect, catalog, process, cryopreserve, and distribute the lenticules (for future therapeutic needs) could be advantageous. In this study, we validated the safety of lenticule banking that involved the collection of human lenticules from our eye clinic, transportation of the lenticules to a Singapore Ministry of Health-licensed lenticule bank, processing, and cryopreservation of the lenticules, which, after 3 months or, a longer term, 12 months, were retrieved and transported to our laboratory for implantation in rabbit corneas. The lenticule collection was approved by the SingHealth Centralised Institutional Review Board (CIRB). Both short-term and long-term cryopreserved lenticules, although not as transparent as fresh lenticules due to an altered collagen fibrillar packing, did not show any sign of rejection and cytotoxicity, and did not induce haze or neovascularization for 16 weeks even when antibiotic and steroidal administration were withdrawn after 8 weeks. The lenticular transparency progressively improved and was mostly clear after 4 weeks, the same period when we observed the stabilization of corneal hydration. We showed that the equalization of the collagen fibrillar packing of the lenticules with that of the host corneal stroma contributed to the lenticular haze clearance. Most importantly, no active wound healing and inflammatory reactions were seen after 16 weeks. Our study suggests that long-term lenticule banking is a feasible approach for the storage of stromal lenticules after refractive surgery. Impact statement Since 2011, close to 3 million refractive lenticule extraction procedures have been performed. The majority of the extracted lenticules are discarded. The lenticules could have been cryopreserved and retrieved at a later date for therapeutic or refractive applications. Therefore, establishing a lenticule bank to collect, catalog, process, cryopreserve, and distribute the lenticules could be advantageous. In this study, we simulated a lenticule banking service in a validated health authority-licensed facility and showed that long-term cryopreservation of the lenticules in the facility was safe and feasible in vivo.

Review of Presbyopia Treatment with Corneal Inlays and New Developments.

Presbyopia may represent the largest segment of refractive errors that is without an established and effective refractive surgery treatment. Corneal Inlays are materials (synthetic or allogenic) implanted in the stroma of patients' corneas to improve presbyopia. These inlays, introduced into the United States in 2015 via the small-aperture corneal inlay (KAMRATM, SightLife Surgical/CorneaGen, Seattle, Washington, United States), were met with an initial wave of enthusiasm. Subsequent models like the shape-changing corneal inlay (RAINDROPTM, Revision Optics, Lake Forest, California, United States) offered excellent results for patients, but longer-term research raised questions about patient safety. At the time of this article, no synthetic corneal inlays are available in the United States for the correction of presbyopia. Other options for presbyopia correction include allograft corneal inlays, trifocal synthetic corneal inlays, pharmacologic therapies, scleral incisions or additive techniques and PresbyLASIK. Presently, allograft inlays consist of corneal lenticules removed from patients undergoing Small Incision Lenticule Extraction (SMILE). We will review corneal inlays and other alternative procedures that may provide effective and predictable treatments for patients with presbyopia.

Double crescentic edge separation for the management of cap-lenticular adhesion in small incision lenticule extraction.

We describe a modified technique of lenticule extraction for the management of cap-lenticular adhesions (CLAs). In cases where the lenticule edge could not be delineated, a Sinskey hook was introduced through the cap side-cut with the hook facing up (toward the cap), advanced to the periphery of lenticule at 3'o clock (for right-handed surgeons) and used to nudge the underside of the cap in the region of lenticule side-cut. The diagnosis of CLA was confirmed on observing a crescentic gap between the lenticule-side cut and the rolled lenticule edge. The gap was enlarged to create a crescentic area of separation spanning 2-3 clock hours. A similar crescentic area of separation was created on the opposite side (9'o clock). A microforceps was used to segmentally separate the lenticule from both edges toward the midline followed by lenticule extraction. Our technique was successfully applied in 11 cases of CLA with no complications.

Comparison of the Different Preservative Methods for Refractive Lenticules following SMILE.

Purposes: To (i) evaluate various methods for preserving refractive lenticules (RLs) from myopic eyes following small-incision lenticule extraction (SMILE), in order to (ii) establish a sound, standard storage RL preservative for clinical uses. Methods: In this prospective study, we compared freshly excised post-SMILE RLs (control group) with post-SMILE RLs (experimental group). Experimental group RLs were preserved in one of several preservatives: glycerol, allochroic silicagel desiccant, or Optisol. Following preservation in one of these three media, samples were evaluated by light microscopy (LM), and transmission (TEM) and scanning (SEM) electron microscopy on days-1, -3, -7, and -14. Results: Changes in cellular morphology were observed at all time points. Compared with fresh control-group RLs, there were significant histological changes in RLs preserved in glycerol and allochroic silicagel, but not Optisol. Comparison of the three methods revealed Optisol to be the best, followed by allochroic silica gel desiccant, followed by glycerol. RLs preserved in Optisol maintained the highest degree of viability and integrity. And the RLs viability and collagen density decreased with prolongation of storage time all. Conclusions: Optisol is a midterm corneal storage medium, which can maintain post-SMILE corneal RLs for 14 days, is a feasible and effective method for tissue storage.

Small incision lenticule extraction (SMILE) techniques: patient selection and perspectives.

Refractive lenticule extraction is becoming the procedure of choice for the management of myopia and myopic astigmatism owing to its precision, biomechanical stability, and better ocular surface. It has similar safety, efficacy, and predictability as femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and is associated with better patient satisfaction. The conventional technique of small incision lenticule extraction (SMILE) involves docking, femtosecond laser application, lenticule dissection from the surrounding stroma, and extraction. It has a steep learning curve compared to conventional flap-based corneal ablative procedures, and the surgical technique may be challenging especially for a novice surgeon. As SMILE is gaining worldwide acceptance among refractive surgeons, different modifications of the surgical technique have been described to ease the process of lenticule extraction and minimize complications. Good patient selection is essential to ensure optimal patient satisfaction, and novice surgeons should avoid cases with low myopia (thin refractive lenticules), difficult orbital anatomy, high astigmatism, or uncooperative, anxious patients to minimize complications. A comprehensive MEDLINE search was performed using "small incision lenticule extraction," "SMILE," and "refractive lenticule extraction" as keywords, and we herein review the patient selection for SMILE and various surgical techniques of SMILE with their pros and cons. With increasing surgeon experience, a standard technique is expected to evolve that may be performed in all types of cases with optimal outcomes and minimal adverse effects.

Lamellar keratoplasty using femtosecond laser intrastromal lenticule for limbal dermoid: case report and literature review.

Small incision refractive lenticule extraction (SMILE) is a femtosecond laser technique to correct myopia and myopic astigmatism. Herein, we report a technique where intrastromal lenticule obtained from the SMILE procedure served as a graft for lamellar keratoplasty in the management of a limbal dermoid. An 18-year-old woman presented to the clinic with a corneal-limbal mass in the right eye. Slit-lamp examination revealed a vascularized circular mass of approximately 6 mm × 5 mm, which was attached at 7 o'clock in the inferotemporal region of the corneal limbus; this suggested limbal dermoid. Anterior segment optical coherence tomography revealed superficial involvement of the cornea. The patient was treated with excision and lamellar keratoplasty by using femtosecond intrastromal lenticule. The lenticule was sutured over the cornea with 10-0 interrupted nylon sutures. On postoperative follow-up, best-corrected visual acuity was 20/20; there was no corneal neovascularization and no sign of rejection. This case of limbal dermoid was managed by simple surgical excision and lamellar keratoplasty with a SMILE-extracted lenticule. This method may serve as an alternative surgical approach for management of limbal dermoid.

Changes of anterior and posterior corneal curvature and anterior chamber depth after SMILE / 国际眼科杂志(Guoji Yanke Zazhi)

·AIM:To observe the changes of anterior and posterior corneal curvature and anterior chamber depth after small incision lenticule extraction ( SMILE ) for low and high myopic astigmatism.·METHODS: Sixty-three cases ( 88 eyes ) undergone SMILE in our hospital were included. The patients were divided into two groups based on astigmatism degree:the Group A: -2. 00D to -4. 00D astigmatism, the Group B: - 0. 25D to - 1. 00D astigmatism. Patients were examined at 1wk, 1 and 3mo after operations. Visual acuity, intraocular pressure, refraction, corneal curvature and anterior chamber depth were recorded. The change of anterior and posterior corneal curvature and anterior chamber depth was compared. Spearman correlation analysis and independent t test were used for statistical analysis.·RESULTS: Surgery was done well in all patients without complications. No statistically significant difference was found between the two groups in posterior corneal curvature and anterior chamber depth preoperatively, postoperatively 7d,1 and 3mo (P>0. 05). One week postoperatively, the anterior corneal curvature was statistically significant from that of preoperative in both groups (P<0. 05), while there were no significant differences at 1 and 3mo after operation (P>0. 05).·CONCLUSION: No significant change of anterior and posterior corneal curvature and anterior chamber depth was found after SMILE for correcting low and high myopic astigmatism. One week after SMILE the anterior corneal curvature become stable.

Comparison of higher-order aberration changes in anterior corneal surface between FS-LASIK and SMILE surgery / 安徽医科大学学报

84 eyes that underwent femtosecond laser-assisted laser in situ keratomileusis ( FS-LASIK) , and 110 eyes that underwent small incision lenticule extraction ( SMILE) surgery were included in this prospective case se-ries study. HOAs included ( total HOAs, spherical aberration, horizontal coma aberration, and vertical coma aber-ration) were measured preoperatively after 1 week, 1 month , and 3 months postoperatively by Pentacam. The ab-errations were described as Zernike polynomials. Significantly increased total HOAs and SA and significantly de-creased vertical coma were noted at 1 week, 1 month, and 3 months after FS-LASIK ( P<0.05 ) . However, no significant increase was found in postoperatively horizontal coma. There were significant increases in total HOAs, SA, and horizontal coma and a decrease in the vertical coma at each postoperative examination in SIMLE group ( P<0.05 ) . The total HOAs and SA were significantly smaller in SMILE group than that in FS-LASIK group at 1 week, 1 month, and 3 months postoperatively. The changes in total HOAs and SA were also significantly smaller in SMILE group than that in FS-LASIK group at each postoperative examination. Compared with FS-LASIK, SMILE can induce fewer total higher-order aberrations and spherical aberration after operation.