Femtosecond Laser-Assisted Small Incision Sutureless Intrastromal Lamellar Keratoplasty (SILK) for Corneal Transplantation in Keratoconus

Lenticule addition keratoplasty for the treatment of keratoconus: A systematic review and critical considerations

Keratoconus is a corneal disorder characterized by the progressive thinning and bulging of the cornea. Currently, the major goal of management is to halt its progression, restore normal corneal strength, prevent acute complications, and save vision. Penetrating keratoplasty and deep anterior lamellar keratoplasty as conventional surgical methods for advanced keratoconus are limited by relatively high rates of immune intolerance, slow post-operational recovery, high costs, and shortage of donor corneas. Recently, the development of lenticule addition keratoplasty enables the restoration of corneal thickness simply by implanting a lenticule into the stromal pocket created with the femtosecond laser, which can originate from cadaver corneas or more appealing, be extracted from patients via a small-incision lenticule extraction (SMILE) surgery. As the first systematic review in this field, we critically review publications on lenticule addition keratoplasty and provide our perspectives on its clinical application and the focus of future research.

[Intracorneal selective stromal transplantation]

Deep anterior lamellar keratoplasty or penetrating keratoplasty are currently considered the optimal methods of surgical treatment of stromal dystrophies and corneal degeneration. Despite certain advantages and benefits of these methods, they also have significant limitations: involvement of superficial corneal layers in the surgery, need for suturing, development of post-keratoplasty astigmatism etc.

PURPOSE

This study aimed to test and describe the new method of closed sutureless keratoplasty (intracorneal selective stromal transplantation), which was indicated in isolated dystrophic and degenerative pathology of the stroma.

MATERIAL AND METHODS

Intracorneal selective stromal transplantation was performed in a 62-year-old patient with stromal degeneration and intact corneal layers between the altered stroma and the Descemet's membrane posteriorly, and the Bowman's layer anteriorly. The patient also had immature senile cataract. Corneal stroma was removed and replaced with a graft in the optical center of the lens, while the endothelium, the Descemet's membrane and the Bowman's layer remained intact.

RESULTS

The proposed technique of intracorneal selective stromal transplantation makes it possible to replace only the pathologically altered stroma through closed surgical approach, without affecting the anterior and posterior surfaces of the cornea. Best-corrected visual acuity has increased in the patient from 0.01 to 0.6, while mean endothelial cell density has not changed in the course of 24-months follow-up.

CONCLUSION

The proposed keratoplasty method can be used in patients with dystrophy or degeneration of the corneal stroma and preserved endothelial cells, intact Descemet's membrane and Bowman layer. Since the superficial corneal layers are not involved during the surgery, intracorneal selective stromal transplantation combined the advantages of both deep anterior lamellar keratoplasty and endothelial keratoplasty. The biologically favorable result in this first clinical case allows a preliminary conclusion on the technical possibility and functional effectiveness of the proposed method, but further long-term observation and more clinical cases are required.

Meniscus-Shaped Stromal Lenticule Addition Keratoplasty for Corneal Regularization and Thickening in Advanced Keratoconus

PURPOSE

The aim of this study was to investigate the outcome of the meniscus-shaped stromal lenticule addition keratoplasty (MS-SLAK) in corneal regularization and thickness.

METHODS

Patients waiting for deep anterior lamellar keratoplasty for advanced keratoconus with an intolerance to contact lenses (CLs) underwent the MS-SLAK procedure by FSL 80 kHz ablation (VICTUS, Technolas Perfect Vision, DE). Customized positive meniscus-shaped stromal lenticules were obtained and implanted. Examination was performed at baseline and at 3-, 6-, and 12-month follow-up and included corrected distance visual acuity both with spectacles and CLs (spectacle CDVA and CL-CDVA), manifest refraction spherical equivalent, slit-lamp examination, anterior segment optical coherence tomography, corneal topography, and in vivo confocal microscopy.

RESULTS

Fifteen patients completed the study. Statistical increases in corneal thickness values were found from the first follow-up ( P < 0.001). Improvement in the Surface Asymmetry Index ( P = 0.04), Symmetry Index ( P = 0.02), spherical aberration ( P < 0.001), coma ( P = 0.18), high-order aberration ( P = 0.37), and anterior asphericity index (Q) ( P = 0.31) were found at 12 months. At the 12-month follow-up, no improvement were found in spectacle CDVA ( P = 0.23); however, all patients reported CL wearing tolerance recovery, and significant improvement in CL-CDVA ( P = 0.002) was found. The confocal microscopy at 12 months showed a significant increase in keratocyte density within the lenticule and absence of fibrotic reactions in both anterior and posterior interfaces.

CONCLUSIONS

MS-SLAK seems to be effective in regularizing the corneal surface as showed by the significant improvement in topographic symmetry indices, coma, and high-order aberration. The corneal regularization is also confirmed by the results in anterior Q and the recovery of the CL wearing tolerance.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Fresh Human Myopic Lenticule Intrastromal Implantation for Keratoconus Using SMILE Surgery in a Long-term Follow-up Study: Ultrastructural Analysis by Transmission Electron Microscopy

PURPOSE

To investigate new intrastromal histological structures that develop after myopic human lenticular implantation in keratoconus with femtosecond laser-assisted small incision lenticule extraction (SMILE) surgery using transmission electron microscopy.

METHODS

Sixty eyes with advanced keratoconus indicated for corneal transplantation were included in this study. Fresh myopic lenticular implants were placed in all eyes through SMILE surgery. Lenticular implants were extracted from patients with myopic refractive errors of the cornea, untreated keratoconus, and treated keratoconus following 1, 2, and 3 years of surgery. These five lenticular samples were examined under the electron microscope and compared.

RESULTS

Disorganized and thinned collagen fibers were observed in the stroma with degenerative stromal cells (telocyte-like cells and keratocytes) in the keratoconic cornea. Apoptotic bodies and cell debris were easily observed near the disorganized fibers. In contrast, the myopic refractive error of the control and treatment groups demonstrated well-organized parallel lamellar structures. Healthy keratocytes and telocyte-like cells were observed in samples obtained 1, 2, and 3 years after lenticular implantation. Thus, telocyte-like cells may be activated by appropriate stimuli, such as stem cells, and be involved in stromal regeneration.

CONCLUSIONS

Fresh myopic intrastromal lenticular implantation is a safe, economical, and reliable technique that leads to increased corneal thickness, improved visual acuity, and the regeneration of healthy keratocytes and telocyte-like cells that are involved in stromal regeneration. [J Refract Surg. 2022;38(8):520-528.].

Effects of Corneal Stromal Lens Collagen Cross-Linking Regraft on Corneal Biomechanics

Background

Corneal collagen cross-linking (CXL) therapy, a method that uses a combination of riboflavin and ultraviolet-A light (UVA), can promote the formation of covalent cross-linking of amino acid residues of corneal collagen and enhance the hardness of the cornea. In this study, we explored the effects of corneal stromal lens collagen cross-linking regraft on corneal biomechanics.

Methods

A total of 15 New Zealand white rabbits were divided into 3 groups: normal control group (group A), SMILE + uncross-linked lens implantation group (Group B), and SMILE + cross-linking lens implantation group (group C). The design parameters of SMILE surgery were as follows: the corneal cap was 120 um thick, the lens diameter was 6.5 mm, and the diopter was -6.0D. Riboflavin and ultraviolet-A (UVA) were used as corneal stromal lens CXL, which was implanted into the allogeneic rabbit corneal stromal bag 24 hours after the operation. Postoperative corneal thickness (CCT), refraction, AS-OCT, and corneal biomechanics were performed before and then at 1 and 3 months after the operation.

Results

All corneas appeared transparent and smooth 3 months after surgery. The corneal thicknesses of both group B and group C were lower than those before the operation. The corrected refraction of group B and group C after lens implantation was also lower than the expected corrected power; there was no significant difference between the two groups (P > 0.05). AS-OCT results showed an uneven surface and thickness of the corneal stromal lens in two eyes of group B. Moreover, corneal elastic deformation increased with intraocular pressure in each group; displacement from large to small was group B > group C and > group A. The creep from large to small was group B > group C > group A. The fiberboard layers of groups B and C were disordered, and there were a few autophagosomes in the fibroblasts of group B by transmission electron microscopy (TEM).

Conclusions

Allograft graft of corneal stromal lens collagen cross-linked can significantly increase the biomechanical properties of the cornea.

Femtosecond laser-assisted minimally invasive lamellar keratoplasty for the treatment of advanced keratoconus

BACKGROUND

To evaluate the initial safety and efficacy of femtosecond laser-assisted minimal invasive lamellar keratoplasty (FL-MILK) for advanced keratoconus.

METHODS

Twenty-two patients (22 eyes) with advanced keratoconus were included in this prospective study. All the involved eyes underwent FL-MILK. The femtosecond laser was used to create an intrastromal pocket with a 2.3 mm incision in the recipient cornea. Then a stromal button with a diameter of 9.0 mm and a depth of 200 μm was gently inserted into the intrastromal pocket through the 2.3 mm incision and flattened. No sutures were applied. Follow-up was conducted for 24 months.

RESULTS

Twenty-two patients completed follow-up data for 12 months, 16 patients had 24 months follow-up. No epithelial implantation, infection or allogeneic rejection were observed during the follow-up. Based on baseline values, postoperative 12 months values and postoperative 24 months values, clinical significantly improvement was recorded in corrected distance visual acuity (CDVA) (0.40 ± 0.18 logMAR vs. 0.30 ± 0.12 logMAR and 0.23 ± 0.13 logMAR), the anterior central corneal elevation (29.14 ± 15.33 μm vs. 14.45 ± 13.75μm and 11.38 ± 8.33 μm), and corneal higher-order aberrations (3.536 ± 1.503 vs. 2.761 ± 1.517 and 0.994 ± 0.391). Corneal biomechanical properties in all eyes improved significantly. SP-A1 increased from 48.64 ± 12.87 preoperatively to 87.26 ± 21.01 postoperative 12 months and 88.77 ± 18.26 postoperative 24 months; deformation amplitude (DA) decreased from 1.36 ± 0.15 preoperatively to 1.21 ± 0.12 postoperative 12 months and 1.19 ± 0.19 postoperative 24 months.

CONCLUSIONS

Initial experience suggests that this minimally invasive transplantation may be a feasible option for advanced keratoconus. A larger cohort and longer follow-up are required to validate our results and establish long-term safety and efficacy of the procedure.

[On the tactics for surgical treatment of keratoconus in significantly altered corneal thickness]

PURPOSE

To evaluate the clinical and functional outcomes of bandage therapeutic-optical keratoplasty (BTOK) surgery in patients with keratoconus (KC) and significant changes in corneal thickness.

MATERIAL AND METHODS

Surgical treatment was performed in 15 patients (15 eyes) with stage IV KC aged from 22 to 51 years (mean age - 32.61±7.94 years). The follow-up period lasted 3 years. All patients underwent BTOK surgery using an interlamellar graft with a thickness of 320 to 350 µm.

RESULTS

Uncorrected and best corrected visual acuity increased in all patients after BTOK surgery and did not change statistically significantly during the entire follow-up period (3 years), amounting to 0.47±0.12 and 0.53±0.13, respectively. Keratometric parameters also remained stable by that observation time point and amounted to: K_max - 53.01±2.30 D; K_min - 41.63±2.24 D; K_m - 47.32±1.91 D.

CONCLUSION

The BTOK surgery helps achieve long-term (3 years) visual, optical and strengthening outcomes in stage IV KC patients when the use of other known techniques (corneal collagen crosslinking, corneal segments) is technically impossible because of the risk of complications due to significantly thinned cornea (less than 400 µm).

Bowman-stromal inlay using an intraocular lens injector for management of keratoconus

A simple approach for transplanting Bowman layer and anterior stroma Bowman-stromal inlay (BSI) in keratoconic patients as an intervention to cease progression of ectasia and increase the overall thickness is described. A femtosecond laser was used to create BSI from human eye bank donor corneas and form an intrastromal pocket in the host cornea. The inlay was placed in the intrastromal space using an intraocular lens injector. This technique was performed successfully in 10 eyes of patients with progressive corneal ectasia. Postoperatively, the increased host pachymetry was as per BSI thickness. The tomography parameters remained stable, suggesting stabilization of keratoconus over a mean 15.9 months of follow-up. The BSI may offer a technically easy and safe technique of stromal augmentation to arrest keratoconus progression. It also opens up the possibility of surface ablation in the future for visual rehabilitation.

Intrastromal Allogeneic Inclusions for the Management of Keratoconus: A Review of Current Literature

ABSTRACT

A new therapeutic alternative has been developed in the past 6 years to treat severe keratoconus in young patients. Those patients had only corneal transplantation as an option, but now a variety of surgical alternatives in the form of allogeneic corneal inclusions have bloomed and are becoming more popular. Although Bowman layer transplantation is the most studied technique, recent studies have described different options with very promising preliminary results. Mostly all the techniques described improve corneal curvature, visual acuity, pachymetry, contact lens tolerance, and foremost, manage to avoid or postpone corneal transplantation. Very few complications have been described so far, which makes these techniques not only feasible but also safe. Herein, we focus on reviewing recently published studies describing these techniques and their first results.

Corneal Stromal Regeneration: A Review of Human Clinical Studies in Keratoconus Treatment

The use of advanced therapies with stem cells to reconstruct the complex tissue of corneal stroma has gained interest in recent years. Besides, collagen-based scaffolds bioengineering has been offered as another alternative over the last decade. The outcomes of the first clinical experience with stem cells therapy on corneal stroma regeneration in patients with advanced keratoconus were recently reported. Patients were distributed into three experimental groups: Group 1 (G-1) patients underwent implantation of autologous adipose-derived adult stem cells (ADASCs) alone, Group 2 (G-2) received a 120 μm decellularized donor corneal stromal laminas, and Group 3 (G-3) received a 120 μm recellularized donor laminas with ADASCs. A follow up of 36 months of clinical data, and 12 months of confocal microscopy study was performed, the authors found significant clinical improvement in almost all studied mean values of primary and secondary outcomes. Corneal confocal microscopy demonstrated an increase in cell density in the host stroma, as well as in the implanted tissue. Using different approaches, allogenic small incision lenticule extraction (SMILE) implantation was applied in cases with advanced keratoconus. Some authors reported the implantation of SMILE intrastromal lenticules combined with accelerated collagen cross-linking. Others performed intrastromal implantation of negative meniscus-shaped corneal stroma lenticules. Others have compared the outcomes of penetrating keratoplasty (PKP) vs. small-incision Intralase femtosecond (IFS) intracorneal concave lenticule implantation (SFII). Femtosecond laser-assisted small incision sutureless intrasotromal lamellar keratoplasty (SILK) has been also investigated. The published evidence shows that the implantation of autologous ADASCs, decellularized or recellularized human corneal stroma, allogenic SMILE lenticules corneal inlay, and recombinant cross-linked collagen have shown initially to be potentially effective for the treatment of advanced keratoconus. In light of the present evidence available, it can be said that the era of corneal stromal regeneration therapy has been already started.

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 (K_m) 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.

Femtosecond Lasers in Cornea & Refractive Surgery

Since the introduction of femtosecond laser (FS) systems for corneal flap creation in laser-assisted in-situ keratomileusis there have been numerous applications for FS laser in corneal surgery. This manuscript details the utility of FS lasers in corneal surgical procedures including refractive laser surgeries, intracorneal ring segment tunnels, presbyopic treatments, and FS-assisted keratoplasty. We also review the role of FS lasers in diagnostic procedures such as two photon excitation fluorescence and second harmonic generation.

Corneal Stroma Regeneration: New Approach for the Treatment of Cornea Disease

Corneal grafting is one of the most common forms of human tissue transplantation. The corneal stroma is responsible for many characteristics of the cornea. For these reasons, an important volume of research has been made to replicate the corneal stroma in the laboratory to find an alternative to classical corneal transplantation techniques.There is an increasing interest today in cell therapy of the corneal stroma using induced pluripotent stem cells or mesenchymal stem cells since these cells have shown to be capable of producing new collagen within the host stroma and even to improve its transparency.The first clinical experiment on corneal stroma regeneration in advanced keratoconus cases has been reported and included. Fourteen patients were randomized and enrolled into 3 experimental groups: (1) patients underwent implantation of autologous adipose-derived adult stem cells alone, (2) patients received decellularized donor corneal stroma laminas, and (3) patients received implantation of recellularized donor laminas with adipose-derived adult stem cells. Clinical improvement was detected with all cases in their visual, pachymetric, and topographic parameters of the operated corneas.Other recent studies have used allogenic SMILE implantation lenticule corneal inlays, showing also an improvement in different visual, topographic, and keratometric parameters.In the present report, we try to summarize the available preclinical and clinical evidence about the emerging topic of corneal stroma regeneration.