Comparison of fresh and preserved decellularized human corneal lenticules in femtosecond laser-assisted intrastromal lamellar keratoplasty

Substantial evidence has demonstrated the application of fresh and decellularized human corneal lenticules from increasing myopic surgeries. Further preservation of decellularized corneal lenticules would extend its clinical application. However, whether fresh and preserved decellularized lenticules have the same effects in vivo, including refractive correction, remains unclear. Here, we made comprehensive comparisons between fresh human lenticules (FHLs) and preserved decellularized human lenticules (DHLs). Another group of decellularized lenticules was combined with crosslinking for potential keratoconus therapy. Optical transparency, biomechanical properties, and fibrillar ultrastructure were analyzed to evaluate the DHLs and crosslinked DHLs (cDHLs) in vitro. The DHLs retained high transparency and regular ultrastructure, with genetic materials mostly being eliminated. The strength of lenticules in the cDHL group was markedly increased by crosslinking. Moreover, after storage in glycerol for 3 months, the lenticules were reimplanted into rabbit corneal lamellar pockets assisted by a femtosecond laser. The rabbits were followed for another 3 months. There were no obvious rejective complications in any of the three groups. From 1 week to 3 months postoperatively, the host corneas of the FHL group remained highly transparent, while slight hazes were observed in the DHL group. However, the corneas of the cDHL group displayed opacity throughout the 3-month postoperative period. Furthermore, all the lenticules could effectively induce corneal steepening and refractive changes. Taken together, our data indicated that FHLs are ideal inlay products, whereas preserved DHLs could be an alternative for intrastromal lamellar keratoplasty. Our study provides new insights into the clinical application of human lenticule recycling. STATEMENT OF SIGNIFICANCE: : Currently, substantial evidence has demonstrated the application of fresh and decellularized human corneal lenticules from increasing myopic surgeries. Further preservation of decellularized lenticules would extend its clinical application. However, whether fresh and preserved decellularized lenticules have the same effects in vivo, including refractive correction, remains unclear. Herein, we decellularized human lenticules with or without mechanically strengthened crosslinking. After storage in glycerol for 3 months, the lenticules were reimplanted into rabbit corneas. Comprehensive comparisons were performed among fresh human lenticules (FHLs), decellularized human lenticules (DHLs) and crosslinked DHLs. Our study indicated that FHLs are ideal inlay products, whereas preserved DHLs could be an alternative for intrastromal lamellar keratoplasty. Our study provides new insights into the clinical application of human lenticule recycling.

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.

Recent developments in regenerative ophthalmology

Regenerative medicine (RM) is one of the most promising disciplines for advancements in modern medicine, and regenerative ophthalmology (RO) is one of the most active fields of regenerative medicine. This review aims to provide an overview of regenerative ophthalmology, including the range of tools and materials being used, and to describe its application in ophthalmologic subspecialties, with the exception of surgical implantation of artificial tissues or organs (e.g., contact lens, artificial cornea, intraocular lens, artificial retina, and bionic eyes) due to space limitations. In addition, current challenges and limitations of regenerative ophthalmology are discussed and future directions are highlighted.

Three-Dimensional Neurite Characterization of Small Incision Lenticule Extraction Derived Lenticules

Purpose

We study the density and excitatory response of neurites, and Schwann cells (SCs) in fresh and cryopreserved stromal lenticules derived from small incision lenticule extraction (SMILE).

Methods

Human stromal lenticules (n = 23) were immunostained for β III-tubulin and imaged using spinning disk confocal laser microscopy, followed by three-dimensional reconstruction, to reveal neurite distribution. The lenticule neurite density (LND) was assessed using a validated neurite tracing and length measurement method with NeuronJ. LND was compared among groups of different lenticule thickness (71-165 μm) obtained from -3 to >-6 diopters (D) corrections. SCs were identified by marker expression and the laser effect on SC-neurite interaction was examined under transmission electron microscopy (TEM). Fresh porcine SMILE-lenticules (n = 18) were used for LND comparison among storage conditions and functional excitatory calcium response assay.

Results

Using a validated neurite length measurement method, we found an inverse correlation of LND with lenticule thickness. Higher LND was found in thinner lenticules obtained from lower power of correction (r = -0.8925, P < 0.0001), whereas total lenticule neurite lengths did not alter significantly with regards to lenticule thickness. SCs were identified by GAP43 and p75NTR expression and were closely associated with lenticule neurites under TEM. In porcine lenticules, LND and excitatory calcium response were reduced after cold and cryogenic storage, when compared to fresh lenticules.

Conclusions

The stromal neurites showed variations in density related to SMILE lenticule thickness and cryopreservation. With the presence of SC support and excitatory response, these neurite residues could retain minimal functionality that might serve as a potential advantage in the event of lenticule implantation.

Intrastromal Lenticule Rotation for Treatment of Astigmatism Up to 10.00 Diopters Ex Vivo in Human Corneas

PURPOSE

To evaluate the feasibility of intrastromal lenticule rotation (ISLR) as a novel technique for management of astigmatism up to 10.00 diopters (D).

METHODS

Eighteen human donor corneas were mounted on an artificial anterior chamber. After laser application and dissection, the lenticule was rotated 90° in the intrastromal pocket. Scheimpflug tomography (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany) was acquired preoperatively and following ISLR. The attempted astigmatic correction was twice the cylindrical magnitude of the lenticule referenced to the corneal plane: 4.80 D (5.00 D group, n = 9) and 9.32 D (10.00 D group, n = 9), respectively. The change in keratometric astigmatism was evaluated by vector analysis.

RESULTS

In the 5.00 D group, ISLR caused a mean absolute surgical induced astigmatism (SIA) of 5.30 ± 1.14 D with a correction index (CI) of 1.14 ± 0.25 and an angle of error (AoE) of -0.80° ± 4.61°. In the 10.00 D group, the SIA averaged 9.57 ± 1.10 D with a CI of 1.03 ± 0.12 and an AoE of 2.75° ± 3.60°. The average total corneal refractive power (TCRP) increased 1.36 ± 0.67 and 1.95 ± 1.57 D in the 5.00 D and 10.00 D groups, respectively. Postoperative optical coherence tomography revealed stromal redistribution in the periphery of the optical zone with tissue addition in the preoperative steep meridian and tissue reduction in the preoperative flat meridian.

CONCLUSIONS

ISLR seemed feasible and precise for management of regular astigmatism up to 10.00 D ex vivo in human donor corneas. A myopic shift was observed in TCRP. The in vivo corneal remodeling after ISLR warrants investigation. [J Refract Surg. 2019;35(7):451-458.].

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.

Corneal remodelling and topography following biological inlay implantation with combined crosslinking in a rabbit model

Implantation of biological corneal inlays, derived from small incision lenticule extraction, may be a feasible method for surgical management of refractive and corneal diseases. However, the refractive outcome is dependent on stromal remodelling of both the inlay and recipient stroma. This study aimed to investigate the refractive changes and tissue responses following implantation of 2.5-mm biological inlays with or without corneal collagen crosslinking (CXL) in a rabbit model. Prior to implantation, rotational rheometry demonstrated an almost two-fold increase in corneal stiffness after CXL. After implantation, haze gradually subsided in the CXL-treated inlays (p = 0.001), whereas the untreated inlays preserved their clarity (p = 0.75). In-vivo confocal microscopy revealed reduced keratocyte cell count at the interface of the CXL inlays at week 8. Following initial steepening, regression was observed in anterior mean curvature from week 1 to 12, being most prominent for the non-CXL subgroups (non-CXL: -12.3 ± 2.6D vs CXL: -2.3 ± 4.4D at 90 μm depth, p = 0.03; non-CXL: -12.4 ± 8.0D vs CXL: -5.0 ± 4.0D at 120 μm depth, p = 0.22). Immunohistochemical analysis revealed comparable tissue responses in CXL and untreated subgroups. Our findings suggest that CXL of biological inlays may reduce the time before refractive stabilization, but longer postoperative steroid treatment is necessary in order to reduce postoperative haze.

Biological Lenticule Implantation for Correction of Hyperopia: An Ex Vivo Study in Human Corneas

PURPOSE

To evaluate changes in corneal tomography after stromal lenticule implantation ex vivo, with respect to the dependency of the lenticule thickness and implantation depth on the corneal curvature and the postoperative biomechanical strength at increased chamber pressure.

METHODS

Twenty-eight human donor corneas underwent pocket implantation of refractive stromal lenticules. Four groups were created by the combination of two implantation depths (110 and 160 µm) and two lenticule thicknesses (95 µm = 4.00 diopters [D], 150 µm = 8.00 D). Sagittal keratometry and total corneal refractive power (TCRP_{4mm,apex,zone}) were obtained for the front and back curvature with Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) at chamber pressures of 15 and 40 mm Hg.

RESULTS

The anterior curvature steepening was comparable between the 4.00 D and 8.00 D groups (P > .141), but more pronounced with 110 µm implantation depth (P < .038). The posterior curvature flattened significantly more after implantation of 8.00 D than 4.00 D lenticules (P < .002), but was similar at 110 and 160 µm implantation depths (P > .071). Average ΔTCRP for the 4.00 D and 8.00 D groups was 3.10 ± 0.60 and 5.30 ± 1.66 diopters (D) at 110-µm depth, respectively (P = .003), but 1.99 ± 0.79 and 3.36 ± 1.45 D at 160-µm depth, respectively (P = .066). The relative correction achieved was 66% to 78% at 110-µm depth and 42% to 50% at 160-µm depth, but similar when using 4.00 D and 8.00 D lenticules. Increased chamber pressure caused significant anterior and posterior curvature steepening after implantation in all four groups (P < .001), but not before implantation (P > .632).

CONCLUSIONS

The power of the implanted lenticule must be higher than the intended correction, and customized to the chosen implantation depth. Biomechanical strength seems to decrease after lenticule implantation. [J Refract Surg. 2018;34(4):245-252.].

Femtosecond Laser-Assisted Small Incision Endokeratophakia Using a Xenogeneic Lenticule in Rhesus Monkeys

PURPOSE

To evaluate the feasibility and safety of xenogeneic endokeratophakia in rhesus monkeys and to explore the effects of a concave lenticule on refractive power.

METHODS

Three adult New Zealand white rabbits and 6 healthy rhesus monkeys were used. The xenogenic concave grafts were created from the rabbits using a modified small incision lenticule extraction technique; after being cryopreserved in glycerol for 1 week, the grafts were implanted into the monkey recipient corneas. Spherical equivalent (SE), central corneal thickness, and keratometry curvature were assessed preoperatively, 1 week, 1, 4 and 6 months postoperatively. The quality of the xenogenic graft was also assessed by slit-lamp microscopy, in vivo confocal microscopy, and optical coherence tomography with anterior segment imaging.

RESULTS

The graft appeared to be swollen a day after the operation but reduced considerably after a week. A trend of a lower refractive power (hyperopic shift) was demonstrated in relation to the SE after concave graft implantation. The mean SE increased from -0.60 ± 1.31 (median -0.69, interquartile range -1.00 to 0.50) preoperatively to 0.75 ± 1.27 (median 1.38, interquartile range -0.25 to 1.63) at 1 month postoperatively (P = 0.01). Central corneal thickness was significantly thicker each time after surgery compared with that recorded preoperatively (P < 0.01). The anterior and posterior interface between the graft and stroma was visible during the study. Corneal nerve regeneration was evident at 6 months postoperatively. The xenogeneic concave graft was stable and transparent at follow-up. Severe adverse events or evidence of a rejection response were not observed.

CONCLUSIONS

Femtosecond laser-assisted small incision endokeratophakia using a xenogeneic corneal lenticule seems to be feasible and safe, which may provide a new method for myopia correction and keratoconus treatment.