Minimally Invasive Repetitive UVA Irradiation along with Riboflavin Treatment Increased the Strength of Sclera Collagen Cross-Linking

Effects of Different Scleral Photo-Crosslinking Modalities on Scleral Stiffness and Hydration

Purpose

The purpose of this study was to evaluate the biomechanical and hydration differences in scleral tissue after two modalities of collagen cross-linking.

Methods

Scleral tissue from 40 adult white rabbit eyes was crosslinked by application of 0.1% Rose Bengal solution followed by 80 J/cm2 green light irradiation (RGX) or by application of 0.1% riboflavin solution followed by 5.4 J/cm2 ultraviolet A irradiation (UVX). Posterior scleral strips were excised from treated and untreated sclera for tensile and hydration-tensile tests. For tensile tests, the strips were subjected to uniaxial extension after excision. For hydration-tensile tests, the strips were dehydrated, rehydrated, and then tested. Young's modulus at 8% strain and swelling rate were estimated. ANOVAs were used to test treated-induced differences in scleral biomechanical and hydration properties.

Results

Photo-crosslinked sclera tissue was stiffer (Young's modulus at 8% strain: 10.7 ± 4.5 MPa, on average across treatments) than untreated scleral tissue (7.1 ± 4.0 MPa). Scleral stiffness increased 132% after RGX and 90% after UVX compared to untreated sclera. Scleral swelling rate was reduced by 11% after RGX and by 13% after UVX. The stiffness of the treated sclera was also associated with the tissue hydration level. The lower the swelling, the higher the Young's modulus of RGX (-3.8% swelling/MPa) and UVX (-3.5% swelling/MPa) treated sclera.

Conclusions

Cross-linking with RGX and UVX impacted the stiffness and hydration of rabbit posterior sclera. The Rose Bengal with green light irradiation may be an alternative method to determine the efficacy and suitability of inducing scleral tissue stiffening in the treatment of myopia.

A wireless battery-free eye modulation patch for high myopia therapy

The proper axial length of the eye is crucial for achieving emmetropia. In this study, we present a wireless battery-free eye modulation patch designed to correct high myopia and prevent relapse. The patch consists of piezoelectric transducers, an electrochemical micro-actuator, a drug microneedle array, μ-LEDs, a flexible circuit, and biocompatible encapsulation. The system can be wirelessly powered and controlled using external ultrasound. The electrochemical micro-actuator plays a key role in precisely shortening the axial length by driving the posterior sclera inward. This ensures accurate scene imaging on the retina for myopia eye. The drug microneedle array delivers riboflavin to the posterior sclera, and μ-LEDs' blue light induces collagen cross-linking, reinforcing sclera strength. In vivo experiments demonstrate that the patch successfully reduces the rabbit eye's axial length by ~1217 μm and increases sclera strength by 387%. The system operates effectively within the body without the need for batteries. Here, we show that the patch offers a promising avenue for clinically treating high myopia.

Shaping Eyeballs by Scleral Collagen Cross-Linking: A Hypothesis for Myopia Treatment

The global prevalence of myopia has brought to the attention of the different eye and vision specialists, who make way to control its progression. Evidence have shown that a proactive reshaping of the eyeball is the core point of myopia developing process, which particularly includes the weakening, thinning, and expanding of the sclera. Thus, the sclera is considered to be a prime target for therapeutic manipulation in halting progressive myopia. In the past decades, corneal collagen cross-linking has been applied in clinical practice for treating aberrant corneal remodeling diseases. In this article, we hypothesize that scleral collagen cross-linking (SXL) has a huge potential in stabilizing myopic process by shaping the eyeball and preventing the aberrant scleral remodeling. In contrast with the current methods of optometry correction, such as physiotherapy, pharmacotherapy, spectacles, contact lenses, refractive surgeries, etc., eyeball-shaping method using SXL is a fundamental intervention which aims at the pathogenesis of progressive visual loss of myopia. Compared with the current posterior scleral reinforcement, the most advantage of SXL is that there is no allotransplant into the myopic eye, which means less expenditure, lower risk, and easier to handle in operating.

Advanced Research in Scleral Cross-Linking to Prevent From Progressive Myopia

ABSTRACT

Riboflavin-ultraviolet A (UVA) collagen cross-linking (CXL) has been applied in clinical settings to prevent the progression of keratoconus and corneal dilatation caused by other reasons in past decades. As CXL with riboflavin-UVA can enhance the stiffness of collagen-rich tissues, this technique has been further used on sclera to investigate as a safe and effective myopia prevention treatment. Despite the riboflavin-UVA scleral CXL is still in the animal and in vitro experimental phases and the mechanism is not very clear, it is promising to control myopia development clinically. In this article, researches on the laboratory experiments of riboflavin-UVA scleral CXL on scheme exploration and mechanism were reviewed in order to provide more laboratory evidence for scleral CXL in clinical myopia prevention and control in the future.

Evaluation of the Safety and Long-term Scleral Biomechanical Stability of UVA Cross-linking on Scleral Collagen in Rhesus Monkeys

PURPOSE

To investigate the changes of retinal and choroidal parameters, scleral biomechanical strength, and ocular histopathology after scleral ultraviolet-A (UVA) cross-linking (CXL) in rhesus monkeys eyes, and to evaluate the safety and long-term biomechanical stability of scleral CXL for preventing myopia from progressing further in clinic.

METHODS

Six 3-year-old male rhesus monkeys (12 eyes) were randomized to receive UVA-CXL procedures applied on the superotemporal equatorial sclera. Optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) were used for examination before and 1 week and 1, 3, 6, and 12 months after CXL. The stress-strain behaviors of equatorial scleral strips were analyzed 12 months postoperatively by a biomaterial tester. Hematoxylin-eosin and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining were performed 12 months postoperatively.

RESULTS

For central retinal thickness, choroidal thickness, and flow density of central retinal superficial vascular networks, no statistical difference was noted between CXL eyes and control eyes at 12 months postoperatively (P > .05). The biomechanical stability of sclera was increased. The scleral stress and Young modulus at 8% strain corresponded to 184% and 183%, respectively, of the control values at 12 months (each P < .001). No retinal damage was detected on histology in scleral CXL eyes. There was no obvious difference between scleral CXL eyes and control eyes by hematoxylin-eosin and TUNEL staining (P > .05).

CONCLUSIONS

Scleral CXL with riboflavin/UVA in rhesus monkey eyes could strengthen the biomechanical properties of scleral tissues and maintain the stability for 12 months postoperatively. The UVA-CXL on the sclera of rhesus monkey eyes seems to be effective and safe. [J Refract Surg. 2020;36(10):696-702.].

Selective Equatorial Sclera Crosslinking in the Orbit Using a Metal-Coated Polymer Waveguide

Purpose

Photochemical crosslinking of the sclera is an emerging technique that may prevent excessive eye elongation in pathologic myopia by stiffening the scleral tissue. To overcome the challenge of uniform light delivery in an anatomically restricted space, we previously introduced the use of flexible polymer waveguides. We presently demonstrate advanced waveguides that are optimized to deliver light selectively to equatorial sclera in the intact orbit.

Methods

Our waveguides consist of a polydimethylsiloxane cladding and a polyurethane core, coupled to an optical fiber. A reflective silver coating deposited on the top and side surfaces of the waveguide prevents light leakage to nontarget, periorbital tissue. Postmortem rabbits were used to test the feasibility of in situ equatorial sclera crosslinking. Tensometry measurements were performed on ex vivo rabbit eyes to confirm a biomechanical stiffening effect.

Results

Metal-coated waveguides enabled efficient light delivery to the entire circumference of the equatorial sclera with minimal light leakage to the periorbital tissues. Blue light was delivered to the intact orbit with a coefficient of variation in intensity of 22%, resulting in a 45 ± 11% bleaching of riboflavin fluorescence. A 2-fold increase in the Young's modulus at 5% strain (increase of 92% P < 0.05, at 25 J/cm2) was achieved for ex vivo crosslinked eyes.

Conclusions

Flexible polymer waveguides with reflective, biocompatible surfaces are useful for sclera crosslinking to achieve targeted light delivery. We anticipate that our demonstrated procedure will be applicable to sclera crosslinking in live animal models and, potentially, humans in vivo.