Early Changes of Ocular Biological Parameters in Rhesus Monkeys After Scleral Cross-linking With Riboflavin/Ultraviolet-A

Experimental Evaluation of Ocular Rigidity and Pressure-Volume Relationship After Ex-Vivo Scleral Cross-Linking With Riboflavin and Ultraviolet A in Porcine Eyes

PURPOSE

Scleral cross-linking (SXL) with ultraviolet A (UVA) and riboflavin has already been used in laboratory studies for scleral stiffness increase as a potential treatment for progressive myopia and scleral ectasia. This study aims to investigate whether the regional application of scleral cross-linking (SXL) with ultraviolet A (UVA) and riboflavin in fresh porcine eye globes affects the ocular rigidity as well as its impact on intraocular pressure after an induced acute increase in the volume of intraocular fluid.

METHODS

The study included two groups of fresh porcine eyes: an experimental group (n=20) that underwent scleral cross-linking (SXL) with riboflavin and UVA applied to the posterior sclera and a control group (n=20) that did not receive SXL treatment. Subsequently, a balanced salt solution (volumes 50, 100, 150, and 200 μL) was administered into porcine globes via a syringe, and, at the same time, the intraocular pressure (IOP) was continuously monitored by a pressure sensor that was cannulated to the vitreous chamber. The relationship between volume and pressure was obtained, and the ocular rigidity coefficient (K) was calculated according to Friedenwald's law. Finally, scleral strips were dissected from the globes and were examined macroscopically.

RESULTS

In the control group, the mean IOP observed entails gradual, statistically significant increases for higher volumes. Specifically, the mean IOP at 0 μL equals 10 mmHg (SD=0), whereas at 200 μL the mean IOP equals 33.83 mmHg (SD=4.060). The differences were statistically significant with p-values <0.001 in all cases. Similarly, the observed gradual IOP increases in the SXL group were statistically significant with p < 0.001 in all cases except for the comparison of volume 0 μL measurements to volume 50 μL, where the p-value equaled 0.003. Specifically in the SXL group, the mean IOP at 0 μL equals 10.00 mmHg (SD=0.000), the mean IOP at 50 μL equals 13.31 mmHg (SD=2.011), whereas the mean IOP at 200 μL equals 32.06 mmHg (SD=3.078). At no additional injected volume, the differences between the control and the SXL groups were statistically significant. The analysis regarding ocular rigidity indicated significantly higher scores in the control group (K50=0.00812, SD=0.03) compared to the SXL group (K50=0.00552, SD=0.027), t=2.844; p=0.007. The difference regards measures of volumes 0 to 50 μL, while all other rigidity measures were found to be non-significant. Interestingly, the ocular rigidity coefficient in the SXL-treated group did not show changes with an increase in IOP. The macroscopic appearance of the scleral strips showed a significantly increased stiffness of the SXL scleras against the control ones.

CONCLUSION

This study showed that stiffened scleras did not induce substantial change in ocular rigidity and significant IOP elevations. Studying the biomechanical ocular response of laboratory scleral crosslinking applications supports the development of next-generation crosslinking procedures that may constitute potential therapeutic options for severe ophthalmic diseases like pathologic myopia.

Parallel comparison of ocular metrics in non-human primates with high myopia by LS900, ultrasonography and MRI-based 3D reconstruction

We investigate the ocular dimensions and shape by using Lenstar900 (LS900), A-scan ultrasonography, and Magnetic Resonance Imaging (MRI) in highly myopic Macaca fascicularis. The ocular dimensions data of LS900, A-scan ultrasonography and MRI was assessed from 8 eyes (4 adult male cynomolgus macaque) with extremely high myopia (≤-1000DS) and compared by means of coefficients of concordance and 95% limits of agreement. Multiple regression analysis was performed to explore the associations between ocular biometry, volume, refraction and inter-instrument discrepancies. Test-retest reliability of three measurements of ocular parameters at two time points was almost equal (intraclass correlation = 0.831 to 1.000). The parallel-forms reliability of three measurements was strong for vitreous chamber depth (VCD) (coefficient of concordance = 0.919 to 0.981), moderate for axial length (AL) (coefficient of concordance = 0.486 to 0.981), and weak for anterior chamber depth (ACD) (coefficient of concordance = 0.267 to 0.621) and lens thickness (LT) (coefficient of concordance = 0.035 to 0.631). The LS900 and MRI systematically underestimated the ACD and LT comparing to A-scan ultrasonography (P < 0.05). Notably, the average AL on LS900 displayed a significant correlation with those on MRI (r = 0.978, P < 0.001) and A-scan ultrasonography (r = 0.990, P < 0.001). Almost 4/5 eyeballs were prolate. The mean eyeball volume positively correlated with AL (r = 0.782, P = 0.022), the width (r = 0.945, P = 0.000), and the length (r = 0.782, P = 0.022) of eyeball, while negatively correlated with SER (r = -0.901, P = 0.000). In conclusion, there was a high inter-instrument concordance for VCD with LS900, A-scan ultrasonography and MRI, while ACD and LT were underestimated with LS900 compared to A-scan ultrasonography, and the LS900 and A-scan ultrasonography could reliably measure the AL. MRI further revealed an equatorial globe shape in extremely myopic non-human primates.

Effects of riboflavin/ultraviolet-A(UVA) scleral crosslinking on the mechanical behavior of the scleral fibroblasts of lens-induced myopia Guinea pigs

Myopia is becoming increasingly severe, and studies have shown that the cellular mechanics of scleral fibroblasts are altered following myopia. Scleral UVA-Riboflavin Collagen Crosslinking（sCXL） is a promising treatment for myopia prevention and control of axial growth. Understanding the mechanical properties of scleral fibroblasts is crucial, as it influences the cellular response and limits the extent of molecular deformation triggered. Thus, our study aimed to investigate the effect of mechanical properties of scleral fibroblasts in a lens-induced myopic guinea pig model following sCXL. For this purpose, we performed the 0.1% riboflavin/UVA scleral crosslinking (365 nm,3 mW/cm2,30 min) in the right eyes of guinea pigs in Group CXL. In Group LIM, the right eyes were only administrated negative lens for 6 weeks. No treatment was performed in both eyes of the guinea pigs in group Control. The scleral fibroblasts were isolated and cultured from the scleral tissue at the cross-linking area in Group CXL and the corresponding area in Group LIM and control. The curve of the length of microtubules inhaled by cells under negative pressure was measured by a microaspiration-based isolation technique, and the equilibrium Young's modulus and apparent viscosity of scleral fibroblasts were calculated by formula fitting. The equilibrium Young's modulus of scleral fibroblasts in group CXL was significantly lower than that in the LIM group (P < 0.01, two-sample t-test between pairs）, and there was no significant difference between groups CXL and control. The results show that sCXL can effectively moderate the phenomenon that scleral fibroblasts are not easy to deform after myopia. The apparent viscosity modulus in the CXL group was higher than the groups' control and LIM. Taken together, our data demonstrate the biomechanics of the scleral fibroblasts altered after Riboflavin/UVA scleral collagen cross-linking in a lens-induced myopia model.

Therapeutic non-ectasia applications of cornea cross-linking

Corneal cross-linking is a photopolymerization technique traditionally used to strengthen corneal tissue. Corneal cross-linking utilizes riboflavin (vitamin B2) as a photosensitizer and ultraviolet-A light (UVA) to create strong covalent bonds within the corneal stroma, increasing tissue stiffness. Multiple studies have demonstrated corneal cross-linking's effectiveness in treating corneal ectasia, a progressive, degenerative, and non-inflammatory thinning disorder, as quantified by key tomographic, refractive, and visual parameters. Since its introduction two decades ago, corneal cross-linking has surpassed its original application in halting corneal ectatic disease and its application has expanded into several other areas. Corneal cross-linking also possesses antibacterial, antienzymolytic and antioedematous properties, and has since become a tool in treating microbial keratitis, correcting refractive error, preventing iatrogenic ectasia, stabilising bullous keratopathy and controlling post keratoplasty ametropia. This review provides an overview of the current evidence base for the therapeutic non-ectasia applications of cornea cross-linking and looks at future developments in the field.

Clinical Feasibility and Safety of Scleral Collagen Cross-Linking by Riboflavin and Ultraviolet A in Pathological Myopia Blindness: A Pilot Study

INTRODUCTION

To investigate the feasibility and safety of scleral ultraviolet A (UVA) cross-linking (scleral CXL) on pathologically blindness.

METHODS

This was a prospective, observational clinical study. Five patients with monocular blindness due to pathological myopic maculopathy were enrolled. Eyes with best corrected visual acuity (BCVA) under 0.05 were defined as experimental eyes. The fellow eyes were defined as control eyes. Patients first underwent posterior scleral reinforcement (PSR) surgery in the control eye. Thereafter, scleral CXL surgery was performed in the experimental eye on the same day. Visual acuity, BCVA, slit lamp biomicroscopic examination, intraocular pressure measurement, corneal specula microscopies, axis length measurement, funduscopy with pupil dilation, color fundus photography, full-field flash electroretinography, optical coherence tomography, and color Doppler flow imaging were performed at baseline, 1 week, 1 month, 3 months, 6 months, and 12 months after surgery.

RESULTS

No signs of inflammation were observed after operation and throughout the follow-up period. Retinoschisis was improved, while choroidal neovascularization fibrosis and retinal and choroidal atrophy were unchanged after scleral CXL. There were no statistically significant differences in the ophthalmic artery, central retinal artery, and posterior ciliary artery parameters of color Doppler flow imaging or in retinal thickness, within experimental and control eyes, at baseline, 1 week, 1 month, 3 months, or 12 months (P > 0.05).

CONCLUSIONS

This pilot study verified the feasibility and safety of scleral CXL on human blindness. The UVA-CXL on the sclera of human eyes seems to have the same effect as PSR in preventing progressive pathological myopia in the future.

TRIAL REGISTRATION

Chinese Clinical Trial Registry (ChiCTR2100042422).

Effects of riboflavin/ultraviolet-A scleral collagen cross-linking on regional scleral thickness and expression of MMP-2 and MT1-MMP in myopic guinea pigs

OBJECTIVE

To investigate the effects of scleral collagen cross-linking (SXL) using riboflavin and ultraviolet A (UVA) light on the scleral thickness of different regions and expression of matrix metalloproteinase 2 (MMP-2) and membrane-type MMP-1 (MT1-MMP) in guinea pigs with lens-induced myopia.

METHODS

Forty-eight 4-week-old guinea pigs were assigned to three groups (n = 16 per group): SXL group, lens-induced myopia (LIM) group, and control group. The sclera of the right eye of the guinea pig in the SXL group was surgically exposed, riboflavin was dropped on the treatment area for 10 minutes before the 30-minute UVA irradiation. The same surgical procedure was performed in the LIM group without UVA irradiation. The -10.00 D lenses were then placed on the right eyes of guinea pigs in the SXL and LIM groups for six weeks. The control group received no treatment. The left eyes were untreated in all groups. The ocular axial length (AXL) and refraction were measured at 4 weeks and 10 weeks of age. 10-week-old guinea pigs were sacrificed, and the right eyes were enucleated and evenly divided for preparation of hematoxylin and eosin (HE) stained sections, quantitative real-time polymerase chain reaction (qPCR) and western blotting. The scleral thickness of different regions was measured on HE stained sections. The temporal half of the sclera was harvested to measure the expression of MMP-2 and MT1-MMP by qPCR and western blotting.

RESULTS

The AXL was significantly shorter, and the degree of myopic refraction was significantly lower in the SXL group than those in the LIM group at 10 weeks of age. The scleral thickness of the cross-linked area was significantly greater in the SXL group than that of the corresponding area in the LIM group, while the scleral thickness of the untreated nasal side was not significantly different between the SXL group and the LIM group. The expression of MMP-2 and MT1-MMP of the cross-linked sclera was significantly downregulated compared with that of the corresponding area in the LIM group.

CONCLUSION

Riboflavin/UVA SXL could slow myopia progression and thicken the cross-linked sclera in guinea pigs, which might be related to the downregulation of MMP-2 and MT1-MMP expression during the scleral remodeling process.

Scleral Remolding-Related Gene Expression After Scleral Collagen Cross-Linking Using Ultraviolet A and Riboflavin in Myopic Guinea Pig Model

PURPOSE

This study was conducted to evaluate scleral remolding-related gene expression after scleral collagen cross-linking (SCXL) using ultraviolet A (UVA) and riboflavin in lens-induced myopia (LIM) guinea pigs.

METHODS

A total of 100 4-week-old pigmented guinea pigs were randomly divided into five groups (n = 20): SCXL + LIM, LIM, SCXL, Sham, and Control. Refraction, anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL) were measured using streak retinoscope and A-scan ultrasonography. SCXL was performed using 0.1% riboflavin solution and 365 nm UVA irradiation. Lens-induced myopia was achieved by wearing -10 D concave lenses. Quantitative real-time PCR (qPCR) and western blot were used to measure mRNA and protein levels, respectively.

RESULTS

Myopia was successfully induced in the LIM group, while myopic refraction was higher and ACD and AL were shorter in SCXL + LIM compared with LIM, suppressing myopia progression. The scleral COL1A1 mRNA levels were significantly decreased and MMP2 and ACTA2 mRNA levels were significantly increased in LIM compared with other groups, while COL1A1 mRNA levels were increased and MMP2 and ACTA2 mRNA levels were decreased in SCXL + LIM compared with LIM. The scleral COL1A1 protein levels were significantly increased at 1 week and 4 weeks and MMP2 protein levels were significantly decreased at 1 week in SCXL compared with SCXL + LIM, LIM and Control. MMP2 protein levels were significantly decreased in SCXL + LIM and SCXL compared with LIM at 4 weeks. The differences in TGFB1, BMP2, CCN2, ITGA2, and ITGB1 mRNA levels and ACTA2 protein levels between the five groups were not significantly different.

CONCLUSION

SCXL using UVA and riboflavin could influence the expression of scleral remolding-related genes, including COL1A1, MMP2, TIMP2, and ACTA2, and thus contribute to improving collagen synthesis and reducing collagen degradation and might have an effect on slowing myopia progression.

Comparing the Differences in Slowing Myopia Progression by Riboflavin/Ultraviolet A Scleral Cross-linking before and after Lens-induced Myopia in Guinea Pigs

PURPOSE

To compare the effectiveness and differences in slowing myopia progression in Guinea pigs by riboflavin/ultraviolet A (UVA) scleral cross-linking (sCXL) before and after lens-induced myopia (LIM).

METHODS

Forty 4-week-old Guinea pigs were randomly divided into four groups (n = 10 per group): CXL-A, CXL-B, LIM, and Control groups. The right eyes in CXL-A, CXL-B, LIM groups were treated with -10.00 D lenses from 4 to 10-week old and the left eyes were untreated. In CXL-A and CXL-B groups, riboflavin/UVA sCXL was performed on the right eyes at 4 weeks and 8 weeks of age, respectively. Both eyes were untreated in Control group. The intraocular pressure (IOP), the axial length (AXL), and the refraction were measured in vivo at 4, 8, and 10 weeks of age. At 10 weeks of age, the right eyes were enucleated for the tensile test and transmission electron microscopy observations.

RESULTS

The myopia has been successfully induced in LIM and CXL-B groups during 4-8 weeks. In CXL-A group, the growth rate of AXL and myopic refraction was markedly inhibited during 4-8 weeks and the inhibitory effects diminished during 8-10 weeks. During 8-10 weeks, the growth rate of AXL and myopic refraction in CXL-B were marked suppressed. At 10 weeks of age, the myopia refraction was lower and the AXL was shorter in CXL-A group in comparison to CXL-B group. The IOP was not significantly different among the 4 groups of eyes at 4, 8, and 10 weeks of age. The scleral stiffness, the fibril diameters, and the fibril density of the sclera were significantly increased in CXL-A and CXL-B groups compared to LIM group.

CONCLUSION

Riboflavin/UVA sCXL administrated before and after the myopia modeling could both slow the myopia progression in Guinea pigs. The before-myopia preventative sCXL showed lower myopic refraction in the same age comparison between the cross-linked groups. The effect of riboflavin/UVA sCXL might reduce over time and the long-term effect should be further investigated. This sCXL intervention might control the ultrastructure alterations of the sclera during the myopia remodeling.

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.].