Corneal collagen cross-linking for the treatment of progressive keratoconus: 3-year prospective outcome

Collagen changes in rabbit conjunctiva after conjunctival crosslinking

This study aims to determine the ultrastructural changes in collagen fibrils in rabbit conjunctiva after conjunctival crosslinking using riboflavin and ultraviolet A (UVA) light at an irradiation intensity of 45 mW/cm². Conjunctival crosslinking may increase conjunctival stiffness. The supertemporal quadrants of the right eyes of 24 adult rabbits were treated with a topical riboflavin solution (0.25%) before irradiation with UVA light at 45 mW/cm² for 4 min. After 3 weeks, the collagen fibrils in fibril bundles were examined by electron microscopy. Immunohistochemical staining was used to detect the expression levels of collagen I and collagen III in the rabbits' conjunctiva. The diameter of the collagen fibrils in the fibril bundles varied slightly, ranging from 30 to 60 nm in the conjunctival stroma of the control group. In the treatment group, the diameter of collagen fibrils ranged from 60 to 90 nm. The thickest collagen fibrils were observed in the treatment group (up to 90 nm in diameter). In contrast, those in the conjunctival stroma of the control group were considerably smaller (up to 60 nm in diameter). However, thicknesses of collagen fibrils displayed a unimodal distribution. Both collagen I and collagen III increased after treatment with riboflavin and UVA light irradiation at 45 mW/cm². The data indicate that in rabbits, conjunctival crosslinking with riboflavin and UVA light at 45 mW/cm² for 4 min is safe and does not induce ultrastructural alterations of the conjunctival cells. The conjunctival crosslinking with riboflavin and UVA light at 45 mW/cm² can increase the diameter of collagen fibrils, but the average densities of collagen I and collagen III have no statistical significance.

Evaluation of Corneal Parameters and Meibomian Gland Alterations After Corneal Cross-Linking in Patients With Progressive Keratoconus

OBJECTIVES

The aim of the study was to evaluate the changes in corneal parameters and meibomian gland alterations after corneal cross-linking (CXL) for progressive keratoconus.

METHODS

Thirty nine eyes of 39 keratoconus patients were treated with CXL. Corneal topography, specular microscopy, the Ocular Surface Disease Index© (OSDI), noninvasive tear break-up time (NITBUT), and meibography indices were evaluated preoperatively and at the first, third, and sixth months after CXL.

RESULTS

The flattest keratometry (K1) ( P =0.003), steepest keratometry (K2) ( P <0.001), apex, central, and thinnest corneal thicknesses ( P <0.001) showed significant differences after cross-linking, whereas the changes in the maximum keratometry (Kmax) were not significant ( P =0.140). The endothelial cell density, coefficient of variation, and hexagonality were unchanged. The NITBUT values decreased after cross-linking; however, there was no significant change in OSDI index ( P =0.313), meiboscore ( P =0.392), and meibomian gland loss degrees ( P =0.300). No change was detected in the morphology of the meibomian glands after CXL.

CONCLUSION

In eyes with keratoconus, a flattening in keratometry readings and thinning in corneal thickness were observed after CXL. The corneal endothelium is protected by dextran-free riboflavin. Cross-linking procedure causes dry eye by changing the corneal structure without affecting the morphology of the meibomian glands.

Tear proteome profile in eyes with keratoconus after intracorneal ring segment implantation or corneal crosslinking

Purpose

Keratoconus (KC) is a corneal ectasia characterized by structural changes, resulting in progressive thinning and biomechanical weakening that can lead to worsening visual acuity due to irregular astigmatism. Corneal collagen Crosslinking (CXL) and Intracorneal Ring Segment (ICRS) are widely used treatments in KC disease, but the alterations they cause in biomechanical mediators are still poorly understood. The aim of this study was to analyze the tear proteome profile before and after treatments to identify biomarkers altered by surgery.

Materials and methods

An observational, prospective, case-control pilot study was conducted, analyzing tear samples from KC patients by nano-liquid chromatography-mass spectrometry (nLC-MS/MS). Data are available via ProteomeXchange with identifier PXD035655. Patients with KC who underwent ICRS surgery (n = 4), CXL (n = 4), and healthy subjects (Ctrl, n = 4) were included in this study. Clinical parameters were measured and tear samples were collected before and 18 months after surgery. Proteins with ≥2 expression change and p-value &lt; 0.05 between groups and times were selected to study their role in post-operative corneal changes.

Results

These analyses led to the identification of 447 tear proteins, some of which were dysregulated in KC patients. In comparisons between the two surgical groups and Ctrls, the biological processes that were altered in KC patients at baseline were those that were dysregulated as a consequence of the disease and not of the surgical intervention. Among the biological processes seen to be altered were: immune responses, cytoskeleton components, protein synthesis and metabolic reactions. When comparing the two treatment groups (ICRS and CXL), the process related to cytoskeleton components was the most altered, probably due to corneal thinning which was more pronounced in patients undergoing CXL.

Conclusion

The changes observed in tears after 18 months post-operatively could be due to the treatments performed and the pathology. Among the deregulated proteins detected, A-kinase anchor protein 13 (AKAP-13) deserves special attention for its involvement in corneal thinning, and for its strong overexpression in the tears of patients with more active KC and faster disease progression. However, it should be kept in mind that this is a pilot study conducted in a small number of patients.

Corneal Biomechanics and Intraocular Pressure Following Scleral Lens Wear in Penetrating Keratoplasty and Keratoconus

OBJECTIVE

To compare corneal biomechanics and intraocular pressure (IOP) in keratoconus and penetrating keratoplasty eyes before and after nonfenestrated scleral lens wear.

METHODS

Twenty-three participants were enrolled, and 37 eyes were included in the analysis (11 penetrating keratoplasty and 26 keratoconus). A range of corneal biomechanical parameters and IOP were measured using the CORVIS ST before and after 8 hr of nonfenestrated scleral lens wear (Keracare, Acculens, Denver, CO).

RESULTS

Before lens wear, penetrating keratoplasty eyes displayed significantly greater median values for central corneal thickness (97 μm thicker, P=0.02), IOP (3.89 mm Hg higher, P=0.01), and biomechanical parameter A2 length (0.48 mm longer, P=0.003) compared with keratoconic eyes. No significant changes in corneal biomechanical parameters or IOP were observed after scleral lens wear in either group (all P>0.05).

CONCLUSION

Although nonfenestrated scleral contact lenses can induce a subatmospheric pressure after lens settling and compress tissue surrounding the limbus, no significant changes were detected in the corneal biomechanical parameters studied using CORVIS ST after scleral lens wear in eyes with penetrating keratoplasty and keratoconus.

Detecting Mechanical Anisotropy of the Cornea Using Brillouin Microscopy

Purpose

The purpose of this study was to detect the mechanical anisotropy of the cornea using Brillouin microscopy along different perturbation directions.

Methods

Brillouin frequency shift of both whole globes (n = 10) and cornea punches (n = 10) were measured at different angles to the incident laser, thereby probing corneal longitudinal modulus of elasticity along different directions. Frequency shift of virgin (n = 26) versus cross-linked corneas (n = 15) over a large range of hydration conditions were compared in order to differentiate the contributions to Brillouin shift due to hydration from those due to stromal tissue.

Results

We detected mechanical anisotropy of corneas, with an average frequency shift increase of 53 MHz and 96 MHz when the instrument probed from 0° to 15° and 30° along the direction of the stromal fibers. Brillouin microscopy did not lose sensitivity to mechanical anisotropy up to 96% water content. We experimentally measured and theoretically modeled how mechanical changes independent of hydration affect frequency shift as a result of corneal cross-linking by isolating an approximately 100 MHz increase in frequency shift following a cross-linking procedure purely due to changes of stromal tissue mechanics.

Conclusions

Brillouin microscopy is sensitive to mechanical anisotropy of the stroma even in highly hydrated corneas. The agreement between model and experimental data suggested a quantitative relationship between Brillouin frequency shift, hydration state of the cornea, and stromal tissue stiffness.

Translational Relevance

The protocol and model validated throughout this study offer a path for comprehensive measurements of corneal mechanics within the clinic; allowing for improved evaluation of the long-term mechanical efficacy of cross-linking procedures.

Effect of corneal cross-linking on endothelial cell density and morphology in the peripheral cornea

BACKGROUND

To compare the endothelial cell density and morphology in the peripheral cornea before and after corneal cross-linking (CXL).

METHODS

This study evaluated thirty-one eyes of 31 patients who were treated with standard CXL for progressive keratoconus. Preoperatively and 6 months postoperatively, we compared the corneal endothelial cell density (ECD), the coefficient of variation in cell size (CV), and the percentage of hexagonal cells (HEX), in the peripheral regions of the cornea, using a non-contact specular microscope (EM-3000, Tomey).

RESULTS

All keratoconic eyes in this series were measurable in the peripheral regions. No significant differences were found in the peripheral ECD preoperatively and 6 months postoperatively at each point (Wilcoxon signed-rank test, superior, p = 0.16, nasal superior, p = 0.12, temporal superior, p = 0.17, inferior, p = 0.37, nasal inferior, p = 0.28, temporal inferior, p = 0.17). The mean percentage of the ECD loss was 1.3, 1.3, 1.0, 1.4, 0.7, and 1.4%, respectively. No significant differences in the peripheral CV or HEX were found preoperatively and 6 months postoperatively at each point.

CONCLUSIONS

Standard CXL does not cause significant changes in endothelial cell density, polymegethism, or polymorphism, in the peripheral regions of the cornea. It is suggested that CXL is a minimally invasive surgical approach for progressive keratoconus, even in terms of peripheral endothelial cells.

TRIAL REGISTRATION

University Hospital Medical Information Network Clinical Trial Registry (000031162).

Transepithelial versus Epithelium off Crosslinking for Treating Keratoconus among Jordanians

Background:

The progression of keratoconus is stabilized with the help of corneal collagen cross-linking (CXL) supported through photosynthesized riboflavin.

Objective:

This study aims to compare the effectiveness of the transepithelial procedure and epithelium off procedure of corneal collagen crosslinking among keratoconus patients in Jordan.

Methods:

The study recruited 80 patients suffering from progressive keratoconus, from a tertiary care setting in Jordan. These participants were randomly divided into two groups; group 1 with 40 participants subjected to transepithelial (Corneal collagen cross-linking) CXL; and 40 participants in group 2 received conventional epithelium off CXL.

Results:

Improvement was observed in the mean contact lens, which corrected distance visual acuity (CDVA) from logMAR 0.332 ± 0.09 (group 1), 0.35 ± 0.09 (group 2) to 0.241 ± 0.07 (group 1), 0.21 ± 0.07 (group 2), respectively at the end of follow-up (12 months). The mean pachymetry improved from 429.81 ± 18.96 μm (group 1), 430.08 ± 17.05 μm (group 2) to 436.5 ± 15.49 μm (group 1), 436.44 ± 12.53 μm (group 2), respectively, after twelve months. Additionally, the mean Sim K astigmatism declined from 7.0 ± 2.0 (group 1), 6.73 ± 1.98 (group 2) to 5.97 ± 1.88 (group 1), 5.53 ± 0.08 (group 2) respectively at twelve months post-treatment. Majority of the patients in group 2 experienced more pain as compared to group 1 participants.

Conclusion:

The effectiveness of a cross-linking procedure related to keratometry readings and corneal thickness showed that conventional (epithelium off) CXL method is more effective than transepithelial CXL.

Long-term Evaluation of Corneal Biomechanical Properties After Corneal Cross-linking for Keratoconus: A 4-Year Longitudinal Study

PURPOSE

To compare the long-term changes in corneal biomechanics, topography, and tomography before and 4 years after corneal cross-linking (CXL) with the Dresden protocol and correlate these changes with visual acuity.

METHODS

In this longitudinal study, 18 eyes of 18 patients with progressive keratoconus who were treated with CXL were included. All patients received a standard ophthalmological examination and were examined by Placido disc-based topography, Scheimpflug tomography, and biomechanical assessments with the Corvis ST (OCULUS Optikgeräte GmbH, Wetzlar, Germany) and Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY) before and 4 years after CXL. The main outcome measures were dynamic corneal response (DCR) parameters obtained from the Corvis ST, corneal hysteresis (CH), corneal resistance factor (CRF), visual acuity, refraction, corneal curvature, and corneal thickness.

RESULTS

There were no significant differences in mean visual acuity, refraction, intraocular pressure, corneal topography, corneal astigmatism in both corneal surfaces, maximum keratometry, corneal thickness at apical and thinnest points, thickness profile indices, corneal volume, and specular microscopy before and 4 years after CXL (P > .05). Significant changes were observed in many DCR parameters, including radius at highest concavity and integrated inverse radius, both of which were consistent with stiffening. The CH and CRF values after CXL were not statistically significant. The new parameters using the Corvis ST include integrated inverse concave radius, which showed a significant decrease 1.07 ± 0.93 mm^-1, consistent with stiffening. The corneal stiffness parameter at the first applanation, Ambrósio's Relational Thickness to the horizontal profile, deformation amplitude ratio, and Corvis Biomechanical Index as a combined biomechanical screening parameter did not show significant changes.

CONCLUSIONS

CXL is a minimally invasive treatment option to prevent keratoconus progression over 4 years. Pressure-derived biomechanical parameters obtained from the ORA did not show any change following CXL at 4 years of follow-up, whereas the Corvis ST DCR parameters detected changes in corneal biomechanical properties. [J Refract Surg. 2018;34(12):849-856.].

Epi-Off versus Epi-On Corneal Collagen Cross-Linking in Keratoconus Patients: A Comparative Study through 2-Year Follow-Up

Aim

To evaluate two different techniques of cross-linking: standard epithelium-off (CXL epi-off) versus transepithelial (CXL epi-on) cross-linking in patient with progressive keratoconus.

Methods

Forty eyes from 32 patients with progressive keratoconus were prospectively enrolled from June 2014 to June 2015 in this nonblinded, randomized comparative study. Twenty eyes were treated by CXL epi-off and 20 by CLX epi-on, randomly assigned, and followed for 2 years. All patients underwent a complete ophthalmologic testing that included uncorrected and best corrected visual acuity, central and peripheral corneal thickness, corneal astigmatism, simulated maximum, minimum, and average keratometry, corneal confocal microscopy, Schirmer I and break-up time (BUT) tests, and the Ocular Surface Disease Index. Intra- and postoperative complications were recorded. The solution used for CXL epi-off comprised riboflavin 0.1% and dextran 20.0% (Ricrolin), whereas the solution for CXL epi-on (Ricrolin TE) comprised riboflavin 0.1%, dextran 15.0%, trometamol (Tris), and ethylenediaminetetraacetic acid. Ultraviolet-A treatment was performed with a UV-X system at 3 mW/cm².

Results

In both groups, a significant improvement in visual function (Group 1: baseline 0.36 ± 0.16 logMAR, two-year follow-up 0.22 ± 0.17 logMAR, p=0.01; Group 2: baseline 0.32 ± 0.18 logMAR, 2-year follow-up 0.27 ± 0.19 logMAR, p=0.01) was recorded. Keratometry remained unchanged in both groups. The mean corneal thickness showed a significant reduction (mean difference of corneal thickness: −55 micron and −71 micron, resp.). One-month after treatment, OSDI^© reached 13.56 ± 2.15 in Group 1 (p=0.03) and 11.26 ± 2.12 in Group 2 (p=0.04). At confocal microscopy, abnormal corneal nerve alterations were found in both groups. Fibrotic reaction (43.75%) and activated keratocyte (62.6%) were more commonly recorded in Group 1 than in Group 2 (25.0% and 18.75%), with p=0.668 and 0.356, respectively.

Conclusion

Our findings demonstrate that both procedures are able to slow keratoconus progression. Both treatment modalities are equivalent in terms of results and related complications. CXL epi-on technique is preferable to CXL epi-off since it preserves the corneal thickness and improves visual acuity, also reducing the postoperative ocular discomfort during the study period.

Corneal Cross-Linking in Pediatric Patients: Evaluating Treated and Untreated Eyes-5-Year Follow-Up Results

PURPOSE

To evaluate the long-term results of corneal collagen cross-linking (CXL) for treatment of pediatric keratoconus and the long-term outcomes of the fellow untreated keratoconic eye in patients younger than 18 years old.

METHODS

A retrospective case analysis was performed on 88 eyes of 44 patients aged 18 years or younger, with keratoconus, who underwent CXL in at least 1 eye. Follow-up measurements, for the treated and untreated eye pair, taken up to 5 years after treatment, were compared with baseline values. Parameters included uncorrected distance visual acuity (UCDVA), best spectacle-corrected distance visual acuity (BCDVA), manifest refraction, pachymetry, and corneal topography and tomography.

RESULTS

Mean age of patients was 15.6 ± 2.1 years. For the treated eyes, during all years of follow-up, UCDVA improved significantly (from 0.83 ± 0.30 to 0.72 ± 0.28 logMAR; P = 0.01). Improvement in BCDVA was not statistically significant (from 0.28 ± 0.19 to 0.23 ± 0.15 logMAR; P = 0.06). The manifest cylinder showed a significant reduction (from 5.8 ± 3.6 to 4.3 ± 2.5 diopters; P = 0.006). There was no significant change in maximum keratometry. Average keratometry and corneal thickness reduced significantly (P = 0.009 and P = 0.002, respectively). Five patients had very mild corneal haze after CXL. For the fellow untreated eyes-during 5 years of follow-up, UCDVA showed a slight decrease that was not statistically significant. BCDVA, average keratometry, and maximum keratometry remained stable.

CONCLUSIONS

Our long-term follow-up study suggests that CXL is a safe procedure in the pediatric age, and there is no urgency in treating pediatric patients with keratoconus without proof of progression.

Influence of the beam profile crosslinking setting on changes in corneal topography and tomography in progressive keratoconus: Preliminary results

PURPOSE

To evaluate the effect of accelerated corneal crosslinking (CXL) with a "higher peripheral intensity" profile setting compared with a standard "top hat" profile setting performed using different CXL systems.

SETTING

Department of Ophthalmology, University Hospital Carl Gustav Carus, Dresden, Germany.

DESIGN

Retrospective case series.

METHODS

Eyes from patients with progressive keratoconus were included. Group 1 included eyes treated with the higher peripheral intensity profile. Group 2 included eyes treated with the top hat profile. Accelerated CXL was performed based on the modified Dresden protocol (9 mW/cm², 10 minutes). Corneal-topography and tomography are characterized using the Pentacam Scheimpflug system.

RESULTS

The study comprised 45 eyes (25 eyes in Group 1, 20 eyes in Group 2) from 45 patients. The keratometry (K) at the apex (maximum K) decreased significantly from 54.95 diopters (D) ± 6.73 (SD) to 53.21 ± 6.05 D for Group 1 (P < .001) and from 57.29 ± 7.16 D to 56.48 ± 6.88 D for Group 2 (P = .01). In Group 1, flat K (K1) and steep K (K2) decreased significantly after treatment (P < .05). The thinnest corneal thickness decreased significantly by -17.5 ± 21.9 μm (P = .001) in Group 1. In Group 2, no significant flattening was observed in K1 and K2 (P > .05), and the thinnest corneal thickness showed a slight but not significant thinning (P = .097).

CONCLUSIONS

In Group 1 (the higher peripheral intensity group), the corneal topographic and tomographic parameters improved significantly after accelerated CXL. The higher peripheral intensity profile effect on keratoconic cornea flattening seemed to be more pronounced compared with the top hat profile.

Current perspectives on corneal collagen crosslinking (CXL)

Corneal collagen crosslinking has revolutionized the treatment of keratoconus and post-refractive corneal ectasia in the past decade. Corneal crosslinking with riboflavin and ultraviolet A is proposed to halt the progression of keratectasia. In the original "Conventional Dresden Protocol" (C-CXL), the epithelium is removed prior to the crosslinking process to facilitate better absorption of riboflavin into the corneal stroma. Studies analyzing its short- and long-term outcomes revealed that although there are inconsistencies as to the effectiveness of this technique, the advantages prevail over the disadvantages. Therefore, corneal crosslinking (CXL) is widely used in current practice to treat keratoconus. In an attempt to improve the visual and topographical outcomes of C-CXL and to minimize time-related discomfort and endothelial-related side effects, various modifications such as accelerated crosslinking and transepithelial crosslinking methods have been introduced. The comparison of outcomes of these modified techniques with C-CXL has also returned contradictory results. Hence, it is difficult to clearly identify an optimal procedure that can overcome issues associated with the CXL. This review provides an up-to-date analysis on clinical and laboratory findings of these popular crosslinking protocols used in the treatment of keratoconus. It is evident from this review that in general, these modified techniques have succeeded in minimizing the immediate complications of the C-CXL technique. However, there were contradictory viewpoints regarding their effectiveness when compared with the conventional technique. Therefore, these modified techniques need to be further investigated to arrive at an optimal treatment option for keratoconus.

Use of Donors Predisposed by Corneal Collagen Cross-linking in Penetrating Keratoplasty for Treating Patients With Keratoconus

PURPOSE

To investigate whether use of donors predisposed by corneal collagen cross-linking (CXL) reduced myopic refractive errors for keratoconic eyes after penetrating keratoplasty (PK).

DESIGN

Randomized controlled trial.

METHODS

One hundred sixteen eyes of 116 patients with keratoconus from Zhongshan Ophthalmic Center were enrolled. Using stratified block randomization, we assigned eligible eyes to the CXL graft group (Group 1) or conventional graft group (Group 2). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), spherical equivalent (SE), and topographic data were compared 12, 24, and 36 months after surgery.

RESULTS

Group 1 had better UDVA and CDVA than Group 2 after 1 year follow-up. Also, Group 1 had a lesser degree of SE and lower manifest cylinder than Group 2. At 3 years follow-up, mean CDVA was 0.17 ± 0.10 logarithm of the minimum angle of resolution (logMAR) in Group 1 vs 0.23 ± 0.12 logMAR in Group 2 (P = .004). Mean SE was -3.50 ± 2.93 diopter (D) in Group 1 and -4.02 ± 2.57 D in Group 2 (P = .034). Mean manifest cylinder was -5.22 ± 2.64 D and -6.35 ± 2.80 D in Group 1 and Group 2, respectively (P = .013). At 3 years follow-up, simulated keratometry in the steepest meridian (Kmax) was 46.85 ± 2.85 D vs 49.37 ± 2.92 D (P = .036); corneal power was 44.41 ± 2.89 D vs 46.35 ± 2.87 D (P = .001); and keratometric astigmatism was 4.53 ± 1.06 D vs 5.98 ± 1.28 D (P < .001) in Group 1 and Group 2, respectively.

CONCLUSIONS

Use of donors predisposed by CXL could reduce topographic readings after PK for the treatment of keratoconus, and consequently reduce myopic refractive errors and improve visual acuity.

Differences in corneal clinical findings after standard and accelerated cross-linking in patients with progressive keratoconus

Background

The purpose of this study was to identify differences in clinical corneal findings after standard and accelerated epithelial off cross-linking (CXL) during a long-term follow-up.

Methods

Two hundred forty-one patients (184 male) were included in this monocentric, retrospective, non-randomized and unmasked study. One hundred forty-eight eyes were treated with the accelerated protocol and 138 with the standard protocol with epithelial off CXL, if diagnosed with keratoconus and a progression in Kmax of more than one dioptre during the preceding 6 months, plus a minimal pachymetry measurement of 400 μm in keratometry (Pentacam, Oculus GmbH, Wetzlar, Germany). Exclusion criteria were previous surgery, other corneal conditions or age above 50 years. Follow-up time was 36 months with clinical examination and keratometry at every visit. Outcome measures were the observed rate of corneal changes, differences between treatment groups and correlation with keratometry measurements.

Results

In patients with accelerated CXL, significantly more clear corneas were seen at three (p = 0.015) and six (p = 0.002) months after surgery than following the standard protocol. The rate of clear corneas dropped from 52.2% pre-operation (OP) to a minimum of 19.3% after 6 months in the standard protocol group compared with 50.7% clear corneas pre-OP and a minimum of 40.8% in the accelerated group. In the standard protocol group, more striae were found 3 months after intervention than in the accelerated group (p = 0.05).

Conclusions

In patients with accelerated CXL, fewer morphological corneal changes were observed than after conventional CXL. However, rarely, corneal changes persisted for a long time.

Updates on corneal collagen cross-linking: Indications, techniques and clinical outcomes

Purpose

To review the historical background and basic principles of collagen cross-linking, to bring together the data regarding the outcomes and complications of collagen cross-linking and finally to explore the efficacy and safety of new variations of this technique.

Methods

A literature review was performed using PubMed and Scopus. The following keywords were used for literature search: cross linking, crosslinking, cross-linking, keratoconus, keratectasia.

Results

In contrast to traditional treatment modalities for keratoconus (KCN), this new technique addresses the progression of the disease. Several clinical studies have been conducted to assess the efficacy of corneal collagen cross-linking (CXL) in the last decade. The results were promising as collagen cross-linking showed significant improvement in visual acuity and keratometric values. Moreover, initial results show that it is a safe procedure with few reported complications.

Conclusion

CXL is an emerging treatment method in ophthalmology that offers the possibility to effectively treat progressive KCN.

Biomechanics of sclera crosslinked using genipin in rabbit

AIM

To strengthen the biomechanics of collagen by crosslinking rabbit scleral collagen with genipin to develop a new therapy for preventing myopic progression.

METHODS

Ten New Zealand rabbits were treated with 0.5 mmol/L genipin injected into the sub-Tenon's capsule in the right eyes. Untreated contralateral eyes served as the control. The treated area was cut into scleral strips measuring 4.0 mm×10.0 mm for stress-strain measurements (n=5). The remaining five treated eyes were prepared for histological examination.

RESULTS

Compared to the untreated scleral strips, the genipin-crosslinked scleral strips showed that the ultimate stress and Young's modulus at 10% strain were increased by the amplitude of 130% and 303% respectively, ultimate strain was decreased by 24%. There had no α-smooth muscle actin (α-SMA) positive cells in control and treated sclera. Histologically, there was no sign of apoptosis in the sclera, choroid, and retina; and no side effects were found in the peripheral cornea and optic nerve adjacent to the treatment area.

CONCLUSION

Genipin induced crosslinking of collagen can increase its biomechanical behavior by direct strengthening of the extracellular matrix in rabbit sclera, with no α-SMA expression seen in the myofibroblasts. As there is no evidence of cytotoxicity in the scleral, choroidal, and retinal cells, genipin is likely a promising agent to strengthen the weakened sclera to prevent myopic progression.

Efficacy of Corneal Collagen Cross-Linking for the Treatment of Keratoconus: A Systematic Review and Meta-Analysis

PURPOSE

To examine the efficacy of corneal collagen cross-linking (CXL) for the treatment of keratoconus (KCN).

METHODS

A systemic literature review and meta-analysis of ocular functional and structural parameters of patients with KCN undergoing cross-linking procedures were performed using PubMed and the web of science. A literature search was performed for relevant peer-reviewed publications on population-based studies. Data were analyzed with R software (Meta library), and heterogeneity was assessed with the Cochran Q and I. A random-effects model was used for high heterogeneity; otherwise a fixed model was used. Sensitivity analysis of particular tested groups was used to explain high heterogeneity. The main outcome measures extracted from the articles were corrected distance visual acuity, uncorrected distance visual acuity, and maximum K.

RESULTS

An improvement in visual acuity of 1 to 2 Snellen lines was found 3 months or more after undergoing CXL. Changes were more pronounced in uncorrected visual acuity. Some topography parameters were found to be improved (0.6-1 diopters) 12 to 24 months after CXL. The refractive cylinder improved by 0.4 to 0.7 diopters. Endothelial cell density decreased by 225 cells per square millimeter in the first 3 months and thereafter returned to normal. Corneal thickness was reduced by 10 to 20 μm in the year following CXL but not after 24 months. No changes in intraocular pressure were noted.

CONCLUSIONS

CXL is a safe and effective method for halting the deterioration of KCN, while slightly improving visual function.

One-year Outcomes of Pachymetry and Epithelium Thicknesses after Accelerated (45 mW/cm(2)) Transepithelial Corneal Collagen Cross-linking for Keratoconus Patients

The thickness of corneal pachymetry and the epithelium after accelerated (45 mW/cm(2)) transepithelial corneal collagen cross-linking (CXL) for keratoconus were assessed in this prospective case series study. Twenty-eight patients were treated for keratoconus. The mean Kmax was 56.18 ± 7.90. The thinnest point, as assessed by optical coherence tomography (OCT), was 443.18 ± 39.75 μm. Accelerated transepithelial CXL was performed, and corrected distance visual acuity (CDVA), corneal topography, and OCT were recorded at 1 week postoperatively as well as at 1, 3, 6, and 12 months. The surgery was uneventful in all eyes. Postoperative epithelial edema was observed and faded in 3 days. The postoperative Kmax was 54.56 ± 8.81, 55.78 ± 8.11, 56.37 ± 8.71, 55.80 ± 7.92, and 55.47 ± 8.24 at 1 week, 1 month, 3 months, 6 months, and 12 months, respectively (all, P > 0.05). The thinnest postoperative corneal point, 439.04 ± 44.99 μm, was observed at 12 months (P = 0.109). The epithelial thickness decreased during the first postoperative week then showed a gradual recovery. Postoperative pachymetry thickness showed no significant changes for up to 12 months. Postoperative epithelial thickness decreased temporarily, then stabilized at month 12. Accelerated transepithelial CXL was shown to be effective and safe for the treatment of keratoconus.

Transepithelial High-Intensity Cross-Linking for the Treatment of Progressive Keratoconus: 2-year Outcomes

PURPOSE

To report 2-year outcomes of transepithelial high-intensity cross-linking (CXL) procedure in the treatment of patients with progressive keratoconus.

METHODS

Forty-eight eyes of 48 consecutive progressive keratoconus patients who underwent transepithelial accelerated CXL procedure were enrolled in the study. Each patient underwent pre- and postoperative comprehensive ophthalmologic examinations including determination of refractive error as spherical equivalent (SE) and corrected distant visual acuity (CDVA), slit lamp biomicroscopic examination, fundoscopy, and a detailed analysis on a Scheimplug+Placido device (Sirius, CSO, Florence, Italy). The riboflavin solution, which was composed of riboflavin 0.25% with hydroxypropyl methylcellulose (HPMC) and benzalkonium chloride (BAC) (ParaCel, Avedro), was used in the procedure. The cornea was exposed to ultraviolet A light (KXL System, Avedro Inc., Waltham, MS, USA) for 2 minutes and 40 seconds at an irradiance of 45 mW/cm².

RESULTS

The mean age of the patients was 25.9 ± 4.0 (ranging from 18 to 33) years. No significant changes were observed in the mean CDVA, SE, and topographic indices at year 1 and year 2 visits compared to preoperative examination. The mean corneal thickness at the thinnest point was significantly higher at year 1 and year 2 visits than at preoperative examination (p1 = 0.014 and p2 = 0.017, respectively). No intra- or postoperative complications or adverse reactions were observed.

CONCLUSIONS

Transepithelial high-intensity (irradiance of 45 mW/cm² for 2 minutes and 40 seconds) CXL using 0.25% riboflavin solution was a safe and effective method to halt the progression of keratoconus for a 2-year follow-up period.

Collagen cross-linking: when and how? A review of the state of the art of the technique and new perspectives

Since the late 1990s corneal crosslinking (CXL) has been proposed as a new possibility to stop progression of keratoconus or secondary corneal ectasia, with the promising aim to prevent progressive visual loss due to the evolution of the pathology and to delay or avoid invasive surgical procedures such as corneal transplantation. The possibility of strengthening corneal tissue by means of a photochemical reaction of corneal collagen by the combined action of Riboflavin and ultraviolet A irradiation (UVA), radically modified the conservative management of progressive corneal ectasia. This is a review of the state of the art of CXL, reporting basic and clinical evidence. The paper describes basic principles, advantages and limits of different CXL techniques and possible future evolution of the procedure.

Investigation of the efficiency of intrastromal ring segments with cross-linking using different sequence and timing for keratoconus

AIM

To evaluate and compare the efficacy and stability of intrastromal corneal ring segment (ICRs) implantation with cross-linking (CXL) using different sequence and timing.

METHODS

In this single retrospective study, 86 keratoconic eyes subjected the ICRs implantation. We analyzed only 41 eyes that had complete follow-ups. They were divided into three groups: ICRs implantation was applied only (group normal), ICRs first followed by CXL immediately (group CXL-S), CXL first followed by ICRs long after (group CXL-B). The visual acuity, refractive results, keratometry were compared preoperatively and 1y postoperatively. Their differences among the three groups were also analyzed.

RESULTS

Group normal comprised 25 eyes, group CXL-S 8 eyes, and group CXL-B 8 eyes. There were improvements in the mean uncorrected distance visual acuity (UDVA) and the mean corrected distance visual acuity (CDVA) compared preoperatively and 1y postoperatively {UDVA: 0.31 (P=0.030) logarithmic minimum angle of resolution [logMAR] group normal, 0.4 (P=0.020) group CXL-S, 0.45 (P=0.001) group CXL-B; CDVA: 0.21 logMAR (P=0.013) group normal, 0.30 (P=0.036) group CXL-S; 0.26 (P=0.000) group CXL-B}. The refractive and topographic outcomes also showed improvements. In terms of comparisons among the three groups, all the P values were above 0.05, showing no significant difference. But only group CXL-B had improvement in UDVA and CDVA for all the patients.

CONCLUSION

With safety and good visual outcomes, ICRs implantation is a viable alternative for keratoconus. No significant difference was found among these three groups.

Progression in keratoconus and the effect of corneal cross-linking on progression

Ultraviolet corneal collagen cross-linking (CXL) has been shown to possibly delay, halt, or even reverse disease progression in keratoconus. Understanding of keratoconic progression in untreated eyes, however, is still incomplete and is hampered by the varying definitions and metrics used to evaluate corneal changes. As a result, the CXL literature varies widely in criteria for progression and parameters for successful outcomes. To date, there have been few long-term, well-controlled clinical trials supporting the efficacy of CXL to prevent progression in keratoconus. Review of our data on keratoconus suggests the course of corneal change is difficult to predict and that many keratoconic eyes appear stable once the eyes begin to exhibit frank changes in corneal curvature typical of keratoconus. Better-defined metrics for progression in keratoconus are needed. Larger, long-term randomized clinical trials may more clearly establish the efficacy and safety of CXL in the management of keratoconus and determine which patients are the best candidates for this procedure.

Efficacy of corneal collagen cross-linking for treatment of keratoconus: a meta-analysis of randomized controlled trials

Objective

To evaluate the efficacy of corneal collagen cross-linking (CXL) for the treatment of keratoconus.

Methods

We performed a literature search for randomized controlled trials that assessed the effect of CXL in slowing progression of keratoconus. The primary outcome measures included changes of topographic parameters, visual acuity, and refraction. Efficacy estimates were evaluated by weighted mean difference (WMD) and 95% confidence interval (CI) for absolute changes of the interested outcomes.

Results

Significant decrease in mean keratometry value, maximum keratometry value and minimum keratometry value were demonstrated in the CXL group compared with the control group (WMD = -1.65; 95% CI: -2.51 to -0.80; P < 0.00001; WMD = -2.05; 95% CI: -3.10 to -1.00; P < 0.00001; WMD = -1.94; 95% CI: -2.63 to -1.26; P < 0.00001; respectively). Best spectacle-corrected visual acuity improved significantly in CXL group (WMD = -0.10; 95% CI: -0.15 to -0.05; P < 0.00001), whereas uncorrected visual acuity did not differ statistically. Manifest cylinder error decreased significantly in patients undergoing CXL procedure compared with control patients in sensitivity analysis (WMD = -0.388; 95% CI: -0.757 to -0. 019; P = 0.04). The changes in central corneal thickness and intraocular pressure were not statistically significant.

Conclusion

CXL may be an effective option in stabilizing keratoconus. Further long-term follow-up studies will be necessary to assess the persistence of CXL.

Safety and Visual Outcome of Visian Toric ICL Implantation after Corneal Collagen Cross-Linking in Keratoconus: Up to 2 Years of Follow-Up

Purpose. To evaluate the long-term safety and clinical outcome of phakic Visian toric implantable collamer lens (ICL) insertion after corneal collagen cross-linking (CXL) in progressive keratoconus. Methods. This was a retrospective study of 30 eyes (19 patients), with progressive keratoconus, who underwent sequential CXL followed by Visian toric ICL implantation after 6 months. Results. At baseline, 6 eyes had stage I, 14 eyes stage II, and 10 eyes stage III keratoconus graded by Amsler-Krumeich classification. At 6 months after CXL, only K (steep) and K (max) decreased significantly from baseline, with no change in visual acuity or refraction. Flattening in keratometric readings was stable thereafter. There was significant improvement in mean uncorrected distance visual acuity (1.57 ± 0.56 to 0.17 ± 0.06 logMAR, P < 0.001) and mean corrected distance visual acuity (0.17 ± 0.08 to 0.11 ± 0.05 logMAR, P < 0.001) at 12 months after ICL implantation that was maintained at the 2-year follow-up. Mean cylinder power and mean spherical equivalent (SE) also decreased significantly after ICL implantation. A small hyperopic shift in SE (+0.25 D) was observed at 2 years that did not alter visual outcomes. Conclusions. Visian toric ICL implantation following CXL is an effective option for improving visual acuity in patients with keratoconus up to 2 years.

Treatment options for advanced keratoconus: A review

Traditionally, the mainstay of treatment for advanced keratoconus (KC) has been either penetrating or deep anterior lamellar keratoplasty (PK or DALK, respectively). The success of both operations, however, has been somewhat tempered by potential difficulties and complications, both intraoperatively and postoperatively. These include suture and wound-healing problems, progression of disease in the recipient rim, allograft reaction, and persistent irregular astigmatism. Taken together, these have been the inspiration for an ongoing search for less troublesome therapeutic alternatives. These include ultraviolet crosslinking and intracorneal ring segments, both of which were originally constrained in their indication exclusively to eyes with mild to moderate disease. More recently, Bowman layer transplantation has been introduced for reversing corneal ectasia in eyes with advanced KC, re-enabling comfortable contact lens wear and permitting PK and DALK to be postponed or avoided entirely. We offer a summary of the current and emerging treatment options for advanced KC, aiming to provide the corneal specialist useful information in selecting the optimal therapy for individual patients.

Trans-epithelial versus conventional corneal collagen crosslinking: A randomized trial in keratoconus

Purpose:

The purpose was to compare transepithelial versus epithelium off technique of corneal collagen crosslinking (CXL) in patients of keratoconus.

Materials and Method:

Totally, 40 eyes (40 patients) with progressive keratoconus were subjected to transepithelial CXL (20 eyes; Group I), and conventional CXL (20 eyes; Group II). Patients were evaluated for uncorrected distance visual acuity, best corrected visual acuity (BCVA), slit lamp-biomicroscopy, keratometry, 9-point pachymentry, orbscan II, and endothelial cell count at baseline and post CXL at 1, 3, and 6 months.

Results:

The two groups were similar with respect to the evaluated parameters both at baseline and at the end of 6 months. There was an improvement in mean BCVA from Log Mar 0.327 ± 0.1 (Group 1), 0.36 ± 0.08 (Group 2) to 0.23 ± 0.08 (Group 1; P < 0.001), 0.22 ± 0.06 (Group 2; P < 0.001), respectively, at 6 months. Mean Sim K astigmatism decreased from 6.6 ± 1.93 D (Group 1), 6.64 ± 1.93 D (Group 2) to 5.14 ± 1.86 D (Group 1; P = 0.001), and 4.77 ± 0.06 (Group 2; P = 0.001), respectively, at 6 months. The mean pachymetry increased from 432.05 ± 19.36 μm (Group 1), 429.91 ± 16.66 μm (Group 2) to 447.8 ± 16.09 μm (Group 1; P < 0.001), 440.25 ± 11.18 um (Group 2; P = 0.002), respectively, at 6 months. All cases showed stabilization of keratoconus two eyes in epithelium off group developed persistent stromal haze. Most of the patients in Group II experienced pain and photophobia during first 2 days, but not of Group I.

Conclusion:

Trans-epithelial technique offers visual and topographic outcomes similar to the conventional method with superior patient comfort postintervention.

Imaging mass spectrometry by matrix-assisted laser desorption/ionization and stress-strain measurements in iontophoresis transepithelial corneal collagen cross-linking

PURPOSE

To compare biomechanical effect, riboflavin penetration and distribution in transepithelial corneal collagen cross-linking with iontophoresis (I-CXL), with standard cross linking (S-CXL) and current transepithelial protocol (TE-CXL).

MATERIALS AND METHODS

The study was divided into two different sections, considering, respectively, rabbit and human cadaver corneas. In both sections corneas were divided according to imbibition protocols and irradiation power. Imaging mass spectrometry by matrix-assisted laser desorption/ionization (MALDI-IMS) and stress-strain measurements were used. Forty-eight rabbit and twelve human cadaver corneas were evaluated.

RESULTS

MALDI-IMS showed a deep riboflavin penetration throughout the corneal layers with I-CXL, with a roughly lower concentration in the deepest layers when compared to S-CXL, whereas with TE-CXL penetration was considerably less. In rabbits, there was a significant increase (by 71.9% and P = 0.05) in corneal rigidity after I-CXL, when compared to controls. In humans, corneal rigidity increase was not significantly different among the subgroups.

CONCLUSIONS

In rabbits, I-CXL induced a significant increase in corneal stiffness as well as better riboflavin penetration when compared to controls and TE-CXL but not to S-CXL. Stress-strain in human corneas did not show significant differences among techniques, possibly because of the small sample size of groups. In conclusion, I-CXL could be a valid alternative to S-CXL for riboflavin delivery in CXL, preserving the epithelium.