Safety of Corneal Collagen Cross-linking With UV-A and Riboflavin in Progressive Keratoconus

Does collagen cross linking have any effect on retinal circulation in patients with keratoconus? An optical coherence tomography angiography (OCTA) study

BACKGROUND

We aimed to employ Optical Coherence Tomography Angiography (OCTA) to comprehensively assess changes in the optic nerve head (ONH) and macular perfusion before and after the Corneal Collagen Cross-Linking (CCL) procedure in patients with keratoconus.

METHODS

A total of 22 keratoconus patient's candidate for CCL procedures were included based on specific criteria, with meticulous exclusion criteria in place to minimize potential confounders. Participants underwent OCTA assessments of the ONH and macula using the Spectralis OCT (Heidelberg) before CCL, as well as at 1- and 3-months post-CCL. MATLAB software was utilized for image analysis.

RESULTS

The mean age of the participants was 20.09 ± 6.11, including 59% male, and the mean intraocular pressure (IOP) before the surgery was 13.59 ± 2.85 mmHg. Peripapillary Retinal nerve fiber layer (ppRNFL) thickness and overall retinal thickness remained stable post-CCL. However, significant alterations were observed in macular vessel density, emphasizing regional variations in vascular response. For macular large vessel density (LVD), both superficial and deep vascular complex (SVC and DVC) demonstrated significant differences between before surgery and the 3 months post-surgery follow-up (p < 0.001 and p = 0.002, respectively). Optic nerve head markers demonstrated relative stability, except for changes in avascular complex density, which was 49.2 ± 2.2% before the surgery and decrease to 47.6 ± 1.7% three months after the operation (P-value = 0.005).

CONCLUSION

While CCL appears to maintain the integrity of certain ocular structures, alterations in macular perfusion post-CCL suggest potential effects on retinal blood supply. Long-term monitoring is crucial to understand the implications of these changes, particularly in the context of conditions such as diabetes.

Riboflavin-Vancomycin Conjugate Enables Simultaneous Antibiotic Photo-Release and Photodynamic Killing against Resistant Gram-Positive Pathogens

Decades of antibiotic misuse have led to alarming levels of antimicrobial resistance, and the development of alternative diagnostic and therapeutic strategies to delineate and treat infections is a global priority. In particular, the nosocomial, multidrug-resistant "ESKAPE" pathogens such as Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus spp (VRE) urgently require alternative treatments. Here, we developed light-activated molecules based on the conjugation of the FDA-approved photosensitizer riboflavin to the Gram-positive specific ligand vancomycin to enable targeted antimicrobial photodynamic therapy. The riboflavin-vancomycin conjugate proved to be a potent and versatile antibacterial agent, enabling the rapid, light-mediated, killing of MRSA and VRE with no significant off-target effects. The attachment of riboflavin on vancomycin also led to an increase in antibiotic activity against S. aureus and VRE. Simultaneously, we evidenced for the first time that the flavin subunit undergoes an efficient photoinduced bond cleavage reaction to release vancomycin, thereby acting as a photoremovable protecting group with potential applications in drug delivery.

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.

Accelerated CXL Versus Accelerated Contact Lens-Assisted CXL for Progressive Keratoconus in Adults

PURPOSE

To compare the clinical and tomographic properties of adult patients with keratoconus treated with accelerated corneal cross-linking (A-CXL) versus accelerated contact lens-assisted corneal cross-linking (A-CACXL).

METHODS

Patients who underwent A-CXL and A-CACXL due to progressive keratoconus were enrolled from January 2015 to January 2018 in this retrospective case-control study. The treatment group (minimum corneal thickness of less than 400 µm after epithelium removal; 30 patients, 30 eyes) was treated with A-CACXL; the control group (minimum corneal thickness of 400 µm or greater, 32 patients, 32 eyes) was treated with A-CXL. Assessments occurred before treatment and 12 months postoperatively. Demographic, clinical, and tomographic data were obtained from outpatient clinic reports.

RESULTS

Significant improvement in visual acuity was evident at 12-month follow-up for the control group in uncorrected distance visual acuity (0.62 ± 0.42 vs 0.43 ± 0.31 logMAR, P = .01) and the treatment group in corrected distance visual acuity (0.51 ± 0.30 vs 0.40 ± 0.49 logMAR, P = .03). Progression of keratoconus was halted at similar rates for both groups (76.7% treatment, 84.4% control, P = .21). Mean minimum corneal thickness showed minor but significant thinning at the 12-month follow-up visit compared to baseline (control group = 463 ± 31 vs 450 ± 35 µm, P > .01; treatment group = 398 ± 32 vs 388 ± 41 µm, P = .02).

CONCLUSIONS

A-CACXL halted keratoconus progression in 76.7% of eyes and achieved regression in 33.3% of eyes, with rates comparable to A-CXL. Visual outcomes improved for both groups, with similar keratometry changes. A-CACXL is an effective and safe option for patients with keratoconus and thin corneas, with results similar to A-CXL treatment in patients with a minimum corneal thickness of 400 µm or greater. [J Refract Surg. 2021;37(9):623-630.].

Collagen Bioinks for Bioprinting: A Systematic Review of Hydrogel Properties, Bioprinting Parameters, Protocols, and Bioprinted Structure Characteristics

Bioprinting is a modern tool suitable for creating cell scaffolds and tissue or organ carriers from polymers that mimic tissue properties and create a natural environment for cell development. A wide range of polymers, both natural and synthetic, are used, including extracellular matrix and collagen-based polymers. Bioprinting technologies, based on syringe deposition or laser technologies, are optimal tools for creating precise constructs precisely from the combination of collagen hydrogel and cells. This review describes the different stages of bioprinting, from the extraction of collagen hydrogels and bioink preparation, over the parameters of the printing itself, to the final testing of the constructs. This study mainly focuses on the use of physically crosslinked high-concentrated collagen hydrogels, which represents the optimal way to create a biocompatible 3D construct with sufficient stiffness. The cell viability in these gels is mainly influenced by the composition of the bioink and the parameters of the bioprinting process itself (temperature, pressure, cell density, etc.). In addition, a detailed table is included that lists the bioprinting parameters and composition of custom bioinks from current studies focusing on printing collagen gels without the addition of other polymers. Last but not least, our work also tries to refute the often-mentioned fact that highly concentrated collagen hydrogel is not suitable for 3D bioprinting and cell growth and development.

Safety of accelerated corneal collagen cross-linking in keratoconus patients on the basis of macular segmentation

PURPOSE

To investigate the safety of accelerated corneal collagen cross-linking (A-CXL) in patients with keratoconus on the basis of thickness analysis measurements of retinal layers and retinal morphology.

STUDY DESIGN

This was a retrospective and comparative study.

METHODS

The study included 64 eyes of 32 patients with keratoconus disease. One eye of the patients underwent A-CXL for progressive keratoconus (CXL group) and the fellow eye was followed due to the absence of progression. Patients with at least 1-year follow-up after A-CXL were included. Keratometry, pachymetry and corrected-distance visual acuity (CDVA) levels of the patients were compared. The segmentation analysis of the individual retinal layers of the eyes with (CXL group) and without CXL (no CXL group) was compared with spectral domain-optical coherence tomography automatic segmentation program at baseline and at the last follow-up. The thickness of the retinal nerve fiber layer, ganglion cell layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer and retina pigment epithelium layer in the central 1-mm subfield defined by the ETDRS was analyzed.

RESULTS

The mean age of keratoconus patients was 23.9 ± 5.4 years, patients were more likely to be male (21/11, 65.6%), and the mean follow-up duration was 13.9 ± 1.5 months. When keratometry, pachymetry and CDVA levels were compared, only a significant difference was found between CDVA at the last follow-up (0.21 vs. 0.11 LogMAR). No significant difference was observed in neither retinal morphology nor segmentation of individual retinal layers at baseline and at the final evaluation (P > 0.05).

CONCLUSIONS

It has been observed that the A-CXL protocol did not cause a significant change in both retinal layer thickness and macular morphology.

A Prospective, Comparative, Clinical Study to Evaluate the Safety and Efficacy of Two Different 0.1% Riboflavin Solutions Used in Collagen Crosslinking Treatment for Patients with Keratoconus

Purpose

To compare the safety and efficacy of 0.1% riboflavin in two different solutions which is used in corneal collagen crosslinking (CXL) for the treatment of keratoconus.

Methods

This was a prospective, randomized, comparison study which included 100 eyes of 61 patients with progressive keratoconus who underwent CXL with riboflavin 0.1% solution as a photosensitizer, using the standard Dresden protocol of using 3mW/cm² UV-A irradiation for 30 minutes which corresponds to a total energy of 5.4 J/cm². The recruited patients were divided into 2 groups ie, Flavin Group and Peschke-D group by computer generated randomization. Postoperative examinations were conducted on 1 day, 1 month, 3 months, 6 months and 12 months after the crosslinking.

Results

For both groups, the mean manifest spherical equivalent (SE), astigmatism, best corrected distance visual acuity, keratometry values, thinnest pachymetry values, demarcation line depth and endothelial cell density preoperatively and at postoperative 12 months were comparable with no statistically significant differences. At 12 months postoperatively, 62% of eyes in the Flavin group, and 68% of eyes in the Peschke-D group had postoperative manifest SE of within ± 1.00 D. During UV-A exposure, the cornea in the Flavin group showed intraoperative thinning of 112 microns (27%) as compared with a thinning of 108.12 microns (26.5%) observed in the Peschke group (p=1.67) from the initial pachymetry readings. No eye in either group had any immediate or long-term postop vision threatening complications such as infectious keratitis, corneal melt, non-resolving corneal oedema or endothelial decompensation.

Conclusion

Both riboflavin solutions were equally safe and effective in the management of progressive keratoconus, and resulted in similar changes in terms of mean manifest spherical equivalent (SE), astigmatism, best corrected distance visual acuity, keratometry values, thinnest pachymetry values, demarcation line depth and endothelial cell density at the end of 12 months postoperatively.

Trial Registration Number

Ctri/2019/11/021841 (Www.ctri.nic.in).

The Effect of Sodium Iodide on Stromal Loading, Distribution and Degradation of Riboflavin in a Rabbit Model of Transepithelial Corneal Crosslinking

Purpose

To evaluate effects of sodium iodide (NaI) on riboflavin concentration in corneal stroma before and during ultraviolet A (UVA) light exposure using a novel transepithelial corneal collagen crosslinking (CXL) procedure (EpiSmart CXL system, CXL Ophthalmics, Encinitas CA).

Methods

Riboflavin solutions with NaI (Ribostat, CXL Ophthalmics, Encinitas CA) and without NaI were used for CXL in rabbits using EpiSmart. A pilot study determined sufficient riboflavin loading time. Four rabbits were dosed and monitored. Riboflavin fluorescence intensity was assessed from masked slit-lamp photos. A 12 min loading time was selected. Sixteen additional rabbits received the two formulae in contralateral eyes for CXL. Riboflavin uptake was assessed at 0, 10, 15, 20, 25, and 30 min of UVA exposure using a scale for riboflavin fluorescence previously validated against stromal concentration. Post sacrifice, corneal stromal samples were analyzed for concentrations of riboflavin and riboflavin 5ʹ-phosphate.

Results

Eyes dosed with NaI riboflavin had higher riboflavin grades compared to eyes dosed with the NaI-free riboflavin formulation immediately after riboflavin loading and persisting throughout UVA exposure, with significantly higher (P < 0.01 to < 0.05) riboflavin grades from 15 through 25 min of UVA exposure. Riboflavin grades decreased more slowly in eyes dosed with NaI riboflavin through 25 minutes of UVA exposure. Minor conjunctival irritation was noted with or without NaI.

Conclusion

The addition of NaI to riboflavin solution is associated with increased riboflavin concentration in corneal stroma throughout a clinically relevant time course of UVA exposure. This effect may be a combination of enhanced epithelial penetration and reduced riboflavin photodegradation and should enhance intrastromal crosslinking.

Corneal Collagen Cross-Linking Pretreatment Mitigates Injury-Induced Inflammation, Hemangiogenesis and Lymphangiogenesis In Vivo

Purpose

The purpose of this study was to evaluate if corneal collagen cross-linking (CXL) pretreatment dampens suture-induced hemangiogenesis and lymphangiogenesis driven by inflammation.

Methods

Four weeks after CXL pretreatment, suture emplacement was performed in rats. The time dependent effects were compared of this procedure in three groups: (1) suture-induced neovascularization (SNV group); (2) CXL treatment prior to suture-induced neovascularization (CXL + SNV group); (3) Normal control (NC group). Serial morphometric measurements evaluated suture-induced hemangiogenesis and lymphangiogenesis. CD45 and CD68 immunofluorescent staining pattern changes determined immune cell activation, stromal leucocyte, and macrophage infiltration. The real-time quantitative polymerase chain reaction (RT-qPCR) determined angiogenic and lymphangiogenic gene expression level changes. Western blots evaluated protein expression levels of vascular endothelial cell CD31 and lymphatic vessel endothelial hyaluronan receptor (LYVE-1).

Results

On days 7 and 14 after suture emplacement, the rises in angiogenesis, lymphangiogenesis, CD45+ and CD68+ cell infiltration were less in the CXL pretreated (CXL + SNV) group than in the untreated (SNV) group. Angiogenic and lymphangiogenic mRNA levels and CD31 and LYVE-1 protein and proinflammatory cytokines were also suppressed, confirming that CXL pretreatment improved the wound healing response.

Conclusions

CXL pretreatment inhibits injury-induced angiogenesis and lymphangiogenesis. These reductions suggest that prior CXL therapy decrease ocular inflammation reactivated by secondary trauma.

Translational Relevance

CXL pretreatment induces increases in stromal stiffness which in turn reduces trauma or microbial driven increases in inflammation, angiogenesis, and lymphangiogenesis. These beneficial effects suggest that this novel procedure may improve therapeutic management of trauma-induced corneal disease in a clinical setting.

Corneal Cross-linking as an Adjunct for The Management of Refractory Fungal Keratitis

PURPOSE:

To evaluate the effectiveness of ultraviolet (UV)-A/Riboflavin corneal cross-linking (CXL) for the treatment of the refractory cases of fungal keratitis.

METHODS:

In this prospective interventional study, 9 patients with the diagnosis of fungal keratitis that were referred to our emergency eye center were included. These patients were resistant to conventional treatment and underwent therapeutic UV-A/Riboflavin CXL. Response to the treatment was considered as good if rapid epithelialization and rapid decrease in stromal infiltration was occurred after PACK-CXL, and poor when the emergency transplantation was necessary to eradicate the infection.

RESULTS:

Nine patients treated with CXL due to recalcitrant fungal keratitis. Culture of the corneal scrapings showed Aspergillus species in 4 patients, Candida albicans in 1 patient and Fusarium species in the remainder of them. CXL was performed from 1 to 20 days after the presentation of corneal ulcers (Mean: 9.12 ± 4.02; range: 5–20 days). Postoperatively, the mean time to epithelialization was 14.25 ± 2.38 days, and mean time to resolution of stromal infiltration was 22.5 ± 7.29 days, in responsive cases. Four out of 9 eyes showed good response, and five patients showed no response, and corneal transplantation was performed to eradicate the infection. There was no statistically significant difference in mean depth of infiltration and mean size of ulcer between responsive and unresponsive patients (P = 0.86 and 0.08, respectively).

CONCLUSION:

Although UV-A/Riboflavin CXL is not a definite treatment for all of the fungal keratitis, it seems promising in the management of some refractory cases.

Study on patterned photodynamic cross-linking for keratoconus

PURPOSE

This study examined the patterned treatment of corneal collagen cross-linking (CXL) for keratoconus to reduce the complications caused by ultraviolet (UV) irradiation. By modifying the method of UV irradiation during the cross-linking process, cross-linking with a special structure is achieved, and the cross-linking effect is analyzed and compared to that of traditional cross-linking. By constructing an animal model of keratoconus, the process and effect of corneal cross-linking can be investigated more fundamentally. These studies provide valuable references for future cross-linking precision improvement and specialization.

METHOD

By injecting exogenous collagenase into the corneal stroma of rabbits, the balance between collagenase and collagenase inhibitor in the corneal stroma was disrupted, the collagen fiber structure of the cornea was broken to simulate the pathogenesis of keratoconus, and an animal model of keratoconus was thus constructed. Two custom cross-linking patterns were designed with reference to the cable dome structure, and these two special patterns were irradiated and cross-linked by a DMD chip. The cross-linking effect was evaluated by optical coherence tomography (OCT), corneal topography and corneal biaxial tensile tests. The experimental rabbits were divided into four groups: group A, cross-linking of the bird's nest structure; group B, cross-linking of the honeycomb structure; group C, cross-linking of the traditional spot structure; and group D, normal (without modeling and cross-linking).

RESULT

Following collagenase treatment, the collagen fiber structure of the rabbit cornea was destroyed, the central thickness of the cornea was reduced, the mechanical properties of the cornea were weakened, and no keratitis, ulcers or haze occurred. After the three cross-linking treatments, the morphology of the cornea improved, the density of the stromal layer increased, and the mechanical properties were enhanced. For the improvement of keratoconus mechanical properties, the average relative difference (Δ) of the four outcome measures was 61.98% for bird's nest cross-linking versus keratoconus (Wilcoxon rank sum test, P = 0.024), 16.13% for honeycomb cross-linking versus keratoconus (Wilcoxon rank sum test, P = 0.025), and 21.07% for traditional spot cross-linking versus keratoconus (Wilcoxon rank sum test, P = 0.014). All these differences are statistically significant.

CONCLUSION

All three methods of cross-linking can improve the morphology and tissue structure of keratoconus and significantly improve the biomechanical properties of the cornea. Among them, the corneal cross-linking of the bird's nest structure attains the best biomechanical properties, followed by the corneal cross-linking of the traditional spot structure and of the honeycomb structure. This suggests that similar or better cross-linking effects can be achieved by designing custom structures with less UV exposure. This provides a direction for future research on better and more accurate pattern cross-linking treatments.

Decreased Riboflavin Impregnation Time Does Not Increase the Risk for Endothelial Phototoxicity During Corneal Cross-Linking

Purpose

To evaluate the riboflavin (RF) concentration and distribution in the corneal stroma and the risk for endothelial photodamage during corneal crosslinking (CXL) following 10- and 30-minute impregnation.

Methods

De-epithelialized rabbit corneas were subjected to impregnation for 10 and 30 minutes with different RF formulations. Human corneal endothelial cells (HCECs) were subjected to different RF concentrations and ultraviolet A (UVA) dosages. Assays included fluorescence imaging, absorption spectroscopy of corneal buttons and anterior chamber humor, and cell viability staining.

Results

After 10 and 30 minutes of impregnation, respectively, anterior chamber fluid showed an RF concentration of (1.6 ± 0.21)•10⁻⁴% and (5.4 ± 0.21)•10⁻⁴%, and trans-corneal absorption reported an average corneal RF concentration of 0.0266% and 0.0345%. This results in a decrease in endothelial RF concentration from 0.019% to 0.0056%, whereas endothelial UVA irradiance increases by 1.3-fold when changing from 30 to 10 minutes of impregnation. HCEC viability in cultures exposed to UVA illumination and RF concentrations as concluded for the endothelium after 10- and 30-minute impregnation was nonstatistically different at 51.0% ± 3.9 and 41.3 ± 5.0%, respectively.

Conclusions

The risk for endothelial damage in CXL by RF/UVA treatment does not increase by shortened impregnation because the 30% increase in light intensity is accompanied by a 3.4-fold decrease of the RF concentration in the posterior stroma. This is substantiated by similar endothelial cell toxicity seen in vitro, which in fact appears to favor 10-minute impregnation.

Translational Relevance

This study offers compelling arguments for (safely) shortening RF impregnation duration, reducing patients’ burden and costly operation room time.

Novel Use of Vitamin B2 as a Fluorescent Tracer in Aerosol and Droplet Contamination Models in Otolaryngology

Objective:

During the COVID-19 era, a reliable method for tracing aerosols and droplets generated during otolaryngology procedures is needed to accurately assess contamination risk and to develop mitigation measures. Prior studies have not investigated the reliability of different fluorescent tracers for the purpose of studying aerosols and small droplets. Objectives include (1) comparing vitamin B2, fluorescein, and a commercial fluorescent green dye in terms of particle dispersion pattern, suspension into aerosols and small droplets, and fluorescence in aerosolized form and (2) determining the utility of vitamin B2 as a fluorescent tracer coating the aerodigestive tract mucosa in otolaryngology contamination models.

Methods:

Vitamin B2, fluorescein, and a commercial fluorescent dye were aerosolized using a nebulizer and passed through the nasal cavity from the trachea in a retrograde-intubated cadaveric head. In another scenario, vitamin B2 was irrigated to coat the nasal cavity and nasopharyngeal mucosa of a cadaveric head for assessment of aerosol and droplet generation from endonasal drilling. A cascade impactor was used to collect aerosols and small droplets ≤14.1 µm based on average aerodynamic diameter, and the collection chambers were visualized under UV light.

Results:

When vitamin B2 was nebulized, aerosols ≤5.4 µm were generated and the collected particles were fluorescent. When fluorescein and the commercial water tracer dye were nebulized, aerosols ≤8.61 µm and ≤2.08 µm respectively were generated, but the collected aerosols did not appear visibly fluorescent. Endonasal drilling in the nasopharynx coated with vitamin B2 irrigation yielded aerosols ≤3.30 µm that were fluorescent under UV light.

Conclusion:

Vitamin B2’s reliability as a fluorescent tracer when suspended in aerosols and small droplets ≤14.1 µm and known mucosal safety profile make it an ideal compound compared to fluorescein and commercial water-based fluorescent dyes for use as a safe fluorescent tracer in healthcare contamination models especially with human subjects.

Current methods of collagen cross-linking: Review

This review provides a report on cross-linking methods used for collagen modifications. Collagen materials have attracted significant academic interest due to its biological properties in native state. However, in many cases the mechanical properties and degradation rate should be tailored to especial biomedical and cosmetic applications. In the proposed review paper, the structure, preparation, and properties of several collagen based materials have been discussed in general, and detailed examples of collagen cross-linking methods have been drawn from scientific literature and practical work. Both, physical and chemical methods of improvement of collagenous materials have been reviewed. In the review paper the cross-linking with glutaraldehyde, genipin, EDC-NHS, dialdehyde starch, chitosan, temperature, UV light and enzyme has been discussed. A critical comparison of currently available cross-linking methods has been shown.

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).

<p>Vector Analysis of Astigmatism in Keratoconic Eyes After Combined Intrastromal Corneal Ring Segments Implantation and Collagen Cross-Linking</p>

Purpose

To analyze astigmatic changes after intrastromal corneal ring segments (ICRSs) implantation accompanied by corneal collagen cross-linking (CXL) in keratoconic eyes using the Alpins vectorial method.

Patients and Methods

Twenty-eight eyes of 18 patients with keratoconus were included in this retrospective non-comparative study. All patients had combined femtosecond laser-assisted Keraring implantation and CXL, and completed at least 2 years of follow-up. Both manifest and corneal astigmatic changes were analyzed using the Alpins vectorial parameters based on 3 vectors; target induced astigmatism (TIA), surgically induced astigmatism (SIA) and difference vector (DV).

Results

Regarding analysis of manifest astigmatism, the TIA arithmetic mean was 5.22 D while the vector mean was 3.13 D Ax 173. The SIA arithmetic mean was 5.41 D while the vector mean was 2.38 D Ax 173. The DV arithmetic mean was 2.10 D while the vector mean was 0.75 D Ax 175. Regarding analysis of corneal astigmatism, the TIA arithmetic mean was 5.22 D while the vector mean was 3.13 D Ax 173. The SIA arithmetic mean was 5.23 D while the vector mean was 1.8 D Ax 12. The DV arithmetic mean was 4.28 D while the vector mean was 2.04 D Ax 157.

Conclusion

Vector analysis of manifest and corneal astigmatism in keratoconic eyes with previous ICRS and CXL reveals more accuracy and predictability of manifest refraction in calculating SIA.

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Intrastromal Corneal Ring Segments Implantation And Corneal Cross-Linking For Keratoconus In Children With Vernal Keratoconjunctivitis - Three-Year Results

Purpose

To assess the 3-year safety and efficacy of femtosecond laser-assisted intrastromal corneal ring segments' (ICRS) implantation followed or accompanied by transepithelial accelerated corneal collagen cross-linking (TE-ACXL) as a treatment of keratoconus in children with vernal keratoconjunctivitis (VKC).

Patients and methods

Fifty two eyes of 28 children with keratoconus and vernal VKC were included in this study. Cases were divided into 2 groups; the first group had been treated with femtosecond laser-assisted ICRS (Keraring) implantation accompanied or followed by TE-ACXL, while the second group had been treated by TE-ACXL only and all cases completed a follow-up period of 3 years.

Results

In group 1: the mean uncorrected (UCVA) and best-corrected (BCVA) visual acuity, spherical equivalent, K-max and Q-value improved markedly from 0.97 ± 0.19, 0.67 ± 0.18, −8.75 ± 4.55, 60.41 ± 4.98, and −1.18 ± 0.54 preoperatively to 0.61 ± 0.27, 0.39±0.21, −3.25 ± 3.56, 55.22 ± 5.72, and −0.44 ± 0.68 postoperatively respectively. While in group 2: the preoperative mean UCVA, BCVA, spherical equivalent, K-max and Q-values were 0.68 ± 0.28, 0.38 ± 0.24, −2.84 ± 2.59, 50.29 ± 4.04, and-0.58 ± 0.23 respectively while their corresponding postoperative values were 0.58 ± 0.34, 0.19 ± 0.17, −2.35 ± 2.07, 49.58 ± 3.26, and −0.57 ± 0.25. Only one case in group 1 required repeat cross-linking.

Conclusion

Although the long-term safety and efficacy of femtosecond laser-assisted ICRS implantation accompanied or followed by TE-ACXL in children with keratoconus and VKC is high, some cases still may need repeat cross-linking.

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Proteomic analysis of retinal pigment epithelium cells after exposure to UVA radiation

Background

Age-related macular degeneration (AMD) is the primary cause of blindness and severe vision loss in developed countries and is responsible for 8.7% of blindness globally. Ultraviolet radiation can induce DNA breakdown, produce reactive oxygen species, and has been implicated as a risk factor for AMD. This study investigated the effects of UVA radiation on Human retinal pigment epithelial cell (ARPE-19) growth and protein expression.

Methods

ARPE-19 cells were irradiated with a UVA lamp at different doses (5, 10, 20, 30 and 40 J/cm²) from 10 cm. Cell viability was determined by MTT assay. Visual inspection was first achieved with inverted light microscopy and then the DeadEnd™ Fluorometric TUNEL System was used to observe nuclear DNA fragmentation. Flow cytometry based-Annexin V-FITC/PI double-staining was used to further quantify cellular viability. Mitochondrial membrane potential was assessed with JC-1 staining. 2D electrophoresis maps of exposed cells were compared to nonexposed cells and gel images analyzed with PDQuest 2-D Analysis Software. Spots with greater than a 1.5-fold difference were selected for LC-MS/MS analysis and some confirmed by western blot. We further investigated whether caspase activation, apoptotic-related mitochondrial proteins, and regulators of ER stress sensors were involved in UVA-induced apoptosis.

Results

We detected 29 differentially expressed proteins (9 up-regulated and 20 down-regulated) in the exposed cells. Some of these proteins such as CALR, GRP78, NPM, Hsp27, PDI, ATP synthase subunit alpha, PRDX1, and GAPDH are associated with anti-proliferation, induction of apoptosis, and oxidative-stress protection. We also detected altered protein expression levels among caspases (caspase 3 and 9) and in the mitochondrial (cytosolic cytochrome C, AIF, Mcl-1, Bcl-2, Bcl-xl, Bax, Bad, and p-Bad) and ER stress-related (p-PERK, p-eIF2α, ATF4 and CHOP) apoptotic pathways.

Conclusions

UVA irradiation suppressed the proliferation of ARPE-19 cells in a dose-dependent manner, caused quantitative loses in transmembrane potential (ΔΨm), and induced both early and late apoptosis.

Corneal Cross-Linking: The Science Beyond the Myths and Misconceptions

PURPOSE

There has been a recent explosion in the variety of techniques used to accomplish corneal cross-linking (CXL) for the treatment of ectatic corneal diseases. To understand the success or failure of various techniques, we review the physicochemical basis of corneal CXL and re-evaluate the current principles and long-standing conventional wisdom in the light of recent, compelling, and sometimes contradictory research.

METHODS

Two clinicians and a medicinal chemist developed a list of current key topics, controversies, and questions in the field of corneal CXL based on information from current literature, medical conferences, and discussions with international practitioners of CXL.

RESULTS

Standard corneal CXL with removal of the corneal epithelium is a safe and efficacious procedure for the treatment of corneal ectasias. However, the necessity of epithelium removal is painful for patients, involves risk and requires significant recovery time. Attempts to move to transepithelial corneal CXL have been hindered by the lack of a coherent understanding of the physicochemistry of corneal CXL. Misconceptions about the applicability of the Bunsen-Roscoe law of reciprocity and the Lambert-Beer law in CXL hamper the ability to predict the effect of ultraviolet A energy during CXL. Improved understanding of CXL may also expand the treatment group for corneal ectasia to those with thinner corneas. Finally, it is essential to understand the role of oxygen in successful CXL.

CONCLUSIONS

Improved understanding of the complex interactions of riboflavin, ultraviolet A energy and oxygen in corneal CXL may provide a successful route to transepithelial corneal CXL.

Macular phototoxicity after corneal cross-linking

Purpose

To assess potential vascular, structural, and functional changes to the macula in patients with keratoconus that underwent ultraviolet A (UVA)–riboflavin-mediated corneal collagen cross-linking (CXL) therapy.

Patients and methods

Seventeen eyes from 17 patients of age 16 years or older with keratoconus undergoing CXL treatment were studied. The same eye served as its own control (before CXL vs after CXL). Eyes were evaluated in terms of best-corrected visual acuity (BCVA), refractive error, intraocular pressure, Amsler grid, retinography, fluorescein angiography, autofluorescence, and spectral domain optical coherence tomography (SD-OCT) prior to CXL and 7 and 30 days after treatment. Multifocal electroretinography (mfERG) was recorded prior to and 7 days after CXL.

Results

Mean (SD) BCVA by logMAR chart was 0.47 (±0.12) pre-CXL, 0.55 (±0.15) 7 days post-CXL (P=0.57), and 0.46 (±0.10) 30 days post-CXL (P=0.87). Mean (SD) SD-OCT central macular thickness (µm) was 253.62 (±20.9) pre-CXL, 260.5 (±18.7) 7 days post-CXL (P=0.48), and 256.44 (±21.6) 30 days post-CXL (P=0.69). In 12 eyes, mfERG revealed a statistically significant increase (P=0.0353) in P1 latency (ms) of ring four from the pre-CXL period (39.45±2.05) to 7 days post-CXL (41.04±1.28) period. Regression analysis showed that the increase in P1 latency was correlated with the increase in central macular thickness (P=0.027). Furthermore, nine patients experienced a significant decrease in P1 amplitudes of rings 1 (P=0.0014), 2 (P=0.0029), 3 (P=0.0037), 4 (P=0.0014), and 5 (P=0.0012) from pre-CXL to 7 days post-CXL. Conclusion: In this pilot study, most of the patients exhibited slight changes in their mfERG parameters and OCT thickness, despite a lack of vascular abnormalities observed on fluorescein angiography/autofluorescence imaging, no alteration in BCVA, and no reports of symptoms. These changes could, therefore, be categorized as a mild subclinical effect of the corneal cross-linking procedure.

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.

5-year follow-up of combined non-topography guided photorefractive keratectomy and corneal collagen cross linking for keratoconus

AIM

To evaluate the visual outcomes of simultaneous non-topography guided photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) in eyes with keratoconus 5y after the procedure.

METHODS

Prospective, interventional, non-randomized, and non-controlled case series design was used. Sixty eyes of 30 patients (16 males and 14 females; age: 21-41y) with mild, non-progressive (stages 1-2) keratoconus were enrolled. Refraction, uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA), flat and steep keratometry readings, and adverse events were evaluated preoperatively and postoperatively. Data were collected preoperatively and postoperatively at 3mo, 1, 2, 3, 4, and 5y follow-up visits after combined non-topography-guided PRK with CXL was performed. All patients had at least 5y of follow-up.

RESULTS

All study parameters showed a statistically significant improvement at 5y over baseline values. The mean follow-up time was 68.20±4.71mo (range: 60-106mo). Patients showed a significant improvement in UDVA from 1.24±0.79 logMAR prior to combined non-TG-PRK+CXL to 0.06±0.15 logMAR postoperatively at the time of their last follow-up visit. CDVA significantly increased from 0.06±0.19 logMAR preoperatively to 0.03±0.12 logMAR postoperatively. A significant decrease in the mean spherical equivalent (SE) refraction was observed from -2.28±1.8 to -0.79±0.93 diopters (D) (P<0.05), and the manifest sphere decreased from -1.62±1.23 to -0.27±0.21 D (P=0.001). The manifest cylinder significantly decreased from -1.73±0.86 to -0.29±0.34 D postoperatively (P=0.001). The mean steep keratometry was 45.13±1.32 vs 47.28±2.12 D preoperatively (P<0.05), and the preoperative mean steepest keratometry (Kmax) 48.6±3.1 was reduced significantly to 46.8±2.9 postoperatively (P<0.05).

CONCLUSION

Combined non-TG-PRK with 15min CXL is an effective and safe option for correcting mild refractive error and improving visual acuity in patients with mild stable keratoconus.

Sequential Keraring implantation and corneal cross-linking for the treatment of keratoconus in children with vernal keratoconjunctivitis

Purpose

The purpose of this study was to assess the safety and efficacy of femtosecond laser-assisted Keraring implantation followed by transepithelial accelerated corneal collagen cross-linking (CXL) for the treatment of keratoconus in children with vernal keratoconjunctivitis (VKC).

Study design

This is a prospective interventional non-comparative case series.

Patients and methods

Eighteen eyes of 11 children with keratoconus and VKC were included in this study. All the cases were treated with femtosecond laser-assisted Keraring implantation followed after 2 weeks by transepithelial accelerated CXL, and the patients were followed up for 1 year.

Results

The preoperative mean uncorrected visual acuity (UCVA) was 1.01±0.2 (logMAR), whereas the postoperative mean UCVA was 0.6±0.2. The preoperative mean best-corrected visual acuity (BCVA) was 0.6±0.1, whereas the postoperative mean BCVA was 0.40±0.2. The preoperative average keratometry was 50.3±2.7 D, whereas the postoperative average keratometry was 45.8±3.1 D.

Conclusion

The results of this study suggest that femtosecond laser-assisted Keraring implantation followed by CXL is safe and effective in the management of keratoconus in children with VKC. However, studies with a longer follow-up period are needed.

Evaluation of UVA Cytotoxicity for Human Endothelium in an Ex Vivo Corneal Cross-linking Experimental Setting

PURPOSE

To evaluate endothelial cytotoxicity after exposure of human corneas to ultraviolet-A (UVA) (λ = 365 nm; 5.4 J/cm(2)) in an experimental ex vivo corneal cross-linking setting.

METHODS

Sixteen pairs of human donor corneas were cut into two pieces. One piece of each cornea was treated with 0.025% riboflavin solution prior to UVA irradiation (5 minutes; 18 mW/cm(2)), whereas the other piece was not irradiated but treated with riboflavin (right eye) or preservation medium (left eye). By irradiating from the endothelial side, the UVA dosage applied to endothelial cells exceeded at least eight times the cytotoxic threshold established in animal models (0.65 J/cm(2)). Endothelial cell counts were performed by two independent investigators after storage (4 to 5 days at 31 °C) and staining (trypan blue, alizarin red). Normality (Q-Q plot; Shapiro-Wilk test) and equivalence (mixed-effects modeling with a 10% equivalence threshold) of the endothelial cell counts of the different groups were evaluated.

RESULTS

Equivalence of mean endothelial cell density between both groups was observed: 2,237 ± 208 cells/mm(2) in UVA-irradiated pieces and 2,290 ± 281 cells/mm(2) in control pieces (mean difference of 53 ± 240 cells/mm(2) between both groups).

CONCLUSIONS

Despite direct irradiation of human donor endothelium using the clinical dosage for cross-linking, equivalence in endothelial cell counts was observed between irradiated tissues and controls. Ex vivo human corneal endothelial cells seem to be far more resistant to riboflavin-enhanced UVA irradiation than previously estimated by animal experiments.

Transepithelial Corneal Cross-Linking With Vitamin E-Enhanced Riboflavin Solution and Abbreviated, Low-Dose UV-A: 24-Month Clinical Outcomes

Purpose:

To report the clinical outcomes with 24-month follow-up of transepithelial cross-linking using a combination of a d-alpha-tocopheryl polyethylene-glycol 1000 succinate (vitamin E-TPGS)-enhanced riboflavin solution and abbreviated low fluence UV-A treatment.

Methods:

In a nonrandomized clinical trial, 25 corneas of 19 patients with topographically proven, progressive, mild to moderate keratoconus over the previous 6 months were cross-linked, and all patients were examined at 1, 3, 6, 12, and 24 months. The treatments were performed using a patented solution of riboflavin and vitamin E-TPGS, topically applied for 15 minutes, followed by two 5-minute UV-A treatments with separate doses both at fluence below 3 mW/cm² that were based on preoperative central pachymetry.

Results:

During the 6-month pretreatment observation, the average Kmax increased by +1.99 ± 0.29 D (diopter). Postoperatively, the average Kmax decreased, changing by −0.55 ± 0.94 D, by −0.88 ± 1.02 D and by −1.01 ± 1.22 D at 6, 12, and 24 months. Postoperatively, Kmax decreased in 19, 20, and 20 of the 25 eyes at 6 months, 12 months, and 24 months, respectively. Refractive cylinder was decreased by 3 months postoperatively and afterward, changing by −1.35 ± 0.69 D at 24 months. Best spectacle-corrected visual acuity (BSCVA) improved at 6, 12, and 24 months, including an improvement of −0.19 ± 0.13 logarithm of the minimum angle of resolution units at 24 months. There was no reduction in endothelial cell count. No corneal abrasions occurred, and no bandage contact lenses or prescription analgesics were used during postoperative recovery.

Conclusions:

Transepithelial cross-linking using the riboflavin-vitamin E solution and brief, low-dose, pachymetry-dependent UV-A treatment safely stopped keratoconus progression.

Combined femtosecond laser-assisted intracorneal ring segment implantation and corneal collagen cross-linking for correction of keratoconus

Purpose

To assess the safety, predictability, and effectiveness of Keraring intrastromal corneal ring segments (ICRS) insertion assisted by femtosecond laser and corneal collagen cross-linking (CXL) for keratoconus correction.

Patients and methods

In this prospective, noncomparative, and interventional case series, 160 eyes of 100 adult keratoconus patients with poor best-corrected visual acuity (BCVA) (less than 0.7) and intolerance to contact lens wear were included. Patients underwent femtosecond laser-assisted placement of ICRS and CXL. All patients were examined for a complete ophthalmological test: uncorrected visual acuity (UCVA), BCVA, spherical equivalent, keratometry (K1-flat and K2-steep), pachymetry, and Scheimpflug imaging with the Pentacam at 1 week and at 1, 3, and 6 months postoperatively.

Results

At 6 months, a significant difference was observed (P<0.001) in mean UCVA and BCVA from 0.92±0.677 and 0.42±0.600 logMAR preoperatively to 0.20±0.568 and 0.119±0.619 logMAR, respectively. Mean spherical equivalent refractions were significantly lower (P<0.001) at 6 months. Mean keratometry (K) also significantly reduced (P<0.001) from 50.93±5.53 D (K1-flat) and 55.37±5.76 D (K2-steep) to 47.32±4.61 and 51.08±5.38 D, respectively. In terms of pachymetry, no significant difference was observed preoperatively versus postoperatively (P=1.000).

Conclusion

Keraring ICRS insertion assisted by femtosecond laser and corneal CXL provided significant improvement in visual acuity, spherical equivalent, and keratometry, which suggests that it may be effective, safe, and predictable for keratoconus correction.

Higher incidence of steroid-induced ocular hypertension in keratoconus

BACKGROUND

To compare intraocular pressure (IOP) changes following topical dexamethasone administration for 1 month in keratoconic versus normal eyes.

METHODS

This is a retrospective, single-center, non-randomized case series evaluation of 350 eyes. Two groups were formed: normal/control Group A (nA =73), eyes that underwent excimer laser photorefractive keratectomy; and keratoconic (KCN) Group B (nB =277), eyes that were subjected to partial laser photorefractive keratectomy combined with collagen cross-linking (The Athens Protocol). All eyes received the same post-operative regimen of topical dexamethasone 0.1 % for at least 1 month. Goldmann applanation tonometry IOP readings and central corneal thickness (CCT) measurements were monitored. Cases with induced ocular hypertension (OHT, defined as post-operative IOP higher than 21 mmHg), were identified and correlated to refractive procedure, gender, and corneal thickness.

RESULTS

At 4 weeks postoperatively, OHT was noted on 27.4 % (20 /73 eyes) in Group A, and 43.7 % (121 /277 eyes) in KCN Group B, (p <0.01). Six months post-operatively (following 5-months of discontinuing topical dexamethasone treatment and commencing treatment of IOP-lowering medications), OHT rate was 1.8 % in Group A and 3.9 % in the KCN Group B.

CONCLUSION

This study demonstrates a potentially significant pre-disposition of keratoconic eyes to the development of steroid-induced OHT.

Reshaping procedures for the surgical management of corneal ectasia

Corneal ectasia is a progressive, degenerative, and noninflammatory thinning disorder of the cornea. Recently developed corneal reshaping techniques have expanded the treatment armamentarium available to the corneal specialist by offering effective nontransplant options. This review summarizes the current evidence base for corneal collagen crosslinking, topography-guided photorefractive keratectomy, and intrastromal corneal ring segment implantation for the treatment of corneal ectasia by analyzing the data published between the years 2000 and 2014.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

[Long-term efficacy of corneal collagen cross-linking in patients with progressive keratoconus]

AIM

to study the efficacy of corneal collagen cross-linking in patients with progressive keratoconus over longer (up to 2 years) follow-up periods.

MATERIAL AND METHODS

A total of 52 patients (104 eyes) aged 23-34 years with stage I-III progressive keratoconus were enrolled. Besides routine examinations (automatic refractometry, uncorrected and best corrected visual acuity (UCVA and BCVA) evaluation, pneumatic tonometry), Pentacam keratotopography and pachymetry ("Oculus", Germany) were performed in all cases. Corneal biomechanical properties were assessed with an Ocular Response Analyzer ("Reichert", USA). In all patients cross-linking procedure was carried out in the eye with more advanced keratoconus, the fellow eye being used as the control.

RESULTS

Judging from the results of UCVA and BCVA evaluation, keratotopography, and pachymetry obtained 2 years after the standard corneal cross-linking procedure, stabilization has been achieved in 97% of cases. In the remaining 3% of eyes corresponding parameters declined, although to a lesser extent than in the controls. Indices describing biomechanical properties of the cornea, such as corneal hysteresis, corneal resistance factor, as well as elastonometry results did not differ significantly throughout the whole observation period, which agrees with literature data.

CONCLUSION

Corneal collagen cross-linking has been proved capable of stopping keratoconus progression in most of the patients (97%). Further studies with even longer follow-up periods are needed.

Corneal collagen cross-linking for treating keratoconus

BACKGROUND

Keratoconus is a condition of the eye that affects approximately 1 in 2000 people. The disease leads to a gradual increase in corneal curvature and decrease in visual acuity with consequent impact on quality of life. Collagen cross-linking (CXL) with ultraviolet A (UVA) light and riboflavin (vitamin B2) is a relatively new treatment that has been reported to slow or halt the progression of the disease in its early stages.

OBJECTIVES

The objective of this review was to assess whether there is evidence that CXL is an effective and safe treatment for halting the progression of keratoconus compared to no treatment.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014, Issue 7), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to August 2014), EMBASE (January 1980 to August 2014), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to August 2014), Cumulative Index to Nursing and Allied Health Literature (CINAHL) (1982 to August 2014), OpenGrey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organisation International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We used no date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 28 August 2014.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) where CXL with UVA light and riboflavin was used to treat people with keratoconus and was compared to no treatment.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened the search results, assessed trial quality, and extracted data using standard methodological procedures expected by Cochrane. Our primary outcomes were two indicators of progression at 12 months: increase in maximum keratometry of 1.5 dioptres (D) or more and deterioration in uncorrected visual acuity of more than 0.2 logMAR.

MAIN RESULTS

We included three RCTs conducted in Australia, the United Kingdom, and the United States that enrolled a total of 225 eyes and analysed 219 eyes. The total number of people enrolled was not clear in two of the studies. Only adults were enrolled into these studies. Out of the eyes analysed, 119 had CXL (all using the epithelium-off technique) and 100 served as controls. One of these studies only reported comparative data on review outcomes. All three studies were at high risk for performance bias (lack of masking), detection bias (only one trial attempted to mask outcome assessment), and attrition bias (incomplete follow-up). It was not possible to pool data due to differences in measuring and reporting outcomes. We identified a further three unpublished trials that potentially had enrolled a total of 195 participants.There was limited evidence on the risk of progression. Analysis of the first few participants followed up to one year in one study suggested that eyes given CXL were less likely to have an increase in maximum keratometry of 1.5 D or more at 12 months compared to eyes given no treatment, but the confidence intervals (CI) were wide and compatible with no effect or more progression in the CXL group (risk ratio (RR) 0.12, 95% CI 0.01 to 2.00, 19 eyes). The same study reported the number of eyes with an increase of 2 D or more at 36 months in the whole cohort with a RR of 0.03 favouring CXL (95% CI 0.00 to 0.43, 94 eyes). Another study reported "progression" at 18 months using a different definition; people receiving CXL were less likely to progress, but again the effect was uncertain (RR 0.14, 95% CI 0.01 to 2.61, 44 eyes). We judged this to be very low-quality evidence due to the risk of bias of included studies, imprecision, indirectness and publication bias but noted that the size of the potential effect was large.On average, treated eyes had a less steep cornea (approximately 2 D less steep) (mean difference (MD) -1.92, 95% CI -2.54 to -1.30, 94 eyes, 1 RCT, very low-quality evidence) and better uncorrected visual acuity (approximately 2 lines or 10 letters better) (MD -0.20, 95% CI -0.31 to -0.09, 94 eyes, 1 RCT, very low-quality evidence) at 12 months. None of the studies reported loss of 0.2 logMAR acuity. The data on corneal thickness were inconsistent. There were no data available on quality of life or costs. Adverse effects were not uncommon but mostly transient and of low clinical significance. In one trial, 3 out of 12 participants treated with CXL had an adverse effect including corneal oedema, anterior chamber inflammation, and recurrent corneal erosions. In one trial at 3 years 3 out of 50 participants experienced adverse events including mild diffuse corneal oedema and paracentral infiltrate, peripheral corneal vascularisation, and subepithelial infiltrates and anterior chamber inflammation. No adverse effects were reported in the control groups.

AUTHORS' CONCLUSIONS

The evidence for the use of CXL in the management of keratoconus is limited due the lack of properly conducted RCTs.

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.

Comparison of the findings of endothelial specular microscopy before and after corneal cross-linking

Background:

To report the long-term findings of corneal cross-linking (CXL) with riboflavin drops on the corneal endothelial cell.

Materials and Methods:

In this prospective non-randomized study, we aim to assess the long-term safety of CXL on the corneal endothelium for the treatment of progressive keratoconus, by endothelial specular microscopy. A total of 68 eyes of 42 keratoconus patients were selected. We checked the corneal thickness (with ultrasonic pachymetry), endothelial cell density, pleomorphism, and polymegathism (with specular microscopy) of the endothelial cells, before CXL and one year after this procedure.

Results:

The mean ± SD of the preoperative and postoperative corneal thicknesses were 470 ± 40 μm and 469.8 ± 42 μm, respectively (p-value = 0.591). The mean ± SD of the preoperative and postoperative endothelial cell densities were 2753 ± 230 cells/mm[2] and 2699 ± 210 cells/mm,[2] respectively (p-value = 0.004). We found reduction in the endothelial cell density after CXL, but this reduction was less significant in a corneal thickness of less than 400 μm (which was treated with hypo-osmolar riboflavin 0.1% drops) compared to the corneal thickness of more than 450 μm. We did not find any significant differences in the cell shapes (pleomorphism) (p-value = 0.517), but the cell sizes (polymegathism) were changed after the procedure (p-value = 0.021).

Conclusion:

We found a significant decrease in endothelial corneal cell density after CXL, but this reduction was low; also the size of these cells increased after CXL. We believe that other parameters besides the corneal thickness may be the determinant factors for the changing of cell density and cell size in corneal endothelial cells.

Non-topography-guided PRK combined with CXL for the correction of refractive errors in patients with early stage keratoconus

PURPOSE

To evaluate the safety and clinical outcome of combined non-topography-guided photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) for the treatment of mild refractive errors in patients with early stage keratoconus.

METHODS

A retrospective, nonrandomized study of patients with early stage keratoconus (stage 1 or 2) who underwent simultaneous non-topography-guided PRK and CXL. All patients had at least 2 years of follow-up. Data were collected preoperatively and postoperatively at the 6-month, 1-year, and 2-year follow-up visit after combined non-topography-guided PRK and CXL.

RESULTS

Seventy-nine patients (140 eyes) were included in the study. Combined non-topography-guided PRK and CXL induced a significant improvement in both visual acuity and refraction. Uncorrected distance visual acuity significantly improved from 0.39 ± 0.22 logMAR before combined non-topography-guided PRK and CXL to 0.12 ± 0.14 logMAR at the last follow-up visit (P <.001) and corrected distance visual acuity remained stable (0.035 ± 0.062 logMAR preoperatively vs 0.036 ± 0.058 logMAR postoperatively, P =.79). The mean spherical equivalent decreased from -1.78 ± 1.43 to -0.42 ± 0.60 diopters (D) (P <.001), and the mean cylinder decreased from 1.47 ± 1.10 to 0.83 ± 0.55 D (P <.001). At the last follow-up visit mean keratometry flat was 43.30 ± 1.75 vs 45.62 ± 1.72 D preoperatively (P = .03) and mean keratometry steep was 44.39 ± 3.14 vs 46.53 ± 2.13 D preoperatively (P = .02). Mean central corneal thickness decreased from 501.74 ± 13.11 to 475.93 ± 12.25 µm following combined non-topography-guided PRK and CXL (P < .001). No intraoperative complications occurred. Four eyes developed mild haze that responded well to a short course of topical steroids. No eye developed infectious keratitis.

CONCLUSIONS

Combined non-topography-guided PRK and CXL is an effective and safe option for correcting mild refractive error and improving visual acuity in patients with early stable keratoconus.

Initial results from mechanical compression of the cornea during crosslinking for keratoconus

PURPOSE

To compare refractive changes after corneal crosslinking with and without mechanical compression of the cornea.

METHODS

In a prospective, open, randomized case-control study conducted at the Department of Ophthalmology, Umeå University Hospital, Sweden, sixty eyes of 43 patients with progressive keratoconus aged 18-28 years planned for corneal crosslinking and corresponding age- and sex-matched control subjects were included. The patients were randomized to conventional corneal crosslinking (CXL; n = 30) or corneal crosslinking with mechanical compression using a flat rigid contact lens sutured to the cornea during treatment (CRXL; n = 30). Subjective refraction and ETDRS best spectacle-corrected visual acuity (BSCVA), axial length measurement, keratometry and pachymetry were performed before and 1 and 6 months after treatment.

RESULTS

The keratoconus patients had poorer BSCVA, higher refractive astigmatism and higher keratometry readings than the control subjects at baseline (p < 0.01). In the CXL group, BSCVA increased from 0.19 ± 0.26 to 0.14 ± 0.18 logMar (p = 0.03), and the spherical equivalent improved from -1.9 ± 2.8 D to -1.4 ± 2.4 D (p = 0.03). Maximum keratometry readings decreased after CXL from 53.1 ± 4.9 D to 52.6 ± 5.2 D (p = 0.02), and the axial length decreased in the CXL group, likely due to post-treatment corneal thinning (p = 0.03). In the CRXL group, all the above variables were unaltered (p > 0.05).

CONCLUSION

At 6 months, the refractive results from CRXL did not surpass those of conventional CXL treatment. Rather, some variables indicated a slightly inferior effect. Possibly, stronger crosslinking would be necessary to stabilize the cornea in the flattened configuration achieved by the rigid contact lens.

[Complications of corneal cross-linking]

BACKGROUND

More than 10 years after the clinical introduction of corneal cross-linking (CXL) the indications and contraindications are still not yet defined. Fundamental for such a list is the incidence of complications.

METHODS

A PubMed search for complications of corneal crosslinking published up to March 2013 was carried out.

RESULTS

The published complication rates ranged from 1 % to 10 % depending on the stage of keratoconus. Early postoperative complications were transient stromal haze, sterile infiltrates, endothelium decompensation, delayed epithelial healing and infectious keratitis. Stromal opacity can be a delayed postoperative event.

CONCLUSIONS

Complications after corneal cross-linking treatment for keratoconus are rare but the management of these complications may need keratoplasty.

Photorefractive keratectomy in patients with mild to moderate stable keratoconus: a five-year prospective follow-up study

Background

The purpose of this study was to evaluate the visual outcome of photorefractive keratectomy (PRK) in patients with mild to moderate stable keratoconus and to assess the risk of progression of the disease after the excimer laser procedure.

Methods

In this prospective study, carried out at the Clemenceau Medical Center, an affiliate of Johns Hopkins International, in Beirut, Lebanon, 119 eyes from 72 patients with grade 1–2 keratoconus (Amsler–Krumeich classification) underwent PRK. Forty-seven patients had both eyes treated and 25 patients had one eye treated. The procedure was done using the Wavelight Eye Q Excimer laser. Uncorrected and best-corrected visual acuity, corneal topography, and pachymetry were assessed before the procedure and 3, 6, 12, 36, and 60 months after the procedure.

Results

Mean uncorrected visual acuity showed a statistically significant improvement (P < 0.05) at one, 3, and 5 years follow-up. One hundred and seventeen eyes (98.3%) showed no progression while two eyes (1.7%) showed progression of the disease at 5 years follow-up, as documented by corneal topography and pachymetry. These two eyes were treated with corneal collagen crosslinking.

Conclusion

PRK in mild to moderate keratoconus is a safe and effective procedure for improving uncorrected vision in patients with mild refractive errors. However, close follow-up of patients is needed to detect any progression of the disease. Longer follow-up is needed to assess the overall effect of this procedure on progression of the disease.

Corneal cross-linking in 9 horses with ulcerative keratitis

BACKGROUND

Corneal ulcers are one of the most common eye problems in the horse and can cause varying degrees of visual impairment. Secondary infection and protease activity causing melting of the corneal stroma are always concerns in patients with corneal ulcers. Corneal collagen cross-linking (CXL), induced by illumination of the corneal stroma with ultraviolet light (UVA) after instillation of riboflavin (vitamin B2) eye drops, introduces crosslinks which stabilize melting corneas, and has been used to successfully treat infectious ulcerative keratitis in human patients. Therefore we decided to study if CXL can be performed in sedated, standing horses with ulcerative keratitis with or without stromal melting.

RESULTS

Nine horses, aged 1 month to 16 years (median 5 years) were treated with a combination of CXL and medical therapy. Two horses were diagnosed with mycotic, 5 with bacterial and 2 with aseptic ulcerative keratitis. A modified Dresden-protocol for CXL could readily be performed in all 9 horses after sedation. Stromal melting, diagnosed in 4 horses, stopped within 24 h. Eight of nine eyes became fluorescein negative in 13.5 days (median time; range 4-26 days) days after CXL. One horse developed a bacterial conjunctivitis the day after CXL, which was successfully treated with topical antibiotics. One horse with fungal ulcerative keratitis and severe uveitis was enucleated 4 days after treatment due to panophthalmitis.

CONCLUSIONS

CXL can be performed in standing, sedated horses. We did not observe any deleterious effects attributed to riboflavin or UVA irradiation per se during the follow-up, neither in horses with infectious nor aseptic ulcerative keratitis. These data support that CXL can be performed in the standing horse, but further studies are required to compare CXL to conventional medical treatment in equine keratitis and to optimize the CXL protocol in this species.

Corneal absorption of a new riboflavin-nanostructured system for transepithelial collagen cross-linking

Corneal collagen cross-linking (CXL) has been described as a promising therapy for keratoconus. According to standard CXL protocol, epithelium should be debrided before treatment to allow penetration of riboflavin into the corneal stroma. However, removal of the epithelium can increase procedure risks. In this study we aim to evaluate stromal penetration of a biocompatible riboflavin-based nanoemulsion system (riboflavin-5-phosphate and riboflavin-base) in rabbit corneas with intact epithelium. Two riboflavin nanoemulsions were developed. Transmittance and absorption coefficient were measured on corneas with intact epithelia after 30, 60, 120, 180, and 240 minutes following exposure to either the nanoemulsions or standard 0.1% or 1% riboflavin-dextran solutions. For the nanoemulsions, the epithelium was removed after measurements to assure that the riboflavin had passed through the hydrophobic epithelium and retained within the stroma. Results were compared to de-epithelialized corneas exposed to 0.1% riboflavin solution and to the same riboflavin nanoemulsions for 30 minutes (standard protocol). Mean transmittance and absorption measured in epithelialized corneas receiving the standard 0.1% riboflavin solution did not reach the levels found on the debrided corneas using the standard technique. Neither increasing the time of exposure nor the concentration of the riboflavin solution from 0.1% to 1% improved riboflavin penetration through the epithelium. When using riboflavin-5-phosphate nanoemulsion for 240 minutes, we found no difference between the mean absorption coefficients to the standard cross-linking protocol (p = 0.54). Riboflavin nanoemulsion was able to penetrate the corneal epithelium, achieving, after 240 minutes, greater stromal concentration when compared to debrided corneas with the standard protocol (p = 0.002). The riboflavin-5-phosphate nanoemulsion diffused better into the stroma than the riboflavin-base nanoemulsion.

Persistent corneal edema after collagen cross-linking for keratoconus

PURPOSE

To present a new complication of persistent corneal edema after collagen cross-linking (CXL) in keratoconus patients.

DESIGN

Retrospective case series of postoperative corneal edema after CXL.

METHODS

study population: All patients who underwent CXL treatment with subsequent corneal edema. Patients with stromal haze were excluded. intervention: The CXL treatments used the Dresden protocol with corneal thickness of more than 400 μm after epithelium was removed. main outcome measure: The resolution of corneal edema after surgery.

RESULTS

Postoperative corneal edema was identified in 10 (2.9%) of 350 patients who were followed up for a mean of 14 ± 4 months. The edema started on postoperative day 1 (10/10) and increased for 3 weeks. Additional findings included: deep vascularization (2 eyes; 20%), iris atrophy (6 eyes; 60%), pigment dispersion (5 eyes; 50%), persistent epithelial defect (3 eyes; 30%), and infectious keratitis (1 eye; 10%). Specular microscopy was unsuccessful, but the fellow untreated eyes had normal endothelial counts. Intraocular pressure and lenticular evaluations were normal. Corneal edema improved in 4 patients and resolved in 1 patient. In these 5 patients, the logarithm of the minimal angle of resolution best-corrected visual acuity was 0.5 ± 0.18. Penetrating keratoplasty was offered to 5 patients when improvement plateaued at 3 months, but only 2 patients underwent penetrating keratoplasty.

CONCLUSIONS

CXL is a safe and effective procedure with few known side effects. This case series reports the possibility of corneal endothelial damage with visually significant corneal edema after CXL treatment. Based on the extent of endothelial damage, patients may require penetrating keratoplasty.

Corneal collagen cross-linking: an introduction and literature review

BACKGROUND

This literature review analyzes the scientific evidence available regarding corneal collagen cross-linking (CXL) as a treatment option for progressive keratectasia.

METHODS

A literature search was performed using dates from 1990 to August 2010 regarding CXL Specific areas of focus for the literature review include safety and efficacy of the procedure as a stand-alone treatment or when used in conjunction with Intacs® corneal implants (Addition Technology™) or photorefractive keratectomy (PRK).

RESULTS

A total of 50 clinical trials and studies were identified, 20 of which met the inclusion criteria. Results of the included literature support the conclusion that CXL is a safe and efficacious treatment for progressive keratectasia. The results of CXL alone have shown stabilization or improvement in the maximum keratometry readings, best-corrected visual acuity, uncorrected visual acuity, and spherical and cylinder refractive measurements. CXL has been shown to enhance the effects of Intacs and has been proven successful when used in conjunction with PRK.

CONCLUSION

CXL is an effective treatment for limiting the progression of keratectasia, thus reducing the need for penetrating keratoplasty. CXL has a similar side-effect profile and similar risk level as PRK.

In vivo confocal laser-scanning microscopy to characterize wound repair in rabbit corneas after collagen cross-linking

BACKGROUND

Collagen cross-linking using the photosensitizer riboflavin combined with ultraviolet A light was developed to stiffen the cornea by increasing its mechanical and biochemical stability. Investigation of post-treatment events, such as wound healing, is important to evaluate possible risks and to optimize treatment protocols. This in vivo confocal laser-scanning microscopy study in rabbits was conducted to provide a quantitative and qualitative analysis of corneal wound repair over 16 weeks following collagen cross-linking.

METHODS

Six New Zealand White rabbits underwent riboflavin/ultraviolet A cross-linking. In vivo confocal laser-scanning microscopy using a Heidelberg Retina Tomograph equipped with a Rostock Cornea Module was performed preoperatively and at 2, 4, 8, 12 and 16 weeks postoperatively.

RESULTS

From 2 weeks onwards the epithelium demonstrated no abnormalities. Evidence of inflammation was visualized in the intermediate, basal cells and Bowman's membrane. Nerve fibre regeneration was first noted at 12 weeks. Keratocyte activation and hyperreflective extracellular matrix were observed consistently, but by 16 weeks keratocyte activation was diminished, and extracellular matrix resumed normal reflectivity. Cell density in the posterior stroma and endothelium regained preoperative values by 4 weeks, although anterior stroma keratocyte cell density was still reduced by about 10% at 16 weeks.

CONCLUSIONS

Complete qualitative and quantitative characterization of corneal wound repair was achieved by in vivo confocal laser-scanning microscopy over 16 weeks following collagen cross-linking in rabbits. In terms of assessing the ever-increasing range of cross-linking protocols, in vivo confocal laser-scanning microscopy may contribute to minimizing the number of experimental animals, because multiple examinations of the same cases are possible over time.

Spatial distribution of corneal light scattering after corneal collagen crosslinking

PURPOSE

To assess the spatial distribution and time course of increased corneal light scattering after corneal collagen crosslinking (CXL) with riboflavin and ultraviolet-A irradiation.

SETTING

Umeå University Hospital Eye Clinic, Umeå, Sweden.

DESIGN

Case series.

METHODS

Eyes with keratoconus were examined with Scheimpflug photography before and 1 and 6 months after CXL. Corneal light scattering was quantified throughout the corneal thickness at 8 measurement points 0.0 to 3.0 mm from the central cornea.

RESULTS

The study comprised 11 eyes of 11 patients. Central corneal light scattering increased significantly 1 month after CXL (P<.001). At 6 months, it decreased (P = .002); however, it was still higher than pretreatment values (P<.001). Light scattering at 1 month was more pronounced in the superficial stroma, gradually diminishing to zero at 240 μm depth. It was greater at the corneal center than 1.0 to 3.0 mm from the center. At 6 months, a second peak of light scattering occurred between 240 μm and 340 μm depth. No increased light scattering deeper than 340 μm was seen at either time point.

CONCLUSIONS

Corneal light scattering after CXL showed distinctive spatial and temporal profiles. Analysis of corneal light scattering may give an impression of tissue changes, the depth of the CXL treatment effect, and the corneal response to the treatment. Scheimpflug photography appears to be useful for this purpose.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Corneal collagen cross-linking using riboflavin and ultraviolet-A irradiation: a review of clinical and experimental studies

Corneal collagen cross-linking (CXL) using riboflavin and ultraviolet-A irradiation is a common method of tissue stabilization and has been developed primarily to address the need of treating keratoconus. CXL's promising results on keratoconus indicated that it might be effective in other corneal diseases as well. This new treatment promises a slowing effect on the progression of these diseases and its initial results show that it is safe and reasonably curative. The purpose of this review is to critically evaluate this treatment, to explore its benefits, to highlight its limitations in terms of efficacy and long-term safety and finally to identify areas for future research in this topic with a significant potential to change the way we treat our patients. In addition, in this unbiased review we try to bring together all the scientific information from both laboratory and clinical trials that have been conducted during recent years and to review the most recent publications regarding the therapeutic indications of CXL.

Riboflavin and ultraviolet light a therapy as an adjuvant treatment for medically refractive Acanthamoeba keratitis: report of 3 cases

PURPOSE

To present the first 3 cases of Acanthamoeba keratitis (AK), unresponsive to medical treatment, that were successfully treated with a novel adjunctive therapy using ultraviolet light A (UVA) and riboflavin (B2).

DESIGN

Interventional case series.

PARTICIPANTS

Two patients with confirmed AK and 1 patient with presumptive AK, which were all refractive to multidrug conventional therapy.

INTERVENTION

Two treatment sessions involving topical application of 0.1% B2 solution to the ocular surface combined with 30 minutes of UVA irradiation focused on the corneal ulcer.

MAIN OUTCOME MEASURES

Clinical examination by slit lamp, confocal microscopy, and histopathology, when available.

RESULTS

All patients in these series showed a rapid reduction in their symptoms and decreased ulcer size after the first treatment session. The progress of the clinical improvement began to slow after 1 to 3 weeks of the first application and was then renewed after the second application. All ancillary signs of inflammation mostly resolved after the second treatment session. The ulcers in all patients continued to decrease and were closed within 3 to 7 weeks of the first application. Two patients developed dense central corneal scars, and penetrating keratoplasty was performed for visual rehabilitation. Histopathologic examination of the excised tissue revealed no Acanthamoeba organisms. The remaining patient had no symptoms or signs of infection, both clinically and by confocal microscopy, and was left with a semitransparent eccentric scar that did not affect visual acuity.

CONCLUSIONS

The adjunctive use of UVA and B2 therapy seems to be a possible alternative for selected cases of medication-resistant AK.