Significance of the riboflavin film in corneal collagen crosslinking

Comparative Evaluation of Anterior Segment Optical Coherence Tomography Findings Following Accelerated Corneal Crosslinking Protocols Using Different Riboflavin Formulations and Soaking Durations

PURPOSE

To comparatively evaluate the influence of different riboflavin formulations and soaking durations on the anterior segment optical coherence tomography (AS-OCT) findings following accelerated corneal crosslinking (ACXL) at 9 mW/cm2 for in progressive keratoconus.

METHODS

In this prospective study, consecutive patients with progressive keratoconus were randomized into 4 groups. Group 1: hydroxypropyl methylcellulose (HPMC)-based riboflavin for 10 min; Group 2: HPMC-based riboflavin for 20 min; Group 3: dextran-based riboflavin (0.1%) for 30 min. Riboflavin soaking was followed by ultraviolet-A irradiation at 9 mW/cm2 for 10 min in all three groups. Group 4 underwent conventional CXL (CCXL) using Dresden protocol. The AS-OCT features of the crosslinked cornea were evaluated at postoperative month 1 and correlated to the clinical outcomes at postoperative month 12.

RESULTS

The study enrolled 26 eyes of 26 patients in each group. In groups 1 and 2, the AS-OCT findings were similar (p > .05) and the demarcation lines depth (DLD) were deep as obtained following CCXL. The DLD was significantly shallower in group 3 compared to the other groups (p < .01). There were no between-group differences in regards to the visual, refractive, keratometric, and tomographic outcomes at postoperative month 12. No significant endothelial cell loss or any other clinically significant adverse event was encountered in any patient's eye at 12 months follow-up.

CONCLUSION

Although structural variations were noted in the crosslinked cornea, DLDs observed following ACXL (9 mW/cm2) using HPMC-based solution for 10 or 20 min were similar to those observed following CCXL. Whereas, ACXL (9 mW/cm2) using dextran-based solution for 30 min resulted in the shallowest DLD. Despite these remodeling differences, the visual, refractive and tomographic outcomes of all groups were comparable at postoperative 1-year follow-up. Studies with a greater number of patients and longer follow-ups are required to establish any relation between AS-OCT characteristics of crosslinked cornea and ACXL efficacy.

Assessment of the Predictive Ability of Theranostics for Corneal Cross-linking in Treating Keratoconus: A Randomized Clinical Trial

PURPOSE

To validate the ability of theranostic imaging biomarkers in assessing corneal cross-linking (CXL) efficacy in flattening the maximum keratometry (Kmax) index.

DESIGN

Prospective, randomized, multicenter, masked clinical trial (ClinicalTrails.gov identifier, NCT05457647).

PARTICIPANTS

Fifty patients with progressive keratoconus.

INTERVENTION

Participants were stratified to undergo epithelium-off (25 eyes) and epithelium-on (25 eyes) CXL protocols using an ultraviolet A (UV-A) medical device with theranostic software. The device controlled UV-A light both for performing CXL and assessing the corneal riboflavin concentration (riboflavin score) and treatment effect (theranostic score). A 0.22% riboflavin formulation was applied onto the cornea for 15 minutes and 20 minutes in epithelium-off and epithelium-on protocols, respectively. All eyes underwent 9 minutes of UV-A irradiance at 10 mW/cm2.

MAIN OUTCOME MEASURES

The primary outcome measure was validation of the combined use of theranostic imaging biomarkers through measurement of their accuracy (proportion of correctly classified eyes) and precision (positive predictive value) to classify eyes correctly and predict a Kmax flattening at 1 year after CXL. Other outcome measures included change in Kmax, endothelial cell density, uncorrected and corrected distance visual acuity, manifest spherical equivalent refraction and central corneal thickness 1 year after CXL.

RESULTS

Accuracy and precision of the theranostic imaging biomarkers in predicting eyes that had >0.1 diopter (D) of Kmax flattening at 1 year were 91% and 95%, respectively. The Kmax value significantly flattened by a median of -1.3 D (IQR, -2.11 to -0.49 D; P < 0.001); both the uncorrected and corrected distance visual acuity improved by a median of -0.1 logarithm of the minimum angle of resolution (logMAR; IQR, -0.3 to 0.0 logMAR [P < 0.001] and -0.2 to 0.0 logMAR [P < 0.001], respectively). No significant changes in endothelial cell density (P = 0.33) or central corneal thickness (P = 0.07) were noted 1 year after surgery.

CONCLUSIONS

The study demonstrated the efficacy of integrating theranostics in a UV-A medical device for the precise and predictive treatment of keratoconus with epithelium-off and epithelium-on CXL protocols. Concentration of riboflavin and its UV-A light mediated photoactivation in the cornea are the primary factors determining CXL efficacy.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Comparative evaluation of biomechanical changes and aberration profile following accelerated collagen cross-linking using hypo-osmolar and iso-osmolar riboflavin: A prospective study

PURPOSE

To compare the changes encountered in corneal biomechanics and aberration profile following accelerated corneal collagen cross-linking (CXL) using hypo-osmolar and iso-osmolar riboflavin in corneal thicknesses of <400 and >400 microns, respectively.

METHODS

This is a prospective, interventional, comparative study involving 100 eyes of 75 patients with progressive keratoconus. Eyes were divided into two groups based on corneal thickness: group 1 included eyes with a corneal thickness of <400 microns who underwent hypo-osmolar CXL, and group 2 included eyes with a corneal thickness of >400 microns who underwent iso-osmolar CXL. Corneal biomechanical and aberration profiles were evaluated and compared between groups.

RESULTS

In group 1, all higher-order aberrations (HOA) except secondary astigmatism significantly decreased from baseline; however, in group 2, only coma and trefoil decreased. The corneal resistance factor and corneal hysteresis significantly improved in both groups, which was significantly greater in group 2 than in group 1. The change in inverse radius, deformation amplitude, and tomographic biomechanical index was significantly improved in group 2 as compared to group 1.

CONCLUSION

Improvement in corrected distance visual acuity and decrease in HOA were significantly better in the hypo-osmolar CXL group; however, the improvement in biomechanical strength of the cornea was significantly better in the iso-osmolar group.

Evaluation of Keratoconus Disease with Tear Cytokine and Chemokine Levels Before and After Corneal Cross-Linking Treatment

OBJECTIVES

To compare tear cytokine and chemokine levels of keratoconus (KC) patients with controls to perceive etiology distinctly and to clarify the molecular changes after cross-linking (CXL).

METHODS

Tear samples were gathered from 34 participants in this prospective study. Participants underwent anterior and posterior segment examinations with slit-lamp biomicroscopy. Patients were assessed by corneal topography before and 3 months after CXL. Flat (K1), steep (K2), and average keratometry (Kmean), cylinder (CYL), and central corneal thickness (CCT) values were evaluated. After 3 months from CXL, samples were re-collected, and comparisons were made with preoperative values.

RESULTS

Levels of IFN-gamma, IL-8, IL-12, IL-17, TNF-α, IL-4 and IL-13 were detected higher in KC patients (p= 0.008, p= 0.047, p= 0.001, p= 0.001, p= 0.001, p= 0.001, p= 0.027, respectively). After CXL IL-4, IL-5, IL-6, IL-7, IL-8, TNF-α levels showed significant decrease (p= 0.005, p= 0.045, p= 0.010, p= 0.022, p= 0.001, p=0.002, respectively). As for the topographic measurements, postoperative CCT values were increased whereas Kmean reduced after CXL (p < 0.001, p = 0.015, respectively). (p= 0.001, p= 0.027, respectively).

CONCLUSION

Our findings imply that inflammation plays a key role in the development of KC and that this link is influenced by CXL therapy.

An in vitro investigation into the impact of corneal rinsing on riboflavin/UVA corneal cross-linking

BACKGROUND

Corneal cross-linking (CXL) using riboflavin and ultraviolet-A light (UVA) is a treatment used to prevent progression of keratoconus. This ex vivo study assesses the impact on CXL effectiveness, as measured by tissue enzymatic resistance and confocal microscopy, of including a pre-UVA corneal surface rinse with balanced salt solution (BSS) as part of the epithelium-off treatment protocol.

METHODS

Sixty-eight porcine eyes, after epithelial debridement, were assigned to six groups in three experimental runs. Group 1 remained untreated. Groups 2-6 received a 16-min application of 0.1% riboflavin/Hydroxypropyl methylcellulose (HPMC) drops, after which Group 3 was exposed to 9 mW/cm2 UVA for 10 min, and Groups 4-6 underwent corneal surface rinsing with 0.25 mL, 1 mL or 10 mL BSS followed by 9 mW/cm2 UVA exposure for 10 min. Central corneal thickness (CCT) was recorded at each stage. Central 8.0 mm corneal buttons from all eyes were subjected to 0.3% collagenase digestion at 37 °C and the time required for complete digestion determined. A further 15 eyes underwent fluorescence confocal microscopy to assess the impact of rinsing on stromal riboflavin concentration.

RESULTS

Application of riboflavin/HPMC solution led to an increase in CCT of 73 ± 14 µm (P < 0.01) after 16 min. All CXL-treated corneas displayed a 2-4 fold greater resistance to collagenase digestion than non-irradiated corneas. There was no difference in resistance between corneas that received no BSS rinse and those that received a 0.25 mL or 1 mL pre-UVA rinse, but each showed a greater level of resistance than those that received a 10 mL pre-UVA rinse (P < 0.05). Confocal microscopy demonstrated reduced stromal riboflavin fluorescence after rinsing.

CONCLUSIONS

All protocols, with and without rinsing, were effective at enhancing the resistance to collagenase digestion, although resistance was significantly decreased, and stromal riboflavin fluorescence reduced with a 10 mL rinse. This suggests that a 10 mL surface rinse can reduce the efficacy of CXL through the dilution of the stromal riboflavin concentration.

Glycosaminoglycans and collagen fibril distribution at various depths of the corneal stroma of normal and CXL treated rats

Corneal collagen cross-linking (CXL) is widely used to treat keratoconus and ecstatic corneal disorders. The present studies were carried out to investigate the distribution of glycosaminoglycans (GAGs) and collagen fibril (CF) at different depths of the normal and CXL treated corneal stroma of four week old rats 7 days after standard CXL application. Ten Wistar rats' corneas were used for the study. The epithelium of the cornea from the left eye of each rat was removed and treated with standard CXL application using riboflavin and Ultraviolet-A (UVA) (3 mW/cm2 for 30 min). The cornea from the right eye was used as the control cornea. The cornea was removed from the eye and processed for transmission electron microscopy. A bottom mounted Quemesa camera was used to capture digital images and these images were analysed using iTEM software. In the control cornea, the GAGs area size was not significantly different in the anterior, middle, and posterior stroma. In the CXL treated rats the GAGs area size gradually increased from the anterior to the posterior stroma whereas the spacing between the GAGs gradually decreased. There were very large GAGs present in the posterior stroma of the CXL treated rats. When comparing the control and CXL cornea, the GAGs area in the CXL cornea was significantly higher and inter-GAGs-spacing was smaller than in the control cornea. In the control cornea, the collagen fibrils diameter was higher in the anterior stroma and lowest in the posterior stroma. In the CXL treated cornea, the CF diameter and the interfibrillar spacing gradually decreased from the anterior to the posterior stroma. On comparison between the control and the CXL treated cornea, the interfibrillar spacing was significantly smaller in the CXL treated cornea than the control cornea in the anterior, middle, and posterior stroma but there was no difference in the diameter. The CXL treatment significantly increased the GAGs area and decreased the inter-GAGs-spacing, and inter-CF-spacing. This could be due to the gradual decline in the availability of riboflavin, UVA, and oxygen in the middle and posterior stroma. Further studies are required to investigate the role of keratan sulphate and chondroitin sulphate by using monoclonal antibodies with immunogold technique.

Comparison of topographic outcomes between HPMC based and vitamin E TPGS based riboflavin solutions after corneal cross-linking

PURPOSE

To compare the visual and topographic results between patients who underwent epithelium-off cross-linking using riboflavin solutions compounds hydroxypropyl methylcellulose (HPMC) 1.1% and D-alpha-tocopheryl polyethylene-glycol 1000 succinate (VE-TPGS).

METHODS

In this study, 37 eyes treated with HPMC and 29 eyes treated with VE-TPGS were evaluated retrospectively. Spherical equivalent (SE), refractive cylinder, corrected distance visual acuity tests (CDVA), corneal topography indices (flat and steep meridians' keratometry (K1 and K2)), maximum keratometry (K max), central, thinnest, and apical corneal thicknesses, the front and back keratoconus vertex index (KVf, KVb), and the surface asymmetry index of the front and back surface (SIf, SIb), and endothelial cell density were compared at baseline and postoperative follow-up visits (1, 3, 6, and 12months).

RESULTS

At the end of the 12th-month, K1, K2, and Kmax were decreased in both groups. In comparison to baseline, there was a decline in the HPMC group in the 3rd- month Kmax change, an increase was observed in the VE-TPGS group. In the 12th-month KVb change, an increase was observed in the HPMC group compared to the baseline, while a decrease was observed in the VE-TPGS group. The other parameters did not show a statistically significant difference between the groups (p > 0.05).

CONCLUSION

At the end of 12 months, both riboflavins were effective in stopping the progression of keratoconus and were safe for endothelium. Although both riboflavins provide a decrease in keratometry values, it can be said that VE-TPGS is superior to HPMC in correcting the ectasia on the posterior corneal surface.

National survey of corneal cross-linking (CXL) practice patterns in the United Kingdom during 2019

OBJECTIVE

To provide an insight into trends in corneal cross-linking (CXL) practice in the UK, including criteria for progression of corneal ectasia, identification of patients for CXL, the CXL procedure itself and post-operative management.

METHODS

All ophthalmologist members of the UK Cross-linking (UK-CXL) Consortium were invited to complete an online survey about CXL practice for the year 2019. The data collected was anonymised by site and analysed with descriptive statistics.

RESULTS

Responses were received from 16 individual CXL centres (16/38; 42% response rate) and the data represented ~2,000 CXL procedures performed in the UK in 2019. The commonest indication for CXL was progressive keratoconus. Between centres, there were variations in diagnostic evaluation, patient selection for CXL, the CXL procedure and the pre- and post-operative monitoring of patients.

CONCLUSION

Consistent with the wide number of CXL treatment techniques described in the published literature world-wide, variations in the monitoring of corneal ectasia, indications for CXL, CXL practice and post-CXL follow-up were found to exist between UK-based CXL centres.

Management of keratoconus: an updated review

Keratoconus is the most common corneal ectatic disorder. It is characterized by progressive corneal thinning with resultant irregular astigmatism and myopia. Its prevalence has been estimated at 1:375 to 1:2,000 people globally, with a considerably higher rate in the younger populations. Over the past two decades, there was a paradigm shift in the management of keratoconus. The treatment has expanded significantly from conservative management (e.g., spectacles and contact lenses wear) and penetrating keratoplasty to many other therapeutic and refractive modalities, including corneal cross-linking (with various protocols/techniques), combined CXL-keratorefractive surgeries, intracorneal ring segments, anterior lamellar keratoplasty, and more recently, Bowman's layer transplantation, stromal keratophakia, and stromal regeneration. Several recent large genome-wide association studies (GWAS) have identified important genetic mutations relevant to keratoconus, facilitating the development of potential gene therapy targeting keratoconus and halting the disease progression. In addition, attempts have been made to leverage the power of artificial intelligence-assisted algorithms in enabling earlier detection and progression prediction in keratoconus. In this review, we provide a comprehensive overview of the current and emerging treatment of keratoconus and propose a treatment algorithm for systematically guiding the management of this common clinical entity.

Innovations in Corneal Crosslinking

PURPOSE

Corneal Crosslinking (CXL) strengthens the keratoconus cornea and prevents further disease progression. Modified crosslinking protocols and different riboflavin solutions have been proposed to optimize the procedure and improve treatment success.

METHODS

PubMed research of relevant publications and report of own experiences with different CXL protocols.

RESULTS

Accelerated CXL shows comparable efficiency with shorter surgery time and similar complication rates. Customized CXL provides improved results with faster epithelial healing. CXL in a hyperoxic environment seems to be a safe and effective transepithelial alternative with presumably less complications and fewer side effects. Thin corneas (<400 µm) can be treated safely by corneal swelling using hypoosmolar riboflavin solutions and reducing the applied UV-energy. The combination of CXL with photorefractive keratectomy (PRK) can be considered in patients with contact lens intolerance improving visual acuity, however, with increased risk of visual loss compared to CXL alone. Two-Photon (2Ph) CXL is a promising new technology enabling three-dimensional CXL.

DISCUSSION

Recently developed CXL protocols offer advantages over the standard "Dresden-protocol" and should be considered in patients with progressive keratectasia.

Current clinical practice in corneal crosslinking for treatment of progressive keratoconus in four Nordic countries

PURPOSE

To evaluate clinical practice in the diagnosis and treatment of progressive keratoconus with corneal crosslinking (CXL) in four Nordic countries.

METHODS

A questionnaire was sent to all centres at which keratoconus patients are evaluated and CXL is performed in Sweden, Denmark, Norway and Iceland. Nineteen of 20 centres participated.

RESULTS

CXL is performed approximately 1300 times per year in these four Nordic countries with a population of around 21.7 million (2019). In most cases, progression is evaluated using the Pentacam HR, and the maximum keratometry reading (K_max ) is considered the most important parameter. The most frequently used treatment protocol in Scandinavia is the 9 mW/cm² epi-off protocol, using hydroxylpropyl methylcellulose riboflavin (HPMC-riboflavin). The participants deemed the following areas to be in most need of improvement: adaptation of the CXL protocol to individual patients (5/19), the development of effective epi-on treatment protocols (4/19), optimal performance of CXL in thin corneas (4/19), improvement of the definition of progression (2/19), and diagnosis of the need for re-treatment (2/19).

CONCLUSIONS

We concluded that the diagnosis of progressive keratoconus and the diagnostic equipment used are similar. Treatment strategies are also similar but are suitably different to provide an interesting basis for the comparison of treatment outcomes. The high degree of participation in this survey indicates the possibility of future scientific collaboration on CXL focusing on the areas deemed to need improvement. It would also be of interest to evaluate the possibility of creating a Nordic CXL Registry. The high number of CXL treatments performed ensures sufficient statistical power to solve many questions. Such a registry could be an important contribution to evidence-based care and would allow for longitudinal evaluation.

Long-term Safety and Efficacy of Corneal Collagen Crosslinking in a Pediatric Group With Progressive Keratoconus: A 7-year Follow-up

PURPOSE

To assess effectiveness and safety of corneal crosslinking (CXL) to reduce keratoconus (KC) progression and improve visual acuity among children with progressive KC and to analyze the use of 20% dextran-based (Dextran) and 1% hydroxypropyl methylcellulose-based (HPMC) riboflavin.

DESIGN

Prospective, clinical cohort study METHODS: Standard CXL (SCXL) was performed in 74 eyes (58 patients, 45 males, mean age 13.0 ± 2.1 years): 53 eyes with HPMC and 21 with Dextran. Examinations were performed at baseline, 3 and 6 months, and 1, 2, 3, 4, 5, and 7 years of follow-up, including uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), a complete ophthalmologic examination, anterior segment ocular coherence tomography, Scheimpflug corneal tomography, and specular microscopy.

RESULTS

UDVA and CDVA improved at all periods with statistically significant differences in CDVA at 1, 2, and 3 years. Compared with baseline, maximum K (Max K) reduced throughout the 7-year follow-up. Mean thinnest pachymetry (Th Pachy) decreased significantly at 3 months and remained low; in the Dextran group, the Th Pachy mean value returned to baseline 6 months postoperatively. After CXL, 1.5 diopter progression in max K was 1.4% to 14.6% of eyes; worsening was found at 4 to 7 years postoperatively.

CONCLUSION

SCXL reduced KC progression in children up to 7 years of follow-up and revealed improvement and stability of UDVA and CDVA in 82% of eyes. For visual acuity and KC stability, no statistically significant difference was observed between Dextran-HPMC. The HPMC group showed persistent cornea thinning, raising concerns about its use in SCXL.

The Impact of Different Rose Bengal Formulations on Corneal Thickness and the Efficacy of Rose Bengal/Green Light Corneal Cross-linking in the Rabbit Eye

PURPOSE

To examine central corneal thickness (CCT) changes during in vivo rose bengal-green light corneal cross-linking (RG-CXL) and compare the CXL efficacy of different rose bengal formulations.

METHODS

After epithelium removal, the right eyes of rabbits were immersed in rose bengal solution prepared by different solvents (water, phosphate buffered saline, dextran, and hydroxypropyl methylcellulos [HPMC]) for 2 or 20 minutes, then the rose bengal distribution in the corneal stroma was analyzed by confocal fluorescence detection. During the RG-CXL process, the CCT was measured at seven time points. The left eyes served as the untreated control group. Corneal enzymatic resistance and corneal biomechanics were tested to compare the RG-CXL efficacy.

RESULTS

The rose bengal infiltration depths were 120 and 200 µm for the 2- and 20-minute groups, respectively. CCT increased significantly after infiltration, then decreased significantly in the first 200 seconds of irradiation and decreased slowly for the next 400 seconds. The CCT of the 20-minute groups was significantly thicker than that of the 2-minute groups (P < .0001). All RG-CXL treatments improved the corneal enzymatic resistance and corneal biomechanics, with the effects being greater in the 20-minute groups. The inclusion of 1.1% HPMC in the rose bengal formulation helped to maintain CCT during irradiation while not affecting either the infiltration of rose bengal or the efficacy of RG-CXL.

CONCLUSIONS

Within the range studied, RG-CXL efficacy increased with infiltration time. The incorporation of a 20-minute infiltration of 0.1% rose bengal-1.1% HPMC into the RG-CXL procedure may further improve the safety of the treatment and its prospects for clinical use. [J Refract Surg. 2022;38(7):450-458.].

Excimer laser-assisted corneal epithelial pattern ablation for corneal cross-linking

Purpose

To determine corneal cross‐linking (CXL) efficacy and chromophore penetration after excimer laser‐assisted patterned de‐epithelialization.

Methods

Two‐hundred‐twenty porcine eyes were de‐epithelialized ex vivo, either fully (mechanical; n = 88) or patterned (excimer laser; n = 132). Consecutively, corneas were impregnated with hypo‐ or hyperosmolar riboflavin (RF; n = 20, RF‐D; n = 40, respectively) or water‐soluble taurine (WST11; n = 40, and WST‐D; n = 40, respectively), or kept unimpregnated (n = 80). Sixty corneas were subsequently irradiated, inducing CXL, with paired contralateral eyes serving as controls. Outcome measurements included strip extensiometry to assess CXL efficacy, and spectrophotometry and fluorescence microscopy to determine stromal chromophore penetration.

Results

All tested chromophores induced significant CXL (p < 0.001), ranging from 7.6% to 14.6%, with similar stiffening for all formulations (p = 0.60) and both de‐epithelialization methods (p = 0.56). Light transmittance was significantly lower (p < 0.001) after full compared with patterned de‐epithelialization. Stromal chromophore penetration was comparable between fully and patterned de‐epithelialized samples, with full penetration in RD and RF‐D samples and penetration depths measuring 591.7 ± 42.8 µm and 592.9 ± 63.5 µm for WST11 (p = 0.963) and 504.2 ± 43.2 µm and 488.8 ± 93.1 µm for WST‐D (p = 0.669), respectively.

Conclusions

Excimer laser‐assisted patterned de‐epithelialization allows for effective CXL. Stromal chromophore concentration is, however, reduced, which may have safety implications given the need for sufficient UVA attenuation in RF/UVA CXL. The different safety profile of near‐infrared (NIR) may allow safe WST11/NIR CXL even with reduced stromal chromophore concentration values. In vivo studies are needed to evaluate the benefits and further assess safety of excimer laser‐assisted patterned de‐epithelialization for corneal CXL.

The utility of contact lens-assisted corneal cross-linking (CACXL) in progressive keratoconus patients with thin corneas

PURPOSE

To evaluate efficacy and safety of contact lens-assisted corneal cross-linking (CACXL) among progressive keratoconus patients with thin corneas.

SETTING

Private eye hospital.

DESIGN

Cross-sectional study.

METHODS

Thirty-six eyes of 36 consecutive patients with progressive keratoconus and thinnest corneal thickness of 380-400 µm after epithelium removal were included. CACXL was performed based on use of a dextran-free isotonic (>0.1%) riboflavin solution with hydroxypropyl methylcellulose (HPMC, 1.1%) after epithelial removal and placement of a riboflavin-soaked contact lens without an ultraviolet filter on the cornea and ultraviolet irradiance. Data on best distance corrected (CDVA) and uncorrected (UDVA) visual acuity, manifest sphere (D), manifest cylinder (D), K1 (D), K2 (D), mean keratometry (D) and Kmax (D) values, endothelial cell count and mean depth of demarcation line were recorded preoperatively and at the postoperative 1-year.

RESULTS

Post-operative 1-year data revealed significant increases in UDVA (0.23  ±  0.15 vs. 0.17  ±  0.13 D, p < 0.001) and CDVA (0.44  ±  0.18 vs. 0.36  ±  0.17 D, p < 0.001) values and a significant reduction in the mean Kmax (from 56  ±  3.3D to 55  ±  3.2 D, p < 0.001), K2 (from 49.7  ±  3.2 D to 49.52  ±  3.11 D, p  =  0.049), manifest sphere (from -1.93  ±  2.21 D to -1.55  ±  2.02 D, p  =  0.001) and manifest cylinder (from -2.83  ±  1.67 D to -2.39  ±  1.36 D, p < 0.001) values along with a similar endothelial cell count. The mean depth of demarcation line was mean 230 (SD17.05, range 200 to 262) at postoperative 1-month.

CONCLUSIONS

Our findings indicate favourable 1-year postoperative outcome of CACXL in progressive keratoconus patients with thin cornea in terms of improved visual acuity and keratectasia status as well as endothelial safety.

Multi modal imaging in corneal edema after corneal collagen cross-linking (CXL); a case-based literature review

Background

Keratoconus (KCN) is a common ectatic disorder of the cornea. Corneal collagen cross-linking (CXL) is used as an effective option to slowdown the disease progression. Although CXL is considered a safe procedure, corneal endothelial damage, especially in corneal thickness of less than 400 μm, has been reported.

Case presentation

A 25-year-old man known case of KCN was referred with complaints about blurred vision and discomfort of the right eye 3 days after performing CXL. The preoperative thinnest point was 461 μm. His presenting BCVA was CF at 1 m. Examination showed central corneal edema and stromal haziness. ASOCT demonstrated increased central corneal thickness and very deep CXL line. In the confocal scan, anterior stroma showed hyper-reflective lines without recognizable cells and nerves, the middle stroma showed rare active and edematous keratocytes and a hyper-reflective reticular pattern with elongated keratocytes and needle-like structures involving the posterior stroma indicated increased depth of CXL. To manage the patient, debridement of loosened epithelium was done. Non-preservative steroid 1% eye drop was prescribed frequently. The corneal edema was completely resolved during 2 months with no need for surgical procedure and BCVA of 20/30 in his right eye.

Conclusion

The corneal thickness of more than 400 μm cannot guarantee the absence of corneal edema after corneal collagen cross-linking, which can pertain to several factors such as inadvertently using of higher energy as well as the incorrect observance of all guidelines, instructions, and other precautions, even by a trained surgeon.

Long-term visual, refractive, tomographic and aberrometric outcomes of corneal collagen crosslinking (CXL) with or without hypoosmolar riboflavin solution in the treatment of progressive keratoconus patients with thin corneas

PURPOSE

To evaluate the long-term visual, refractive, tomographic, and aberrometric outcomes of corneal collagen crosslinking (CXL) with or without hypoosmolar riboflavin solution in the treatment of progressive keratoconus patients with thin corneas.

METHODS

Charts of consecutive progressive keratoconus patients with thinnest corneal thickness less than 470 µm who underwent corneal collagen CXL with or without hypoosmolar riboflavin solution and using a standardized protocol for treatment and examinations were analyzed retrospectively. The indication for hypoosmolar riboflavin use was a central corneal thickness less than 400 µm as measured by ultrasound pachymetry after epithelial debridement and before exposure to ultraviolet A (UVA) light. Uncorrected distance visual acuity (UDVA), best spectacle-corrected distance visual acuity (CDVA), manifest refraction, slit lamp biomicroscopy, corneal tomography, corneal aberrometry, and endothelial cell counts were evaluated at baseline and yearly at all postoperative follow-up examinations until month 36. The outcomes of corneal CXL procedure performed using hypoosmolar riboflavin were compared to those performed using the standard procedure.

RESULTS

Twenty-three eyes (19 patients) were treated using hypoosmolar riboflavin application, and 30 eyes (28 patients) were treated using the standard procedure. Compared to baseline, the mean UDVA, CDVA, and keratometric readings improved statistically significantly in both groups at postoperative year 3, without any statistically significant between-group differences. Progression was not observed in any patient eye in either group. No significant endothelial cell loss and no sight threating complication were observed in any patient eye.

CONCLUSION

At 3 years follow-up, the safety and efficacy of CXL using hypoosmolar riboflavin solution seems to be similar to that of standard CXL in progressive keratoconic eyes with thin corneas. The visual, refractive, keratometric, tomographic and aberrometric outcomes of the two procedures were comparable, as well.

Oxidative Stress Induces a Breakdown of the Cytoskeleton and Tight Junctions of the Corneal Endothelial Cells

Purpose: To investigate the impact of oxidative stress, which is a hallmark of Fuchs dystrophy, on the barrier function of the corneal endothelial cells. Methods: Experiments were carried out with cultured bovine and porcine corneal endothelial cells. For oxidative stress, cells were supplemented with riboflavin (Rf) and exposed to UV-A (15-30 min) to induce Type-1 photochemical reactions that release H₂O₂. The effect of the stress on the barrier function was assayed by transendothelial electrical resistance (TER) measurement. In addition, the associated changes in the organization of the microtubules, perijunctional actomyosin ring (PAMR), and ZO-1 were evaluated by immunocytochemistry, which was also repeated after direct exposure to H₂O₂ (100 μM, 1 h). Results: Exposure to H₂O₂ led to the disassembly of microtubules and the destruction of PAMR. In parallel, the contiguous locus of ZO-1 was disrupted, marking a loss of barrier integrity. Accordingly, a sustained loss in TER was induced when cells in the Rf-supplemented medium were exposed to UV-A. However, the addition of catalase (7,000 U/mL) to rapidly decompose H₂O₂ limited the loss in TER. Furthermore, the adverse effects on microtubules, PAMR, and ZO-1 were suppressed by including catalase, ascorbic acid (1 mM; 30 min), or pretreatment with p38 MAP kinase inhibitor (SB-203580; 10 μM, 1 h). Conclusions: Acute oxidative stress induces microtubule disassembly by a p38 MAP kinase-dependent mechanism, leading to the destruction of PAMR and loss of barrier function. The response to oxidative stress is reminiscent of the (TNF-α)-induced breakdown of barrier failure in the corneal endothelium.

Corneal riboflavin gradients and UV-absorption characteristics after topical application of riboflavin in concentrations ranging from 0.1 to 0.5

Avoiding damage of the endothelial cells, especially in thin corneas, remains a challenge in corneal collagen crosslinking (CXL). Knowledge of the riboflavin gradients and the UV absorption characteristics after topical application of riboflavin in concentrations ranging from 0.1% to 0.5% could optimize the treatment. In this study, we present a model to calculate the UV-intensity depending on the corneal thickness. Ten groups of de-epithelialized porcine corneas were divided into 2 subgroups. Five groups received an imbibition of 10 min and the other five groups for 30 min. The applied riboflavin concentrations were 0.1%, 0.2%, 0.3%, 0.4% and 0.5% diluted in a 15% dextran solution for each subgroup. After the imbibition process, two-photon fluorescence microscopy was used to determine fluorescence intensity, which was compared to samples after saturation, yielding the absolute riboflavin concentration gradient of the cornea. The extinction coefficient of riboflavin solutions was measured using a spectrophotometer. Combining the obtained riboflavin concentrations and the extinction coefficients, a depth-dependent UV-intensity profile was calculated for each group. With increasing corneal depth, the riboflavin concentration decreased for all imbibition solutions and application times. The diffusion coefficients of 10 min imbibition time were higher than for 30 min. A higher RF concentration and a longer imbibition time resulted in higher UV-absorption and a lower UV-intensity in the depth of the cornea. Calculated UV-transmission was 6 percentage points lower compared to the measured transmission. By increasing the riboflavin concentration of the imbibition solution, a substantially higher UV-absorption inside the cornea is achieved. This offers a simple treatment option to control the depth of crosslinking e.g. in thin corneas, resulting in a lower risk of endothelial damage.

The intra-operative corneal pachymetry changes during accelerated corneal cross-linking in progressive keratoconus patients with thin corneas

Purpose

To report the intra-operative corneal pachymetry changes during accelerated corneal cross-linking (A-CXL) in progressive keratoconus patients with thin corneas.

Methods

Thirty-six eyes (mean age: 22.26 ± 4.02 years) with progressive keratoconic thin corneas (< 400 µm without epithelium) who underwent A- CXL with ultraviolet A (9 mW/cm2) using isotonic RF-HPMC (riboflavin5-phosphate 0.1% with 1.1% hydroxypropyl methycellulose/Mediocross M®) were included in this retrospective study. Intra-operative corneal pachymetric changes were noted before the procedure, after removal of epithelium, after RF-HPMC instillation, before and after UV irradiation. The mean of corneal pachymetric values were compared statistically.

Results

The mean corneal pachymetry reduced from 415.72±29.66 µm to 369.50±23.45 µm after removal of the epithelium (p<0.05). After the application of RF-HPMC solution the mean TCP increased to 412.89±26.94 µm. Statistically significant increase was observed in TCP after saturation with RF-HPMC (p=0.001). The mean corneal pachymetry was before and after UV-A irradiation respectively 419.86±10.41 µm, 417.47±8.25 µm (p>0.05).

Conclusion

Isotonic RF-HPMC lead to a significant increase in intra-operative mean TCP. RF-HPMC seems to be a favorable riboflavin option in keratoconus patients with thin corneas.

Adverse events after riboflavin/UV-A corneal cross-linking: a literature review

BACKGROUND

Riboflavin/UV-A corneal cross-linking (CXL) for treating keratoconus and iatrogenic corneal ectasia has been well-established as first treatment option to stabilize corneal tissue biomechanical instability. Although the plethora of clinical studies has been published into the field, there is no systematic review assessing the type and frequency of adverse events after CXL.

METHODS

A systemic literature review on clinical safety and adverse events after CXL in patients with keratoconus and corneal ectasia was performed using PubMed. A literature search was performed for relevant peer-reviewed publications. The main outcome measures extracted from the articles were adverse events, endothelial cell density, corrected distance visual acuity and maximum simulated keratometry.

RESULTS

The most frequent adverse events after CXL were corneal haze and corneal edema, which were mild and transient. The severe adverse events were infrequent (cumulative incidence: < 1.3%) after CXL. The clinical benefits of CXL highly outweighed the risks for the treatment of keratoconus and corneal ectasia.

CONCLUSIONS

The severe adverse events with permanent sequelae are infrequent after CXL and all are associated with corneal de-epithelialization, such as infectious keratitis and corneal scarring.

Topo-Pachimetric Accelerated Epi-On Cross-Linking Compared to the Dresden Protocol Using Riboflavin with Vitamin E TPGS: Results of a 2-Year Randomized Study

In the present study (clinical trial registration number: NCT05019768), we compared the clinical outcome of corneal cross-linking with either the standard Dresden (sCXL) or the accelerated custom-fast (aCFXL) ultraviolet A irradiation protocol using riboflavin–D-α-tocopheryl poly(ethylene glycol)-1000 succinate for progressive keratoconus. Fifty-four eyes of forty-one patients were randomized to either of the two CXL protocols and checked before treatment and at the 2-year follow-up. The sCXL group was subjected to CXL with 30 min of pre-soaking and 3 mW/cm² UVA irradiation for 30 min. The aCFXL group was subjected to CXL with 10 min of pre-soaking and UVA irradiation of 1.8 ± 0.9 mW/cm² for 10 min ± 1.5 min. In both groups, a solution of riboflavin–vitamin E TPGS was used. Uncorrected distance visual acuity, corrected distance visual acuity, pachymetry, Scheimpflug tomography, and corneal hysteresis were performed at baseline and after 24 months. Both groups showed a statistically significant improvement in corrected distance visual acuity, and keratometric and corneal hysteresis compared to baseline conditions; no statistically significant differences in outcomes between the two groups were observed. Improvement in refractive, topographic, and biomechanical parameters were observed after sCXL and aCFXL, making the riboflavin–VE-TPGS solution an effective option as a permeation enhancer in CXL procedures. Deeper stromal penetration of riboflavin could be complemented by photo-protection against UVA and free radicals formed during photoinduced processes.

Structural Changes in Thin Keratoconic Corneas Following Crosslinking with Hypotonic Riboflavin: Findings on In Vivo Confocal Microscopy

Purpose

To report structural changes observable in in vivo confocal microscopy (IVCM) in keratoconic corneas < 400 μm treated with hypotonic riboflavin and collagen crosslinking (CXL).

Methods

Ten eyes of ten patients with progressive keratoconus and corneal thickness between 350 and 399 μm underwent CXL with hypotonic riboflavin. IVCM was performed preoperatively and at one month, three months, and six months after the procedure.

Results

IVCM analysis one month postoperatively showed complete absence of the subepithelial nerve plexus with gradual regeneration over six months in 8 of the 10 eyes, and poor regeneration in the remaining 2 eyes. The anterior stroma showed extracellular lacunae and hyper-reflective cytoplasm in a honeycomb appearance signifying edema at one month which gradually decreased over six months post CXL. Stromal keratocyte apoptosis was evident in the anterior stroma in all cases and extended to the posterior stroma in four eyes with gradual regeneration evident at three and six months. The specular endothelial count decreased by 8% (P = 0.005) post-CXL, but no corneas developed clinical signs of endothelial trauma.

Conclusion

IVCM analysis of thin corneas after hypotonic CXL showed posterior corneal structural changes. Posterior stromal changes were accompanied by a decrease in the endothelial cell count. This case series was a preliminary feasibility study that might necessitate conducting a well-designed controlled study.

Corneal Cross-Linking: The Evolution of Treatment for Corneal Diseases

Corneal cross-linking (CXL) using riboflavin and ultraviolet A (UVA) light has become a useful treatment option for not only corneal ectasias, such as keratoconus, but also a number of other corneal diseases. Riboflavin is a photoactivated chromophore that plays an integral role in facilitating collagen crosslinking. Modifications to its formulation and administration have been proposed to overcome shortcomings of the original epithelium-off Dresden CXL protocol and increase its applicability across various clinical scenarios. Hypoosmolar riboflavin formulations have been used to artificially thicken thin corneas prior to cross-linking to mitigate safety concerns regarding the corneal endothelium, whereas hyperosmolar formulations have been used to reduce corneal oedema when treating bullous keratopathy. Transepithelial protocols incorporate supplementary topical medications such as tetracaine, benzalkonium chloride, ethylenediaminetetraacetic acid and trometamol to disrupt the corneal epithelium and improve corneal penetration of riboflavin. Further assistive techniques include use of iontophoresis and other wearable adjuncts to facilitate epithelium-on riboflavin administration. Recent advances include, Photoactivated Chromophore for Keratitis-Corneal Cross-linking (PACK-CXL) for treatment of infectious keratitis, customised protocols (CurV) utilising riboflavin coupled with customised UVA shapes to induce targeted stiffening have further induced interest in the field. This review aims to examine the latest advances in riboflavin and UVA administration, and their efficacy and safety in treating a range of corneal diseases. With such diverse riboflavin delivery options, CXL is well primed to complement the armamentarium of therapeutic options available for the treatment of a variety of corneal diseases.

Comparison of Contact Lens Assisted and Transepithelial Corneal Cross Linking with Standard 'Epithelium Off' Cross Linking for Progressive Keratoconus: 24 Month Clinical Results

PURPOSE

To compare outcomes of contact lens assisted corneal cross linking (CACXL) and transepithelial corneal cross linking (TECXL) with standard 'epithelium off'' ('epi -off') cross linking (CXL) for progressive keratoconus.

SETTING

Advanced Eye Centre, Post Graduate Institute of Medical Education and Research, Chandigarh , India.

DESIGN

Retrospective, comparative study.

METHODS

Patients with progressive keratoconus undergoing CXL with a minimum follow up of 24 months were included. CACXL and TECXL was performed in patients with 'epithelium on' minimal pachymetry between 350 µm to 450 µm. Main outcome measures included change in maximum keratometry (Kmax), corrected distance visual acuity (CDVA), and efficacy in halting progression (increase in Kmax ≥ 1 diopter [D]).

RESULTS

Standard 'epi -off' CXL, CACXL and TECXL was performed in 34,14 and 10 eyes respectively. Baseline Kmax and CDVA were comparable for all groupsKmax reduced significantly by -2.83 ± 3.35 D, -3.18 ± 2.74D and -2.02 ± 1.66 D in standard 'epi-off' CXL (p<0.01), CACXL (p=0.001) and TECXL (p=0.004) groups respectively; the reduction was comparable for all groups (p=0.63). CDVA improved by -0.14 ± 0.24 , -0.04 ± 0.19 and -0.12 ± 0.17 logMAR units in the standard 'epi -off' CXL (p =0.006), CACXL (p=0.42) and TECXL (p=0.05) groups respectively; the reduction was comparable for all groups (p=0.46). Progression was documented in 2 eyes (6%) of the standard 'epi -off' CXL group and 0% eyes of the CACXL and TECXL groups (p=0.61).

CONCLUSIONS

CACXL and TECXL were comparable to standard 'epi -off' CXL for progressive keratoconus.

Endothelial Cell Loss after Accelerated Corneal Crosslinking using Pachymetry-Guided Hypo-Osmolar Riboflavin Dosing in Thin Keratoconic Corneas

PURPOSE

To report the intra-operative changes in corneal pachymetry, efficacy and safety of accelerated corneal crosslinking (A-CXL) treatment using only hypo-osmolar riboflavin (HO-RF) solution in progressive keratoconus patients with thin corneas.

SETTING

University of Health Sciences, Prof. Dr. Cemil Tascioglu City Hospital, Istanbul, Turkey.

STUDY DESIGN

Retrospective study.

METHODS

Thirty-one eyes of 25 patients (mean age: 24.17±3.07 years) with thin keratoconic corneas (<400 µm without epithelium) who had A-CXL (9 mW/cm2-10 minutes) with HO-RF solution application were enrolled in the study. Peroperative corneal pachymetric changes and uncorrected-corrected distance visual acuities (UCVA-CDVA), refraction power values, topographic values and endothelial cell density (ECD) measurements were recorded pre-operatively and at 1st, 3rd, 6th and 12th month follow-up after surgery.

RESULTS

The mean thinnest corneal pachymetry (TCP) was 423 µm preoperatively and the thickness was reduced to a mean value of 375 µm after removing the epithelium. The mean thickness increased to 438 µm (p=0.001) after the application of HO-RF solution, and it was reduced to 424 µm (p=0.001) after ultraviolet irradiation. At all postoperative visits after month 1, there was a significant increase in both UCVA (p<0.05) and CDVA (p<0.01) values, and a significant decrease in both Kmax (p<0.05) and ECD (p<0.01) values.

CONCLUSION

Accelerated corneal CXL with only hypo-osmolar riboflavin solution application throughout the procedure in thin corneas is effective, but seems to result in a significant endothelial cell density decrease postoperatively.

Effect of Scleral Crosslinking Using Multiple Doses of Genipin on Experimental Progressive Myopia in Tree Shrews

Purpose

To evaluate the effect of scleral crosslinking (SXL) on slowing experimental progressive myopia in tree shrew eyes using sub-Tenon's injections of genipin (GEN) at different concentrations and number of injections.

Methods

Three or five sub-Tenon's injections of GEN at 0 mM (sham), 10 mM, or 20 mM were performed in one eye every other day starting at 18 days of visual experience. Form deprivation (FD) myopia was induced in the injected eye between 24 and 35 days of visual experience; the fellow eye served as control. Tree shrews were randomly assigned to five experimental groups: FD (n = 8); FD + 5 × sham injections (n = 6); FD + 3 × GEN injections at 10 mM (n = 6) and 20 mM (n = 6); and FD + 5 × GEN injections at 20 mM (n = 6). Refractive state and ocular dimensions were measured daily.

Results

Compared with the FD group, the sham-injected group showed a transient effect on slowing vitreous chamber elongation. With increasing GEN dose, SXL had an increasing treatment effect on slowing vitreous chamber elongation and myopia progression. In addition, SXL led to a dose-dependent shortening of the aqueous chamber depth and corneal thickening. Lens thickening was observed in the group with the highest concentration.

Conclusions

We have shown that SXL using GEN can slow axial elongation and myopia progression in tree shrews. The extent of this treatment effect was dose dependent. Several unexpected effects were observed (corneal thickening, decrease of the anterior chamber depth, and lens thickening), which require further optimization of the GEN delivery approach before clinical consideration.

Translational Relevance

The results of this preclinical study suggest that scleral crosslinking using genipin can slow myopia progression.

Chemically-Boosted Corneal Cross-Linking for the Treatment of Keratoconus through a Riboflavin 0.25% Optimized Solution with High Superoxide Anion Release

The purpose of this study was to evaluate the effectiveness and safety of a novel buffered riboflavin solution approved for corneal cross-linking (CXL) in progressive keratoconus and secondary corneal ectasia. Following the in vivo preclinical study performed on New Zealand rabbits comparing the novel 0.25% riboflavin solution (Safecross^®) containing 1% hydroxypropyl methylcellulose (HPMC) with a 0.1% riboflavin solution containing 0.10% EDTA, accelerated epithelium-off CXL was performed on 10 patients (10 eyes treated, with the contralateral eye used as control) through UV-A at a power setting of 9 mW/cm² with a total dose of 5.4 J/cm². Re-epithelialization was evaluated in the postoperative 7 days by fluorescein dye test at biomicroscopy; endothelial cell count and morphology (ECD) were analyzed by specular microscopy at the 1st and 6th month of follow-up and demarcation line depth (DLD) measured by anterior segment optical coherence tomography (AS-OCT) one month after the treatment. We observed complete re-epithelization in all eyes between 72 and 96 h after surgery (88 h on average). ECD and morphology remained unchanged in all eyes. DLD was detected at a mean depth of 362 ± 50 µm, 20% over solutions with equivalent dosage. SafeCross^® riboflavin solution chemically-boosted corneal cross-linking seems to optimize CXL oxidative reaction by higher superoxide anion release, improving DLD by a factor of 20%, without adverse events for corneal endothelium.

Morphological alterations of the cornea following crosslinking treatment (CXL)

INTRODUCTION

Corneal crosslinking (CXL) has revolutionized the treatment of keratoconus during the past decade. In the present study, the morphological changes in the corneal collagen fibrils (CFs) following crosslinking treatment are described.

MATERIALS AND METHODS

Ten pairs of porcine and rabbit corneas were retrieved. In each pair, one cornea was the control and the other underwent CXL treatment. The central corneal thickness (CCT) was measured before and after CXL treatment. Each treated and control cornea was examined with light microscopy and by transmission electron microscopy.

RESULTS

(a) The mean CCT was significantly reduced following treatment. (b) CFs were more closely packed in the anterior region and loosely packed in the posterior region. (c) CF diameter increased significantly in the anterior and intermediate regions but declined gradually towards the deeper regions. (d) There was a statistically significant decrease in the interfibrillar distance over the different regions of the cornea, except for the posterior region in porcine corneas, where there was no change. (e) The distance between adjacent collagen lamellae was significantly decreased in all regions of treated rabbit corneas. There was no change in porcine corneas.

CONCLUSION

CXL treatment resulted in increased the CF diameter and decreased interfibrillar distance in the anterior and intermediate regions, while its effects on the posterior region differed among species. The effect on interlamellar distance was more prominent in the rabbit model than the porcine model. CXL treatment stiffened the corneas by increasing CF diameter and decreasing interfibrillar distance in both rabbit and pig corneas.

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.

Corneal UV Protective Effects of a Topical Antioxidant Formulation: A Pilot Study on In Vivo Rabbits

This study aimed to evaluate the protective effect of a topical antioxidant and ultraviolet (UV) shielding action formulation containing riboflavin and D-α-tocopherol polyethylene glycol succinate (TPGS) vitamin E against corneal UV-induced damage in vivo rabbit eyes. In vivo experiments were performed using male albino rabbits, which were divided into four groups. The control group (CG) did not receive any UV irradiation; the first group (IG) was irradiated with a UV-B−UV-A lamp for 30 min; the second (G30) and third (G60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with one drop of the antioxidant and shielding formulation every 15 min, starting one hour before irradiation, until the end of UV exposure. The cornea of the IG group showed irregular thickening, detachment of residual fragments of the Descemet membrane, stromal fluid swelling with consequent collagen fiber disorganization and disruption, and inflammation. The cornea of the G30 group showed edema, a mild thickening of the Descemet membrane without fibrillar collagen disruption and focal discoloration, or inflammation. In the G60 group, the cornea showed a more severe thickening, a more abundant fluid accumulation underneath the Descemet membrane with focal detachment, and no signs of severe tissue alterations, as were recorded in the IG group. Our results demonstrate that topical application of eye drops containing riboflavin and TPGS vitamin E counteracts UV corneal injury in exposed rabbits.

Comparative Two-Photon Fluorescence Microscopy Analysis of Riboflavin Penetration in Two Different Solutions: Dextran and Hydroxypropyl Methylcellulose

Purpose

This study compared riboflavin penetration in porcine corneas using two different solutions: dextran and hydroxypropyl methylcellulose (HPMC).

Methods

Porcine corneas were de-swollen and after prepared in an artificial anterior chamber with balanced saline solution. The pressure was checked with a portable tonometer. We used 0.1% riboflavin in 20% dextran for 30 min or 0.1% riboflavin in 1% HPMC for 10 min. The fluorescence intensity in multiphoton microscopy was used to evaluate concentration into the cornea, and ultrasonic pachymetry was performed before and after using riboflavin.

Results

Riboflavin concentration up to 340 μm was higher in the HPMC group (p 0.146). From 340 microns to 500 μm, the concentration was higher in the dextran group (p 0.248). There was no statistically significant difference between the groups when considering all the corneal thickness studied (p 0.528). Pachymetric measurements in the group with dextran showed a 12.9% corneal thickness decrease after 30 min, while the HPMC group showed a 9.1% increase after 10 min.

Conclusion

We concluded that 1% HPMC riboflavin for 10 min had the same level of safety when compared to the Dresden protocol with dextran riboflavin for 30 min. Ultrasonic pachymetry during corneal crosslinking has fundamental importance in controlling corneal hydration due to changes in thickness caused by different types of riboflavin. This study used different methods than previous studies to better simulate corneal physiological conditions and used 1% HPMC concentration which differs from previous studies performed with 1.1% HPMC.

Effects of an antioxidant protective topical formulation on retinal tissue of UV-exposed rabbits

PURPOSE

The aim of this study has been to evaluate the protective effect of a topical antioxidant formulation containing riboflavin, d-α-tocopheryl polyethylene glycol (TPGS vitamin E), proline, glycine, lysine, and leucine against UV-B-induced damage in in vivo rabbit retina.

METHODS

Twenty male albino rabbits were used. Animals were divided into four groups of five animals each. Control group did not receive any UV irradiation. The first group (IG) was irradiated with a UV-A lamp for 30 min; the second (IG30) and the third (IG60) groups received UV irradiation for 30 and 60 min, respectively, and were topically treated with 1 drop (approximately 50 µl) of the antioxidant formulation, every 15 min, starting 1 h before irradiation, until the end of the UC exposure.

RESULTS

The retina of IG group showed extensive destruction of the retinal pigment epithelium (RPE) and of the cones and rods layer. The retina of G30 group showed a lesser destruction of both RPE and cones and rods layer. In the G60 group, retina showed an irregular thickening of the RPE, with massive edema of the inner and outer layer immediately adjacent together with a significant reduction of the photoreceptor number.

CONCLUSION

Our results demonstrate that a topical application of eye drops containing riboflavin, d-α-tocopheryl polyethylene glycol (TPGS vitamin E), proline, glycine, lysine, and leucine counteracts UV retinal injury in exposed retina rabbits.

Transepithelial corneal crosslinking for keratoconus

PURPOSE

To evaluate outcomes of corneal crosslinking (CXL) using a transepithelial technique for the treatment of keratoconus.

SETTING

Cornea and refractive surgery subspecialty practice.

DESIGN

Prospective case series.

METHODS

Transepithelial CXL was performed in keratoconic eyes using riboflavin 0.1% and topical anesthetic containing benzalkonium chloride to facilitate riboflavin diffusion through the epithelium. Eyes were randomized to receive riboflavin administration either every 1 minute or every 2 minutes during ultraviolet-A exposure at 3mW/cm². The principal outcome was change in maximum keratometry (K) and secondary outcomes included uncorrected (UDVA) and corrected (CDVA) distance visual acuities, mean K, and comparison of randomized groups.

RESULTS

Eighty-two eyes of 56 patients were treated. At 1 year, maximum K decreased significantly by 0.45 diopters (D) ± 1.94 (SD); it improved by 2.0 D or more in 11 eyes (13%) and worsened by 2.0 D or more in 4 eyes (5%). The mean UDVA significantly improved by 0.7 lines, whereas the CDVA improved by 0.2 lines. Two eyes showed both continued progression with loss of CDVA. Only the 1-minute subgroup showed significant improvements in maximum K (-0.73 D) and UDVA. Transient corneal erosion and epitheliopathy were reported in 21% of eyes.

CONCLUSIONS

Transepithelial CXL resulted in significant improvements in maximum K and UDVA over 1 year. There was a suggestion that increased riboflavin dosing might improve procedure outcomes. Further study is required to determine the relative advantages and disadvantages of different transepithelial approaches to the standard CXL protocol with epithelial removal.

Depth-Dependent Reduction of Biomechanical Efficacy of Contact Lens-Assisted Corneal Cross-linking Analyzed by Brillouin Microscopy

PURPOSE

To determine the relative impact of contact lens- assisted corneal cross-linking (CACXL) and standard protocol CXL (CXL) on regional corneal stiffness using Brillouin microscopy.

METHODS

CXL and CACXL were performed on 30 intact fresh porcine eyes (15 per group). Depth profile of stiffness variation and averaged elastic modulus of anterior, middle, and posterior stroma were determined by Brillouin maps. Corneas were cut into strips to conduct mechanical stress-strain tests after Brillouin microscopy to evaluate stiffness difference between CXL and CACXL. Each eye served as its own control.

RESULTS

CXL had a greater impact on corneal stiffness, with a maximum increase of 5.74% compared to 3.99% for CACXL (P < .001). CXL increased longitudinal modulus by 7.8% in the anterior, 1.7% in the middle, and -0.7% in the posterior regions compared to CACXL, which increased longitudinal modulus by 5.5% in the anterior (P < .001), 1.2% in the middle (P = .15), and -0.4% in the posterior regions (P = .60). Mechanical stress-strain tests showed that at 10% strain averaged Young's modulus was 5 MPa for CXL and 2.97 MPa for CACXL (P < .001).

CONCLUSIONS

Both CACXL and standard protocol CXL induced significant corneal stiffening primarily concentrated in the anterior cornea. CACXL leads to less stiffening compared with CXL. An attenuated but continuous stiffening effect can be observed through the whole cornea for both CACXL and CXL, although CACXL has a smaller stiffness gradient. [J Refract Surg. 2019;35(11):721-728.].

Optimization of Oxygen Dynamics, UV-A Delivery, and Drug Formulation for Accelerated Epi-On Corneal Crosslinking

Purpose: Corneal collagen crosslinking (CXL) through an intact epithelium (epi-on) at high irradiance could potentially improve patient comfort, visual recovery, and clinical workflow compared to conventional epi-off CXL. However, intact epithelium limits stromal delivery of the oxygen, photosensitizer, and ultraviolet-A (UV-A) radiation needed to drive CXL. This ex vivo study evaluated three different epi-on CXL protocols compared to positive and negative controls, specifically focusing on the impact of supplemental oxygen. Endpoints included stromal oxygen levels, stiffness of crosslinked tissue, and acute flattening of whole eyes.Materials & Methods: Ex vivo porcine eyes were held in a custom environmental chamber. Intrastromal oxygen levels were continuously measured before, during, and after UV illumination by a fiberoptic probe inserted into a laser-cut flap. Accelerated, high irradiance, epi-on CXL protocols using riboflavin formulated with benzalkonium chloride (BAC) were studied, with and without supplemental oxygen. These were compared to an alternate, low irradiance, epi-on protocol using riboflavin formulated with sodium iodide. Both negative (no CXL) and positive (epi-off modified Dresden protocol) controls were performed. Post-CXL elastic modulus was measured using extensiometry and anterior tangential curvature was measured using a Scheimpflug tomographer.Results: Protocols including supplemental oxygen resulted in an approximately 5-fold increase in stromal oxygen levels prior to CXL. During epi-on, high-irradiance UV-A delivery under hyperoxic conditions, an aerobic state was maintained. Conversely, under normoxic conditions, stromal oxygen rapidly depleted to 0-5% for all other protocols. The combination of supplemental oxygen, BAC formulation, and high-irradiance UV-A resulted in the largest biomechanical changes and most pronounced flattening effects of the three epi-on protocols.Conclusions: Ex vivo analysis of stromal oxygen levels, corneal stiffness, and acute anterior curvature change indicates that simultaneous optimization of the oxygen environment, riboflavin formulation, and UV-A protocol can significantly increase the effects of corneal collagen crosslinking.

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.

Effect of Riboflavin Solution With Hydroxypropyl Methylcellulose and Eyelid Speculum on Pachymetry Changes During Accelerated Collagen Crosslinking

PURPOSE

To assess corneal thickness changes with isotonic riboflavin (RF) solution with hydroxylpropyl methylcellulose in patients undergoing accelerated corneal collagen crosslinking (CXL) with and without an eyelid speculum.

METHODS

Fifty-two eyes of 48 patients with progressive keratoconus were enrolled in this study. The patients in this study were divided into 2 groups: in group 1 an eyelid speculum was removed during 20-minute RF (0.1%) + hydroxylpropyl methylcellulose (Mediocross M; Avedro Inc, Waltham, MA) instillation, and in group 2 the eyelid speculum was retained in place during the entire CXL procedure. All patients underwent accelerated CXL using continuous ultraviolet-A (UVA) light exposure at 9 mW/cm for 10 minutes; total energy dose was 5.4 J/cm. Intraoperative ultrasound pachymetry measurements were obtained before and after epithelial removal, after RF loading, and after UVA light exposure at 5 and 10 minutes.

RESULTS

The preoperative pachymetric measurements decreased in both groups after the removal of epithelium [group 1 (n = 26): -25 μm, group 2 (n = 26): -31 μm, P = 0.234]. Although the thinnest pachymetry significantly increased after soaking in both group 1 (52.26 μm) and group 2 (27.88 μm, P < 0.001), closure of the eyelids during RF instillation further increased the pachymetry readings (P < 0.0001). The corneal thickness remained stable in both groups during UVA irradiation at 5 and 10 minutes (P > 0.05).

CONCLUSIONS

Closure of the eyelids further induces corneal swelling that may offer an advantage to improve safety of the procedure particularly in thin corneas.

Superior outcome of corneal collagen cross-linking using riboflavin with methylcellulose than riboflavin with dextran as the main supplement

PURPOSE

To compare the effect of corneal collagen cross-linking (CXL) on progressive keratoconus using 0.1% riboflavin with either dextran or methylcellulose as the main supplement.

METHODS

In a comparative case series, CXL was performed in 40 patients (40 eyes) using a riboflavin solution containing either dextran (dextran-riboflavin; n = 20) or methylcellulose (methylcellulose-riboflavin; n = 20). Changes in central corneal thickness (CCT), Scheimpflug tomography, maximal keratometry reading (K_max ), visual acuity (VA) and endothelial cell density (ECD) were recorded. Stromal changes one month after surgery were analysed using optical coherence tomography (OCT) and in vivo confocal microscopy (IVCM).

RESULTS

The CCT was significantly higher in the methylcellulose-riboflavin group during the CXL procedure. The IVCM demarcation line depth was 274 ± 80 (SD) μm in the dextran-riboflavin group and 442 ± 80 μm in the methylcellulose-riboflavin group (p < 0.001). Complete absence of keratocytes in the pre-endothelial stroma was found in none of the corneas treated with dextran-riboflavin and in 42% of the corneas treated with methylcellulose-riboflavin. Visibility of the OCT demarcation line was significantly lower in the methylcellulose-riboflavin group. K_max and corrected distance visual acuity were improved in the methylcellulose-riboflavin group and stable in the dextran-riboflavin group after 2 years. Endothelial cell density (ECD) was stable in both groups.

CONCLUSION

We found deeper structural changes in the methylcellulose-riboflavin group than in the dextran-riboflavin group. This may be explained by different riboflavin solution properties and raises safety concerns. The study also indicates improved effect using methylcellulose-riboflavin than dextran-riboflavin, possibly explained by deeper stromal CXL effect.

Current concepts in crosslinking thin corneas

Corneal cross-linking (CXL), introduced by Wollensak et al. in 2003, is a minimally invasive procedure to halt the progression of keratoconus. Conventional CXL is recommended in eyes with corneal thickness of at least 400 microns after de-epithelialization to prevent endothelial toxicity. However, most of the keratoconic corneas requiring CXL may not fulfill this preoperative inclusion criterion. Moderate-to-advanced cases are often found to have a pachymetry less than this threshold. There are various modifications to the conventional method to circumvent this issue of CXL thin corneas while avoiding the possible complications. This review is an update on the modifications of conventional CXL for thin corneas.

Two-year outcomes of a randomized controlled trial of transepithelial corneal crosslinking with iontophoresis for keratoconus

PURPOSE

To evaluate the 2-year clinical outcomes of corneal crosslinking (CXL) using transepithelial iontophoresis CXL (T-ionto CXL) in comparison with standard CXL for the treatment of progressive keratoconus.

SETTING

Single-site study.

DESIGN

Randomized controlled clinical trial with identifier code NCT02117999.

METHODS

The eyes of the participants were randomized to have either T-ionto CXL and/or standard CXL. Assessments of uncorrected (UDVA) and corrected (CDVA) distance visual acuities (logarithm of the minimum angle of resolution [logMAR]), manifest refraction spherical equivalent, maximum simulated keratometry (K) (diopters [D]), corneal higher-order aberrations (HOAs), central corneal thickness (CCT), and endothelial cell density (ECD) were performed at 3 days, 7 days, and 1, 3, 6, 12, and 24 months postoperatively.

RESULTS

The study comprised 34 eyes (25 patients). There were 22 eyes in the T-ionto CXL group and 12 eyes in the standard CXL group. Two years after T-ionto CXL and standard CXL, the mean maximum K flattened by -1.05 ± 1.20 D (P = .07) (20 eyes) and -1.51 ± .89 D (P < .001) (11 eyes), respectively. Two study cases (10%) and no control showed maximum K steepening of more than 1.0 D at 24 months postoperatively. The mean change in CDVA was -0.08 ± 0.15 logMAR (P = .04) and -0.02 ± 0.06 logMAR (P = .34) after T-ionto CXL and standard CXL, respectively. A significant average decrease in the myopic defocus (+0.81 D; P < .05) was found in both groups. No significant differences in the outcome measures between treatments were found at 24 months. The corneal HOAs, CCT, and ECD values did not change significantly in any group at 2 years postoperatively.

CONCLUSIONS

Clinically significant topographic, visual, and refractive improvements were found 2 years after T-ionto CXL; standard CXL showed more significant corneal apex flattening than the transepithelial iontophoresis protocol.

Comparison of Standard Versus Accelerated Corneal Collagen Cross-Linking for Keratoconus: A Meta-Analysis

Purpose

To systematically compare epithelial-off standard (SCXL) to accelerated corneal collagen cross-linking (ACXL) for the treatment of keratoconus.

Methods

PubMed, Embase, the Cochrane Library, and the US trial registry were searched for trials comparing SCXL and ACXL for keratoconus up to October 2017. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were calculated. Primary outcomes were changes in uncorrected distance visual acuity, maximum keratometry (Kmax), and mean keratometry (mean K). Secondary outcomes were changes in corrected distance visual acuity, mean refractive spherical equivalent, central corneal thickness (CCT), and endothelial cell density (ECD).

Results

Eleven trials were included. For primary outcomes, SCXL showed a greater reduction in Kmax (SMD 0.32; 95% CI 0.16, 0.48) than ACXL. For secondary outcomes, the decrease in CCT (SMD 0.32; 95% CI 0.03, 0.61) and ECD (SMD 0.26; 95% CI 0.06, 0.46) was less with ACXL than with SCXL. For the other outcomes, there were no statistically significant differences.

Conclusions

SCXL has a greater effect in terms of reduction in Kmax than ACXL, while ACXL induces less reduction in CCT and ECD than SCXL. Further well-designed randomized controlled trials comparing ACXL and SCXL are indicated.

Biomechanical efficacy of contact lens-assisted collagen cross-linking in porcine eyes

PURPOSE

Contact lens-assisted corneal cross-linking (CACXL) has been proposed for the cross-linking treatment in thin corneas. The aim of this study was to assess the biomechanical efficacy of this treatment.

METHODS

Post-mortem porcine eyes were treated with standard cross-linking and with cross-linking placing a contact lens soaked with isoosmolar riboflavin solution on the debrided cornea with or without an adherent precorneal riboflavin film of up to 100 μm thickness. Three soft contact lenses (Air Optix Aqua, SofLens and Galifa) with different degrees of hydrophilic properties were tested. After cross-linking with a surface UVA irradiance of 3 mW/cm² for 30 min (fluence 5.4 J/cm²), a 400 μm deep anterior corneal flap was created using a lamellar rotating microkeratome. Biomechanical stress-strain measurements and thermal shrinkage tests were performed.

RESULTS

In the Air Optix Aqua group (30% hydration) without riboflavin film, Young's modulus and stress at 8% strain were increased significantly versus untreated controls and the effect was 92.4% respectively 86.35% of the standard CXL value. In the SofLens group (59% hydration) without riboflavin film, Young's modulus and stress at 8% strain were increased significantly versus untreated controls and the effect was 67.04% respectively 65.28% of the standard CXL value. In the Galifa group (72% hydration) without riboflavin film, Young's modulus and stress at 8% strain were increased significantly versus untreated controls and the effect was about 68.48% respectively 75.52% of the standard CXL value. In all samples with a precorneal riboflavin film under the contact lens, there was no significant biomechanical effect compared to the untreated controls. Similarly, in the hydrothermal experiments at 70°C, there was a typical mushroom pattern with increased resistance to thermal shrinkage in the anterior stroma after standard CXL, a markedly reduced mushroom effect using a riboflavin-soaked contact lens only and no effect with the use of a riboflavin-soaked contact lens plus a precorneal riboflavin film.

CONCLUSION

The biomechanical effect of CACXL in porcine corneas is about one-third less than after standard CXL. The efficacy of CACXL might be improved by reducing or omitting the riboflavin film on the contact lens. Further risk assessment studies are necessary.

Corneal Cross-Linking: Current USA Status: Report From the Cornea Society

The initial published clinical report on riboflavin/ultraviolet A corneal cross-linking (CXL) for treatment of progressive keratoconus dates back to 2003. CXL has since then been widely used outside the United States for treatment of progressive keratoconus and post-laser in situ keratomileusis ectasia. The Food and Drug Administration (FDA) approved Avedro Inc.'s corneal cross-linking system (KXL) for treatment of patients with progressive keratoconus and post-laser in situ keratomileusis ectasia in April 2016. The procedure is not currently approved for stable keratoconus. There are 2 FDA-approved topical ophthalmic solutions for use in CXL. Riboflavin 5'-phosphate in 20% dextran ophthalmic solution 0.146% (Photrexa Viscous) and Riboflavin 5'-phosphate ophthalmic solution 0.146% (Photrexa) are intended for use with the KXL system. Photrexa Viscous is used in all CXL procedures, whereas Photrexa is indicated for use when the corneal stroma is thinner than 400 µm after completion of the Photrexa Viscous induction period. The FDA-approved procedure using the Dresden protocol (UV-A, 3 mW/cm for 30 min) induces cytologic and morphologic changes in the anterior 250 to 300 µm of the corneal stroma. It has been believed that a minimum thickness of 400 μm was necessary to protect the corneal endothelium from potential damage. The CXL procedure using the standard Dresden protocol is established as the gold standard for treatment of progressive keratoconus. CXL treatment is indicated for a list of conditions ranging from corneal ectasia to infectious keratitis. Newer protocols, treatment regimens, and expanded indications will require further refinements, investigations, and long-term studies.

Intraoperative corneal thickness change and clinical outcomes after corneal collagen crosslinking: Standard crosslinking versus hypotonic riboflavin

PURPOSE

To determine intraoperative changes in corneal thickness and outcomes of corneal collagen crosslinking (CXL) using 2 intraoperative regimens: riboflavin-dextran or hypotonic riboflavin.

SETTING

Cornea and refractive surgery practice, Teaneck, New Jersey, USA.

DESIGN

Prospective randomized case series.

METHODS

Eyes with keratoconus or corneal ectasia were treated. All eyes received preloading with riboflavin 0.1% in 20% dextran. During ultraviolet-A (UVA) exposure, patients were randomly assigned to 1 of 2 study arms; that is, riboflavin-dextran or hypotonic riboflavin. Intraoperative pachymetry was measured before and after the corneal epithelium was removed, after initial riboflavin loading, and after UVA light exposure. Patients were evaluated for maximum keratometry (K), uncorrected distance visual acuity (UDVA), corrected distance visual acuity, corneal thickness, and endothelial cell count (ECC).

RESULTS

Forty-eight eyes were treated. After removal of the epithelium and riboflavin loading, the mean pachymetry was 430 μm and 432 μm in the standard group and hypotonic group, respectively. Immediately after 30-minute UVA administration, the mean pachymetry was 302 μm and 342 μm, respectively. There was no statistically significant difference in the postoperative maximum K change, UDVA, corneal thickness, or ECC between the 2 groups.

CONCLUSIONS

The cornea thinned substantially during the CXL procedure. The use of hypotonic riboflavin rather than riboflavin-dextran during UVA administration decreased the amount of corneal thinning during the procedure by 30%, from 128 μm to 90 μm. However, there were no significant differences in clinical efficacy or changes in ECC or function between groups postoperatively. In general, corneal thinning during CXL did not seem to compromise the safety of the endothelium.

FINANCIAL DISCLOSURES

Dr. Hersh is a consultant to Avedro, Inc. Dr. Rosenblat has no financial or proprietary interest in any material or method mentioned.

Biomechanical efficacy of corneal cross-linking using hypoosmolar riboflavin solution

Purpose:

The use of hypoosmolar riboflavin solution has been suggested for cross-linking thin corneas. The aim of this study was to compare the biomechanical efficacy of corneal cross-linking using hypoosmolar dextran-free riboflavin solution (HCXL) versus isoosmolar standard corneal cross-linking treatment (CXL).

Methods:

A total of 24 postmortem porcine eyes with debrided corneas were subdivided into three treatment groups: Controls, the isoosmolar group with isoosmolar 0.1% riboflavin-20% dextran solution and the hypoosmolar group with dextran-free, 0.1% riboflavin solution. The samples were irradiated with UVA light of 365 nm wavelength and an irradiance of 3 mW/cm² for 30 min (dose 5.4 J/cm²). For the biomechanical measurements, 400-µm-deep anterior corneal flaps were created using a lamellar rotating microkeratome. Uniaxial stress–strain measurements were performed.

Results:

In the isoosmolar treatment group, stress and Young’s modulus at 8% strain were significantly increased by 67.97%, respectively, 62.62% versus the controls. In the hypoosmolar treatment group, stress and Young’s modulus at 8% strain were significantly increased by 81.21%, respectively, 51.40% versus the controls. There was no significant difference between the iso- and hypoosmolar groups in biomechanical efficacy. On histology, there was no edema in the anterior 200 µm of the corneas after stromal swelling by the hypoosmolar riboflavin solution.

Conclusion:

Corneal cross-linking using isoosmolar or hypoosmolar riboflavin solution induces a comparable biomechanical effect. This is explained by the localization of the maximum cross-linking effect in the anterior 200 µm of the cornea which are not affected by the swelling effect of hypoosmolar riboflavin solution.