Standard corneal collagen crosslinking versus transepithelial iontophoresis-assisted corneal crosslinking, 24 months follow-up: randomized control trial

Permeation characteristics and cross-linking efficacy of iontophoresis-assisted riboflavin delivery for accelerated riboflavin-ultraviolet A scleral collagen cross-linking in porcine eyes

The purpose of this study is to investigate whether the iontophoresis-assisted riboflavin delivery to posterior sclera with less delivery time, can achieve the same riboflavin permeation efficiency as the passive soaking way, and its effect on the mechanical properties of posterior sclera for accelerated scleral collagen cross-linking (A-SXL). In this study, 0.1% riboflavin solution was applied into the posterior sclera of porcine eyes either by the iontophoresis-assisted or passive soaking method, with delivery time of 5, 7.5, 10, 12.5, 15, 17.5, and 20 min, respectively. The fluorescence intensity and the distribution of riboflavin concentration in the 10 μm frozen sections of the sclera were evaluated by fluorescence inverted microscope. The posterior sclera with riboflavin treatment through either the iontophoresis-assisted or the passive soaking method for different durations ranging from 5 to 20 min was treated with ultraviolet A (UVA) irradiation at an intensity of 10 mW/cm2 for 9 min. The elastic modulus was determined at the physiological strain level using the uniaxial tensile test after ASXL. The results showed that the fluorescence intensity of riboflavin increased by prolonging the delivery time in both the iontophoresis and passive soaking groups, and the permeation depth of riboflavin remained constant over 15 min. The fluorescence intensity in the iontophoresis group was significantly higher than in the passive soaking group at 12.5 min and 15 min, respectively. The elastic modulus at 12.5 min in the iontophoresis group was significantly higher than in the passive soaking group at the same delivery time and showed no significant difference compared to the passive soaking group at 20 min. In conclusion, it indicated that iontophoresis-assisted delivery could not only shorten the surgery time but also achieve similar mechanical performance to the passive soaking method in ASXL.

Spatial targeted delivery of riboflavin with a controlled corneal iontophoresis delivery system in theranostic-guided UV-A light photo-therapy

Seven human donor eye globes underwent corneal cross-linking using theranostic UV-A device with accessory corneal iontophoresis system for patterned delivery of a 0.22% riboflavin solution. Theranostic-guided UV-A light illumination assessed riboflavin distribution and treated corneas at 10 mW/cm2 for 9 min with a 5.0-mm beam size. Corneal topography maps were taken at baseline and 2-h post-treatment. Analysis utilized corneal topography elevation data, with results showing controlled riboflavin delivery led to a consistent gradient, with 40% higher levels centrally (248 ± 79 μg/cm3) than peripherally (180 ± 72 μg/cm3 at ±2.5 mm from the center). Theranostic-guided UV-A light irradiation resulted in significant changes in corneal topography, with a decrease in best-fit sphere value (-0.7 ± 0.2 D; p < 0.001) and consistent downward shift in corneal elevation map (-11.7 ± 3.7 μm). The coefficient of variation was 2.5%, indicating high procedure performance in achieving significant and reliable corneal flattening.

Clinical and Morphological in Vivo Confocal Microscopy Findings following a Modified Biphasic Higher Fluence Transepithelial Corneal Crosslinking

Purpose: To compare the refractive efficacy and morphological changes in the cornea following a novel biphasic higher fluence transepithelial corneal crosslinking (BI-TE-CXL) and transepithelial corneal crosslinking (TE-CXL) in adults keratoconus.Methods: Patients with progressive keratoconus who required corneal crosslinking were assigned to the BI-TE-CXL group (32 eyes, phase 1: 7.2 J/cm2 for 5 min and 20 s of pulsed-light exposure, KXL, Glaukos-Avedro; phase 2: 3.6 J/cm2 for 6 min and 40 s of continuous light exposure at the front curvature apex with a 6 mm diameter light spot, UVX-2000, IROC) or the TE-CXL group (32 eyes, uniform 7.2 J/cm2 for 5 min and 20 s of pulsed-light exposure, KXL, Glaukos-Avedro). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), corneal fluorescein staining (CFS), corneal topography, anterior segment optical coherence tomography (AS-OCT), and in vivo corneal confocal microscopy (IVCM) were performed 3, 6, 12 and 24 months after surgery.Results: The CFS scores in the BI-TE-CXL group were significantly higher than those in the TE-CXL group on the first two days after surgery (p < 0.001). The Kmax (at 12 and 24 months) and CDVA (logMAR) were significantly lower in the BI-TE-CXL group than those in the TE-CXL group (p < 0.05). The corneal demarcation line under AS-OCT was visible in 81.3% of patients in the BI-TE-CXL group and 15.6% in the TE-CXL group. The depth of the demarcation line under IVCM was significantly deeper in the BI-TE-CXL group (248.3 ± 25.0 μm) than that of the TE-CXL group (136.5 ± 15.6 μm) in the central cornea (p < 0.001). The cross-linked collagen structures in the central cornea were still present after 12 months in the BI-TE-CXL group. No significant difference in sub-basal nerve density between the two groups (p > 0.05).Conclusions: Following BI-TE-CXL, CDVA was significantly improved, accompanied by deeper demarcation line depth and persistent crosslinked structures in the central corneal stroma.

[Comparative analysis of clinical and functional parameters in patients with stable stage II-III keratoconus after implantation of corneal segments and fitting of scleral rigid contact lenses]

The modern treatment strategy for keratoconus (KC) involves sequential application of medical technologies aimed at stabilizing pathological changes in the cornea and restoring visual acuity.

PURPOSE

This study compares the effect of implantation of intrastromal corneal ring segment (ICRS) and fitting of individual scleral rigid contact lenses (RCLs) on visual functions in patients with stage II-III KC after previously performed corneal collagen cross-linking.

MATERIAL AND METHODS

The Helmholtz National Medical Research Center of Eye Diseases examined and treated 34 patients (69 eyes) aged 18 to 33 years with stage II-III KC. The study included patients who had previously undergone standard corneal collagen cross-linking. Depending on the type of optical correction, the patients were divided into two groups: patients in group 1 underwent ICRS implantation using a femtosecond laser; patients in group 2 were fitted with individual scleral RCLs.

RESULTS

Improvement in clinical and functional parameters was observed in both groups. A higher clinical and functional result was achieved in group 2.

CONCLUSION

For patients with stable stage II-III KC, it is advisable to recommend fitting of individual scleral RCLs for visual rehabilitation.

Dexpanthenol/sodium hyaluronate eye drops for corneal epithelial healing following corneal cross-linking in patients with keratoconus

PURPOSE

To evaluate the effect of dexpanthenol 2%/sodium hyaluronate 0.15% eye drops on corneal epithelial healing and corneal microstructural changes following corneal cross-linking (CXL) in patients with keratoconus.

METHODS

The study included 42 eyes of 21 patients with keratoconus who underwent CXL on both eyes. One eye of each patient was instilled dexpanthenol 2%/sodium hyaluronate 0.15% eye drops (DP/SH group) and the fellow eye was instilled unpreserved sodium hyaluronate 0.15% eye drops (SH group). The epithelial healing process was assessed every day until complete reepithelialization was achieved. The in vivo confocal microscopy (IVCM) findings were also recorded.

RESULTS

The mean epithelial defect size 48.6 ± 6.7 mm2 for the DP/SH group and 48.2 ± 5.3 mm2 for the SH group. Complete reepithelialization was seen after 2.24 ± 0.44 days (range 2-4 days) in the DP/SH group and 3.43 ± 0.60 days (3 to 5 days) in the SH group. Posterior keratocyte density and endothelial cell density were similar in both groups. The mean subbasal nerve plexus density was significantly higher in the DP/SH group (postoperative 1 month: 1.13 ± 1.51, 3 months: 3.53 ± 2.55, 6 months: 7.07 ± 1.42) compared to the SH group (postoperative 1 month: 0.87 ± 1.43, 3 months: 2.89 ± 2.62, 6 months 6.33 ± 1.29). The DP/SH group revealed faster subbasal nerve regeneration and less edema compared to the SH group.

CONCLUSION

Dexpanthenol 2%/sodium hyaluronate 0.15% eye drops were effective and safe for corneal epithelial healing, and promoted faster corneal reepithelialization, nerve regeneration, and keratocyte repopulation with reduced corneal edema compared to sodium hyaluronate eye drops.

Five-year results of iontophoresis-assisted transepithelial corneal cross-linking for keratoconus

PURPOSE

To assess long-term efficacy and safety of iontophoresis-assisted transepithelial corneal cross-linking (I-CXL) for keratoconus.

PATIENTS AND METHODS

Twenty-seven eyes of 21 patients (15 M, 6F) affected by progressive keratoconus were evaluated. All subjects were treated with iontophoresis-assisted transepithelial CXL. The patients were examined at baseline and each 6 months after the CXL procedure. Only subjects who completed the follow-up of 5 years were considered in this study. The main outcome measures were uncorrected visual acuity (UCVA), corrected visual acuity (CDVA), corneal transparency and corneal parameters such as K-max, central corneal thickness (CCT) and at the thinnest point, and high-order ocular aberrations (HOAs). The ABCD system was used to determine the progression and re-progression of ectasia.

SETTING

Ophthalmology Clinic, University Hospital of Messina, Messina, Italy.

RESULTS

At 5 years, significant improvements of UCVA from 0.53 ± 0.33 logMAR to 0.4 ± 0.33 logMAR (p = 0.001) and HOAs (p = 0.01) were registered. No significant changes of CDVA (p = 0.4), K-max (p = 0.75), CCT (p = 0.5) were observed at the end of follow-up period. The ABCD system showed re-progression in 25.9% of eyes after 5 years. No adverse events such as corneal opacities and infections were reported.

CONCLUSIONS

Iontophoresis-assisted transepithelial CXL resulted to be safe and effective to stabilize progressive keratoconus in adults at a long-term follow-up.

Early findings in a prospective randomised study on three cross-linking treatment protocols: interruption of the iontophoresis treatment protocol

PURPOSE

To present the outcome of the interrupted iontophoresis-assisted treatment arm in an ongoing randomised clinical trial (NCT04427956).

METHODS

A randomised clinical study of corneal cross-linking (CXL) using continuous UV-A irradiation at a rate of 9 mW/cm2 and three different types of riboflavin and riboflavin delivery mode: (1) iso-osmolar dextran-based riboflavin (epithelium-off), (2) hypo-osmolar dextran-free riboflavin (epithelium-off) and (3) iontophoresis-assisted delivery of riboflavin (epithelium-on) for the treatment of progressive keratoconus. Inclusion criteria were an increase in the maximum keratometry value (Kmax) of 1.0 dioptre over 12 months or 0.5 dioptre over 6 months. The primary outcome in evaluating treatment efficacy was Kmax. Recently presented stratified detection limits were used post hoc to confirm the enrolment of patients with truly progressive keratoconus and in the assessment of the need for re-CXL.

RESULTS

Thirteen patients had been randomised to iontophoresis-assisted CXL when the treatment arm was interrupted; two patients dropped out. Of the remaining 11 patients, 7 were deemed as having truly progressive disease according to the more recent stratified detection limits. The disease continued to progress in three patients according to the original definition (increase in Kmax≥1 D), necessitating re-CXL with epithelium-off CXL. This progression was confirmed by post hoc analysis using the stratified detection limits for progression.

CONCLUSIONS

The iontophoresis-assisted CXL protocol failed to halt further disease progression in 27% of the patients. The failure rate increased to 38% when considering only the patients deemed to have truly progressive disease using the stratified detection limits.

Development and validation to predict visual acuity and keratometry two years after corneal crosslinking with progressive keratoconus by machine learning

Purpose

To explore and validate the utility of machine learning (ML) methods using a limited sample size to predict changes in visual acuity and keratometry 2 years following corneal crosslinking (CXL) for progressive keratoconus.

Methods

The study included all consecutive patients with progressive keratoconus who underwent CXL from July 2014 to December 2020, with a 2 year follow-up period before July 2022 to develop the model. Variables collected included patient demographics, visual acuity, spherical equivalence, and Pentacam parameters. Available case data were divided into training and testing data sets. Three ML models were evaluated based on their performance in predicting case corrected distance visual acuity (CDVA) and maximum keratometry (Kmax) changes compared to actual values, as indicated by average root mean squared error (RMSE) and R-squared (R2) values. Patients followed from July 2022 to December 2022 were included in the validation set.

Results

A total of 277 eyes from 195 patients were included in training and testing sets and 43 eyes from 35 patients were included in the validation set. The baseline CDVA (26.7%) and the ratio of steep keratometry to flat keratometry (K2/K1; 13.8%) were closely associated with case CDVA changes. The baseline ratio of Kmax to mean keratometry (Kmax/Kmean; 20.9%) was closely associated with case Kmax changes. Using these metrics, the best-performing ML model was XGBoost, which produced predicted values closest to the actual values for both CDVA and Kmax changes in testing set (R2 = 0.9993 and 0.9888) and validation set (R2 = 0.8956 and 0.8382).

Conclusion

Application of a ML approach using XGBoost, and incorporation of identifiable parameters, considerably improved variation prediction accuracy of both CDVA and Kmax 2 years after CXL for treatment of progressive keratoconus.

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.

Efficacy, Safety, and Outcomes following Accelerated and Iontophoresis Corneal Crosslinking in Progressive Keratoconus

PURPOSE

To investigate the outcomes of accelerated (A-CXL) and iontophoresis (I-CXL) corneal crosslinking in a large retrospective cohort with progressive keratoconus.

METHODS

This retrospective observational cohort study included consecutive patients treated by A-CXL (9 mW/5.4 J/cm²) or I-CXL with a minimal follow-up of 12 months. Visual acuity, manifest refraction, topography, specular microscopy, and corneal optical coherence tomography (OCT) were evaluated at baseline and at the last visit. Progression was defined as an increase in the maximum topographic keratometry (Kmax) of 1D.

RESULTS

302 eyes of 241 patients with a mean age of 25.2 ± 7.5 years were included from 2012 to 2019: 231 and 71 eyes in the A-CXL and I-CXL groups, respectively. The mean follow-up was 27.2 ± 13.2 months (maximum: 85.7 months). Preoperatively, the mean Kmax was 51.8 ± 4.0D, with no differences between groups. Mean topographic measurements and spherical equivalent remained stable during the follow-up. At the last visit, CXL failure was reported in 60 eyes (19.9%): 40 (14.7%) versus 20 (28.2%) in A-CXL versus I-CXL, respectively, p = 0.005. The likelihood of progression after CXL was significantly higher following I-CXL: RR = 1.62, CI95 = [1.02 to 2.59], p = 0.04. Demarcation line presence at 1 month was positively correlated with higher efficacy of CXL, p = 0.03. No endothelial damage was reported, especially in 51 thin corneas (range = 342-399 µm).

CONCLUSIONS

A-CXL seems more effective than I-CXL in stabilizing keratoconus; this is to be taken into account when a therapeutic indication is posed according to the aggressiveness of the keratoconus.

Transepithelial Iontophoresis-Assisted Cross Linking for Progressive Keratoconus: Up to 7 Years of Follow Up

Purpose: To report long-term clinical results of transepithelial cross-linking with iontophoresis (I-CXL) for progressive keratoconus (KC). Methods: Nineteen eyes of 19 patients treated with I-CXL for progressive keratoconus were included in this prospective clinical study. Preoperatively and in all available follow ups (6, 12, 24, 36, 48, 60, 72 and 84 months), the following parameters were measured. Corrected distance visual acuity (CDVA), spherical equivalent and cylinder refraction, corneal topography and aberrometry (Costruzione Strumenti Oftalmici (C.S.O.), Florence, Italy), Scheimpflug tomography (OCULUS Optikgeräte GmbH; Wetzlar, Germany). Definition of progression after I-CXL was 2/3 of the following criteria: increase of “A” value, increase of “B” value, decrease of minimal thickness evaluated with the ABCD progression display above 95% confidence interval for post-CXL population when compared to the scan 12 months post-op. Results: The mean follow-up time of included patients was 63 months (range 12 to 84 months, 5 patients reached 84 months). The general linear model showed no significant change over time in CDVA, Maximum Keratometry, Thinnest point, and A, B, C values of the Belin Progression Display (p > 0.05). Conversely, comatic and high order aberrations decreased significantly over time (both p =< 0.001). Five cases (26.31%) showed significant progression after a mean of 55 months (range 36–72) of follow up. Conclusion: Our study shows the ability of I-CXL to slow down KC progression in the majority of included patients, improving high order and comatic aberrations. A 26% progression rate was reported.

[Ocular iontophoresis]

Iontophoresis in medicine is a combined pharmacological and physical method of treatment that unites the therapeutic effect of an electric current with the pharmacological effect of medicinal substances administered at the same time via an electric current. The article describes the physical basis of the therapeutic effect of direct electric current on biological tissues, and highlights the physical and chemical mechanisms of target administration of pharmaceutical substances into the human body through intact skin or mucous membrane by means of direct electric current. In addition, it presents the results of international as well as Russian domestic scientific studies on the clinical effectiveness of iontophoresis in ophthalmology.

Two-stage treatment of ametropia in patients with keratoconus and cataracts

Keratoconus (KC) is a progressive degenerative corneal disease, leads to the aberration of biomechanical and optical properties and thinning of the cornea, causes astigmatism and decreases visual acuity.Materials and methods. 33 patients (35 eyes) with stages II–III of non-progressive keratoconus and concomitant cataracts of various stages of maturity were operated on. The average age of the patients was 46.5 ± 2.7 (41–63) years old. The operations were performed according to our proposed two-stage method of treating ametropia in patients with KC and cataracts (Patent of the Russian Federation No. 2748634 of 28.05.2021). The first stage was the implantation of FERRARA intrastromal corneal ring segments (ICRS) with thickness from 150 to 350 μm. To correct residual refractive error in 5–7 months after stage 1, patients underwent stage 2: cloudy lens was removed and replaced with toric posterior chamber intraocular lens (TIOL) – AcrySof IQ Toric (Alcon, USA), T-fl ex Toric RayOne (Rayner, UK).Results and discussion. After stage 1 of the operation (ICRS implantation), the uncorrected visual acuity (NCVA) was 0.2 ± 0.03, the best corrected visual acuity (BCVA) was 0.4 ± 0.02. In 1 month after stage 2 (phacoemulsifi cation + TIOL) NCVA was 0.64 ± 0.11 and BCVA was 0.74 ± 0.12. During the entire follow-up period after the surgery visual functions, refraction, and rotational stability of TIOL were stable.Conclusions. Conducting a two-stage surgical intervention in patients with keratoconus and cataracts allows to stop the progression of the disease and effectively correct the ametropia concomitant with keratoconus.

Preliminary Characterization of Predictive Factors of the Visual Change after Epi-On and Epi-Off Corneal Collagen Crosslinking Techniques

Purpose

To investigate the potential predictive factors of the visual change achieved with accelerated epi-on and epi-off corneal collagen crosslinking (CXL) in keratoconus.

Methods

This retrospective comparative study analyzed 67 eyes treated with an accelerated epithelium-on (epi-on group) and epithelium-off (epi-off group) CXL. The clinical outcomes were evaluated and compared during a 1-year follow-up. Likewise, the relationship of the change achieved with both CXL techniques in the corrected distance visual acuity (CDVA) with different preoperative data was investigated.

Results

The mean CDVA change at 3 months postoperatively was −0.04 ± 0.19 and −0.07 ± 0.25 in the epi-on and epi-off groups, respectively (p = 0.809). In the epi-on group, this change was significantly correlated with the preoperative apical (r = −0.375, p = 0.045) and central corneal thickness (r = −0.402, p = 0.031). In the epi-off group, the CDVA change was significantly correlated with not only the preoperative apical (r = 0.402, p = 0.028) and central corneal thickness (r = 0.367, p = 0.046) but also with some topometric and aberrometric indices (r ≤ −0.374, p ≤ 0.042). Furthermore, the change in CDVA in the epi-on group could be predicted from age, preoperative refractive astigmatism J₄₅ component, anterior corneal asphericity, and posterior corneal high order aberration root mean square (p = 0.002, R² = 0.503). In the epi-off group, the CDVA change could be predicted from the preoperative minimum corneal thickness and magnitude of the vertical anterior corneal primary coma component (p = 0.001, R² = 0.446).

Conclusions

Clearly, different predictive factors of the visual change induced with the accelerated epi-on and epi-off CXL techniques are present, suggesting a different mechanism of action for stiffening the cornea and inducing changes in this structure.

Transepithelial Diluted Alcohol and Iontophoresis-Assisted Corneal Crosslinking for Progressive Keratoconus in Adults: 4-Year Clinical Results

PURPOSE

The aim of this study was to compare the 4-year clinical outcomes of transepithelial diluted alcohol and iontophoresis-assisted corneal crosslinking (DAI-CXL) and standard corneal crosslinking (S-CXL) in adults with progressive keratoconus.

METHODS

This retrospective study included 36 eyes of 36 keratoconic patients who underwent DAI-CXL (n = 18) or S-CXL (n = 18). Best spectacle-corrected visual acuity (BSCVA) and corneal topography parameters were analyzed at baseline and at 1, 2, 3, and 4 years of follow-up. Corneal demarcation line depth (DLD) at 1 month was measured, and the relation of DLD with corneal thickness (DL%) was assessed.

RESULTS

BSCVA improved significantly only in S-CXL (P = 0.01). A significant decrease in maximum keratometry and mean keratometry occurred at 4 years in both groups (all P < 0.05), and these changes were similar in both groups (all P > 0.05). There was a significant reduction in the thinnest corneal thickness in S-CXL (P = 0.01); however, the mean thinnest corneal thickness in DAI-CXL remained stable (P = 0.094). Higher-order aberrations and coma aberration decreased significantly in both groups at 4 years (all P < 0.05), with a higher decrease in S-CXL (all P < 0.05). Spherical aberration showed a significant reduction only in S-CXL (P = 0.005). In contrast to the similar mean DLD in both groups, DL% in DAI-CXL was significantly greater than that in S-CXL (P = 0.032). There were no correlations between the improvement in BSCVA, maximum keratometry, mean keratometry, higher-order aberrations, and the mean DLD and DL% (all P > 0.05).

CONCLUSIONS

DAI-CXL was as effective as S-CXL in arresting the progression of keratoconus and showed similar clinical results to S-CXL at the 4-year follow-up.

A New Surgical Technique to Deliver Riboflavin Beneath Corneal Epithelium: The Corneal Cross-Linking Epi-Pocket

PURPOSE

To describe a new technique to deliver riboflavin into the corneal stroma during Corneal Cross-Linking (CXL) without the removal of corneal epithelium.

METHODS

Keratoconus patients underwent CXL for progressive keratoconus. Riboflavin was delivered by manually creating an epithelial pocket (CXL Epi-Pocket). Verbal rating scale was recorded postoperatively. Best-corrected visual acuity, keratometric indices, corneal thickness and corneal densitometry were recorded at baseline and at 12-month follow-up.

RESULTS

Eighteen eyes of 18 patients were included in the study. At a 12-month follow-up, best-corrected visual acuity, K1, K2 and densitometry values were stable. Maximum keratometry (Kmax) reduced from 55.31 ± 6.21 (SD) to 52.34d ± 4.12d (SD) (P value = 0.032). the thinnest point went from 441 ± 21.18 (SD) to 425.4 ± 19.02 (SD) um (P value = 0.041). The verbal rating scale at 1, 2 and 3 days postoperatively were 1.76 ± 0.19 (SD), 1.02 ± 0.51 (SD) and 0.28 ± 0.14 (SD).

CONCLUSIONS

CXL Epi-Pocket is able to deliver riboflavin to halt the progression of keratoconus at a 12-month follow-up.

Transepithelial Versus Epithelium-Off Corneal Crosslinking for Progressive Keratoconus: Findings From a Cochrane Systematic Review

PURPOSE

The purpose of this study was to summarize key findings from a systematic review of the effectiveness and safety of transepithelial corneal crosslinking (CXL) compared with epithelium-off CXL for progressive keratoconus.

DESIGN

Cochrane systematic review.

METHODS

We included in our review only randomized controlled trials (RCTs) in which transepithelial and epithelium-off CXL had been compared among participants with progressive keratoconus. The primary outcome was keratoconus stabilization based on post-operative maximum keratometry (Kmax). We adhered to Cochrane methods for trial selection, data extraction, risk of bias evaluation, and data synthesis.

RESULTS

Thirteen RCTs with 567 participants (661 eyes) were included; 11 studies compared non-iontophoresis-assisted transepithelial with epithelium-off CXL. Keratoconus stabilization was described as an outcome in 2 studies. The estimated difference in Kmax means (ie, the "mean difference," MD) from meta-analysis of 177 eyes in 5 RCTs indicated that there were no differences between intervention groups in Kmax at 12 months or later (MD: 0.99 diopter [D]; 95% confidence interval: -0.11 to 2.09). Meta-analysis of keratometry and visual acuity outcomes at 12 months or longer after surgery from 2 studies that had compared transepithelial CXL using iontophoresis provided no conclusive evidence of an advantage over epithelium-off CXL.

CONCLUSIONS

Lack of precision due to small sample sizes, indeterminate risk of bias due to inadequate reporting, and inconsistency in how outcomes were measured and reported among studies make it difficult to state with confidence whether transepithelial CXL confers an advantage over epithelium-off CXL for patients with progressive keratoconus with respect to stabilization of keratoconus, visual acuity, or patient-reported outcomes based on available data.

Efficacy and Safety of Contact Lens-Assisted Corneal Crosslinking in the Treatment of Keratoconus With Thin Corneas

OBJECTIVE

To evaluate the safety and efficacy of contact lens-assisted crosslinking (CA-CXL) in progressive keratoconus with thin corneas (350-400 µm).

METHODS

Forty eyes (30 patients) underwent epithelium-off CA-CXL with iso-osmolar riboflavin and ultraviolet-A irradiation for 30 min (fluence, 3 mW/cm2). A non-ultra-violet-absorbing soft contact lens (sCL) soaked in riboflavin was applied over the cornea during irradiation. Demarcation line (DL) depth was measured 1 month postoperatively. Endothelial cell count (ECC) was measured preoperatively and 3 months postoperatively. Distance uncorrected visual acuity (UDVA) and best spectacle-corrected visual acuity (BDVA), and maximum keratometric values (K max) were evaluated preoperatively and 9 months postoperatively.

RESULTS

The sCL added a mean thickness of 100.05±1.23 µm. The mean ECC was 2,982±165 cell/mm2 preoperatively and 2,955±125 cell/mm2 postoperatively (endothelial cell loss, 0.9%, P=0.21). The mean DL depth was 204.8±20.2 µm. There was significant improvement in UDVA (P<0.001) and BDVA (P=0.011) with a stable K max (P=0.06).

CONCLUSION

Contact lens-assisted crosslinking was safe and effective, with endothelial loss less than 1% after 3 months and stable corneal tomography over 9 months, with improved visual acuity. Demarcation line depth was found to be shallower than conventional CXL. Therefore, the long-term efficacy of CA-CXL requires further study.

CLINICAL TRIAL REGISTRY NUMBER

NCT04504578 Clinical trials.gov.

Corneal collagen cross-linking epithelium-on vs. epithelium-off: a systematic review and meta-analysis

BACKGROUND

The purpose of the study was to determine the advantages and disadvantages of epi-on corneal cross-linking (CXL) techniques compared with standard epi-off CXL.

METHODS

We searched MEDLINE and EMBASE for randomized controlled trials (RCTs) and non-randomized studies of interventions (NRSIs) and we evaluated the selected papers according to the Cochrane risk of bias tool. We considered, as primary outcomes, average Kmax flattening, changes in uncorrected and corrected distance visual acuity (UDVA and CDVA); as secondary outcomes, we considered changes in pachymetry values and endothelial cell density (ECD). We also investigated adverse events related to the treatments and treatment failure. Meta-analysis was conducted with a fixed or random-effects model using weighted mean difference (MD) with 95% confidence interval (CI) as the effect size.

RESULTS

A total of 15 studies were included and among these 15 trials, 9 were RCTs and 6 were NRSIs, but only 4 studies showed no high risk of bias and were included in this meta-analysis. Our analysis revealed significant postoperative differences in CDVA (MD = 0.07; 95% CI 0.04 to 0.10; P < 0.001), and no significative differences in UDVA, Kmax, central corneal thickness (CCT) and ECD (P > 0.05). Epi-on CXL protocol was found to be significantly less prompt to have risks of delay in epithelial healing (P = 0.035) and persistent stromal haze (P = 0.026).

CONCLUSION

Epi-on CXL is as effective as epi-off CXL. Except for a higher significant improvement in CDVA with current epi-on protocols, our meta-analysis demonstrates that epi-on and epi-off CXL have comparable effects on visual, topographic, pachymetric, and endothelial parameters. Epi-on CXL has clinical advantages in terms of comfort and avoidance of complications as it reduces the risk of developing delay in epithelial healing and persistent stromal haze.

Transepithelial Corneal Crosslinking Using a Novel Ultraviolet Light-Emitting Contact Lens Device: A Pilot Study

Purpose

To evaluate the feasibility of a novel, on-eye UVA light-emitting contact lens device driven by fiber optics for the corneal crosslinking (CXL) of patients with keratoconus.

Methods

In nine corneal transplant candidates with advanced keratoconus a scleral contact lens reservoir containing 0.007% benzalkonium chloride preserved with 0.25% riboflavin-monophosphate was placed on the eye for 30 minutes. The reservoir lens was removed and replaced with the CXLens UVA light-emitting contact lens. A 375-nm UVA light at 4 mW/cm² intensity was delivered for 30 minutes for a dose of 7.2 J/cm². A one-sided paired t-test was used to evaluate mean differences in maximum keratometry, thinnest corneal thickness, and endothelial cell density between screening and 6 months after CXL. A two-sided paired t-test was used to evaluate differences in best-corrected distance visual acuity between screening and 6 months after CXL.

Results

All patients received the treatment as per protocol and adhered to follow-up testing. At 6 months after CXL, treated eyes had an average −1.0 ± 1.6 diopters decrease in the maximum keratometry (P = 0.049), a nonsignificant 2.3 ± 7.5 letter improvement in best-corrected distance visual acuity (P = 0.19), a nonsignificant −17 ± 14 µm decrease in thinnest corneal thickness (P < 0.01), and a nonsignificant −86 ± 266 cells/mm² decrease in endothelial cell density (P = 0.20).

Conclusions

Our pilot study demonstrated the feasibility of the novel CXL device for the treatment of keratoconus and indicates the device is ready for larger scale studies with longer follow-up periods.

Translational Relevance

The novel CXLens on-eye UVA light-emitting contact lens device offers the potential for efficient, high-throughput transepithelial corneal CXL.

A novel Q-value-based nomogram for single intracorneal ring segment implantation versus standard manufacturer's nomogram combined with accelerated cross-linking for treatment of keratoconus: a randomized controlled trial

Purpose

To compare the efficacy of implanting a single Keraring segment according to a novel Q‐value‐based nomogram (QN) to that of segment implantation according to the manufacturer's standard nomogram (SN), for keratoconus treatment.

Methods

This was a prospective, randomized controlled trial of 104 patients (104 eyes) with Amsler‐Krumeich grade 1 or 2 keratoconus, and type 1 or 2 cone asymmetry determined according to manufacturer's classification. They were randomly distributed into two groups: group A patients (n = 52) underwent Keraring implantation according to the SN, and group B patients (n = 52) underwent implantation of a single (210° arc‐length) Keraring segment according to the QN. Both treatments were combined with accelerated transepithelial cross‐linking, and follow‐up was 6 months. Main outcome measures were preoperative and postoperative visual acuity, subjective refraction and corneal topography.

Results

At postoperative month 6, group B exhibited statistically significantly higher values of mean uncorrected distance visual acuity (UDVA), sphere, K2, K‐average, K‐max and Q‐anterior (p = 0.02, 0.01, 0.002, 0.001, 0.0001 and 0.03, respectively) compared to that of group A. However, group A exhibited better refractive cylindrical improvements (p = 0.04). In group A, we documented spontaneous extrusion of one Keraring segment.

Conclusion

Single 210° arc‐length segment implantation using our objective QN was more efficacious for keratoconus treatment than using the subjective SN. The nomograms were comparable when the Q‐anterior value was >−1.00; however, the QN was superior to the SN when the Q‐anterior value was ≤−1.00. The QN yielded greater postoperative UDVA and smoother corneal remodelling than did the SN for treatment of grade 1 and 2 keratoconic eyes.

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.

Transepithelial versus epithelium-off corneal crosslinking for progressive keratoconus

BACKGROUND

Keratoconus is the most common corneal dystrophy. It can cause loss of uncorrected and best-corrected visual acuity through ectasia (thinning) of the central or paracentral cornea, irregular corneal scarring, or corneal perforation. Disease onset usually occurs in the second to fourth decade of life, periods of peak educational attainment or career development. The condition is lifelong and sight-threatening. Corneal collagen crosslinking (CXL) using ultraviolet A (UVA) light applied to the cornea is the only treatment that has been shown to slow progression of disease. The original, more widely known technique involves application of UVA light to de-epithelialized cornea, to which a photosensitizer (riboflavin) is added topically throughout the irradiation process. Transepithelial CXL is a recently advocated alternative to the standard CXL procedure, in that the epithelium is kept intact during CXL. Retention of the epithelium offers the putative advantages of faster healing, less patient discomfort, faster visual rehabilitation, and less risk of corneal haze.

OBJECTIVES

To assess the short- and long-term effectiveness and safety of transepithelial CXL compared with epithelium-off CXL for progressive keratoconus.

SEARCH METHODS

To identify potentially eligible studies, we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2020, Issue 1); Ovid MEDLINE; Embase.com; PubMed; Latin American and Caribbean Health Sciences Literature database (LILACS); ClinicalTrials.gov; and World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not impose any date or language restrictions. We last searched the electronic databases on 15 January 2020.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) in which transepithelial CXL had been compared with epithelium-off CXL in participants with progressive keratoconus.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology.

MAIN RESULTS

We included 13 studies with 723 eyes of 578 participants enrolled; 13 to 119 participants were enrolled per study. Seven studies were conducted in Europe, three in the Middle East, and one each in India, Russia, and Turkey. Seven studies were parallel-group RCTs, one study was an RCT with a paired-eyes design, and five studies were RCTs in which both eyes of some or all participants were assigned to the same intervention. Eleven studies compared transepithelial CXL with epithelium-off CXL in participants with progressive keratoconus. There was no evidence of an important difference between intervention groups in maximum keratometry (denoted 'maximum K' or 'Kmax'; also known as steepest keratometry measurement) at 12 months or later (mean difference (MD) 0.99 diopters (D), 95% CI -0.11 to 2.09; 5 studies; 177 eyes; I² = 41%; very low certainty evidence). Few studies described other outcomes of interest. The evidence is very uncertain that epithelium-off CXL may have a small (data from two studies were not pooled due to considerable heterogeneity (I² = 92%)) or no effect on stabilization of progressive keratoconus compared with transepithelial CXL; comparison of the estimated proportions of eyes with decreases or increases of 2 or more diopters in maximum K at 12 months from one study with 61 eyes was RR 0.32 (95% CI 0.09 to 1.12) and RR (non-event) 0.86 (95% CI 0.74 to 1.00), respectively (very low certainty). We did not estimate an overall effect on corrected-distance visual acuity (CDVA) because substantial heterogeneity was detected (I² = 70%). No study evaluated CDVA gain or loss of 10 or more letters on a logarithm of the minimum angle of resolution (logMAR) chart. Transepithelial CXL may result in little to no difference in CDVA at 12 months or beyond. Four studies reported that either no adverse events or no serious adverse events had been observed. Another study noted no change in endothelial cell count after either procedure. Moderate certainty evidence from 4 studies (221 eyes) found that epithelium-off CXL resulted in a slight increase in corneal haze or scarring when compared to transepithelial CXL (RR (non-event) 1.07, 95% CI 1.01 to 1.14). Three studies, one of which had three arms, compared outcomes among participants assigned to transepithelial CXL using iontophoresis versus those assigned to epithelium-off CXL. No conclusive evidence was found for either keratometry or visual acuity outcomes at 12 months or later after surgery. Low certainty evidence suggests that transepithelial CXL using iontophoresis results in no difference in logMAR CDVA (MD 0.00 letter, 95% CI -0.04 to 0.04; 2 studies; 51 eyes). Only one study examined gain or loss of 10 or more logMAR letters. In terms of adverse events, one case of subepithelial infiltrate was reported after transepithelial CXL with iontophoresis, whereas two cases of faint corneal scars and four cases of permanent haze were observed after epithelium-off CXL. Vogt's striae were found in one eye after each intervention. The certainty of the evidence was low or very low for the outcomes in this comparison due to imprecision of estimates for all outcomes and risk of bias in the studies from which data have been reported.

AUTHORS' CONCLUSIONS

Because of lack of precision, frequent indeterminate risk of bias due to inadequate reporting, and inconsistency in outcomes measured and reported among studies in this systematic review, it remains unknown whether transepithelial CXL, or any other approach, may confer an advantage over epithelium-off CXL for patients with progressive keratoconus with respect to further progression of keratoconus, visual acuity outcomes, and patient-reported outcomes (PROs). Arrest of the progression of keratoconus should be the primary outcome of interest in future trials of CXL, particularly when comparing the effectiveness of different approaches to CXL. Furthermore, methods of assessing and defining progressive keratoconus should be standardized. Trials with longer follow-up are required in order to assure that outcomes are measured after corneal wound-healing and stabilization of keratoconus. In addition, perioperative, intraoperative, and postoperative care should be standardized to permit meaningful comparisons of CXL methods. Methods to increase penetration of riboflavin through intact epithelium as well as delivery of increased dose of UVA may be needed to improve outcomes. PROs should be measured and reported. The visual significance of adverse outcomes, such as corneal haze, should be assessed and correlated with other outcomes, including PROs.

Repeated Corneal Cross-linking (CXL) in Keratoconus Progression After Primary Treatment: Updated Perspectives

Background: Corneal collagen cross-linking (CXL) has recently become the preferred practice in the management of progressive keratoconus and other corneal ectasias as it has been proven to be successful in halting progression of the disease with an excellent safety and efficacy profile. However, there is a known variation regarding the response to CXL, depending on several parameters related either to the treatment protocol, patient characteristics, or corneal biomechanical properties. In fact, continuing progression of keratoconus has been noted in some cases despite prior treatment with CXL.Methods: The aim of this article is to provide an updated review of all published results on repeated-CXL, focusing on the indications and the efficacy of repeated treatment and highlighting possible explanations of progression after primary CXL. Conclusions: The diagnosis of primary treatment failure should always be made based on specific clinical and imaging criteria, with repeated and consistent measurements, in order to exclude pseudoprogression. In cases of confirmed progression, physicians need to decide whether repeating CXL could be an option to enhance corneal stability without any complications.

Comparison of Different Methods of Corneal Collagen Crosslinking: A Systematic Review

Purpose: To review the scientific literature on the comparison of the efficacy of different corneal collagen crosslinking (CXL) protocols for the treatment of progressive keratoconus.Methods: Systematic review of randomized clinical trials (RCTs) on CXL outcomes. A search was carried out using the Cochrane Library, PubMed, EMBASE, Web of Science, Ovid MEDLINE, and Scopus databases. Internal validity was analyzed by applying the filter CASPe (Critical Appraisal Skills Program Spain).Results: The search yielded 1151 articles, and among these, 14 articles met the inclusion and exclusion criteria defined. Conventional (S) crosslinking (CXL) provided better topographic outcomes than transepithelial (TE) CXL, and S-CXL had a better therapeutic effect of corneal flattening than accelerated (A) CXL. The corneal thinning after CXL was lower with hypotonic riboflavin than with riboflavin-dextran. While one study demonstrated a better therapeutic effect of corneal flattening with S-CXL than with A-CXL, another study showed similar results between both techniques. No correlation was found between the depth of the demarcation line and topographic changes, which was not a direct measure of treatment effectiveness. Quality analysis of the literature reviewed yielded a mean score of 8.64, indicating that the RCTs evaluated had an overall acceptable quality.Conclusions: Good-quality RCTs comparing CXL techniques have been conducted, and most of them suggest that epi-off CXL can be considered the standard treatment for progressive keratoconus. TE-CXL and iontophoresis-assisted CXL are mainly indicated in patients with a risk of corneal scarring and patients with pain intolerance, respectively.

New perspectives in keratoconus treatment: an update on iontophoresis-assisted corneal collagen crosslinking

Keratoconus is a bilateral, asymmetric and progressive corneal disease. It usually results in apical thinning and steepening with corneal deformation and impaired vision. Since the early 1990 s, corneal collagen crosslinking (CXL) has remained the primary treatment to stabilize the progression of the disease. Iontophoresis-assisted CXL (I-CXL) has been proposed as a non-invasive alternative to standard epithelium-off technique, showing promising results. In this article, we review up to date literature to provide state of art knowledge and future perspectives of I-CXL.

Comparison of Standard and Transepithelial Corneal Cross-Linking for the Treatment of Keratoconus: A Meta-analysis

Purpose

To compare the clinical results of standard corneal cross-linking (SCXL) with transepithelial corneal cross-linking (TECXL) in progressive keratoconus using a meta-analysis.

Methods

PubMed, EMBASE, and Cochrane Central Register of Controlled Trials were searched up to June 2020 to identify relevant studies. The PRISMA guidelines were followed. Primary outcomes were change in uncorrected distance visual acuity and maximum keratometry (K_max) after CXL. Secondary outcomes were change in corrected distance visual acuity, mean refractive spherical equivalent (MRSE), spherical and cylindrical error, endothelial cells density (ECD), and central corneal thickness (CCT).

Results

Sixteen studies with a total of 690 eyes (SCXL: 332 eyes; TECXL: 358 eyes) were included. At the last follow-up, SCXL provided a greater decrease in maximum keratometry (K_max) than TECXL (weighted mean difference (WMD) −1.12; 95% confidence interval (CI) −1.96, −0.29). For the other outcomes, there were no statistically significant differences.

Conclusions

Except for a greater decrease in Kmax with SCXL group, both groups have a comparable effect on visual, pachymetric, and endothelial parameters at 24 months after surgery. Larger studies with a longer follow-up time are necessary to determine whether these techniques are comparable in the long term.

Keratoconus: cross-linking the window of the eye

Keratoconus is a condition in which the cornea progressively thins and weakens, leading to severe, irregular astigmatism and a significant reduction in quality of life. Although the precise cause of keratoconus is still not known, biochemical and structural studies indicate that overactive enzymes within the cornea break down the constituent proteins (collagen and proteoglycans) and cause the tissue to weaken. As the disease develops, collagen fibres slip past each other and are redistributed across the cornea, causing it to change shape. In recent years, it was discovered that the photochemical induction of cross-links within the corneal extracellular matrix, through the use of riboflavin and ultraviolet (UVA) light, could increase the strength and enzymatic resistance of the tissue and thereby halt keratoconus progression. Worldwide acceptance and use of riboflavin/UVA corneal cross-linking therapy for halting keratoconus progression has increased rapidly, in accordance with the growing body of evidence supporting its long-term effectiveness. This review focusses on the inception of riboflavin/UVA corneal cross-linking therapy for keratoconus, its clinical effectiveness and the latest scientific advances aimed at reducing patient treatment time, improving patient comfort and increasing patient eligibility for treatment.

Plain language summary

Review of current treatments using cross-linking to halt the progress of keratoconus Keratoconus is a disease in which the curved cornea, the transparent window at the front of the eye, weakens, bulges forward into a cone-shape and becomes thinner. This change of curvature means that light is not focussed onto the retina correctly and vision is progressively impaired. Traditionally, the effects of early keratoconus were alleviated by using glasses, specialist contact lenses, rings inserted into the cornea and in severe cases, by performing a corneal transplant. However, it was discovered that by inducing chemical bonds called cross-links within the cornea, the tissue could be strengthened and further thinning and shape changes prevented. The standard cross-linking procedure takes over an hour to perform and involves the removal of the cells at the front of the cornea, followed by the application of Vitamin B2 eye drops and low energy ultraviolet light (UVA) to create new cross-links within the tissue. Clinical trials have shown this standard procedure to be safe and effective at halting keratoconus progression. However, there are many treatment modifications currently under investigation that aim to reduce patient treatment time and increase comfort, such as accelerated cross-linking procedures and protocols that do not require removal of the surface cells. This review describes the different techniques being developed to carry out corneal cross-linking efficiently and painlessly, to halt keratoconus progression and avoid the need for expensive surgery.

Transepithelial versus Epithelium-off Corneal Collagen Cross-linking for Corneal Ectasia: A Systematic Review and Meta-analysis

TOPIC

To evaluate the safety and efficacy of transepithelial corneal cross-linking in comparison with the established epithelium-off technique for corneal ectasia.

CLINICAL RELEVANCE

Considerable debate exists regarding whether transepithelial and epithelium-off cross-linking are comparable in their safety and efficacy.

METHODS

We searched 16 electronic databases, including Medline, Embase, Web of Science, and the grey literature, current to July 8, 2020, for randomized controlled trials comparing transepithelial and epithelium-off cross-linking for corneal ectasia. We excluded studies evaluating cross-linking for nonectatic indications, as well as non-randomized controlled trials. Our primary outcome was the change in maximal keratometry (K_max) at 12 months after cross-linking, and we considered additional topographic, visual, and safety outcomes. We summarized our analyses by calculating weighted mean differences (MDs) with associated 95% confidence intervals (CIs) for continuous outcomes and relative risks (RRs) with corresponding 95% CIs for dichotomous outcomes. We conducted trial sequential analysis to determine whether the required information size was met for each outcome. The quality of individual trials was evaluated using the Cochrane Collaboration's risk of bias assessment tool, and the evidence was assessed at an outcome level using the Grading of Recommendations Assessment, Development, and Evaluation methodology.

RESULTS

Twelve studies totaling 966 eyes were eligible. A significant difference was found between transepithelial and epithelium-off cross-linking groups in the change in K_max at 12 months (MD, 0.75; 95% CI, 0.23-1.28; P = 0.004; primary outcome) and at longest follow-up (MD, 1.20; 95% CI, 0.62-1.77; P < 0.001; secondary outcome) after treatment. No significant difference was found between the 2 groups when examining uncorrected distance visual acuity (MD, 0.04; 95% CI, -0.06 to 0.14; P = 0.386) or corrected distance visual acuity (MD, 0.01; 95% CI, -0.06 to 0.09; P = 0.732). Transepithelial cross-linking was associated with significantly fewer complications than the epithelium-off approach (RR, 0.22; 95% CI, 0.06-0.79; P = 0.020), although it was associated with an increased rate of disease progression at 12 months after treatment (RR, 4.49; 95% CI, 1.24-16.25; P = 0.022). The required information size was met for our primary outcome and trial sequential analysis supported the conventional meta-analysis. The quality of evidence was rated as moderate using the Grading of Recommendations Assessment, Development, and Evaluation methodology.

DISCUSSION

The efficacy of transepithelial cross-linking remains inferior to the epithelium-off approach, although it is significantly safer.

Besifloxacin liposomes with positively charged additives for an improved topical ocular delivery

Topical ophthalmic antibiotics show low efficacy due to the well-known physiological defense mechanisms of the eye, which prevents the penetration of exogenous substances. Here, we aimed to incorporate besifloxacin into liposomes containing amines as positively charged additives and to evaluate the influence of this charge on drug delivery in two situations: (i) iontophoretic and (ii) passive treatments. Hypothesis are (i) charge might enhance the electromigration component upon current application improving penetration efficiency for a burst drug delivery, and (ii) positive charge might prolong formulation residence time, hence drug penetration. Liposomes elaborated with phosphatidylcholine (LP PC) or phosphatidylcholine and spermine (LP PC: SPM) were stable under storage at 6 ºC for 30 days, showed mucoadhesive characteristics, and were non-irritant, according to HET-CAM tests. Electron paramagnetic resonance spectroscopy measurements showed that neither the drug nor spermine incorporations produced evident alterations in the fluidity of the liposome's membranes, which retained their structural stability even under iontophoretic conditions. Mean diameter and zeta potential were 177.2 ± 2.7 nm and − 5.7 ± 0.3 mV, respectively, for LP PC; and 175.4 ± 1.9 nm and + 19.5 ± 1.0 mV, respectively, for LP PC:SPM. The minimal inhibitory concentration (MIC) and the minimal bactericide concentration (MBC) of the liposomes for P. aeruginosa showed values lower than the commercial formulation (Besivance). Nevertheless, both formulations presented a similar increase in permeability upon the electric current application. Hence, liposome charge incorporation did not prove to be additionally advantageous for iontophoretic therapy. Passive drug penetration was evaluated through a novel in vitro ocular model that simulates the lacrimal flow and challenges the formulation resistance in the passive delivery situation. As expected, LP PC: SPM showed higher permeation than the control (Besivance). In conclusion, besifloxacin incorporation into positively charged liposomes improved passive topical delivery and can be a good strategy to improve topical ophthalmic treatments.

[Intraocular correction of ametropia in patients with keratoconus]

This review was conducted due to the growing number of patients with keratoconus requiring cataract surgery and the complexity of surgical planning. The article reviews preoperative planning, intraoperative options, and postoperative management, which can help obtain high functional results. Treatment of cataracts in keratoconic eyes requires a multifaceted approach. In some cases, in the preoperative period, interventions such as crosslinking and implantation of intrastromal segments or corneal ring may be required to ensure stable keratometry values for accurate intraocular lens (IOL) calculations. The use of stabilizing procedures prior to optical biometrics can assist in preoperative lens selection and provide predictable surgical outcomes. To achieve targeted refraction and reduce unwanted optical effects, it is necessary to take a critical approach when choosing the type of lens (toric, monofocal). This is due to the appearance of aberrations of different order after preliminary surgical interventions on the cornea. The intraoperative decision plays important role in choosing the position of the corneal incisions, how to use sutures for wound adaptation, choosing scleral approaches to minimize possible postoperative complications. In the postoperative period, the degree of irregular astigmatism and the need for rigid gas-permeable or scleral lenses should be assessed.

Transepithelial corneal cross-linking assisted by two continuous cycles of iontophoresis for progressive keratoconus in adults: retrospective 5-year analysis

PURPOSE

The aim of this study is to compare the long-term effects of transepithelial corneal crosslinking with two continuous cycles of iontophoresis (EI-CXL) and conventional corneal crosslinking (C-CXL) in adults with progressive keratoconus.

METHODS

A retrospective analysis was conducted in adults who underwent C-CXL or EI-CXL between 2013 and 2015. Visual acuity, corneal tomography, anterior segment optical coherence tomography, in vivo corneal confocal microscopy (IVCM), and endothelial cell count (ECC) were performed preoperatively and 5 years postoperatively.

RESULTS

Sixty-eight patients with a mean age of (24.3 ± 3.8) years were included, 34 for each group. After CXL, UCVA or BCVA remained stable, while the spherical diopter, cylinder diopter, spherical equivalent, and K_max significantly decreased at 1, 2, and 3 years in both groups than baseline (P < 0.05). No significant differences were found in any refractive or tomographic parameters as well as the minimal corneal thickness between groups during follow-up. At 5 years, K_max was slightly higher in EI-CXL group (58.16 ± 6.28) than that of C-CXL group (57.46 ± 4.98). At 3 and 5 years, the minimal corneal thickness in C-CXL group was still significantly lower than baseline (P < 0.05). IVCM demonstrated the demarcation zone at a mean depth of (302.0 ± 41.7) μm after C-CXL, and at (251.2 ± 28.1) μm after EI-CXL (P < 0.001). Keratocyte repopulation was detectable at all follow-up timepoint in both groups. Postoperative complications including progression were recorded in 6 patients (11.7%) after C-CXL and 3 patients (8.8%) after EI-CXL. ECC remained stable in both groups.

CONCLUSION

EI-CXL showed approximate efficacy with C-CXL in stabilizing progressive keratoconus in adults. EI-CXL has the potential to be a preferable transepithelial protocol.

Biomedical applications of electrical stimulation

This review provides a comprehensive overview on the biomedical applications of electrical stimulation (EStim). EStim has a wide range of direct effects on both biomolecules and cells. These effects have been exploited to facilitate proliferation and functional development of engineered tissue constructs for regenerative medicine applications. They have also been tested or used in clinics for pain mitigation, muscle rehabilitation, the treatment of motor/consciousness disorders, wound healing, and drug delivery. However, the research on fundamental mechanism of cellular response to EStim has fell behind its applications, which has hindered the full exploitation of the clinical potential of EStim. Moreover, despite the positive outcome from the in vitro and animal studies testing the efficacy of EStim, existing clinical trials failed to establish strong, conclusive supports for the therapeutic efficacy of EStim for most of the clinical applications mentioned above. Two potential directions of future research to improve the clinical utility of EStim are presented, including the optimization and standardization of the stimulation protocol and the development of more tissue-matching devices.

Comparison between standard and transepithelial corneal crosslinking using a theranostic UV-A device

PURPOSE

To assess corneal concentration of riboflavin in two different corneal crosslinking protocols performed by a novel image-guided therapeutic (or "theranostic") UV-A device.

METHODS

Ten human eye bank donor tissues were used in this work. The tissues underwent corneal cross-linking according to the conventional treatment protocol (n = 5; 30 min of stromal soaking followed by 30 min of 3 mW/cm² UV-A irradiance) and the iontophoresis-assisted transepithelial protocol (n = 5; soaking for 5 min at 1 mA/min and 9 min of 10 mW/cm² UV-A irradiance) using a theranostic UV-A device (Vision Engineering Italy srl, Italy). The device provided real time assessment of riboflavin concentration by hyperspectral image analysis of the cornea. A 0.1% riboflavin hypotonic solution (Ricrolin+, Sooft Italia Spa, Italy) was used in all cases.

RESULTS

Manual application of hypotonic riboflavin for 30 min into the stroma achieved greater corneal riboflavin concentration (425 ± 77 μg/cm³) than transepithelial delivery of riboflavin by corneal iontophoresis (195 ± 35 μg/cm³; P = 0.001). In both UV-A irradiation protocols, corneal riboflavin concentration decreased exponentially with a constant energy rate of 2.3 ± 0.5 J/cm² and 1.8 ± 0.3 J/cm² respectively. At the end of treatment, the average corneal concentration of riboflavin decreased by ≥ 85%, with values of 54 ± 29 μg/cm³ and 31 ± 9 μg/cm³ (P = 0.11), respectively.

CONCLUSION

Manual application of riboflavin onto the stroma achieved almost 50% greater concentration of riboflavin than transepithelial delivery by corneal iontophoresis. The theranostic UV-A device provided a novel approach to estimate corneal concentration of riboflavin non-invasively during treatment.

Corneal collagen cross-linking with and without simultaneous intrastromal corneal ring segment implantation: One-year pilot study

AIM

The aim of this study was to assess and compare the visual, refractive, and topographic outcomes of keratoconic eyes treated with corneal collagen cross-linking combined with and without same day intrastromal corneal ring segment over the first 12 months.

METHODS

This prospective randomized study analyzed 38 eyes of 30 consecutive keratoconus patients aged 26.21 ± 6.97 (range = 15-41) years. A total of 20 eyes were treated with collagen cross-linking alone, and 18 eyes underwent collagen cross-linking combined with simultaneous femtosecond laser-assisted intrastromal corneal ring segment. Visual acuity, manifest refraction, and corneal topography (using a rotating Scheimpflug topographer) were assessed and compared between the two groups at baseline, 6, and 12 months.

RESULTS

On an average follow-up duration of 12.2 ± 0.50 (range = 11-13) months, both collagen cross-linking alone and collagen cross-linking with simultaneous intrastromal corneal ring segment implantation were effective. However, collagen cross-linking plus intrastromal corneal ring segment resulted in an additional improvement of uncorrected distance visual acuity of 0.16 (95% confidence interval = 0.01 to 0.32) logarithm of the minimum angle of resolution units (p = 0.035), cylindrical power by 1.16 D (95% confidence interval = 0.25 to 2.06, p = 0.014), and spherical equivalent by 1.40 D (95% confidence interval = -2.71 to -0.08, p = 0.038) at 1 year. During the study period, no serious intraoperative or postoperative complications were noted in either group.

CONCLUSION

One-year follow-up results suggest that collagen cross-linking with simultaneously combined intrastromal corneal ring segment implantation could yield an additive visual and refractive outcome. The combined procedure is safe and merits consideration for the treatment of progressive keratoconus to achieve better visual rehabilitation.

Corneal refractive surgery combined with simultaneous corneal cross-linking: Indications, protocols and clinical outcomes-A review

Corneal refractive surgery is one of the most common approaches for correction of refractive errors. Combined corneal refractive surgery and corneal cross-linking (CXL) has been proposed as a method to achieve better refractive stability and to prevent iatrogenic corneal ectasia. However, there are concerns regarding its indications, surgical safety, standardization of protocols and long-term effect on corneal tissue. This review article aims to discuss the current knowledge and recent updates on combination of CXL and refractive surgery.

Optimal management of pediatric keratoconus: challenges and solutions

Keratoconus (KC) shows several distinctive features in clinical appearance, disease progression, and treatment in children compared with adults. Therefore, diagnostic, clinical care, and therapeutic approaches are different. However, pediatric keratoconus is often undiagnosed and thus untreated in many cases. Once diagnosis has been made, compliance with treatment recommendations is often poor. Pediatric keratoconus also tends to have more rapid progression than in adults; therefore, early detection and treatment are paramount to prevent serious vision impairment, which can affect the child's development. This review of pediatric keratoconus discusses important issues such as worldwide epidemiology, clinical features in children compared to adults, and challenges in diagnosis and treatment and focuses on the most appropriate management strategies based on the best available current evidence.

Iontophoretic Transepithelial Collagen Cross-Linking Versus Epithelium-Off Collagen Cross-Linking in Pediatric Patients: 3-Year Follow-Up

PURPOSE

To compare 3-year iontophoretic transepithelial corneal cross-linking (I-ON CXL) outcomes with epithelium-off collagen cross-linking (epi-off CXL) in pediatric patients.

METHODS

Forty eyes of 28 consecutive pediatric patients [mean age 14.3 ± 2.5 (SD) years; range, 9-18 years] with keratoconus were evaluated. Twenty eyes of 15 patients underwent I-ON and 20 eyes of 13 patients epi-off CXL. Mean corrected distance visual acuity, spherical equivalent, maximum keratometry (Kmax), posterior elevation of the thinnest point, and thickness of the thinnest point were evaluated. The Student t test was used to compare baseline and postoperative data. Keratoconus progression as a function of preoperative Kmax and cone location was evaluated.

RESULTS

At 36 months, corrected distance visual acuity statistically improved (from 0.18 ± 0.1 to 0.10 ± 0.1 logarithm of the minimum angle of resolution) in epi-off CXL, whereas spherical equivalent and posterior elevation of the thinnest point did not significantly change. Mean Kmax increased from the baseline +0.8 diopters (D) in epi-off and +2.9D in I-ON. In both groups, the thinnest point decreased. Keratoconus progression, defined by an increase of Kmax reading of the anterior corneal surface of at least 1.00D, occurred in 25% of epi-off and 50% of I-ON CXL over the 3-year period. Kmax value in I-ON, and cone location in both groups, seemed to be factors influencing the disease progression.

CONCLUSIONS

In pediatric patients, 3 years after treatment, epi-off CXL halted keratoconus progression in 75% of eyes, whereas I-ON CXL seemed to slow down keratoconus progression in 50% of eyes, mainly in those with highest Kmax and paracentral cone.

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.

Iontophoresis CXL With and Without Epithelial Debridement Versus Standard CXL: 2-Year Clinical Results of a Prospective Clinical Study

PURPOSE

To compare the 2-year follow-up outcomes of three groups of patients with keratoconus treated with transepithelial iontophoresis (I-CXL), iontophoresis with epithelial removal (I-SCXL), and standard epithelium-off (S-CXL) CXL for progressive keratoconus.

METHODS

Sixty eyes of 60 patients treated with CXL for progressive keratoconus were included in this comparative, prospective clinical study. Twenty patients were included in each group (I-CXL, I-SCXL, and S-CXL). Corrected distance visual acuity (CDVA), refraction, corneal topography, Scheimpflug tomography, and aberrometry were assessed at baseline and at 1, 3, 6, 12, and 24 months of follow-up. To assess the long-term safety and efficacy of these treatments, the preoperative values were compared with the values at 24 months of follow-up.

RESULTS

The main outcome of the study was the non-statistically significant difference between the three protocols in induced change in most of the parameters, including visual acuity (P = .665), topographic indexes (all P > .05), and maximum keratometry (P = .611) after 2 years of follow-up. There were no significant differences in the change in refractive error following CXL in all groups or between groups (all P > .05). Conversely, I-CXL induced significantly less corneal thinning (P = .0299 and .0121) and a significantly greater reduction of higher order aberrations and coma (all P < .0001) compared to S-CXL and I-SCXL. All protocols induced a significant increase in visual acuity (S-CXL P = .0004, I-SCXL P = .0045, and I-CXL P = .004).

CONCLUSIONS

The 2-year results of this comparative, prospective clinical study demonstrate the efficacy and safety of I-CXL to treat progressive keratoconus and overcome the limitations of CXL with epithelial debridement. [J Refract Surg. 2019;35(3):184-190.].