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

Hyperbaric Oxygenation Maintains Elevated Stromal Oxygen Availability During Corneal Collagen Crosslinking with and Without Epithelial Removal

PURPOSE

Corneal collagen cross-linking (CXL) can halt corneal ectasia. Leaving corneal epithelium intact during treatment may reduce the incidence of complications. However, it is under debate whether this reduces efficacy and if oxygen supplementation may be necessary to optimize the cross-linking effect. This study aimed to investigate the impact of hyperbaric oxygenation (HBO) on intracorneal oxygen concentrations during epi-off and epi-on CXL.

METHODS

CXL was performed using riboflavin and ultraviolet-A (UV-A) irradiance (3 mW/cm2 for 30 min) on porcine corneas under normobaric and hyperbaric conditions, with and without supplemented oxygen, with and without epithelium. Intracorneal oxygen concentrations were continuously monitored before and during irradiation. Biomechanical properties were assessed through tensile strength testing.

RESULTS

HBO alone did not cause perceivable changes in stromal oxygen concentrations. Oxygen supplementation resulted in higher oxygen concentration in corneal stroma during CXL. HBO may cause a further increase in oxygen levels, although this was not statistically significant in this study. Notably, a tendency of oxygen levels to rise continuously during UV-irradiation was observed using HBO. Biomechanical properties showend no statistically significant differences between any groups.

CONCLUSIONS

In this ex-vivo model, HBO increased stromal oxygen levels during CXL, regardless of the presence of corneal epithelium. The dynamics in oxygen concentrations in corneal stromal tissue during CXL suggest that time is an important factor to consider in modifications of established protocols. Also, we hypothesize that stromal levels of riboflavin and UV-A irradiance may be more critical to the CXL effect when oxygen is supplemented and epithelium is not removed.

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.

Collagen cross-linking beyond corneal ectasia: A comprehensive review

The history of corneal cross-linking (CXL) dates back to 2003 when some German scientists investigated possible treatments to harden the corneal structure to increase its resistance in ectatic corneal diseases. Nowadays, CXL is considered the most effective therapy in ectatic corneal diseases due to its proven efficacy in hardening the cornea, thus halting the development of the disease. Since 2003, CXL applications have dramatically expanded and have been implemented in several other areas such as infectious keratitis, corneal edema, and before performing keratoplasty for various purposes. Moreover, several irradiation patterns are being studied to correct refractive errors, taking into account the corneal refractive changes that occur after the procedure. Currently, scleral cross-linking is also being investigated as a potential therapy in cases of progressive myopia and glaucoma. In this article, we provide a comprehensive overview of the available applications of cross-linking in nonectatic ocular conditions and highlight the possible future indications of this procedure.

Effects of femtosecond laser-assisted minimally invasive lamellar keratoplasty (FL-MILK) on mild-to-moderate and advanced keratoconus

PURPOSE

To compare the outcomes of femtosecond laser-assisted minimally invasive lamellar keratoplasty (FL-MILK) for mild-to-moderate keratoconus (KC) and advanced KC.

METHODS

Prospective case series study. Sixty-three eyes of 56 patients with progressive KC underwent FL-MILK were divided into group 1 [mean keratometry (Kmean) ≤ 53D] and group 2 (Kmean > 53D). Best spectacle-corrected visual acuity (BSCVA), Kmean, maximum keratometry (Kmax), anterior central corneal elevation (ACE), stiffness parameter A1 (SP-A1) and deformation amplitude (DA) were evaluated preoperatively and up to 24 months postoperatively.

RESULTS

Mean BSCVA improved from 0.34 ± 0.13 logMAR preoperatively to 0.25 ± 0.13 logMAR at 24 months postoperatively in group 1 (F = 10.10, P < .0001), and from 0.54 ± 0.31 logMAR to 0.40 ± 0.26 logMAR (F = 9.06, P = .0002) in group 2. Group 2 showed an average Kmax reduction of 10.9 D and an average Kmean reduction of 3.9 D at 24 months postoperatively (both P < .0001), whereas no significant change was observed in group 1. Average ACE decreased from 19.2 ± 10.0 to 5.2 ± 8.4 at 24 months postoperatively in group 1 (F = 28.5, P < .0001), and from 46.2 ± 16.3 to 19.1 ± 9.0 (F = 49.6, P < .0001) in group 2; SP-A1 increased from 53.8 ± 12.7 mmHg/mm to 95.9 ± 20.2 mmHg/mm in group 1 (F = 70.0, P < .0001), and from 38.6 ± 13.4 mmHg/mm to 89.3 ± 18.2 mmHg/mm (F = 96.9, P < .0001) in group 2; DA decreased from 1.30 ± 0.14 mm to 1.17 ± 0.13 mm in group 1 (F = 14.0, P < .0001), and from 1.40 ± 0.16 mm to 1.18 ± 0.10 mm (F = 27.6, P < .0001) in group 2.

CONCLUSIONS

FL-MILK can stabilize progressive KC in mild-to-moderate cases and advanced cases at 24-month follow-up. Steeper corneas are more likely to undergo flattening after FL-MILK.

CLINICAL TRIAL

Date of registration: July 16, 2017. The title of the trail: www.

CLINICALTRIALS

gov Trial registration number: NCT03229239. The name of the trial registry: ClinicalTrials.gov.

Three-year follow-up of accelerated versus standard corneal cross-linking in paediatric Keratoconus

PURPOSE

Standard corneal collagen cross-linking (S-CXL) is an effective treatment to arrest Keratoconus (KC) progression in children. Less is known on the long-term efficacy of accelerated CXL (A-CXL) in paediatric populations.

METHODS

A historical cohort analysis of paediatric patients (≤18 years) with KC who underwent S-CXL and A-CXL at two tertiary referral centres in Israel between 2010-2017. Preoperative and 3-year postoperative evaluation included changes in visual acuity (best spectacle corrected [BSCVA]) and uncorrected [UCVA]), refractive errors, and keratometric data.

RESULTS

Ninety-three eyes of 93 patients were analysed (A-CXL: n = 39; S-CXL: n = 54). Baseline characteristics were similar between groups. Both groups showed a significant improvement in visual acuity compared to baseline (S-CXL: 0.810-0.602 LogMAR UCVA; A-CXL: 0.890-0.306 LogMAR UCVA, p < 0.05 for both). Improvement in BSCVA and UCVA following A-CXL was non-inferior to S-CXL (< ± 0.2 LogMAR). Kmax decreased by a mean of 0.98 ± 5.56 dioptres following S-CXL (p = 0.02) and by 1.48 ± 8.4 dioptres following A-CXL (p = 0.015). Thinnest pachymetry decreased following both treatments (S-CXL: by 26.8 ± 40.7 µm, p = 0.001, A-CXL: by 10.2 ± 13.4 µm, p = 0.028), the difference between groups was within the non-inferiority margin (< ± 10 µm).

CONCLUSIONS

Paediatric patients followed for three years after A-CXL showed improved visual function, reduced corneal astigmatism and Kmax, and decreased thinnest corneal thickness. A-CXL was non-inferior to S-CXL at three years in terms of best-corrected and uncorrected visual acuity, thinnest pachymetry, and astigmatism. For Kmax, non-inferiority could not be concluded.

Clinical Ocular Biomechanics: Where Are We after 20 Years of Progress?

Purpose: Ocular biomechanics is an assessment of the response of the structures of the eye to forces that may lead to disease development and progression, or influence the response to surgical intervention. The goals of this review are (1) to introduce basic biomechanical principles and terminology, (2) to provide perspective on the progress made in the clinical study and assessment of ocular biomechanics, and (3) to highlight critical studies conducted in keratoconus, laser refractive surgery, and glaucoma in order to aid interpretation of biomechanical parameters in the laboratory and in the clinic.Methods: A literature review was first conducted of basic biomechanical studies related to ocular tissue. The subsequent review of ocular biomechanical studies was limited to those focusing on keratoconus, laser refractive surgery, or glaucoma using the only two commercially available devices that allow rapid assessment of biomechanical response in the clinic.Results: Foundational studies on ocular biomechanics used a combination of computer modeling and destructive forces on ex-vivo tissues. The knowledge gained from these studies could not be directly translated to clinical research and practice until the introduction of non-contact tonometers that quantified the deformation response of the cornea to an air puff, which represents a non-destructive, clinically appropriate load. The corneal response includes a contribution from the sclera which may limit corneal deformation. Two commercial devices are available, the Ocular Response Analyzer which produces viscoelastic parameters with a customized load for each eye, and the Corvis ST which produces elastic parameters with a consistent load for every eye. Neither device produces the classic biomechanical properties reported in basic studies, but rather biomechanical deformation response parameters which require careful interpretation.Conclusions: Research using clinical tools has enriched our understanding of how ocular disease alters ocular biomechanics, as well as how ocular biomechanics may influence the pathophysiology of ocular disease and response to surgical intervention.

A randomized clinical trial assessing theranostic-guided corneal cross-linking for treating keratoconus: the ARGO protocol

The Assessment of theranostic guided riboflavin/UV-A corneal cross-linking for treatment of keratoconus (ARGO; registration number NCT05457647) clinical trial tests the hypothesis that theranostic-guided riboflavin/UV-A corneal cross-linking (CXL) can provide predictable clinical efficacy for halting keratoconus progression, regardless of treatment protocol, i.e., either with or without epithelial removal. Theranostics is an emerging therapeutic paradigm of personalized and precision medicine that enables real-time monitoring of image-guided therapy. In this trial, the theranostic software module of a novel UV-A medical device will be validated in order to confirm its accuracy in estimating corneal cross-linking efficacy in real time. During CXL procedure, the theranostic UV-A medical device will provide the operator with an imaging biomarker, i.e., the theranostic score, which is calculated by non-invasive measurement of corneal riboflavin concentration and its UV-A light mediated photo-degradation. ARGO is a randomized multicenter clinical trial in patients aged between 18 and 40 years with progressive keratoconus aiming to validate the theranostic score by assessing the change of the maximum keratometry point value at 1-year postoperatively. A total of 50 participants will be stratified with allocation ratio 1:1 using a computer-generated stratification plan with blocks in two treatment protocols, such as epithelium-off or epithelium-on CXL. Following treatment, participants will be monitored for 12 months. Assessment of safety and performance of theranostic-guided corneal cross-linking treatment modality will be determined objectively by corneal tomography, corneal endothelial microscopy, visual acuity testing and slit-lamp eye examination.

Evaluation of a Post-Operative Therapy Protocol after Epithelium-Off Corneal Cross-Linking in Patients Affected by Keratoconus

A large retrospective study evaluated the safety of a post-operative therapy protocol after epithelium-off corneal collagen cross-linking (CXL). In total, 1703 eyes of the 1190 patients with progressive keratoconus were enrolled in a retrospective cohort study in a tertiary care university hospital. CXL was performed using a standardized technique (Dresden protocol: 0.1% riboflavin solution containing dextran 20% for 30 min during the soaking phase followed by 30-min ultraviolet A irradiation (3 mW/cm²)). Postoperatively, a bandage contact lens was applied, and therapy included a topical fluoroquinolone antibiotic until the epithelium healed, followed by topical fluorometholone treatment for three weeks. Post-operative complications were recorded and analyzed. No cases of infectious keratitis occurred, whereas peripheral sterile infiltrates were observed in 1.17% of cases. Trace haze was typically present but did not have an impact on visual acuity. In fifteen cases (0.88%), visually significant anterior stromal opacity developed. Mild signs of dry eye were observed in 22 eyes (1.29%). The present study demonstrates that a post-operative treatment protocol including fluoroquinolone antibiotics and a BCL in the first phase until complete epithelial healing, followed by a three-week period of topical steroid treatment is safe and not associated with the development of microbial keratitis.

Corneal Crosslinking: Present and Future

Keratoconus is a progressive corneal thinning disorder that can lead to vision loss. In the last 2 decades, corneal crosslinking (CXL) has emerged as an effective method to halt the progression of keratoconus and reduce the number of patients requiring keratoplasty. The procedure has been adopted globally and has evolved to become a part of combination treatments to regularize the cornea and improve visual outcomes. CXL has even been extrapolated in managing other ocular pathologies such as progressive myopia, infectious keratitis, and bullous keratopathy. This review aims to summarize the current role of CXL in keratoconus and its alternative uses, and provide insights into future developments in this fast-developing field.

Femtosecond laser-assisted minimally invasive lamellar keratoplasty for the treatment of advanced keratoconus

BACKGROUND

To evaluate the initial safety and efficacy of femtosecond laser-assisted minimal invasive lamellar keratoplasty (FL-MILK) for advanced keratoconus.

METHODS

Twenty-two patients (22 eyes) with advanced keratoconus were included in this prospective study. All the involved eyes underwent FL-MILK. The femtosecond laser was used to create an intrastromal pocket with a 2.3 mm incision in the recipient cornea. Then a stromal button with a diameter of 9.0 mm and a depth of 200 μm was gently inserted into the intrastromal pocket through the 2.3 mm incision and flattened. No sutures were applied. Follow-up was conducted for 24 months.

RESULTS

Twenty-two patients completed follow-up data for 12 months, 16 patients had 24 months follow-up. No epithelial implantation, infection or allogeneic rejection were observed during the follow-up. Based on baseline values, postoperative 12 months values and postoperative 24 months values, clinical significantly improvement was recorded in corrected distance visual acuity (CDVA) (0.40 ± 0.18 logMAR vs. 0.30 ± 0.12 logMAR and 0.23 ± 0.13 logMAR), the anterior central corneal elevation (29.14 ± 15.33 μm vs. 14.45 ± 13.75μm and 11.38 ± 8.33 μm), and corneal higher-order aberrations (3.536 ± 1.503 vs. 2.761 ± 1.517 and 0.994 ± 0.391). Corneal biomechanical properties in all eyes improved significantly. SP-A1 increased from 48.64 ± 12.87 preoperatively to 87.26 ± 21.01 postoperative 12 months and 88.77 ± 18.26 postoperative 24 months; deformation amplitude (DA) decreased from 1.36 ± 0.15 preoperatively to 1.21 ± 0.12 postoperative 12 months and 1.19 ± 0.19 postoperative 24 months.

CONCLUSIONS

Initial experience suggests that this minimally invasive transplantation may be a feasible option for advanced keratoconus. A larger cohort and longer follow-up are required to validate our results and establish long-term safety and efficacy of the procedure.

Short- and long-term safety and efficacy of corneal collagen cross-linking in progressive keratoconus: A systematic review and meta-analysis of randomized controlled trials

PURPOSE

The purpose of the study is to evaluate the safety and outcomes of corneal collagen cross-linking (CXL) and different CXL protocols in progressive keratoconus (PK) population at short and long-term.

MATERIALS AND METHODS

A systematic review and meta-analysis was conducted. A total of eight literature databases were searched (up to February 15, 2022). Randomized controlled trials (RCTs) comparing CXL versus placebo/control or comparing different CXL protocols in the PK population were included. The primary objective was assessment of outcomes of CXL versus placebo and comparison of different CXL protocols in terms of maximum keratometry (Kmax) or Kmax change from baseline (Δ), spherical equivalent, best corrected visual acuity (BCVA), and central corneal thickness (CCT) in both at short term (6 months) and long term (1^st, 2^nd, and 3^rd year or more). The secondary objective was comparative evaluation of safety. For the meta-analysis, the RevMan5.3 software was used.

RESULTS

A total of 48 RCTs were included. Compared to control, CXL was associated with improvement in Δ Kmax at 1 year (4 RCTs, mean difference [MD], -1.78 [-2.71, -0.86], P = 0.0002) and 2 and 3 years (1 RCT); ΔBCVA at 1 year (7 RCTs, -0.10 [-0.14, -0.06], P < 0.00001); and Δ CCT at 1 year (2 RCTs) and 3 years (1 RCT). Compared to conventional CXL (C-CXL), deterioration in Δ Kmax, ΔBCVA and endothelial cell density was seen at long term in the transepithelial CXL (TE-CXL, chemical enhancer). Up to 2 years, there was no difference between TE-CXL using iontophoresis (T-ionto) and C-CXL. At 2 and 4 years, C-CXL performed better compared to accelerated CXL (A-CXL) in terms of improving Kmax. Although CCT was higher in the A-CXL arm at 2 years, there was no difference at 4 years. While exploring heterogeneity among studies, selection of control eye (fellow eye of the same patient vs. eye of different patient) and baseline difference in Kmax were important sources of heterogeneity.

CONCLUSION

CXL outperforms placebo/control in terms of enhancing Kmax and CCT, as well as slowing disease progression over time (till 3 years). T-ionto protocol, on the other hand, performed similarly to C-CXL protocol up to 2 years.

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.

Systemic supplemental oxygen therapy during accelerated corneal crosslinking for progressive keratoconus: randomized clinical trial

PURPOSE

To investigate the potential additive effect of systemic supplemental oxygen administered during accelerated corneal crosslinking (CXL) for progressive keratoconus (KC).

SETTING

Academic center.

DESIGN

Randomized clinical trial.

METHODS

Eyes with progressive KC randomized to 3 different CXL protocols were included. The first group (OA-CXL) included 19 eyes that underwent an accelerated CXL protocol (9 mW/cm2 for 10 minutes) while receiving systemic oxygen at a rate of 5 L/min for 10 minutes. The second group consisted of 14 eyes undergoing the same accelerated CXL protocol without supplemental oxygen therapy (A-CXL). The third group (C-CXL) comprised 14 eyes undergoing conventional CXL according to the Dresden protocol. All subjects were followed up for at least 6 months. Visual acuity, keratometry and corneal biomechanical parameters including corneal hysteresis and corneal resistance factor (CRF) were measured preoperatively and 6 months postoperatively.

RESULTS

Reduction in maximum keratometry (Kmax) was significantly greater in the OA-CXL group (P = .01). At baseline, the mean Kmax was 54.31 ± 3.64 diopters (D) in the OA-CXL group, 54.66 ± 4.99 D in the A-CXL group, and 56.03 ± 5.28 D in the C-CXL group (P = .58), which reached 53.58 ± 3.24 D, 54.59 ± 4.65 D, and 55.87 ± 4.73 D at 6 months in the 3 study groups, respectively (P = .115). The mean CRF increased significantly only in the OA-CXL group from a baseline value of 6.32 ± 2.12 mm Hg to 7.38 ± 1.88 mm Hg at 6 months (P = .009).

CONCLUSIONS

This study suggests superior efficacy of an accelerated CXL protocol coupled with systemic oxygen supplementation when compared with the accelerated CXL protocol and the conventional protocol in eyes with progressive KC. In addition to greater reduction in Kmax as the primary outcome, improvement in corneal biomechanics was also observed at 6 months.

Epithelial photorefractive keratectomy vs mechanical epithelial removal followed by corneal crosslinking for keratoconus: the Tel-Aviv Protocol

PURPOSE

To compare the Tel-Aviv Protocol, epithelial photorefractive keratectomy (ePRK) combined with corneal crosslinking (CXL), to CXL with alcohol-assisted epithelial removal (Alc-CXL) for progressive keratoconus.

SETTING

Care-Vision Laser Centers, Tel Aviv, Israel.

DESIGN

Retrospective study.

METHODS

All patients underwent Alc-CXL or ePRK, a 50 μm laser ablation of the epithelium with a myopic spherical component and an astigmatic component, followed by CXL. All patients completed at least 1 year of follow-up.

RESULTS

A total of 131 eyes of 131 patients were included in the study. Fifty patients (38%) were included in the Tel-Aviv Protocol group, and 81 patients (62%) were included in the Alc-CXL group. There was a significant improvement in uncorrected distance visual acuity (UDVA) (from 1.22 ± 0.75 logarithm of the minimum angle of resolution [logMAR] to 0.49 ± 0.44 logMAR, P < .001), corrected distance visual acuity (CDVA) (from 0.29 ± 0.17 logMAR to 0.16 ± 0.12 logMAR, P < .001), Kmax (from 48.50 ± 3.00 diopters [D] to 46.50 ± 3.00 D, P < .001), and cylinder (from -3.31 ± 1.70 D to -2.32 ± 1.66 D, P < .001) in the Tel-Aviv Protocol group in comparison with nonsignificant changes in the Alc-CXL group in UDVA (from 0.89 ± 0.62 logMAR to 0.81 ± 0.65 logMAR, P = .23), CDVA (from 0.25 ± 0.21 logMAR to 0.21 ± 0.17 logMAR, P = .10), Kmax (from 46.50 ± 4.50 D to 46.00 ± 4.40 D, P = .08), and cylinder (from -2.99 ± 2.05 D to -2.80 ± 1.75 D, P = .39) at the end of the follow-up period.

CONCLUSIONS

The Tel-Aviv Protocol for progressive keratoconus patients provided good improvement in visual acuity and astigmatism while halting the progression of keratoconus.

[Safety and efficiency of epithelium-off accelerated corneal cross-linking for progressive keratoconus in pediatric patients]

In adults, the management of keratoconus has evolved in recent years to achieve a well-codified treatment algorithm. The technique of cross-linking (CXL) has allowed us to stabilize the progression of keratoconus and has been largely developed. It is very effective, with few postoperative complications. Currently, there is no specific keratoconus management protocol for children. As we already know that keratoconus usually evolves more rapidly in children, we might consider whether a stabilizing treatment should be proposed as first-line therapy at the time of diagnosis. We carried out a retrospective study including patients less than 18 years of age with keratoconus who consulted the ophthalmology department at Edouard Herriot hospital in Lyon between 2013 and 2017. The main study parameter was whether or not CXL was performed. The other parameters were gender, age, ethnicity, eye rubbing, presence or absence of atopic disease, maximum keratometry (Kmax), minimal pachymetry, best corrected visual acuity (BCVA) and spherical equivalent. Forty-eight eyes of 34 patients were included. We found that two-thirds of the patients were Caucasian boys. Half of the patients had allergies, and over 60% of patients rubbed their eyes regularly. Only six percent of patients had a family history of keratoconus. The mean age of the patients was 14 (7-18) years at the time of diagnosis. Thirty-four eyes of 22 patients underwent CXL, for a total of 71% of our cohort. No postoperative complications occurred. After CXL, there was no significant difference in minimum pachymetry (455.6±37.25μm vs. 453.45±42.6μm after treatment (P=0.71)) or Kmax (50.23±7.17D vs. 50.99±7.01D after treatment (P=0.058)). There was a significant improvement in BCVA (from 0.30±0.3LogMar to 0.17±0.17LogMar after CXL (P=0.024)) and spherical equivalent (-1.91±2.1D to -2.54±1.89D after treatment (P=0.009)). The mean duration of follow-up was 32.2 months (12-59). CXL shows long-term disease stabilization in children with keratoconus. Nevertheless, this technique is indicated only for progressive keratoconus. Early diagnosis and management are essential in this population where the disease is rapidly changing. Treatment of atopy and performance of corneal topography when a child has irregular astigmatism should become automatic for early detection of this disease.

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.

Corneal flattening following collagen crosslinking for keratoconus: Findings at 5-year follow-up

PURPOSE

To study the corneal flattening effect of cross-linking (CXL) overtime and to look for a potential association with preoperative topographic variables and the central depth of demarcation line (DDL).

METHODS

201 eyes of 146 patients (mean age of 31.2 ± 7.3 years) with progressive keratoconus who underwent CXL between June 2007 and December 2012 were enrolled in this retrospective study. Follow-up visits were performed at different time intervals for at least 5 years. Preoperative parameters and depth of demarcation line were collected from LaserVision ophthalmology center in Lebanon. Corneal flattening was defined by a change in postoperative Kmax (ΔKmax) greater than 1.00 D.

RESULTS

ΔKmax increased from 50.25% to 61.69%, from first to last follow-up visits. The only factor significantly correlated to ΔKmax during all follow-up visits was preoperative maximum keratometry (Kmax) especially when greater than 50.00 D (OR, 1.92; 95% CI, 1.10-3.34). All eyes showed a corneal demarcation line (mean central depth (DDL): 217.11 ± 26.54 μm), with no statistically significant correlation between DDL and ΔKmax.

CONCLUSION

CXL effect on cornea can be cumulative overtime and delayed flattening occurs in some cases. ΔKmax is positively correlated with preoperative Kmax and no association was found between ΔKmax and DDL. Therefore, DDL may not be a valid measure for the efficacy of CXL.

Fourier Analysis of Keratometric Data in Epithelium Removal versus Epithelial Disruption Corneal Cross-linking

Purpose

To compare epithelium-removal and epithelium-disruption corneal crosslinking (CXL) methods in Fourier analysis of keratometric data and clinical outcomes.

Methods

In this double masked randomized clinical trial, each eye of 34 patients with bilateral keratoconus was randomly allocated to either the epithelium-removal or epithelium-disruption CXL treatment groups. Ocular examination, refraction, uncorrected and best spectacle-corrected visual acuity (UCVA and BSCVA, respectively) measurements, and Pentacam imaging (keratometry, pachymetry, and Fourier analysis) were performed at baseline and at six-month follow-up period.

Results

Patients' mean age was 23.3 ± 3.6 years. The preoperative thickness of the thinnest point was 459.20 ± 37.40 µm and 455.80 ± 32.70 µm in the epithelium-removal and epithelial-disruption CXL groups, respectively (P > 0.05). The corresponding figures were 433.50 ± 33.50 µm and 451.90 ± 39.70 µm, respectively, six months after the treatment (P = 0.0001). Irregularity component of the fourier analysis was 0.030 ± 0.016 µm in the epithelium-removal group and 0.028 ± 0.011 µm in the epithelium-disruption group preoperatively (P > 0.05). This measurement was 0.031 ± 0.016 µm and 0.024 ± 0.009 µm, respectively at month 6 (P = 0.04). The epithelium-disruption CXL group had better results in terms of the thickness of the thinnest point and the irregularity component as compared to the epithelium-removal group. The two study groups were comparable in spherical equivalent, mean keratometry, UCVA, BSCVA, or other Fourier analysis components (spherical R min, spherical eccentricity, central, peripheral regular astigmatism, and maximum decentration) (P > 0.05).

Conclusion

This study shows that epithelium-disruption CXL is superior to epithelium-removal CXL regarding the short-term changes in pachymetry and corneal irregularity. Other evaluated parameters were comparable between the two techniques.

Epithelial Photorefractive Keratectomy and Corneal Cross-linking for Keratoconus: The Tel-Aviv Protocol

PURPOSE

To present the Tel-Aviv Protocol for patients with progressive keratoconus, which consists of epithelial photorefractive keratectomy (ePRK), and corneal cross-linking (CXL).

METHODS

This was a retrospective case series of 20 consecutive patients diagnosed as having progressive keratoconus at Care-Vision Laser Centers, Tel Aviv, Israel. The Tel-Aviv Protocol included laser epithelial ablation using the EX500 excimer laser (Alcon Laboratories, Inc., Fort Worth, TX) with 50% of the manifest refractive astigmatism (on the same axis) while the spherical ablation is added so as not to exceed a total of 50-µm ablation of the epithelium and anterior stroma. Afterward, all patients underwent CXL. Data collected included thinnest corneal thickness (TCT), subjective astigmatism, mean keratometric power, maximum keratometric power (K_max), uncorrected distance visual acuity (UDVA), and corrected distance visual acuity (CDVA).

RESULTS

A total of 20 eyes of 20 patients with a mean age of 28.0 ± 6.5 years (range: 13 to 40 years) and a mean follow-up of 823 ± 337 days (range: 266 to 1,749 days) were included. There was a significant improvement in both UDVA (from 0.95 ± 0.73 to 0.22 ± 0.15 logMAR, P < .001) and CDVA (from 0.24 ± 0.13 to 0.13 ± 0.12 logMAR, P < .001) at the end of the follow-up period. There was a significant improvement in mean keratometry (from 46.86 ± 2.48 to 45.00 ± 2.27 diopters [D], P < .001), K_max (from 48.18 ± 2.74 to 45.97 ± 2.55 D, P < .001), and K_min (from 45.54 ± 2.35 to 44.03 ± 2.12 D, P < .001). TCT was significantly lower following the procedure (from 450.90 ± 35.99 to 404.90 ± 43.96 µm, P < .001). No complications and no progression in keratoconus severity were noticed during the follow-up period.

CONCLUSIONS

The Tel-Aviv Protocol for patients with progressive keratoconus provides good improvement in visual acuity and astigmatism while halting the progression of keratoconus. [J Refract Surg. 2019;35(6):377-382.].

Corneal Collagen Cross-Linking in the Stabilization of Keratoconus

BACKGROUND

Keratoconus is a slowly progressive ectatic deformity of the cornea with a prevalence of 200 to 400 cases per 100 000 persons. The cornea is thinner than normal and irregularly warped; irregular astigmatism and myopia result. Riboflavin-UVA crosslinking (collagen cross-linking) makes corneal tissue more rigid through a photochemical effect and can stop the progression of the disease.

METHODS

This review is based on relevant publications retrieved by a selective search in Medline, as well as on meta-analyses, Cochrane Reviews, and reports of national and international health care institutions.

RESULTS

Pertinent randomized controlled trials (RCTs) have shown that cross-linking prevents the progression of keratoconus to a statistically significant extent, as determined by measurement of topographic parameters. In the largest RCT to date (fol- low-up of 100 eyes for three years), the maximal corneal refractive power increased by 1.75 ± 0.38 diopters in the control group and decreased by -1.03 ± 0.19 diopters in the cross-linking group (p <0.001). This was also the only trial in which data were reported on the patient-relevant endpoint of uncorrected visual acuity, which mildly improved in the cross-linking group (-0.15 ± 0.06 logMAR, p = 0.009). Serious complications of cross-linking are known to date only from a few reports of individual cases. Cohort studies with follow-up times of up to ten years have shown that the condition can continue to progress after cross-linking, especially in younger patients.

CONCLUSION

Cross-linking is the first available treatment for keratoconus that can improve the natural course of the disease.

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.

Different photodynamic effects of blue light with and without riboflavin on methicillin-resistant Staphylococcus aureus (MRSA) and human keratinocytes in vitro

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of infections in humans. Photodynamic therapy using blue light (450 nm) could possibly be used to reduce MRSA on different human tissue surfaces without killing the human cells. It could be less harmful than 300-400 nm light or common disinfectants. We applied blue light ± riboflavin (RF) to MRSA and keratinocytes, in an in vitro liquid layer model, and compared the effect to elimination using common disinfection fluids. MRSA dilutions (8 × 10⁵/mL) in wells were exposed to blue light (450 nm) ± RF at four separate doses (15, 30, 56, and 84 J/cm²). Treated samples were cultivated on blood agar plates and the colony forming units (CFU) determined. Adherent human cells were cultivated (1 × 10⁴/mL) and treated in the same way. The cell activity was then measured by Cell Titer Blue assay after 24- and 48-h growth. The tested disinfectants were chlorhexidine and hydrogen peroxide. Blue light alone (84 J/cm²) eliminated 70% of MRSA. This dose and riboflavin eradicated 99-100% of MRSA. Keratinocytes were not affected by blue light alone at any dose. A dose of 30 J/cm² in riboflavin solution inactivated keratinocytes completely. Disinfectants inactivated all cells. Blue light alone at 450 nm can eliminate MRSA without inactivation of human keratinocytes. Hence, a high dose of blue light could perhaps be used to treat bacterial infections without loss of human skin cells. Photodynamic therapy using riboflavin and blue light should be explored further as it may perhaps be possible to exploit in treatment of skin diseases associated with keratinocyte hyperproliferation.

Intraobserver reproducibility and interobserver agreement of demarcation line depth measurements following corneal cross linking

PURPOSE

The aim of this study was to evaluate the intraobserver reproducibility of demarcation line depth measurement in keratoconic patients after epithelium-off corneal collagen cross linking and assess the interobserver variability/agreement among examiners of various experience levels.

METHODS

56 eyes of 56 patients undergoing corneal collagen cross linking for progressive keratoconus were enrolled. After 4 weeks, all patients underwent an anterior segment optical coherence tomography (AS-OCT; CASIA SS-1000; Tomey, Nagoya, Japan) in the cross-linked eye by four masked examiners (two medical students (S1 and S2) and two corneal fellows (F1 and F2)) in order to identify and measure the demarcation line depth in experienced and non-experienced users. The intraclass correlation coefficient and the coefficient of variation were calculated. Agreement between raters was evaluated using Bland-Altman plots, intraclass correlation coefficient and weighted-kappa statistics comparing raters in pairs.

RESULTS

The average demarcation line depth of all measurements was 254.34 ± 72.3 μm, varying from 84 to 459 μm. The intraclass correlation coefficient evaluating the reproducibility of measurements for F1 was 0.9379 (95% confidence interval (CI) =0.9035-0.9619), for the second (F2), it was 0.9837 (95% confidence interval = 0.9743-0.9901), while intraclass correlation coefficient between medical students was calculated 0.844. The overall intraclass correlation coefficient among all four observers was 0.8706 (95% confidence interval = 0.8061-0.9185). The coefficient of variation for repeated measurements was 5.981 μm (95% confidence interval = 3.966-7.471) and 3.312 μm (95% confidence interval = 2.468-3.981) for F1 and F2 raters, respectively. The percentage of demarcation line detection was 90.32%.

CONCLUSION

The reproducibility of demarcation line measures although very good (intraclass correlation coefficient > 0.9), yielded a difference between the two experienced raters. Furthermore, the novice raters did not reach an excellent level of agreement with the expert ones showing greater variability in their recordings.

Bandage contact lens and topical steroids are risk factors for the development of microbial keratitis after epithelium-off CXL

Objective

To investigate the role of bandage contact lenses (BCL) and topical steroids as risk factors for the development of microbial keratitis after epithelium-off corneal collagen cross-linking (CXL).

Methods and Analysis

Patients undergoing CXL between February 2011 and July 2017 were included. Patients were divided into two groups: those who were treated postoperatively with a BCL, topical antimicrobial and steroids (group 1) and those who received only a topical antimicrobial until healing of the epithelial defect before introduction of topical steroids (group 2).

Results

1273 eyes of 964 patients were included. Group 1 comprised 316 eyes and group 2 comprised 957 eyes. There were no significant differences in the presence of persisting corneal haze or scarring between the two groups (p=0.57). Microbial keratitis occurred in nine eyes (0.71% of eyes) of eight (0.83%) patients (one case was bilateral) out of 1273 eyes. Staphylococcus aureus was cultured from corneal scrapes in seven out of nine (77.8%) cases and from contiguous sites in the two cases. All cases occurred in group 1 (incidence=2.85%) and none in group 2 (p<0.0001). A greater proportion of patients who developed microbial keratitis were atopic (75%, p=0.4).

Conclusion

The use of BCL and topical steroids prior to healing of the epithelium is a significant risk factor for microbial keratitis. S. aureus is the most common micro-organism and is likely to originate from an endogenous site. Not using a BCL and delaying the introduction of topical steroids until epithelial healing significantly reduce the risk of developing microbial keratitis without increasing the risk of persistent corneal haze.

Comparison of Epithelium-Off Versus Transepithelial Corneal Collagen Cross-Linking for Keratoconus: A Systematic Review and Meta-Analysis

PURPOSE

To systematically compare standard epithelium-off corneal collagen cross-linking (SCXL) and transepithelial corneal collagen cross-linking (TECXL) for treating keratoconus.

METHODS

PubMed, EMBASE, the Cochrane Library, the US trial registry (ClinicalTrials.gov), VIP Database, Wanfang Databse, and China National Knowledge Infrastructure searches up to February 2017 were conducted. Primary outcomes were changes at 1 year in uncorrected distance visual acuity, maximum keratometry (Kmax), and mean keratometry (mean K). Secondary outcomes were changes at 1 year in corrected distance visual acuity, mean refractive spherical equivalent, central corneal thickness, endothelial cell density, and the occurrence of adverse events.

RESULTS

Eight studies with a total of 455 eyes were included. For primary outcomes, SCXL showed a greater reduction in mean K [standardized mean difference (SMD) 0.28; 95% confidence interval (CI), 0.03-0.53; P = 0.03] compared with TECXL. Subgroup analysis indicated that SCXL had a comparable effect on reducing mean K with TECXL protocols using chemical enhancers (SMD 0.05; 95% CI, -0.36 to 0.45; P = 0.82) but a greater reduction in mean K compared with TECXL with current iontophoretic protocols (SMD 0.43; 95% CI, 0.10-0.75; P = 0.01). For the other outcomes, there were no statistically significant differences.

CONCLUSIONS

With the exception of less reduction in mean K with current iontophoretic protocols, analysis of the limited number of comparative studies available seems to demonstrate that SCXL and TECXL have a comparable effect on visual, refractive, pachymetric, and endothelial parameters at 1 year after surgery. Further follow-up is required to determine whether these techniques are comparable in the long-term.

Efficacy and safety of transepithelial corneal collagen crosslinking surgery versus standard corneal collagen crosslinking surgery for keratoconus: a meta-analysis of randomized controlled trials

Background

The aim of this study was to evaluate the efficacy and safety of transepithelial corneal collagen crosslinking (transepithelial CXL) versus standard corneal collagen crosslinking (epithelium-off CXL) on keratoconus.

Methods

Eligible studies were identified by systematically searching PubMed, the Cochrane Library and Embase. Topographic parameters, corrected distant visual acuity (CDVA), uncorrected distant visual acuity (UDVA), and corneal thickness (CT) were assessed by the pooled weighted mean differences (WMDs) of the change from baseline to the end of follow up. Quality was assessed according to Cochrane handbook. And we used Review Manager to analysis the included trials.

Results

Three trials involving 244 eyes were evaluated, with 111 eyes in the standard CXL group and 133 eyes in the transepithelial CXL group. The pooled results showed that there were significant differences between the two groups in maximum keratometry (mean difference = 1.05D, 95% CI 0.19 to 1.92, P = 0.02)),and the standard CXL is more effective in decreasing the maximum keratometry at least 12 months after operation; the transepithelial CXL group gained more improvement in CDVA (mean difference = −0.07, 95% CI -0.12 to −0.02, P = 0.007);there were no significant differences in uncorrected distant visual acuity (UDVA) between the two groups (mean difference = −0.03, 95% CI -0.20 to 0.15, P = 0.75). A similar change was found in corneal thickness (mean difference = 4.35, 95% CI -0.43 to 9.13, P = 0.07)).

Conclusions

The standard CXL is more effective in decreasing the maximum keratometry than the transepithelial CXL; the transepithelial CXL provided favorable visual outcomes; they both exhibit similar safety.

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

PURPOSE

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

DESIGN

Randomized controlled trial.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Human in vitro Model Reveals the Effects of Collagen Cross-linking on Keratoconus Pathogenesis

Keratoconus (KC) is a corneal thinning disorder that leads to severe vision impairment As opposed to corneal transplantation; corneal collagen crosslinking (CXL) is a relatively non-invasive procedure that leads to an increase in corneal stiffness. In order to evaluate the effect of CXL on human corneal stromal cells in vitro, we developed a 3-D in vitro CXL model, using primary Human corneal fibroblasts (HCFs) from healthy patients and Human Keratoconus fibroblasts (HKCs) from KC patients. Cells were plated on transwell polycarbonate membranes and stimulated by a stable vitamin C. CXL was performed using a mixed riboflavin 0.1% PBS solution followed by UVA irradiation. Our data revealed no significant apoptosis in either HCFs or HKCs following CXL. However, corneal fibrosis markers, Collagen III and α-smooth muscle actin, were significantly downregulated in CXL HKCs. Furthermore, a significant downregulation was seen in SMAD3, SMAD7, and phosphorylated SMADs -2 and -3 expression in CXL HKCs, contrary to a significant upregulation in both SMAD2 and Lysyl oxidase expression, compared to HCFs. Our novel 3-D in vitro model can be utilized to determine the cellular and molecular effects on the human corneal stroma post CXL, and promises to establish optimized treatment modalities in patients with KC.

Changes in Corneal Density After Accelerated Corneal Collagen Cross-linking With Different Irradiation Intensities and Energy Exposures: 1-Year Follow-up

PURPOSE

To determine and compare the changes in corneal density after 2 different protocols of accelerated corneal collagen cross-linking (A-CXL) in patients with progressive keratoconus.

METHODS

Two groups of eyes received A-CXL treatment; 20 eyes received A-CXL using continuous UVA light exposure at 9 mW/cm for 10 minutes with a total energy dose of 5.4 J/cm, and 24 eyes received A-CXL using continuous UVA light exposure at 30 mW/cm for 4 minutes with a total energy dose of 7.2 J/cm. Corneal density was measured with Scheimpflug tomography at 1, 3, 6, and 12 months of follow-up.

RESULTS

Densitometry peaked at 1 month (mean: 16.34 ± 3.80, P = 0.006, 9-mW/cm A-CXL; mean: 20.90 ± 2.81, P < 0.0001, 30-mw/cm A-CXL) in both groups, and it decreased over time in 30-mW/cm A-CXL. However, in 9-mW/cm A-CXL, increased corneal densitometry plateaued until 6 months postoperatively and started to decrease thereafter. Densitometry completely returned to baseline after 12 months in both groups. The mean change in density at 1- and 3-month follow-up was higher in the 30-mW A-CXL group than in the 9-mW A-CXL group (P = 0.003, P = 0.044; respectively).

CONCLUSIONS

High-energy exposure tends to induce more haze in the early posttreatment period, but it is reversible.

Corneal Collagen Cross-Linking for Keratoconus: Systematic Review

Purpose

To evaluate the efficacy of collagen cross-linking (CXL) one year after treatment for keratoconus compared to no treatment by summarizing randomized controlled trials (RCTs) using a systematic review.

Methods

Trials meeting the selection criteria were quality appraised, and the data were extracted by two independent authors. The outcome parameters included maximum keratometry (K_max), corneal thickness at the thinnest point, best spectacle-corrected visual acuity (BSCVA), uncorrected visual acuity (UCVA), spherical equivalent (SE) refraction, and cylindrical refraction one year after CXL. We compared the changes in the above parameters with the control group.

Results

We identified five RCTs involving 289 eyes that met the eligibility criteria for this systematic review. The changes in BSCVA from baseline to one year exhibited a significant difference between the two groups. There was no statistically significant difference between the two groups for changes in corneal thickness and cylindrical refraction. We did not conduct a meta-analysis in K_max, UCVA, and SE refraction because their I² values were greater than 50%.

Conclusions

According to the systematic review, CXL may be effective in halting the progression of keratoconus for one year under certain conditions, although evidence is limited due to the significant heterogeneity and paucity of RCTs.

A review and meta-analysis of corneal cross-linking for post-laser vision correction ectasia

PURPOSE

The aim of this study was to review the safety and stability of cornea cross-linking (CXL) for the treatment of keratectasia after Excimer Laser Refractive Surgery.

METHODS

Eligible studies were identified by systematically searching PubMed, Embase, Web of Science and reference lists. Meta-analysis was performed using Stata 12.1 software. The primary outcome parameters included the changes of corrected distant visual acuity (CDVA), uncorrected visual acuity (UCVA), the maximum keratometry value (Kmax) and minimum keratometry value (Kmin), the surface regularity index (SRI), the surface asymmetry index (SAI), the keratoconus prediction index (KPI), corneal thickness, and endothelial cell count. Efficacy estimates were evaluated by weighted mean difference (WMD) and 95% confidence interval (CI) for absolute changes of the interested outcomes.

RESULTS

Seven studies involving 118 patients treated with CXL for progressive ectasia after laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) (140 eyes; the follow-up time range from 12 to 62 months) were included in the meta-analysis. The pooled results showed that there were no significant differences in Kmax and Kmin values after CXL (WMD = 0.584; 95% CI: -0.289 to 1.458; P = 0.19; WMD = 0.466; 95% CI: -0.625 to 1.556; P = 0.403, respectively). The CDVA improved significantly after CXL (WMD = 0.045; 95% CI: 0.010 to 0.079; P = 0.011), whereas UCVA did not differ statistically (WMD = 0.011; 95% CI: -0.055 to 0.077; P = 0.746). The changes were not statistically significant in SRI, SAI, and KPI (WMD = 0.116; 95% CI: -0.090 to 0.322; P = 0.269; WMD = 0.240; 95% CI: -0.200 to 0.681; P = 0.285; WMD = 0.045; 95% CI: -0.001 to 0.090; P = 0.056, respectively). Endothelial cell count and corneal thickness did not deteriorate (WMD = 12.634; 95% CI: -29.460 to 54.729; P = 0.556; WMD = 0.657; 95% CI: -9.402 to 10.717; P = 0.898, respectively).

CONCLUSION

The study showed that CXL is a promising treatment to stabilize the keratectasia after Excimer Laser Refractive Surgery. Further long-term follow-up studies are necessary to assess the persistence of the effect of the CXL.

Randomized Controlled Trial Comparing Transepithelial Corneal Cross-linking Using Iontophoresis with the Dresden Protocol in Progressive Keratoconus

PURPOSE

To compare clinical outcomes of transepithelial corneal cross-linking using iontophoresis (T-ionto CL) and standard corneal cross-linking (standard CL) for the treatment of progressive keratoconus 12 months after the operation.

DESIGN

Prospective randomized controlled clinical trial.

PARTICIPANTS

Thirty-four eyes of 25 participants with progressive keratoconus were randomized into T-ionto CL (22 eyes) or standard CL (12 eyes).

METHODS

T-ionto CL was performed using an iontophoresis device with dextran-free 0.1% riboflavin-5-phosphate solution with enhancers and by irradiating the cornea with a 10 mW/cm² ultraviolet A device for 9 minutes. Standard CL was performed according to the Dresden protocol.

MAIN OUTCOME MEASURES

The primary outcome measure was stabilization of keratoconus after 12 months through analysis of maximum simulated keratometry readings (K_max, diopters). Other outcome measures were corrected distance visual acuity (CDVA, logarithm of the minimum angle of resolution [logMAR]), manifest spherical equivalent refraction (D), central corneal thickness (CCT, micrometers) and endothelial cell density (ECD). Follow-up examinations were arranged at 3 and 7 days and 1, 3, 6, and 12 months.

RESULTS

Twelve months after T-ionto CL and standard CL, K_max on average flattened by -0.52±1.30 D (P = 0.06) and -0.82±1.20 D (P = 0.04), respectively. The mean change in CDVA was -0.10±0.12 logMAR (P = 0.003) and -0.03±0.06 logMAR (P = 0.10) after T-ionto CL and standard CL, respectively. The manifest spherical equivalent refraction changed on average by +0.71±1.44 D (P = 0.03) and +0.21±0.76 D (P = 0.38), respectively. The CCT and ECD measures did not change significantly in any group at 12 months. Significant differences in the outcome measures between treatments were found in the first week postoperatively. No complications occurred in the T-ionto CL group; 1 eye (8%) had sterile corneal infiltrates, which did not affect the final visual acuity, in the standard CL group.

CONCLUSIONS

Significant visual and refractive improvements were found 12 months after T-ionto CL, though the average improvement in corneal topography readings was slightly lower than the Dresden protocol in the same period.

Corneal collagen crosslinking for corneal ectasias: a review

PURPOSE

To review the published literature on corneal collagen crosslinking (CXL).

METHODS

Importance has been placed on seminal publications, systemic reviews, meta-analyses, and randomized controlled clinical trials. Where such evidence was not available, cohort studies, case-controlled studies, and case series with follow-up greater than 12 months were examined.

RESULTS

Corneal collagen crosslinking with riboflavin and ultraviolet A (UVA) 370 nm radiation appears to be capable of arresting the progression of ectatic corneal disorders, with most studies reporting significant improvements in visual, keratometric, and topographic measurements. Its mode of action at the molecular level is undetermined. Follow-up is limited to 5-10 years but suggests sustained stability and enhancement in corneal shape with time. Nearly all published long-term data and comparative studies are with epithelium-off techniques. Epithelium-on investigations suggest some efficacy but less than with epithelium-off treatments and long-term data are unavailable. Accelerated techniques with higher UVA fluencies and shorter treatments times, delivering the same UVA energy dosage, are the subject of recent investigation, with some laboratory and clinical studies suggesting reduced efficacy compared to the standard 3 mW/cm2 for 30 minutes irradiation procedure. Combined methodologies of CXL with techniques such as photorefractive keratectomy and intrastromal rings show promise but long-term follow-up is indicated. Sight-threatening complications of CXL are rare.

CONCLUSIONS

Studies of epithelium-off CXL with irradiation at 3 mW/cm2 for 30 minutes support its efficacy. Refinement in techniques may allow for safer and more rapid procedures with less patient discomfort but require further investigation.

Novel Technique of Transepithelial Corneal Cross-Linking Using Iontophoresis in Progressive Keratoconus

In this work, the authors presented the techniques and the preliminary results at 6 months of a randomized controlled trial (NCT02117999) comparing a novel transepithelial corneal cross-linking protocol using iontophoresis with the Dresden protocol for the treatment of progressive keratoconus. At 6 months, there was a significant average improvement with an average flattening of the maximum simulated keratometry reading of 0.72 ± 1.20 D (P = 0.01); in addition, corrected distance visual acuity improved significantly (P = 0.08) and spherical equivalent refraction was significantly less myopic (P = 0.02) 6 months after transepithelial corneal cross-linking with iontophoresis. The novel protocol using iontophoresis showed comparable results with standard corneal cross-linking to halt progression of keratoconus during 6-month follow-up. Investigation of the long-term RCT outcomes are ongoing to verify the efficacy of this transepithelial corneal cross-linking protocol and to determine if it may be comparable with standard corneal cross-linking in the management of progressive keratoconus.

Intraocular Pressure Measurements Referring to the Corneal Thickness in Keratoconic Eyes After Corneal Crosslinking with Riboflavin and Ultraviolet A

Aim:

To determine the possible relation between intraocular pressure (IOP), central corneal thickness (CCT) and corneal resistance (CR) in kerotoconic eyes before, 3,6 and 12 months after collagen crosslinking procedure (CXL) with aim to find out does the thicker cornea means already more resistance cornea followed with higher IOP.

Methods:

Thirty eyes (30 patients) with central keratoconus (KC)were evaluated in retrospective cross sectional study. The corneal biomechanical parameters were taken with Wave Light Allegro Oculyzer produced by Alcon before the CXL, 3, 6 and 12 months after the procedure. IOP were checked by Goldmann applanation tonometry (GAT) before, 3, 6 and 12 months after CXL.

Results:

The value of IOP before the CXL was 12,0 mmHg (10,62-15,25 mmHg), 3 months later 13,5 mmHg (11,0-16,0 mmHg), 6 months 14,0 mmHg (11,0-16,0 mmHg) and 12 months later 15,0 mmHg (10,37-17,25 mmHg) and was statistically significant higher (p=0,015) comparing to the value of IOP 3 months after the CXL, IOP 12 months after CXL procedure was statistically significant higher comparing to preoperative values (p=0,010). There were no statistically significant difference between the values 3 and 6 months after CXL. The CCT before the CXL procedure was 449 (433-505,75 microns), 3 months after CXL was 420 (383-473microns, p < 0,005), 6 months later 437 (401,25-480,25, p=0,001), 12 months after CXL 437 (401-503 microns, p=0,001). However there is statistically significant difference in CCT 12 months after CXL 437 (401-503microns p=0,032) and the value of CCT 3 months later the procedure (p=0,004) and the CCT 12 months after CXL and the value of CXL 6 months after CXL (p=0,036). The value of CCT did not show any statistically significant difference 3 and 6 months postoperatively.

Conclusion:

After riboflavin-UVA CXL in eyes with KC there was significant decrease in central corneal thickness 3 and 6 months after the procedure and the thickness is almost the same 12 months later. However IOP is low before CXL, raising up 3 and 6 months after CXL but significant increase is seen 12 months later. It means the regular measurement of IOP could be the serious and confident indicator of increasing of corneal resistance which is the main goal of CXL treatment.