Accelerated 15 mW pulsed-light crosslinking to treat progressive keratoconus: Two-year clinical results

Pulsed corneal crosslinking in the treatment of Keratoconus: a systematic review and meta-analysis

PURPOSE

Corneal crosslinking (CXL) procedures are the treatment of choice in halting progressive corneal ectasia and preserving visual acuity due to keratoconus. Pulsed crosslinking (P-CXL) was developed using intermittent pulsing ultraviolet (UV) light to mitigate the depletion of oxygen levels that occurs with continuous UV exposure in standard crosslinking protocols (C-CXL). This study aimed to explore the use of P-CXL in the treatment of keratoconus and determine whether the availability of oxygen in P-CXL carries superior efficacy outcomes as an alternative to C-CXL modalities.

METHODS

This review was undertaken in accordance with PRISMA guidelines. A search of several databases conducted with two separate reviewers resulted in 29 papers meeting inclusion criteria for the review, 14 selected for meta-analysis. Primary outcomes assessed by the included papers included maximum keratometry (Kmax), corrected and uncorrected distance visual acuity (CDVA, UDVA), and secondary outcomes included central corneal thickness (CCT), endothelial cell count and demarcation line. Statistical analyses were carried out on Review Manager 5.4 and the meta-analysis employed a random-effects model, which estimated the weighted effect size of raw means using inverse variance weights.

RESULTS

At 12 months P-CXL showed statistically significant reductions in Kmax (-0.75 D; p < 0.001) and improvement in CDVA (-0.10 logMAR; p < 0.001) compared to baseline. The meta-analysis of comparative studies determined that mean differences in Kmax, CDVA, UDVA, Kmean and CCT after 12 months were not statistically significant between pulsed and continuous crosslinking groups.

CONCLUSIONS

Overall, P-CXL is effective in improving visual acuity and keratometry outcomes in keratoconus. The meta-analysis did not show a statistically significant difference in Kmax and CDVA between P-CXL and C-CXL, indicating a non-inferiority of P-CXL. However, findings of the meta-analysis are limited by the fact that different energy levels and exposure times were used for P-CXL in comparison to C-CXL in some studies, making it unsuitable to determine whether the efficacy of CXL is improved by the use of pulsed light.

KEY MESSAGES

What is Known • Pulsed crosslinking (P-CXL) uses intermittent UV light to prevent oxygen depletion when using higher energy protocols, unlike continuous UV exposure in standard continuous crosslinking (C-CXL). • This should theoretically enhance the efficacy of the treatment by maintaining higher oxygen levels that are crucial to the cross-linking process. • There are no systematic reviews or meta-analyses directly comparing the efficacy or safety of P-CXL to C-CXL. What is New • Meta-analysis revealed differences in keratometry between P-CXL and C-CXL groups with equivalent fluence (7.2 J/cm2) at 12 months were not statistically significant (Kmax -0.04 dioptres; p = 0.84). • Meta-analysis revealed differences in visual acuity between P-CXL and C-CXL groups with equivalent fluence (7.2 J/cm2) at 12 months were not statistically significant (CDVA -0.01 logMAR letters; p = 0.57). • The use of intermittent pulsing in higher energy CXL protocols renders statistically similar outcomes as continuous light exposure at equivalent fluence (7.2 J/cm2).

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Ray-Tracing Transepithelial Excimer Laser Central Corneal Remodeling Plus Pachymetry-Guided Accelerated Corneal Crosslinking for Keratoconus

PURPOSE

The aim of this study was to report the 12 to 96 months results of a tissue-preservation algorithm based on ray-tracing-guided transepithelial excimer laser central corneal ablation (RT t-PRK) combined with individualized pachymetry-guided accelerated crosslinking (M nomogram ACXL) in young adult patients with stable keratoconus (KC).

METHODS

This was a prospective interventional study including 38 eyes of 38 young adult patients (stage II KC) with a mean age of 35 years (range 26-46 years) who underwent simultaneous RT with t-PRK plus pachymetry-based ACXL in the worst eye. The treatments were performed using the iViS Suite iRES Excimer Laser (Ligi, Taranto, Italy). Ray-tracing-guided treatments were planned using the customized interactive programmed transepithelial ablation (CIPTA) 2 web software and diagnostic data were assessed by the Precisio 2 tomographer (Ligi, Taranto, Italy) and Sirius tomographer (C.S.O., Florence, Italy). The main outcome measures included uncorrected distance visual acuity, best spectacle-corrected visual acuity, Kmax, high-order aberrations, minimum corneal thickness, and posterior elevation, with a mean follow-up of 52 months (range 12-96 m).

RESULTS

The mean UDVA improved + 3.5 ±1.28 Snellen lines (SL); 38% gained ≥ 4 ±1.34 SLs, 35% ≥ 3 ±1.21 SLs, 22% ≥ 2 ±1.12 SLs, and 5% ≥ 1 ±0.75 SLs. The mean best spectacle-corrected visual acuity increased by + 4.3 ±1.3 SL. Sixty-eight percent gained ≥ 4 ±0.88 SLs and 30% ≥ 3 ±0.78 SL. No SLs were lost.

CONCLUSIONS

RT t-PRK plus ACXL significantly improved the quality of vision in patients with KC, preventing overcorrection and minimizing tissue consumption.

Continuous Intracorneal Ring Implantation in Keratoconus: Efficacy, Predictive Factors, and Complications

Purpose

To examine the clinical outcomes, predictors of visual improvement and complications of continuous intracorneal ring (ICCR) implantation in patients with keratoconus and confirmed contact-lens intolerance (CLI).

Methods

This nonrandomized, multi-centric, retrospective cohort study examined visual, keratometric and clinical outcomes evaluated after a minimum follow-up of 2 months. Among the inclusion criteria for the standard treatment group (STG) were corrected distance visual acuity (CDVA) <20/25 Snellen, no central corneal scars, minimum corneal thickness >350µm, and central mean keratometry reading (meanK) <55 diopters. All other eyes were classified as non-standard treatment group.

Results

A total of 118 eyes of 118 patients with aged 32 ± 11 years were included in this study. At a median follow-up of 161 days (interquartile range: 111-372 days) ICCR implantation improved the CDVA from a mean of 0.38 to 0.15 logMAR (p<0.0001). Our correlation analysis showed lower preoperative CDVA to be the single best predictor of CDVA improvement, with eyes of a CDVA of 20/80 or lower improving by 4.3 ± 2.0 lines on average. Eyes with a meanK >55 diopters gained 9.04±4.83 lines in UDVA and 2.86±3.09 lines in CDVA. However, postoperatively these eyes had a CDVA of 0.32±0.21 logMAR which is significantly inferior to the STG outcome (p=0.001372). Fifteen eyes (12.7%) had to undergo a ring exchange procedure because of refractive under- (9 eyes) or overcorrection (6 eyes). Two eyes (1.7%) experienced medical complications.

Conclusion

This study confirms the inclusion criteria of ICCR implantation in KC eyes with CDVA <20/25 and CLI. Particularly in eyes with a preoperative CDVA <20/80 and a meanK <55 diopters, ICCR implantation should be considered due to its reversibility and low rates of serious complications. The main challenge remains in the low predictability of the magnitude of this improvement in eyes with CDVA >20/30.

Results of the Pinhole Test Correlate with Hybrid Contact Lens Visual Acuity in Patients with Visual Impairment due to Corneal Diseases

Introduction. Trial rigid lens fitting is considered the best approach to determine whether the correction of residual defocus and irregular astigmatism might improve the visual acuity in patients with corneal disorders including keratoconus. This study aimed to analyze the correlation between hybrid lenses and pinhole visual acuity (VA). Methods. Patients undergoing hybrid contact lens fitting at the Hygeia Clinic, Poland, were included. The VA of each patient was assessed as decimal Snellen fractions under the following conditions: (i) uncorrected VA, (ii) VA with spherocylindrical correction (i.e., corrected distance VA), (iii) VA with a single 1.2 mm pinhole occluder, and (iv) VA with the best-fitted hybrid contact lens. Pearson’s correlation coefficient r was used to assess correlations among variables. Results. This study involved 29 eyes of 19 patients, mainly with advanced keratoconus. The uncorrected VA was 0.11 ± 0.10. The pinhole test provided significantly improved VA over corrected distance VA (0.51 ± 0.29 vs. 0.31 ± 0.20, respectively; $p<0.0001$ ). Similarly, the fitted hybrid contact lenses provided improved VA over corrected distance VA (0.66 ± 0.26 vs. 0.31 ± 0.20, respectively; $p<0.0001$ ). The pinhole VA was strongly correlated with the hybrid contact lens VA (r = 0.8135; 95% CI: 0.61–0.92; $p<0.0001$ ). The improvement in the pinhole test over corrected distance VA was moderately correlated with the improvement with the fitted lens over corrected distance VA (r = 0.6269; 95% confidence interval (CI): 0.32–0.80; $p=0.0005$ ). Conclusions. A significant improvement in VA with the pinhole test is a simple predictor of general improvement with hybrid contact lenses. The pinhole test should be used in patients with corneal diseases such as keratoconus to determine whether optical aberrations associated with the disease cause their visual impairment.

A Bibliometric Analysis of 100 Most-Cited Articles on Corneal Cross-Linking

Background

Highly cited papers are expected to have high-quality data that significantly contribute to the body of knowledge. The study aimed to evaluate the characters of the 100 most-cited articles on corneal cross-linking (CXL) through a bibliometric analysis.

Materials and Methods

The Web of Science database was searched to identify papers published from 1950 to 2020. A bibliometric analysis of the top 100-cited articles was conducted in the current study. The citation differences between basic research, clinical research, and reviews were compared by Kruskal-Wallis test. The association between citations and publication year was evaluated by Spearman correlation analysis. The VOSviewer software was used to create networks of co-authorship and keywords map.

Results

The median values of the number of citations, citations/year since publication, and citations since 2013 were 101, 9.5, and 11.92, respectively. A total of 61% of articles were clinical research. The citations since 2013 of clinical research were lower than basic research and the reviews (all p < 0.001). The publication year was positively correlated with the number of publications (r = 0.665, p = 0.013), and the total number of citations decreased for basic research (r = -0.447, p = 0.017), and clinical research (r = -0.433, p < 0.001). The J REFRACT SURG publishes the highest number of articles. The corresponding authors were predominantly from the Italy (N = 17), Germany (N = 16), and United States (N = 15). Spoerl Eberhard has the highest number of citations and total link strength with 15 articles. Extensive collaboration existed among the main core nodes containing "cross-linking (N = 45)," "riboflavin (N = 44)," and "ultraviolet A (UVA) (N = 42)."

Conclusion

The present study focused on the comprehensive analysis of the top 100-cited articles on the CXL research, providing insight into research developments over the past decades.

Performances of Corneal Topography and Tomography in the Diagnosis of Subclinical and Clinical Keratoconus

Aim

The purpose of the study was to assess the efficacy of topographical and tomographical indices given by the Pentacam (pachymetric, tomopetric, and aberometric) in clinical and subclinical keratoconus (KCN) diagnosis.

Material and Methods

In this observational analytic retrospective study, patients with abnormal findings in topography and tomography maps but with no signs on clinical examination (subclinical KCN group, sKCN), patients with clinical keratoconus (KCN group), and healthy subjects (Control group) were evaluated.

Results

The KCN group proved significantly different (p < 0.001) values of the investigated parameters than the Control group. Eleven out of 28 investigated parameters proved significantly different in the sKCN group compared to controls (p < 0.001). Two topographic measurements, namely I-S (cut-off = 1.435, a large value indicates the presence of KCN) and CCT (cut-off = 537, a small value indicates the presence of KCN), showed AUCs equal to 1 [0.999 to 1]. Six other Pentacam measurements, including Back maximum keratometry (Back Kmax) proved to be excellent parameters for case-finding and screening. In distinguishing sKCN from normal eyes, Pentacam index of vertical asymmetry (IVA), inferior-superior difference (I-S) value, thinnest point (TP), Belin Ambrosio Enhanced Ectasia Display (BAD_D) and root mean square total (RMS total) performed best.

Conclusions

In distinguishing sKCN from normal eyes, Back Kmax, IVA, I-S, and RMS total values demonstrated higher accuracy and utility. Six indices, namely ISV, IVA, KISA, PRC, RMS-HOA, and Back Kmax demonstrate excellent utility in case-finding and screening for clinical KCN.

Pachymetric Assessment After EpiSmart® Epithelium-on Cross-Linking for Keratoconus and Post-Surgical Ectasia

Purpose

To assess the change in corneal pachymetry after a novel epithelium-on (EpiSmart^®) corneal crosslinking procedure (CXL).

Methods

Eyes treated as part of the open-label, non-controlled arm of the study “Collagen Crosslinking with Ultraviolet-A in Asymmetric Corneas” (NCT01097447) were examined at baseline, 3-, 6- and 12-months post-CXL. Thinnest pachymetry readings based on Pentacam (OCULUS GmbH, Wetzlar, Germany) were recorded.

Results

A total of 101 eyes met the study inclusion criteria. Thinnest pachymetric readings at baseline averaged 451 ± 50 microns. The mean (± SD) minimum thickness was 450 ± 46 microns at 3 months, 452 ± 47 microns at 6 months, and 451 ± 48 microns at 12 months post-CXL. The changes from baseline (mean ± SE) at 3, 6, and 12 months post-CXL were −1.2 ± 1.5 microns, 0.5 ± 1.6 microns, and 0.4 ± 1.6 microns, respectively. Student’s t-tests showed no statistically significant change in pachymetry from baseline for any exam period.

Conclusion

This study demonstrated that, after EpiSmart^® epithelium-on CXL, there was no substantial corneal thinning observable on Scheimpflug tomography out to 12 months.

Crosslinking vs. Observation in Fellow Eyes of Keratoconus Patients

Purpose

To evaluate whether unilateral crosslinking (CXL) and conservative follow-up of the fellow eye is an acceptable management strategy in patients with keratoconus (KC).

Methods

Seventy-nine fellow eyes of KC subjects that initially underwent unilateral CXL were included. Thirty fellow eyes ultimately received CXL (group 1) whereas 49 fellow eyes were followed (group 2). Best spectacle corrected visual acuity (BSCVA) and corneal tomographic parameters were collected in all eyes preoperatively and at the last follow-up.

Results

Subjects who received CXL in the fellow eye (group 1) were younger than subjects who did not (group 2, p=0.026). Group 1 eyes had higher baseline K1 (p=0.026), K2 (p=0.006), Km (p=0.01), and Kmax (p=0.002) compared to group 2 eyes. Amongst the 49 naïve fellow eyes (group 2), 19 eyes showed evidence of progression. Progressing naïve eyes had higher baseline K1, K2, Km, and Kmax (p < 0.01); progressors also had thinner pachymetry at the pupil, apex, and thinnest point (p < 0.01). Baseline values of K1 ≥ 43.5 Diopter (D), K2 > 45.1D, Km > 44.3D, K_max > 47.9D, astigmatism > 1.4D, pachymetry at the pupil <475 μm, and thinnest pachymetry <478 μm were tentative predictors of progression in the naïve fellow eye.

Conclusions

Unilateral CXL with vigilant follow up of the fellow eye may be an acceptable management strategy in a subset of KC eyes.

Comparison of Long-Term Outcomes and Refractive Stability following SMILE versus SMILE Combined with Accelerated Cross-Linking (SMILE XTRA)

Purpose

To compare the long-term safety, efficacy, predictability, and refractive stability following SMILE versus SMILE combined with accelerated cross-linking (SMILE XTRA), and to specifically study the regression patterns following the two procedures.

Methods

This retrospective study included 54 eyes of SMILE and 54 eyes of SMILE XTRA treated for normal and borderline cases of myopia/myopic astigmatism, respectively, based on certain predefined topographic features and risk factors. Patients in both the groups were matched for age and refractive error. The mean postoperative follow-up for the SMILE group was 22.18 ± 10.41 months and the SMILE XTRA group was 21.81 ± 10.19 months.

Results

At the end of follow-up, the mean sphere, cylinder, and SE reduced to −0.03, −0.09, and −0.08 D in the SMILE group and −0.06, −0.15, and −0.13 D in the SMILE XTRA group. 96% and 93% eyes remained within ±0.50 D in SMILE and SMILE XTRA groups, respectively, and 94% eyes maintained an UDVA of 20/20 or better in the SMILE as well as SMILE XTRA groups. Safety and efficacy indices for the SMILE group were 1.03 and 1.00. For the SMILE XTRA group, the safety and efficacy indices were 1.00 and 0.99. No eye in either group had postoperative ectasia or enhancement performed for significant residual refractive error.

Conclusion

Both the SMILE and SMILE XTRA groups exhibited comparable visual outcomes, safety, and efficacy. Contrary to the belief, combination of prophylactic CXL with SMILE did not result in a hyperopic shift in the long term. No eye in either group encountered postoperative ectasia; however, further follow-up is suggested to establish the long-term effects on refractive and corneal stability following SMILE XTRA, as all the eyes treated in this group were borderline.

Delayed Re-epithelialization After Epithelium-Off Crosslinking: Predictors and Impact on Keratoconus Progression

Purpose: To investigate the demographic and corneal factors associated with the occurrence of delayed reepithelialization (DRE) after epithelium-off crosslinking (epi-off CXL).

Design:Retrospective case series.

Methods:A chart review was performed to identify patients treated with epi-off CXL. DRE was defined as a corneal epithelial defect detected by fluorescein staining that persisted for more than 10 days. Slit-lamp examination, anterior segment optical coherence tomography, corneal topography, and corneal in vivo confocal microscopy (IVCM) were always performed preoperatively and at each follow-up visit (1, 3, 6, 12 months). A generalized estimating equation was used to assess the baseline factors associated with DRE.

Results:Data from 153 eyes were analyzed. The mean age of patients was 24.9 ± 8.5 years, and 47 (30.7%) were women. The average reepithelization time was 4.7 ± 1.8 days. Six eyes (3.9%) experienced DRE. In the multivariate model, both the age of the patient (OR = 1.30; p = 0.02) and the corneal steepest meridian (OR = 0.44, p = 0.047) were associated with DRE. Baseline nerve count was also associated with DRE (0.87, p = 0.03). Male gender was associated with a slower early nerve regrowth (1–6 months) (p = 0.048), but not with the occurrence of DRE (p = 0.27). Preoperative central corneal thickness was not related to DRE (p = 0.16). DRE was not associated with keratoconus progression after epi-off CXL (p = 0.520).

Conclusions:The association between DRE and age may reflect the age-related decrease in the corneal healing response. Also, low baseline corneal nerve count is associated with DRE. Gender seems to affect reinnervation measured by IVCM but not the reepithelization time. DRE does not seem to affect the efficacy of epi-off CXL.

Comparative Results Between "Epi-Off" Accelerated and "Epi-Off" Standard Corneal Collagen Crosslinking-UVA in Progressive Keratoconus - 7 Years of Follow-Up

Purpose

The purpose of the present study was to assess the long-term efficiency and safety of the “epi-off” accelerated CXL (9 mW/cm² for 10 minutes) in comparison to the standard “epi-off” CXL (3 mW/cm² for 30 minutes) in terms of topographical and keratometric parameters, refractive data and visual outcomes at 7 years of follow-up, in progressive keratoconus.

Material and Method

A retrospective and comparative study was performed. A total of 183 eyes from 183 patients with documented progressive keratoconus were included in the study. The patients were divided in two groups: 93 eyes from 93 patients underwent “epi-off” standard cross-linking technique (3 mW/cm² for 30 minutes) (S-CXL group) and 90 eyes from 90 patients underwent accelerated “epi-off” corneal CXL technique (9 mW/cm² for 10 minutes) (A-CXL group).

Results

Improvements in uncorrected distance visual acuity (UDVA) were statistically significant compared to baseline values in both groups at each time-point visit (p=0.0421 at 1 year, p=0.0411 at 7 years for A-CXL and p=0.0375 at 1 year, p=0.0389 at 7 years for S-CXL). At 7 years there was a statistically significant increase in CDVA (p=0.039 in the A-CXL group and p=0.0343 in the S-CXL group at 7 years). Statistically significant reduction was noticed in Ksteep (p=0.0411 in A-CXL group and p=0.0224 in S-CXL group), Kflat (p=0.0198 in A-CXL group and p=0.008 in S-CXL group), K mean (p=0.0106 in A-CXL group and p=0.0193 in S-CXL group) and Kmax (p=0.0413 in A-CXL group and p=0.054 in S-CXL group) at 7 years, compared to baseline values, in both groups, but without any statistically difference between the two procedures, at all time-point visits (p>0.05).

Conclusion

The long-term outcomes of “epi-off” accelerated corneal collagen crosslinking-UVA (9 mW/cm² for 10 minutes) are similar to standard “epi-off” corneal collagen crosslinking procedure in the treatment of progressive keratoconus.

Update on corneal collagen crosslinking for ectasia

PURPOSE OF REVIEW

Corneal collagen crosslinking (CXL) is a minimally invasive treatment that can stabilize corneal ectatic disorders including keratoconus, pellucid marginal degeneration, or postrefractive surgery ectasia. The benefits of CXL have been well documented. New research is focused on modifying current treatment protocols with the goals of maximizing corneal stability while also shortening overall procedure time.

RECENT FINDINGS

Accelerated CXL protocols have the goal of delivering the same ultraviolet A intensity as conventional protocols, but over a shorter time period. Accelerated protocols have shown success to date, but there are concerns for long-term corneal stability. Pulsed protocols may increase the long-term efficacy of the accelerated designs. In addition, transepithelial crosslinking protocols have been designed with the goal of reducing postoperative pain and lower the risk of infectious complications of epithelial-off conventional protocols.

SUMMARY

Newer CXL protocols attempt to make the procedure safer and more effective. Current research is promising, but long-term studies are essential to understand how the new protocols may affect corneal stability.

Long term results of accelerated 9 mW corneal crosslinking for early progressive keratoconus: the Siena Eye-Cross Study 2

Purpose

To assess clinical results of the 9 mW/5.4 J/cm² accelerated crosslinking (ACXL) in the treatment of progressive keratoconus (KC) over a span of 5 years.

Methods

The prospective open non-randomized interventional study (Siena Eye-Cross Study 2) included 156 eyes of 112 patients with early progressive KC undergoing the Epi-Off 9 mW/5.4 J/cm² ACXL at the Siena Crosslinking Centre, Italy. The mean age was 18.05 ± 5.6 years. The 20-min treatments were performed using the New KXL I (Avedro, Waltham, USA), 10 min of 0.1% HPMC Riboflavin soaking (VibeX Rapid, Avedro, Waltham, USA) and 10 min of continuous-light UV-A irradiation. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), Kmax, coma, minimum corneal thickness (MCT), surface asymmetry index (SAI), endothelial cell count (ECC) were measured, and corneal OCT performed.

Results

UDVA and CDVA improved significantly at the 3rd (P = 0.028), Δ + 0.17 Snellen lines and 6th postoperative month, respectively (P < 0.001), Δ + 0.23 Snellen lines. Kmax improved at the 6th postoperative month (P = 0.03), Δ − 1.49 diopters from the baseline value. Also, coma aberration value improved significantly (P = 0.004). A mild temporary haze was recorded in 14.77% of patients without affecting visual acuity and without persistent complications. Corneal OCT revealed a mean demarcation line depth at 332.6 ± 33.6 μm.

Conclusion

The 5-year results of Epi-Off 9 mW/5.4 J/cm² ACXL demonstrated statistically significant improvements in UCVA and CDVA, corneal curvature and corneal higher-order aberrations which confers a long-term stability for progressive ectasia. Based on the results of the Siena Eye-Cross Study 2, the 9 mW/5.4 J/cm² ACXL is a candidate to be  the natural evolution of Epi-Off CXL treatment for the management of early progressive corneal ectasia, and thus optimize clinic workflow.

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.

Selective transepithelial ablation with simultaneous accelerated Corneal Cross-linking for corneal regularization of keratoconus: the STARE-X Protocol

Purpose

To evaluate the changes in refractive outcomes and corneal aberrations in central and paracentral keratoconus after Selective transepithelial topography-guided photorefractive keratectomy combined with Accelerated Corneal Collagen Cross-Linking (STARE-X).

Settings

Centro polispecialistico Mediterraneo, Siena Crosslinking Center and University of Messina (Italy).

Design

Prospective, interventional, multi-centric study.

Methods

One hundred eyes of 100 patients underwent STARE-X protocol. Patients were subdivided into 2 groups: Group 1 with cone located within the central 3-mm zone (50 eyes); and Group 2 (50 eyes) with cone located outside the central 3-mm zone. Follow-up was two years at least for all eyes. Outcome parameters included uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA). Corneal tomography and corneal wavefront aberrations were assessed and compared before and two years after the treatment.

Results

At 2 years UDVA, CDVA improved, as well as sphere, cylinder, K-max reduced after treatment in both groups (p<.001 respectively). Moreover, a statistically significant reduction was observed of total High-Order Aberrations Root Main Square (HOA RMS), Coma RMS and Spherical Aberration (SA RMS) in both groups (p<.001 respectively). However, CDVA improved more in Group 1 than in Group 2 (p<.02).

Conclusion

The STARE-X protocol demonstrated effective results in halting keratoconus progression and improving corneal regularity with a safe and effective profile. STARE-X improved both visual acuity and corneal aberration at 2 years. Longer follow-up studies are warranted to observe further long-term CXL flattening effect on the cone.

Biomechanical Properties in Different Types of Thin Corneas in Menoufia Population

Background

To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in normal thin (NT) healthy corneas with central corneal thickness (CCT) of 470–500 μm with matched thickness in keratoconus suspect (KCS) and keratoconus (KC) eyes.

Methods

A total of 103 eyes in three groups were included prospectively: NT, KCS, and KC groups based on clinical examination and Pentacam findings. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured using the ocular response analyzer (ORA). CCT, CH, and CRF were compared between the three groups and statistically analyzed by variance tests.

Results

The three groups consisted of 44 NT, 26 KCS, and 33 KC. The mean CH measured was 8.689 ± 1.775, 9.051 ± 1.1190, and 8.129 ± 0.8539 mmHg in NT, KCS, and KC eyes, respectively. The mean CRF was 8.441 ± 1.663, 8.337 ± 1.114, and 7.2422 ± 1.3110 mmHg in NT, KCS, and KC eyes, respectively. Within the range of central corneal thickness (470–500 μm), only mean CRF was statistically significantly different between the NT and KC (P < 0.05); there was no statistically significant difference between NT and KCS, nor was the mean CH between each group (P > 0.05).

Conclusions

CRF only can be helpful in differentiating KC from NT eyes; KCS could not be predicted with either corneal biomechanical metrics. There was no benefit from CH in differentiating between the three study groups.

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.

Association between Corneal Stiffness Parameter at the First Applanation and Keratoconus Severity

Objective

The study aimed to evaluate the character of corneal stiffness parameter at the first applanation (SP-A1) in normal and keratoconus eyes and explore the association between SP-A1 and keratoconus severity indicators.

Methods

A total of 351 normal and 351 keratoconus eyes were included in the current study. Keratoconus was diagnosed according to the corneal topography map and slit-lamp examination. The severity of keratoconus was classified to mild (steep keratometry (Ks) < 48D), moderate (48 ≤ Ks < 55D), and severe (Ks ≥ 55D). The SP-A1 was measured using the Corvis ST software. The correlation analyses and receiver operating characteristic (ROC) curve were performed in the current analysis.

Results

The SP-A1 values of keratoconus were lower than that of normal eyes (72.11 (57.02, 83.08) mmHg/mm vs 110.89 (100.45, 122.47) mmHg/mm, P < 0.001). With the severity of keratoconus increasing, the SP-A1 decreased and the value of SP-A1 was 79.54 (70.30, 90.93) mmHg/mm, 65.11 (53.14, 77.46) mmHg/mm, and 47.59 (37.50, 62.14) mmHg/mm in mild, moderate, and severe keratoconus eyes, respectively (P < 0.001). The negative association between SP-A1 and Ks was found in mild, moderate, and severe keratoconus eyes (r _mild = -0.171, r _moderate = -0.317, r _severe = -0.288, all P < 0.05). A positive association between SP-A1 and the thinnest corneal thickness (TCT) was found in all eyes (r_normal = 0.687, r _mild = 0.519, r _moderate = 0.488, r _severe = 0.382, all P < 0.05). SP-A1 was found to be statistically positively associated with intraocular pressure (IOP), biomechanical corrected IOP (bIOP), time from the initiation of air puff until the first applanation (A1T), corneal velocity at the second applanation (A2V), and negatively associated with deformation amplitude (DA), peak distance (PD), corneal velocity at the first applanation (A1V), time from the initiation of air puff until the second applanation (A2T), and DA Ratio Max [2 mm] both in normal and keratoconus eyes (all P < 0.05). The ROC analysis indicated that the AUC (95% CI) of SP-A1 was 0.952 (0.934-0.967) and 0.930 (0.904-0.951) in detecting keratoconus eyes and mild keratoconus eyes from normal eyes, respectively.

Conclusions

The SP-A1 value decreased while the keratoconus severity increased. It was lower in keratoconus than that in normal eyes and could be helpful in identifying keratoconus eyes from normal eyes. Further researches would be warranted to expand the clinical utility of SP-A1.

The Prevalence of Infectious Keratitis after Keratorefractive Surgery: A Systematic Review and Meta-Analysis Study

BACKGROUND

The keratorefractive surgeries (KRS) are one of the most common ocular surgeries. One of the dangerous complications of these surgeries is infectious keratitis (IK), which is the second cause of blindness after cataract surgery. The purpose of this study was to estimate the prevalence of IK after KRS in different parts of the world.

METHODS

In order to obtain relevant studies, all national and international databases including IranMedex, SID, Magiran, IranDoc, Medlib, ScienceDirect, PubMed, Scopus, Cochrane, Embase, Web of Science, and Google Scholar were searched using standard keywords.

RESULTS

IK prevalence after KRS was 0.000496% (0.000145% for the left eye and 0.000149% for the right eye). IK prevalence after KRS in the United States, Europe, and Asia was 0.000667%, 0.000473%, and 0.000045%, respectively, in all of which the common microorganisms were Staphylococci. Meta-regression showed no significant association between IK after KRS and either sample size or publication year of the studies. IK prevalence after KRS in the right eye was more than that in the left one. Also, the probability of IK incidence after LASIK surgery was more than PRK and LASEK. In the evaluation of continents, IK after KRS in the United States was more frequent compared with Europe and Asia.

CONCLUSIONS

This study provided data as to the overall prevalence of IK following KRS and its variations according to the types of eye, surgery, pathogenic microorganism, and geographical location.

Comparative Results of "Epi-Off" Conventional versus "Epi-Off" Accelerated Cross-Linking Procedure at 5-year Follow-Up

Purpose

The aim of our study was to compare the long-term efficacy and safety of “epi-off” conventional and “epi-off” accelerated corneal cross-linking (CXL) in patients with progressive keratoconus.

Methods

“Epithelial-off” (“Epi-off”) CXL using the conventional technique (3 mW/cm², 30 minutes) was performed in 93 eyes of 93 patients (S-CXL group) and “epi-off” accelerated method (9 mW/cm², 10 minutes) in 76 eyes of 76 patients with progressive KCN (A-CXL group). Cases with different stages of keratoconus and topographic evidence of progression were included. Main outcomes comprised refraction, keratometry measurements, uncorrected (UCVA) and best-corrected visual acuity (BCVA), and topographical indices. Micromorphological analysis was assessed by anterior segment ocular coherence tomography (AS-OCT). The follow-up period was 5 years.

Results

In both groups, Kflat presented similar results: decrease at 1 year (p=0.465), at 2 years (p=0.672), at 3 years (p=0.198), at 4 years (p=0.32), and at 5 years (p=0.864). In both groups, Ksteep presented a similar decrease at 1 year (p=0.709), at 2 years (p=0.455), at 3 years (p=0.43), at 4 years (p=0.57), and at 5 years (p=0.494), with no statistically significant difference. Decrease in Kavg was similar in both groups at all analyzed time points (p=0.18 at 1 year, p=0.093 at 2 years, p=0.57 at 3 years, p=0.154 at 4 years, and p=0.247 at 5 years). Kmax had a similar decrease in both groups at 1 year (p=0.06), at 2 years (p=0.09), at 3 years (p=0.126), at 4 years (p=0.113), and at 5 years (p=0.114). There was no statistically significant difference between the cylinder decrease in both groups (p=0.349 at 1 year, p=0.6782 at 2 years, p=0.299 at 3 years, p=0.0943 at 4 years, and p=0.144 at 5 years). The BCVA values were statistically significantly higher than the preoperative values in both groups at all time points (p < 0.05). Topographical indices such as thinnest corneal point (TP), corneal volume (CV), index vertical asymmetry (IVA), index of vertical asymmetry (ISV), index of height asymmetry (IHA), index of height decentration (IHD), Belin/Ambrosio Enhanced Ectasia Display (BAD_D), and Ambrosio retinal thickness (ART Max) were significantly statistically decreased compared with baseline at all time points, in both groups.

Conclusion

“Epi-off” accelerated and conventional CXL have the same efficacy in terms of improvement in visual and topographic outcomes.

Rotational Stability of a New Posterior Chamber Toric Phakic Intraocular Lens

PURPOSE

To evaluate the refractive results and rotational stability of Eyecryl toric phakic intraocular lens (pIOL).

METHODS

In this retrospective single-surgeon case series, manifest refraction, visual acuities, endothelial cell density (ECD), and pIOL rotation were evaluated over 6 months.

RESULTS

43 eyes from 23 patients were included. At 6 months, the SE was within ±0.50  D of emmetropia in 30 (70%) eyes and within ±1.00  D of emmetropia in 39 (91%) eyes. The efficacy and safety indices were 1.25 ± 0.38 and 1.41 ± 0.34, respectively. Mean ECD was 2719 ± 296 cells/mm2 at the preoperative visit and 2779.42 ± 422 cells/mm2 at the 6-month visit (p > 0.05). The mean value of absolute axis orientation error was 4.95 ± 5.28°. Mean absolute change in axis orientation between visits was less than 3° for all visit intervals. Ninety percent or more of lenses were found to rotate 5° or less between all visit intervals. None of the patients experienced a vision-threatening complication, and no patient required secondary IOL repositioning.

CONCLUSION

The pIOL appears to effectively reduce subjective manifest astigmatism and provide good visual acuity. Its position was found to be stable throughout the follow-up.

Efficacy of pulsed-light accelerated crosslinking in the treatment of progressive keratoconus: Two-year results

PURPOSE

The aim of this study was to evaluate the 2-year results of epithelium-off pulsed-light accelerated corneal collagen crosslinking treatment in progressive keratoconus using 30 mW/cm² ultraviolet A light for 6 min with a total dose of 5.4 J/cm².

METHODS

A total of 30 eyes of 22 patients with documented progressive keratoconus and treated with epithelium-off pulsed-light accelerated corneal collagen crosslinking using the KXL® crosslinking device (Avedro Inc, Waltham, MA, USA) were included in this retrospective study. Corneal tomographic measurements and best spectacle-corrected visual acuity were compared using analysis of variance with repeated measurements between the baseline visit (before the corneal collagen crosslinking treatment), and the sixth month, first, and second year visits.

RESULTS

Flat keratometry (K1), steep keratometry (K2), and mean keratometry (Km) decreased significantly at sixth month, first, and second years (p < 0.001, p = 0.001, and p < 0.001, respectively). Maximum keratometry (Kmax) decreased from 55.40 ± 4.90 D at baseline to 54.82 ± 4.68 D, 54.80 ± 5.12 D, and 54.65 ± 5.36 D at sixth month, first year, and second year, respectively (p = 0.007). The best spectacle-corrected visual acuity improved from 0.34 ± 0.24 logMAR at baseline to 0.25 ± 0.16 logMAR, 0.22 ± 0.15 logMAR, and 0.17 ± 0.13 logMAR at sixth month, first year, and second year, respectively (p < 0.001). At the second year visit, best spectacle-corrected visual acuity remained stable (no lines lost) with respect to the baseline in 8 eyes and increased 1 or more lines in 22 eyes.

CONCLUSION

Pulsed-light accelerated corneal collagen crosslinking using 30 mW/cm² ultraviolet A light for 6 min with a total dose of 5.4 J/cm² is an effective treatment modality in cases with progressive keratoconus-it stops progression at 2 years also regresses some of the cases.

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.

Correlation between corneal stromal demarcation line depth and topographic outcomes after two pulsed-light-accelerated crosslinking protocols

Purpose

To report the visual and topographic outcomes of two pulsed-light-accelerated CXL (A-CXL) protocols at a 12-month follow-up and their correlation with the corneal stromal demarcation line (DL) depth.

Patients and methods

Retrospective comparative cohort of patients with documented progressive keratoconus were included. Two epi-off pulsed-light [1s on–1s off] A-CXL protocols were compared: irradiance 30*8 and 45*5:20 (fluence 7.2 J/cm²). UDVA, CDVA, spherical equivalent (SE), topographic astigmatism, K_min, K_max, K_m, central corneal thickness (CCT), thinnest pachymetry (TCT) and endothelial cell density (ECD) were measured preoperatively and months 1, 3, 6 and 12 postoperative. Corneal DL was measured 1 month postoperatively using anterior segment optical coherence tomography.

Results

Fifty eyes (27 patients): 22 eyes in group A-CXL (30*8), 28 eyes in group A-CXL (45*5:20). Mean age (years) was 19.04±4.71 and 20.32±4.57. DL depth (µm) at month 1 was 200.63±10.01 µm and 184.53±19.68 µm for group A-CXL (30*8) and group A-CXL (45*5:20), respectively (p<0.001). Significant improvement in CDVA, topographic astigmatism, K_min, K_max and K_m was observed in both groups (no significant difference between groups) and no significant changes were observed in CCT, TCT and ECD with regard to baseline. Over 85% of the eyes in both protocols achieved stabilization or improvement in maximum K at the end of the follow-up. No significant correlations between DL and any visual or topographic outcomes were observed at 12 months.

Conclusion

No correlation between DL depth and visual or topographic outcomes was observed on either protocol. Although significant improvement on CDVA, topographic astigmatism, K_min, K_max and K_m was observed in both groups at 12 months, further research is needed to assure safety and effectiveness at stabilizing keratoconus progression.

Different accelerated corneal collagen cross-linking treatment modalities in progressive keratoconus

Background

To compare the outcomes of two different protocols of accelerated corneal crosslinking (CXL) on visual, corneal high order aberrations (HOA) and topographic parameters in patients with progressive keratoconus.

Methods

In this prospective comparative study, sixty-six eyes of 66 patients with progressive keratoconus were divided into two groups; 37 eyes in Group 1 received 18 mW/cm² for five minutes, and 29 eyes in Group 2 were treated with 9 mW/cm² for 10 min. The uncorrected distant visual acuity (UCVA), best-corrected distant visual acuity (BCVA), corneal HOAs and topography parameters were measured preoperatively and postoperatively at the end of 12 months. The data for the two groups were compared statistically.

Results

The mean UCVA and BCVA were significantly improved at the postoperative 12 months compared with the preoperative values in both groups (P < 0.05 for all). A significant improvement in corneal HOAs was observed in both groups (P < 0.05 for all). The change in corneal coma value was significantly higher in Group 2 (P < 0.05). The change in keratometric values K1, K2, AvgK and maximum keratometry (AKf) were significantly higher in Group 2 (P < 0.05 for all). The regression model showed that the most important factor predicting the change in AKf was the type of CXL (β = − 0.482, P = 0.005).

Conclusions

Accelerated CXL using 10 min of UVA irradiance at 9 mW/cm² showed better topographic improvements and coma values than five minutes of UVA irradiance at 18 mW/cm² independent of keratoconus severity.

Comparative Functional Outcomes After Corneal Crosslinking Using Standard, Accelerated, and Accelerated With Higher Total Fluence Protocols

PURPOSE

To compare the relative 12-month corneal crosslinking (CXL) functional outcomes using standard protocol and accelerated protocols in patients with progressive keratoconus.

METHODS

CXL was performed using 3 epithelium-off protocols: standard [3 mW/cm for 30 minutes, 5.4 J/cm (S3/30-CXL)], accelerated with equivalent total irradiance [9 mW/cm for 10 minutes, 5.4 J/cm (A9/10-CXL)], and accelerated with increased total irradiance [30 mW/cm for 4 minutes, 7.2 J/cm (A30/4-CXL)]. Efficacy measurements were evaluated 12 months after treatment with Scheimpflug imaging (Pentacam HR) and included change in maximum keratometry (K Max), corrected distance visual acuity (CDVA), other keratometric variables, pachymetry, keratoconus indices, astigmatism, asphericity, manifest refraction, and higher order aberrations.

RESULTS

Ninety-three eyes (67 patients) were evaluated: 35 eyes (26 patients) with S3/30-CXL, 29 eyes (19 patients) with A9/10-CXL, and 29 eyes (22 patients) with A30/4-CXL. Mean [INCREMENT]K Max was -1.53 ± 2.1 diopter (D) for S3/30-CXL, -0.71 ± 1.3 D for A9/10-CXL, and -0.70 ± 2.3 D for A30/4-CXL (P = 0.37). Mean [INCREMENT]CDVA(logMAR) was -0.18 ± 0.2 for S3/30-CXL, -0.13 ± 0.2 for A9/10-CXL, and -0.18 ± 0.2 for A30/4-CXL (P = 0.79). [INCREMENT]K Mean (r = -0.29 to -0.46), anterior asphericity (r = -0.34 to -0.40), and central keratoconus index (r = -0.18 to -0.38) best correlated with [INCREMENT]CDVA. S3/30-CXL had greater changes in index of surface variance, index of vertical asymmetry, keratoconus index, and regularization index compared to A9/10-CXL and A30/4-CXL. There were no other differences between protocols.

CONCLUSIONS

All 3 protocols showed improvements in K Max, CDVA, and other variables, with similar functional outcomes for each despite greater change in keratoconus indices after S3/30-CXL. Correlations between change in measured variables and CDVA were poor overall; however, K Mean, central keratoconus index, and anterior asphericity were better correlated with CDVA than K Max.

Effect of the retention ring-assisted continuous application of riboflavin in pulsed-light accelerated corneal collagen cross-linking on the progression of keratoconus

Background

To investigate the efficacy and safety of the retention ring-assisted continuous application of 0.1% riboflavin in pulsed-light accelerated corneal collagen cross-linking on the progression of keratoconus.

Methods

The medical records of 20 eyes of 18 patients with progressive keratoconus who received collagen cross-linking at Seoul National University Hospital were retrospectively reviewed. Isotonic 0.1% riboflavin was continuously applied for 10 min using an 8.0-mm retention ring before the irradiation and accelerated cross-linking was applied with 30-mW pulsed-ultraviolet light at a wavelength 365 nm for eight minutes (1 s on/1 s off; 30 mW/cm², cumulative dose of 7 .2J/cm²) without further intermittent application of riboflavin. Visual acuity, refractive error, topographic index, corneal thickness, and endothelial cell density were evaluated before the operation and at 1, 3, 6, and 12 months.

Results

The best corrected visual acuity in logMAR improved from preoperative 0.43 to 0.17 in 12 months (p = 0.050). Maximum keratometry decreased from 51.8 D to 50.4 D at 6 months (p = 0.015) and 50.1 D at 12 months (p = 0.0003). Astigmatism decreased from preoperative 5.5 D to 4.1 D at 12 months (p < 0.0001). Thinnest corneal thickness decreased at three and 6 months but recovered in 12 months (p > 0.05). Endothelial cell density decreased at postoperative 1 month (p = 0.02) but gradually recovered in 12 months (p > 0.05).

Conclusions

Retention ring-assisted continuous application of riboflavin for 10 minutes in pulsed-light accelerated cross-linking is a comparably safe and effective treatment for halting the progression of keratoconus in 12 months when compared to outcomes of the standard Dresden protocol shown in previous reports.

Electronic supplementary material

The online version of this article (10.1186/s12886-019-1085-2) contains supplementary material, which is available to authorized users.

Randomized Study of Collagen Cross-Linking With Conventional Versus Accelerated UVA Irradiation Using Riboflavin With Hydroxypropyl Methylcellulose: Two-Year Results

PURPOSE

To compare the clinical outcome 2 years after corneal collagen cross-linking (CXL) with conventional and accelerated ultraviolet A (UVA) irradiation using riboflavin with hydroxypropyl methylcellulose.

METHODS

Prospective randomized controlled study. Forty patients with keratoconus (40 eyes) were randomized to either CXL using conventional 3 mW/cm UVA irradiation for 30 minutes (CXL30 group) or accelerated 9 mW/cm UVA irradiation for 10 minutes (CXL10 group). In both groups, a solution of 0.1% riboflavin with 1.1% hydroxypropyl methylcellulose (methylcellulose-riboflavin) was used. Uncorrected distance visual acuity, corrected distance visual acuity (CDVA), and Scheimpflug tomography were performed at baseline and after 24 months.

RESULTS

Both groups had statistically significant improvement in CDVA and maximum keratometric reading compared with baseline; however, with no statistically significant difference in the change between the 2 groups. No significant changes in flattest, steepest and mean keratometry (K1, K2 and K mean) were found in either of the groups. There were no statistically significant changes in ECD in either group after 2 years or in the difference in the change between the 2 groups. A literature review showed comparative clinical outcome after accelerated CXL compared with conventional CXL; however, in several studies, there was a tendency for less pronounced corneal flattening after accelerated CXL.

CONCLUSIONS

Improvement in visual acuity and maximum keratometric reading 2 years after CXL was found after both conventional and accelerated UVA irradiation using methylcellulose-riboflavin. This suggests that when using riboflavin with methylcellulose, the less time-consuming accelerated protocol is a valuable and effective option in CXL treatment.

Correlation of Demarcation Line Depth With Medium-Term Efficacy of Different Corneal Collagen Cross-Linking Protocols in Keratoconus

PURPOSE

To compare demarcation line depth (DD) and topographic changes among different corneal collagen cross-linking (CXL) protocols and to evaluate the relation of DD with medium-term efficacy of CXL in halting progression of keratoconus.

METHODS

The study included 124 patients (mean age 19 ± 4.8 years) with progressive keratoconus who underwent conventional (3 mW/cm/30 min), accelerated (18 mW/cm/5 min), or transepithelial (TE) CXL (3 mW/cm/30 min) and followed up for at least 2 years. Baseline and final corneal topographic parameters and DD determined with anterior segment optical coherence tomography 1 month after CXL were compared among the protocols and the correlation between DD and topographic changes at the end of 24 months was analyzed. P < 0.05 was considered as statistically significant.

RESULTS

Mean DD was significantly higher in the conventional and accelerated groups (335.19 ± 71.13 μm and 304.97 ± 94.45 μm, respectively) compared with the TE group (239.92 ± 71.37 μm) (P < 0.001). After conventional and TE CXL, keratometric parameters improved remarkably, whereas accelerated CXL only lowered K1 and Kmax (P < 0.05). No correlation was found between DD and topographic changes (P > 0.05). Progression was detected in 3 eyes in the conventional group (4.1%), 3 in the accelerated group (7.7%), and none in the TE group. The use of either riboflavin D or M made no differences in terms of DD and topographic parameters (P > 0.05).

CONCLUSIONS

In conventional and accelerated protocols, corneal stromal demarcation line is deeper compared with TE CXL; however, the DD has no correlation with topographic changes, which means that DD is not a direct measure for the efficacy of CXL.

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

PURPOSE

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

SETTING

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

DESIGN

Retrospective case series.

METHODS

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

RESULTS

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

CONCLUSIONS

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

Current perspectives on corneal collagen crosslinking (CXL)

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