Comparison of Corneal Collagen Cross-Linking Protocols Measured With Scheimpflug Tomography

Accelerated versus conventional corneal collagen cross-linking for keratoconus: A meta-analysis of randomized controlled trials

PURPOSE

To systematically compare the effectiveness of conventional corneal collagen cross-linking (CCXL) protocols and accelerated corneal collagen cross-linking (ACXL) protocols in cases with progressive keratoconus.

METHODS

The Cochrane library, EMBASE, MEDLINE, PubMed, and Web of Science databases were searched for randomized controlled trials (RCTs). Outcomes were clinical results and changes in corneal properties. Standardized mean differences (SMD) and 95% confidence interval (CI) were used to estimate the clinical consequences. All outcomes were distributed by different follow-up durations (6 months, 12 months, and > 12 months). We also compared maximum keratometry (Kmax) and best spectacle-corrected visual acuity (BCVA) in subgroups, which were categorized by the discrepant impregnation time period of riboflavin.

RESULTS

We included 14 RCTs that met the eligibility criteria in this meta-analysis. At the last follow-up, CCXL was superior in postoperative change in demarcation line (SMD: -1.573; 95% CI: -2.897 to -0.248) and in Kmax (SMD:0.302; 95% CI: 0.071 to 0.533), whereas ACXL provided a significantly lower reduction in central corneal thickness (SMD: 0.498; 95% CI: 0.125 to 0.871). No differences in the changes in uncorrected visual acuity, BCVA, manifest refraction spherical equivalent, corneal biomechanical properties, and the endothelial cell density were found among both groups.

CONCLUSION

CCXL was superior to ACXL in greater corneal flattening and deeper demarcation line, while ACXL seemed to cause less reduction in CCT and allow for earlier UDVA stability. To clearly define the comparative safety and clinical consequences of the different regimens of CXL, more RCTs are required.

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 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.

The Independent Effect of Various Cross-Linking Treatment Modalities on Treatment Effectiveness in Keratoconus

PURPOSE

To investigate the 1-year outcomes of using various corneal cross-linking (CXL) techniques for treating keratoconus.

METHODS

Setting: This is a prospective longitudinal cohort study performed at a tertiary academic medical center.

PATIENT POPULATION

Six hundred seventy eyes of 461 patients with progressive keratoconus who underwent CXL were followed up for 1 year.

INTERVENTION

Eight combinations of CXL modalities were assessed, including 2 different CXL techniques (transepithelial or epithelium-off), 7 riboflavin formulations, and 2 ultraviolet-A protocols (conventional 3 mW/cm or accelerated 9 mW/cm). Patients treated using the Dresden protocol were used as the reference group.

MAIN OUTCOME MEASURES

Primary outcomes were maximum keratometry and mean keratometry 1 year after treatment. Multivariable linear regression was used which provides β coefficients (β). Secondary outcomes were uncorrected and corrected distance visual acuity, manifest refractive spherical equivalent, and corneal thickness 1 year after treatment.

RESULTS

Four treatment modalities differed significantly from the reference group regarding both maximum keratometry and mean keratometry: the transepithelial CXL (TE-CXL) group (β = 1.422; P = 0.001), 1 riboflavin formulation (Meran β = 1.210; P = 0.02), and both the 9 mW/cm protocols (Vibex Rapid β = 1.751; P < 0.001 and Collagex β = 1.170, P < 0.001). Overall, the visual outcome, manifest refractive spherical equivalent, and corneal thickness were similar among the treatment modalities. Infections were rare (1.6% of cases); however, re-treatment was required for 33.3% of cases that underwent TE-CXL.

CONCLUSIONS

TE-CXL, the use of Meran riboflavin, and applying the accelerated irradiation protocol appeared to be associated with reduced efficacy regarding controlling keratoconus progression. One-third of cases treated using TE-CXL required re-treatment.

Accelerated, Pulsed Collagen Cross-Linking versus the Dresden Protocol in Keratoconus: A Case Series

PURPOSE

The aim of our study was to compare the depth of the demarcation line developing in the cornea after the standard Dresden protocol versus the accelerated, pulsed, epithelium-off corneal collagen cross-linking (CXL).

METHODS

This was a nonrandomized, retrospective case series. Patients with progressive keratoconus were treated with either the standard Dresden protocol (Group 1) or accelerated, epithelium-off CXL using the Avedro (Waltham, MA, USA) device (Group 2). The accelerated CXL protocol involved 18 min of pulsed ultraviolet-A (20 mW/cm2, 7.2 J/cm2, pulsed pro-file: 1 s on, 2 s off). The depth of the demarcation line was measured about 3 months postoperatively.

RESULTS

Fifty-nine eyes of 35 subjects were included in the analysis. Group 1 consisted of 19 eyes, and Group 2 of 40 eyes. The mean age of the participants was 22.21 years in Group 1 and 26.55 years in Group 2 (p = 0.184). The mean preoperative K value was 44.89 D in Group 1 and 45.20 D in Group 2 (p = 0.768). The depth of the demarcation line was 322.50 μm in Group 1 and 319.95 μm in Group 2 (p = 0.937).

CONCLUSIONS

The demarcation line depth was not statistically significantly different between the two protocols. The significance of the demarcation line depth has not been fully clarified in the literature. Our results support the contention that these two techniques may have similar structural outcomes and ef-ficacies in the treatment of keratoconus.

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

Purpose

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

Methods

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

Results

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

Conclusions

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