Corneal Stability and Visual Acuity 1 Year After Corneal Cross-linking Assessed Using the ABCD Keratoconus Staging System

[Corneal biomechanics before and after cross-linking in patients with keratoconus]

OBJECTIVE

The aim of this study was to analyze the effect of corneal cross-linking (CXL) on corneal biomechanics and visual acuity.

PATIENTS AND METHODS

The examination results before and after CXL in 56 eyes of 56 patients between 2017 and 2021 were evaluated retrospectively. The last preoperative examination was compared to the postoperative follow-up values after 6 and 12 months. The main outcome measures included various biomechanical parameters from the Corvis ST (CST), Pentacam and the visual acuity (logMAR, "logarithm of the Minimal Angle of Resolution"). For longitudinal evaluation, a general linear model for repeated measurements was used. A p-value of less than 0.05 was considered to show a statistically significant result. Bonferroni correction was applied for multiple comparisons.

RESULTS

The maximum corneal refractive power Kmax decreased slightly without statistical significance from 57.1 ± 6.1 diopters (dpt) to 56.6 ± 6.3 dpt after 6 months (p = 0.076) and 56.8 ± 6.6 dpt after 12 months (p = 0.443). The Pentacam parameter Belin/Ambrósio Enhanced Ectasia Total Deviation Display (BAD D) showed a statistically significant increase from the preoperative value of 8.4 ± 3.7 to the postoperative value of 9.1 ± 3.6 after 6 months (p < 0.001) and to 8.9 ± 3.5 after 12 months (p = 0.051). The CST parameter Ambrósio's relational thickness to horizontal profile (ARTh) decreased statistically significantly from 229.9 ± 109.6 to 204.8 ± 84.9 at 6 months (p = 0.017) and 205.3 ± 93.7 at 12 months (p = 0.022). The CST parameter stiffness parameter A1 (SP A1) increased slightly from the preoperative value 69.9 ± 17.2 to 70.4 ± 17.2 after 6 months (p = 1) and 71 ± 18.2 after 1 year (p = 1). Mean best-corrected visual acuity (logMAR) showed an improvement from 0.39 ± 0.3 to 0.34 ± 0.3 at 6 months (p = 0.286) and to 0.31 ± 0.3 at 12 months (p = 0.077). Regarding the ABCD classification, the parameters were determined preoperatively with an average of A2B3C1D2. They showed the same value of A2B3C1D2 after 6 and 12 months.

CONCLUSION

In progressive keratoconus, corneal cross-linking has the potential to positively influence the biomechanics of the cornea and visual acuity as a low complication treatment option.

ABCD progression display for keratoconus progression: a sensitivity-specificity study

OBJECTIVE

To evaluate the sensitivity and specificity of the ABCD progression display for keratoconus progression.

METHODS

Data was collected from patients that underwent at least two Pentacam assessments 6 months apart. Sensitivity and specificity were calculated for the ABCD progression display. Progression was defined by criterion 1: change in two ABCD parameters above 80% confidence interval (CI) or criterion 2: change in one ABCD parameter above 95%CI. Receiver operating characteristic analysis compared the area under the curve (AUC) of all ABCD parameter combinations.

RESULTS

Thirty eyes were evaluated over a median time of 10.3 months. Progression by criterion 1 resulted in a sensitivity of 61.9% and specificity of 88.9%. Progression by criterion 2 resulted in higher sensitivity (80.9%) and specificity (100%). Pairwise comparisons of the ROC curves show that the AUC achieved by criterion 2 was significantly higher than criterion 1 (0.905 vs. 0.754, p = 0.0332). Evaluation of all ABCD combinations with a significant change of 80% or 95% CI did not show superiority over criterion 1 or 2 regarding progression detection. The D parameter had a very low AUC (0.5-0.556).

CONCLUSIONS

The ABCD progression display can assess keratoconus progression with high sensitivity and specificity, thus assisting the patients' decision-making process. The D parameter did not contribute to the sensitivity or specificity of this classification.

Short-Term Effect of Conventional Versus Accelerated Corneal Cross-Linking Protocol on Corneal Geography and Stability

Purpose: To determine the 6-month effect of conventional (CXL30) and accelerated cross-linking with a UVA intensity of 9 mW/cm² (CXL10) on corneal stability and to investigate whether there was a difference in ABCD grading system parameters regarding the two different procedures. Methods: Twenty-eight eyes of 28 patients with a documented keratoconus (KN) progression were included. Patients were selected to undergo either epi off CXL30 or CXL10. At the baseline and the follow-up visits after one (V1), three (V2), and six months (V3), the patients underwent complete ophthalmic examination and corneal tomography. Results: In the CXL30 group, all the parameters from the ABCD grading system significantly changed from baseline to V3; parameter A decreased (p = 0.048), B and C increased (p = 0.010, p < 0.001), and D decreased (p < 0.001). In the CXL10 group, there were no changes in parameters A (p = 0.247) and B (p = 0.933), though parameter C increased (p = 0.001) and D decreased (p < 0.001). After an initial decline after one month, visual acuity (VA) recovered on V2 and V3 (p < 0.001), and median maximal keratometry (Kmax) decreased in both groups (p = 0.001, p = 0.035). In the CXL30 group, there were significant changes in other parameters; average pachymetric progression index (p < 0.001), Ambrósio relational thickness maximum (ARTmax) (p = 0.008), front and back mean keratometry (p < 0.001), pachymetry apex (PA) (p < 0.001), and front elevation (p = 0.042). However, in the CXL10 group, there were significant changes only in ARTmax (p = 0.019) and PA (p < 0.001). Conclusion: Both epi-off CXL protocols showed similar short-term efficacy in improving VA and Kmax, halting the progression of KN, and both similarly changed tomographic parameters. However, the conventional protocol modified the cornea more significantly.

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.