Factors influencing haze formation and corneal flattening, and the impact of haze on visual acuity after conventional collagen cross-linking: a 12-month retrospective study

Background Our aim was to determine associations of pachymetry, keratometry, and their changes with haze formation and corneal flattening after collagen cross-linking, and to analyse the relationship between postoperative haze and visual outcome. Methods Retrospective analysis was performed on 47 eyes of 47 patients with keratoconus using the Pentacam HR Scheimpflug camera before and 1, 3, 6 and 12 months after cross-linking. Corneal backscattered light values in grey scale unit were recorded in the anterior, center and posterior corneal layers and in four concentric rings. Surface area- and thickness-corrected grey scale unit values were assessed with an additional calculation. Friedman test with post hoc Wilcoxon signed-rank test was used to analyse changes in visual acuity, pachymetry, keratometry and densitometry. Spearman’s rank correlation test was used to detect correlations of haze formation and corneal flattening with pachymetry, keratometry and their postoperative change. Generalized estimating equations analysis was used to investigate the influence of densitometry values on postoperative visual acuity after controlling for the effect of preoperative keratometry. Results One year after treatment, significant flattening was observed in maximum and mean keratometry readings (p < 0.001). Significantly increased densitometry values were observed in three central rings compared to baseline (post hoc p < 0.0125). According to receiver operating characteristic curve, densitometry value of the anterior layer of 0–2 mm ring was the most characteristic parameter of densitometry changes after cross-linking (area under the curve = 0.936). Changes in haze significantly correlated with preoperative maximum keratometry (R = 0.303, p = 0.038) and with the changes in maximum keratometry (R = -0.412, p = 0.004). Changes in maximum keratometry correlated with preoperative maximum keratometry (R = -0.302, p = 0.038). Postoperative haze had a significant impact on uncorrected and best corrected distance visual acuity (β coefficient = 0.006, p = 0.041 and β coefficient = 0.003, p = 0.039, respectively). Conclusions Our findings indicate that in more advanced keratoconus more significant corneal flattening effect parallel with haze formation can be observed after cross-linking. Despite significant reduction of keratometry, postoperative corneal haze may limit final visual acuity.

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.

Extreme corneal flattening following collagen crosslinking for progressive keratoconus

Purpose: To study the clinical, tomographic and densitometric features of eyes that showed >5 D of corneal flattening following collagen crosslinking (CXL) for progressive keratoconus and to identify preoperative predictive factors for such a response. Methods: This was a retrospective case control study of 548 eyes with progressive keratoconus which had undergone epithelium-off CXL (Dresden protocol) with a follow-up of 1 to 10 years. Eyes that showed ⩾5 D corneal flattening in maximum keratometry (Kmax) following CXL (group A) were compared with one eye of the remaining patients in the same cohort (group B). Changes in refraction and visual acuity, Kmax and thinnest pachymetry were compared between both groups. Univariate and multivariate regression analysis identified preoperative risk factors for unusual corneal flattening. Results: Forty three eyes in group A were compared with 502 eyes in group B. At the time of maximum flattening, group A showed more flattening (−7.6 ± 3.2 D) and thinning (−53.7 ± 45.2 µ) than group B (−1.69 ± 2.9 D and −26.6 ± 36.7 µ, respectively). Multivariate analysis based on parameters suggested by a univariate regression analysis identified pre-op Kmax to be the most significant predictor of intense corneal flattening. A subgroup analysis of K-matched eyes revealed that the duration of time following CXL was a significant risk factor for extreme corneal flattening following CXL Conclusion: An intense corneal flattening >5 D in Kmax was documented in 7.85% of a cohort of keratoconus patients who underwent CXL. High preoperative Kmax and the duration of time following CXL were significant predictors of this response which was accompanied by significant corneal thinning.

Evolution of corneal flattening after repeated corneal cross-linking during a 6-year follow-up

Purpose: To report the evolution of corneal flattening after repeated corneal cross-linking (CXL) in a patient with progressive keratoconus during a 6-year follow-up. Methods: Case report. Results: A 27-year-old female underwent CXL for progressive keratoconus. Postoperatively, corneal topography revealed keratoconus progression with an increase of 1.20 diopters (D) in maximum keratometry (Kmax) and CXL was repeated. After the second treatment, a continuing significant corneal flattening (up to 16.00 D in Kmax) was observed during the first 5 years followed by stabilization during the last sixth year of follow-up. Both uncorrected and corrected distance visual acuity were improved while corneal thickness was decreased. There were no complications such as corneal opacification or endothelial cells decrease during the follow-up period. Conclusion: Repeated CXL can induce an excessive corneal flattening more pronounced during the first years of follow-up followed by stabilization thereafter.

Increased Corneal Toricity after Long-Term Orthokeratology Lens Wear

Purpose. To investigate the change in corneal toricity and associated refractive astigmatism after discontinuation of long-term orthokeratology (ortho-k) lens wear. Methods. This study investigated 136 subjects aged between 6 and 14 (9.1 ± 1.5) years old at the commencement of ortho-k treatment, who had been undergoing overnight ortho-k treatment for 24 to 72 (37.4 ± 11.9) months. Corneal refractive power and manifest refraction were measured and compared before ortho-k and 1 month after discontinuation of ortho-k lens wear. Changes in corneal curvature were analyzed. Corneal curvature data from a historical longitudinal study were used as control. Results. Compared to pre-ortho-k values, the corneal curvature became significantly flatter in the flatter meridian (−0.22 ± 0.27 D, P<0.001) and steeper in the steeper meridian (0.06 ± 0.34 D, P=0.032) after cessation of ortho-k lens wear, resulting in a significant increase in corneal toricity (0.28 ± 0.43 D, P<0.001), which is associated with an increase in refractive astigmatism (0.57 ± 0.57 D, r=0.465, P<0.001). The amount of residual corneal flattening in the flatter meridian is significantly affected by the length of ortho-k treatment (t=−2.965, P=0.004) and the baseline age of subject (t=−2.841, P=0.005), but not by the baseline spherical or cylindrical refractive error (both P>0.05). In the historical control group, there is no significant change in the corneal curvature over two years in children wearing spectacle lenses (both meridians, P>0.05). Change of corneal toricity was more significant in the ortho-k group than in the spectacle control group (P=0.001). Conclusions. Long-term ortho-k lens wear increases corneal toricity after discontinuation of the treatment, which is associated with an increase in refractive astigmatism. A more pronounced change in corneal toricity was found in subjects who were younger to start ortho-k and have been in a longer period of treatment. This trial is registered with http://www.chictr.org.cn (ChiCTR-TNRC-11001210).

Intrastromal Corneal Ring Segments in Children with Keratoconus

ABSTRACT Purpose To evaluate the long-term follow-up of Ferrara intrastromal corneal ring segments (ICRSs) (Ferrara Ophthalmics, Belo Horizonte, Brazil) implantation for the management of keratoconus in children. Study design Paulo Ferrara Eye Clinic, Belo Horizonte, Minas Gerais, Brazil. Materials and methods A total of 58 eyes of 37 children with keratoconus were included. One or two ring segments were inserted into the cornea, embracing the keratoconus area. Statistical analysis included preoperative and postoperative uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), asphericity, pachymetry, and keratometry. Results Ferrara ICRS implantation significantly improved the mean UDVA and CDVA. Corneal tomography (Pentacam®) showed corneal flattening in all eyes implanted with the Ferrara ring. The mean K decreased, and the corneal asphericity and pachymetry increased in all cases. Conclusion The Ferrara ICRS improved all parameters after 2 years of implantation in children with keratoconus. There was significant corneal flattening after ring implantation with improvement of the UDVA and the CDVA. All studied parameters remained stable over time. How to cite this article Ferrara G, Ferrara P, Torquetti L. Intrastromal Corneal Ring Segments in Children with Keratoconus. Int J Kerat Ect Cor Dis 2017;6(2):45-48.