Post-FDA Approval Results of Epithelium-Off, Full-Fluence, Dresden Protocol Corneal Collagen Crosslinking in the USA

Independent-effect comparison of five crosslinking procedures for Progressive Keratoconus based on Keratometry and the ABCD Grading System using Generalized Estimating Equations (GEE)

PURPOSE

Corneal collagen crosslinking (CXL) is an effective treatment for progressive keratoconus. Multiple CXL modalities are clinically available. The present study compared the 1 year outcomes of five types of CXL procedures for progressive keratoconus in a Chinese population using generalized estimating equations (GEE).

METHODS

This retrospective study included 239 eyes in 171 patients with keratoconus who underwent CXL and were followed up for 1 year. Five CXL procedures were assessed, including Accelerated Transepithelial CXL, Iontophoresis CXL for 10 min, CXL plus phototherapeutic keratectomy (CXL-plus-PTK), High-Fluence Accelerated CXL, and Accelerated CXL. Patients treated with the Accelerated CXL procedure represented the reference group. Primary outcomes were visual acuity change, spherical equivalence, endothelial cell density, mean keratometry (K_mean), maximum keratometry (K_max), minimum corneal thickness (MCT), and the ABCD Grading System, consisting of A (staging index for ARC; ARC = anterior radius of curvature), B (staging index for PRC, PRC = posterior radius of curvature), and C (staging index for MCT) values 1 year postoperatively compared to baseline. Secondary outcomes were corrected GEE comparisons from each procedure versus the Accelerated CXL group.

RESULTS

The Accelerated Transepithelial CXL group had lower performance than the Accelerated CXL group according to K_mean and K_max. The CXL-plus-PTK group performed significantly better than the reference group as reflected by K_max (β = -0.935, P = 0.03). However, the CXL-plus-PTK group did not perform as well for B and C, and the Iontophoresis CXL group performed better for C.

CONCLUSIONS

The CXL-plus-PTK procedure was more effective than the Accelerated CXL procedure based on K_max, and the Iontophoresis CXL procedure performed better on the C value based on the ABCD Grading System.

Properties of the acellular porcine cornea crosslinked with UVA/riboflavin as scaffolds for Boston Keratoprosthesis

The Boston Keratoprosthesis type I (B-KPro) is widely used in the world, but the lack of donor corneas limits its application. This study aims to prepare the acellular porcine cornea (APC) crosslinked with ultraviolet A (UVA)/riboflavin instead of donor corneas as the scaffold for B-KPro. Decellularization of freeze-thaw combined with biological enzymes resulted in approximately 5 ng/mg DNA residue, the a-Gal removal rate of 99%, and glycosaminoglycans retention at a high level of 46.66 ± 2.59 mg/mg. UVA/ riboflavin cross-linking was adopted to induce the formation of new chemical bonds between adjacent collagen chains in the corneal stroma to improve the mechanical properties and resistance to enzymatic hydrolysis. Through comprehensive analysis of the biomechanics, enzyme degradation, immunogenicity and histological structure of the APC crosslinked at different times, CL3 (irradiation conditions, 365 nm, 3 mW/cm, 80 min, both sides) was selected and transplanted into the rabbit cornea model through interlamellar keratoplasty and penetrating keratoplasty as the scaffold of the B-KPro. Compared with the native porcine cornea (NPC) and APC, the experiment of interlamellar pocket indicated that the structure of CL3 was homogeneous without degradation and vascularization in vivo at 12 weeks after surgery. Simultaneously, the results of transplantation of B-KPro showed complete epithelialization of CL3 within 1 week, and neovascularization of the cornea indicated rejection but could be controlled with immunosuppressants. At 3 months postoperatively, the lens of B-KPro remained transparent, and the structure of CL3 was compact and uniform, accompanied by the migration and proliferation of a large number of stromal cells without degradation, suggesting the CL3 could be a promising corneal substitute.

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.

Outcomes After Corneal Crosslinking for Keratoconus in Children and Young Adults

PURPOSE

The aim of this study was to assess the effect of corneal crosslinking on vision and keratometry in children and young adults with progressive keratoconus.

METHODS

A retrospective medical records review of patients aged 22 years or younger with keratoconus who underwent corneal crosslinking between January 2013 and November 2019 at Byers Eye Institute at Stanford University was conducted. Outcome measures included logarithm of the Minimum Angle of Resolution corrected distance visual acuity (CDVA); keratometry, including maximum keratometry (Kmax); pachymetry; and total wavefront aberration. Measurements were taken at baseline and at 12 and 24 months postoperatively.

RESULTS

Fifty-seven eyes of 49 patients aged 12 to 22 years were assessed. The mean preoperative CDVA was logarithm of the Minimum Angle of Resolution 0.38 ± 0.32 (20/48), with a mean postoperative CDVA of 0.29 ± 0.31 (20/39) and 0.31 ± 0.31 (20/41) at 12 and 24 months postoperatively, respectively. Compared with preoperative mean Kmax, there was an improvement of -0.8 diopters (D) to a mean postoperative Kmax of 59.1 ± 9.1 D at 12 months and -1.3 D to 59.7 ± 8.8 D at 24 months. Subanalysis excluding the second eye of patients who underwent bilateral crosslinking showed similar results. Linear mixed modeling showed significant improvement in Kmax at both 12 and 24 months postoperatively. Minimum central corneal thickness initially decreased but stabilized at 24 months after crosslinking. Total wavefront aberration remained stable.

CONCLUSIONS

Corneal crosslinking stabilizes, and in some cases improves, visual and corneal parameters in pediatric and young adult patients with keratoconus. The procedure is safe and well-tolerated and may prevent keratoconus progression in young patients.

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.