Accelerated Epi-On Versus Standard Epi-Off Corneal Collagen Cross-Linking for Progressive Keratoconus in Pediatric Patients: Five Years of Follow-Up

Long-term results of accelerated corneal collagen crosslinking in paediatric patients with progressive keratoconus: 10-year follow-up

OBJECTIVES

To evaluate the 10-year visual, refractive, and tomographic outcomes of epithelium-off accelerated corneal collagen cross-linking (ACCL) in paediatric patients with progressive keratoconus (KC) and to compare the stages in terms of re-progression.

METHODS

Patients under 18 years of age with progressive KC who underwent ACCL between 2010 and 2012 and completed at least 10 years of follow-up were included in this retrospective study. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive errors, and corneal tomography parameters were evaluated preoperatively and at 1, 5, and 10 years postoperatively. The effect of stage and age on re-progression was analysed.

RESULTS

The study included 175 eyes of 97 patients (mean age: 14.46 ± 2.17 years). Improvement in UDVA and CDVA was observed in all postoperative periods compared to the preoperative period (each p-value < 0.05). The increase in spherical equivalent (SE), flattening of keratometry values, and decrease in thinnest corneal thickness (TCT) were statistically significant in the tenth year compared to preoperatively (each p-value < 0.05). Re-progression was observed in 16 eyes (9.14%). Haze was observed in 13 eyes (7.43%), 4 of which were permanent. Deep anterior lamellar keratoplasty was performed in 3 eyes (1.7%) and a second ACCL in 3 eyes (1.7%).

CONCLUSIONS

ACCL is an effective and safe long-term strategy to prevent progression of KC in paediatric patients. In the light of this study with a 10-year follow-up re-progression rate of 9.14%, long-term follow-up of patients after ACCL for possible re-progression and the need for re-CCL or keratoplasty may be recommended.

Conventional Epithelial-Off Corneal Crosslinking in Patients With Progressive Keratoconus: 10-Year Outcomes

PURPOSE

Corneal crosslinking (CXL) is the standard treatment of progressive keratoconus (KC). We evaluated the safety and 10-year outcomes of conventional "epithelial-off" CXL for progressive KC for the first time in a cohort in France.

METHODS

We conducted a retrospective review of patients undergoing conventional CXL (Dresden protocol) in our tertiary ophthalmology department from 2006 to 2011 with 10-year follow-up. The primary outcome was change in preoperative versus postoperative keratometry measured by maximum keratometry (Kmax), steep keratometry (K2), flat keratometry (K1), mean keratometry (Km), and topographic cylinder. Secondary outcomes were changes in visual and refractive outcomes. We report postoperative complications and adverse events.

RESULTS

Eighty-nine eyes from 76 patients (67% male patients, mean age 22.7 ± 7.6 years) were included. Mean Kmax (-2.31 ± 2.98 diopters (D); P < 0.00001), K2 (-2.07 ± 3.15 D; P < 0.00001), K1 (-1.00 ± 2.29 D; P = 0.00008), Km (-1.53 ± 2.47 D; P < 0.00001), and topographic cylinder (-1.15 ± 2.53 D; P = 0.00004) significantly decreased 10 years after CXL compared with preoperative baseline. Significant decreases were still observed between 5 and 10 years after for mean Kmax, mean K2, mean K1, and mean Km. Mean distance best spectacle-corrected visual acuity and mean manifest refraction spherical equivalent were significantly improved after 10 years versus before CXL. The 10-year rate of repeat CXL was n = 3/76 patients (4%) (all younger than 18 years at first CXL) and of loss of >3 lines in best spectacle-corrected visual acuity was n = 1/76 patients (1%).

CONCLUSIONS

Progressive KC was effectively stabilized with a prolonged flattening and maintenance of functional vision improvements after 10 years. Repeat CXL was rare and only required among younger patients.

High-Fluence Epithelium-off Accelerated Pulsed Corneal Cross-linking (15 mW/cm2; 7.2 J/cm2) for Pediatric Keratoconus: A 3-Year Retrospective Analysis

PURPOSE

To assess the safety and efficacy of treatment and secondarily determine the topographic changes, visual outcomes, and demarcation line depth after high-fluence pulsed light accelerated cross-linking (ACXL) in pediatric patients (younger than 18 years) with progressive keratoconus.

METHODS

This retrospective analysis included 32 eyes (25 children, aged 11 to 18 years), with progressive keratoconus treated with high-energy epithelium-off pulsed light ACXL (7.2 J/cm2, 15 mW/cm2, 12 minutes, 2 seconds on/1 second off). Corrected distance visual acuity (CDVA), Scheimpflug tomography, and anterior optical coherence tomography measurements were recorded preoperatively and 1, 2, and 3 years postoperatively.

RESULTS

A total of 32 eyes were included. Significant CDVA improvement, pachymetry, and maximum keratometry reduction were found at all follow-up visits. Mean keratometric values remained stable, and astigmatism showed a mild worsening (< 0.25 D) with statistical significance at 1 and 3 years. Total aberration showed discordant results and coma aberration had a slight improvement without statistical significance. The demarcation line depth was 265 ± 26 μm. Three patients developed mild haze without visual acuity loss. None of the patients underwent a second CXL procedure.

CONCLUSIONS

In pediatric patients, high-fluence epithelium-off pulsed light ACXL appears to be a safe and effective procedure to halt the progression of keratoconus, slightly improving the CDVA and keratometric values. [J Refract Surg. 2024;40(3):e148-e155.].

Transepithelial Accelerated Crosslinking for Progressive Keratoconus: A Critical Analysis of Medium-Term Treatment Outcomes

Purpose

To report the 4-year outcomes of transepithelial accelerated corneal collagen crosslinking (TE-ACXL) in the treatment of eyes with progressive keratoconus (KC).

Methods

Eyes of patients who underwent TE-ACXL (6mW/cm2 for 15 minutes) for progressive KC and presented 48 months of follow-up were included. Corrected distance visual acuity (CDVA), keratometry measurements (Kmax, maximum keratometry, Kmean, mean keratometry and Astg, corneal astigmatism), thinnest corneal thickness (PachyMin), and topographic, and tomographic indices (specifically the posterior radius of curvature from the 3.0 mm centered on the thinnest point of the cornea (PRC), and the D-index) were analysed preoperatively and every 12 months after TE-ACXL, up to 48 months. Progression after TE-ACXL was considered when eyes presented ≥1 criteria: (1) increase of ≥1D in Kmax or increase of ≥0.75D in Kmean or increase of ≥1D in Astg; (2) reduction of ≥0.085 mm in PRC; (3) decrease ≥5% in PachyMin.

Results

41 eyes from 30 patients were included, with a mean age at crosslinking of 20.90±4.69 years. There was a significant increase in Kmean (+0.64±1.04 D, p<0.001; +0.98 ± 1.49 D, p<0.001; +1.27±2.01 D, p<0.001; +1.13±2.00 D, p=0.006) and a significant decrease in PRC throughout follow-up (-0.12±0.22, p=0.002; -0.15±0.24, p<0.001; -0.17±0.43, p=0.021; -0.16±0.43, p=0.027). PachyMin decreased significantly at 36 and 48 months (-8.50±15.93 μm, p=0.004; -7.82±18.37, p=0.033). According to our progression criteria, there was a major progression rate throughout follow-up (57.1%, 61.1%, 58.8%, and 67.9%, respectively). Surgery and follow-up were uneventful in all subjects. Eleven eyes (26.8%) required further procedures, ≥36 months after the initial TE-ACXL, due to persistent progressive disease.

Conclusion

TE-ACXL proved to be a safe therapeutic option for progressive KC. However, its efficacy is deemed unsatisfactory, as a notable proportion of affected eyes may continue to advance within a 4-year timeframe, necessitating additional procedures to halt the disease's course.

Analysis of the outcomes of three different cross-linking protocols for treatment of paediatric keratoconus: A multicentre randomized controlled trial

PURPOSE

To analyse long-term outcomes of standard cross-linking (SCXL), accelerated cross-linking (ACXL) and transepithelial cross-linking (TCXL) in the treatment of progressive paediatric keratoconus regarding stability, safety and efficacy.

METHODS

This prospective multicentre randomized controlled trial included 97 eyes of 97 paediatric patients with stages I-III ABCD keratoconus grading system, who were randomized into three groups; SCXL group (control group, n = 32; 3 mW/cm2  × 30 min/5.4 J/cm2 ), ACXL (n = 33; 18 mW/cm2  × 5 min/5.4 J/cm2 ) and TCXL (n = 32; 18 mW/cm2  × 5 min/5.4 J/cm2 ). Subjective refraction, uncorrected and corrected visual acuity, keratometry and pachymetry measurements using corneal topography were recorded preoperatively and 1, 2 and 3 years postoperatively.

RESULTS

SCXL group exhibited significant successive improvements in the mean visual, refractive and keratometric parameters throughout the entire postoperative 3 years while ACXL group exhibited significant improvements in visual and keratometric parameters in the first postoperative year that remained stable in second and third postoperative years. TCXL group exhibited significant progressive deterioration in all mean parameters compared to SCXL and ACXL (p < 0.0001). Both SCXL and ACXL revealed final 100% success rate with good stability while TCXL revealed final 22% failure rate with keratoconus progression (p < 0.0001).

CONCLUSION

SCXL and ACXL were comparable in halting keratoconus progression and achieved good stability and safety; however, SCXL was more efficient than ACXL as it yielded greater significant postoperative mean visual, refractive and keratometric improvements achieving smoother corneal remodelling. Both SCXL and ACXL were much superior to TCXL. SCXL is the best CXL treatment option for paediatric keratoconus while ACXL is a good and effective alternative.

Diagnosis and management of keratoconus in the paediatric age group: a review of current evidence

The diagnosis and management of keratoconus in the paediatric age group presents additional challenges to those encountered in adults. The most significant of these, encountered in some young patients, are delayed presentation of unilateral disease, more advanced disease at diagnosis, difficulty in obtaining reliable corneal imaging, faster rates of disease progression and challenges in contact lens management. The stabilisation effect of corneal cross-linking (CXL), more extensively studied in adults with randomised trials and long-term follow-up, has been much less rigorously examined in children and adolescents. The high heterogeneity of published studies in younger patients, particularly in the choice of tomography parameters designated as primary outcome measures and the definitions of progression, indicates that improved standardisation for future studies on CXL will be necessary. There is no evidence that corneal transplant outcomes in young patients are poorer than those in adults. This review provides a current perspective on the optimal diagnosis and treatment of keratoconus in children and adolescents.

Paediatric cornea crosslinking current strategies: A review

Background

In the general population, 1 in 2000 people has keratoconus. Indians and other people from Southeast Asia have a higher incidence of keratoconus. Children with keratoconus typically present earlier in life and with a more severe disease. Rubbing the eyes has been identified as a risk factor. Children have a higher incidence and a faster rate of keratoconus progression. Visual rehabilitation in children with keratoconus is challenging. They have a low compliance with contact lens use. Many of these children require penetrating keratoplasty at an early age. Therefore, stopping the progression of keratoconus in children is of paramount importance.

Main text

Compared to treatment, keratoconus progression prophylaxis is not only preferable, but also easier. Corneal collagen cross-linking has been shown to be safe and effective in stopping its progression in children. The Dresden protocol, which involves central corneal deepithelization (7-9 ​mm), saturation of the stroma with riboflavin (0.25%), and 30 ​min UV-A exposure, has proven to be the most successful. Two significant disadvantages of the typical Dresden regimen are the prolonged operating time and the significant post-operative pain. Accelerated-CXL (9 ​mW/cm2 x 10 ​min) has been studied to reduce operative time and has been shown to be equally effective in some studies. Compared to accelerated CXL or traditional CXL, epi-off procedures, transepithelial treatment without the need for de-epithelialization and without postoperative discomfort, have been shown to be safer but less effective. Corneal crosslinking should only be performed after treating children with active vernal keratoconjunctivitis. Corneal opacity, chronic corneal edema, sterile infiltrates, and microbial keratitis have been reported after cross-linking of corneal collagen.

Conclusions

The "Dresden protocol", also known as the conventional corneal cross-linking approach, should be used to halt the progression of keratoconus in young patients. However, if the procedure needs to be completed more rapidly, accelerated corneal crosslinking may be considered. Transepithelial corneal cross-linking has been proven to be less effective at stabilizing keratoconus, although being more safer.

Excimer laser-assisted corneal epithelial pattern ablation for corneal cross-linking

Purpose

To determine corneal cross‐linking (CXL) efficacy and chromophore penetration after excimer laser‐assisted patterned de‐epithelialization.

Methods

Two‐hundred‐twenty porcine eyes were de‐epithelialized ex vivo, either fully (mechanical; n = 88) or patterned (excimer laser; n = 132). Consecutively, corneas were impregnated with hypo‐ or hyperosmolar riboflavin (RF; n = 20, RF‐D; n = 40, respectively) or water‐soluble taurine (WST11; n = 40, and WST‐D; n = 40, respectively), or kept unimpregnated (n = 80). Sixty corneas were subsequently irradiated, inducing CXL, with paired contralateral eyes serving as controls. Outcome measurements included strip extensiometry to assess CXL efficacy, and spectrophotometry and fluorescence microscopy to determine stromal chromophore penetration.

Results

All tested chromophores induced significant CXL (p < 0.001), ranging from 7.6% to 14.6%, with similar stiffening for all formulations (p = 0.60) and both de‐epithelialization methods (p = 0.56). Light transmittance was significantly lower (p < 0.001) after full compared with patterned de‐epithelialization. Stromal chromophore penetration was comparable between fully and patterned de‐epithelialized samples, with full penetration in RD and RF‐D samples and penetration depths measuring 591.7 ± 42.8 µm and 592.9 ± 63.5 µm for WST11 (p = 0.963) and 504.2 ± 43.2 µm and 488.8 ± 93.1 µm for WST‐D (p = 0.669), respectively.

Conclusions

Excimer laser‐assisted patterned de‐epithelialization allows for effective CXL. Stromal chromophore concentration is, however, reduced, which may have safety implications given the need for sufficient UVA attenuation in RF/UVA CXL. The different safety profile of near‐infrared (NIR) may allow safe WST11/NIR CXL even with reduced stromal chromophore concentration values. In vivo studies are needed to evaluate the benefits and further assess safety of excimer laser‐assisted patterned de‐epithelialization for corneal CXL.

Pediatric Crosslinking: Current Protocols and Approach

Keratoconus (KC) is likely to be more aggressive in the pediatric population, with a higher risk of progression and visual loss. Several techniques have been proposed for corneal crosslinking (CXL) so far. The standard CXL (SCXL) technique, or the Dresden Protocol, originally developed by Wollensak et al., has been shown to be safe and effective in the pediatric KC group. With similar efficacy to the conventional method, the accelerated CXL (ACXL) protocols proposed a reduced UVA exposure time by increasing the intensity of UVA irradiation. Transepithelial CXL (TCXL), considered an "epithelium-on" method, emerged as a strategy to improve safety and reduce postoperative complications and discomfort. For thinner corneas, we can highlight the use of hypoosmolar riboflavin and new studies, such as contact lens-assisted CXL (CACXL), the epithelial-island CXL (EI-CXL), and the Sub400 protocol. In addition to the different protocols used, another factor that changes CXL results is the type of carrier used: dextran-based or hydroxypropyl methylcellulose-based (HPMC) riboflavin solutions. There are several ways to perform a CXL surgery, and it is still unclear which method is the safest and most effective in the pediatric group. This review of the literature in English, available in PubMed, provides an update on corneal CXL in the pediatric KC group, exploring the data on the techniques currently used and under investigation, including their advantages, efficacy, safety profiles, risks, and cost analyses.

Comparison of Efficacy and Safety Between Standard, Accelerated Epithelium-Off and Transepithelial Corneal Collagen Crosslinking in Pediatric Keratoconus: A Meta-Analysis

Purpose

The purpose of the study is to compare the efficacy of standard epithelium-off CXL (SCXL), accelerated epithelium-off CXL (ACXL), and transepithelial crosslinking CXL (TECXL) for pediatric keratoconus.

Methods

A literature search on the efficacy of SCXL, ACXL, and TECXL [including accelerated TECXL (A-TECXL)] for keratoconus patients younger than 18 years was conducted using PubMed, Cochrane Library, ClinicalTrials.gov, and EMBASE up to 2021. Primary outcomes were changes in uncorrected visual acuity (UCVA) and maximum keratometry (Kmax) after CXL. Secondary outcomes were changes in best-corrected visual acuity (BCVA), mean refractive spherical equivalent (MRSE), and central corneal thickness (CCT). Estimations were analyzed by weighted mean difference (WMD) and 95% confidence interval (CI).

Results

A number of eleven identified studies enrolled 888 eyes (SCXL: 407 eyes; ACXL: 297 eyes; TECXL: 28 eyes; A-TECXL: 156 eyes). For pediatric keratoconus, except for a significant greater improvement in BCVA at 24-month follow-up in SCXL (WMD = –0.08, 95%CI: –0.14 to –0.01, p = 0.03, I² = 71%), no significant difference was observed in other outcomes between the SCXL and ACXL groups. SCXL seems to provide greater changes in UCVA (WMD = –0.24, 95% CI: –0.34 to –0.13, p < 0.00001, I² = 89%), BCVA (WMD = –0.09, 95% CI: –0.15 to –0.04, p = 0.0008, I² = 94%), and Kmax (WMD = –1.93, 95% CI: –3.02 to –0.85, p = 0.0005, I² = 0%) than A-TECXL, with higher incidence of adverse events.

Conclusion

For pediatric keratoconus, both SCXL and ACXL appear to be comparable in the efficacy of visual effects and keratometric outcomes; SCXL seems to provide greater changes in visual and pachymetric outcomes than A-TECXL.

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.

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.

Advances in the diagnosis and treatment of keratoconus

Keratoconus had traditionally been considered a rare disease at a time when the imaging technology was inept in detecting subtle manifestations, resulting in more severe disease at presentation. The increased demand for refractive surgery in recent years also made it essential to more effectively detect keratoconus before attempting any ablative procedure. Consequently, the armamentarium of tools that can be used to diagnose and treat keratoconus has significantly expanded. The advances in imaging technology have allowed clinicians and researchers alike to visualize the cornea layer by layer looking for any early changes that might be indicative of keratoconus. In addition to the conventional geometrical evaluation, efforts are also underway to enable spatially resolved corneal biomechanical evaluation. Artificial intelligence has been exploited in a multitude of ways to enhance diagnostic efficiency and to guide treatment. As for treatment, corneal cross-linking treatment remains the mainstay preventive approach, yet the current main focus of research is on increasing oxygen availability and developing new strategies to improve riboflavin permeability during the procedure. Some new combined protocols are being proposed to simultaneously halt keratoconus progression and correct refractive error. Bowman layer transplantation and additive keratoplasty are newly emerging alternatives to conventional keratoplasty techniques that are used in keratoconus surgery. Advances in tissue engineering and regenerative therapy might bring new perspectives for treatment at the cellular level and hence obviate the need for invasive surgeries. In this review, we describe the advances in the diagnosis and treatment of keratoconus primarily focusing on newly emerging approaches and strategies.

The biology of corneal cross-linking derived from ultraviolet light and riboflavin

Over the past 20 years, corneal crosslinking (CXL) has been used by surgeons to halt progression in eyes with keratoconus. We reviewed the literature regarding the mechanism of action of CXL, the role of each of its components the strong biologic reaction, and their effects on cell interaction, proteins involved, wound healing, and cytotoxic reaction. CXL surgery involves a photochemical response in which ultraviolet light at a given wavelength and riboflavin participate. The combination of irradiation with UVA light and riboflavin leads to an intense process of apoptosis of keratocytes in the anterior stroma. Differences in light irradiation, as well as the importance of riboflavin and its vehicle, were also detailed. The surgery creates additional chemical bonds between the amino terminals of the collagen side chains and the proteoglycans of the extracellular matrix. A photosensitization reaction catalyzed by riboflavin classically involves the production of singlet oxygen. Microstructure studies show changes in the size of the fibril and potentially in the interfibrillar space, that the most significant changes related to the stiffening effect of CXL occur in the anterior third of the cornea and that short irradiation times, especially below 5 min, may not have the same biological effect. Changes in the riboflavin vehicle, with the incorporation of Hydroxypropyl methylcellulose as a carrier, can lead to faster diffusion and a more intense photochemical reaction. These are findings that can impact the optimal adjustment of irradiation time according to the riboflavin (and its carrier) used. Many studies have suggested that CXL is safe and effective in the standard and accelerated protocols that have been used by surgeons. After the initial depletion of anterior keratocytes, keratocyte density seems to return to average 6-12 months after surgery when corneas are examined with the confocal microscope.