Corneal collagen cross linking (CXL): a review

The Outcome of Corneal Collagen Cross-Linking in Patients with Advanced Progressive Keratoconus: A 2-Year Follow-up Study

PURPOSE:

The aim of this study was to evaluate the safety and efficacy of collagen cross-linking (CXL) in advanced progressive keratoconus with a maximum keratometry (K_max) value of more than 58 diopters (D).

METHODS:

This prospective interventional case series involved patients with advanced progressive keratoconus with a K_max of more than 58 D. The best-corrected visual acuity (BCVA), uncorrected visual acuity (UCVA), K_max, mean keratometry (K_mean) value, corneal astigmatism, and thinnest corneal thickness before surgery and 24 months after CXL were determined for 30 eyes of 27 patients. A Pentacam was used to measure the paraclinical parameters.

RESULTS:

The mean age of the patients was 24.47 ± 3.33 years. The mean logarithm of the minimum angle of resolution (logMAR) of the uncorrected visual acuity UCVA decreased from 0.73 ± 0.36 D at baseline to 0.48 ± 0.30 D (P = 0.01), while the mean thinnest point thickness of the cornea decreased from 438.65 ± 40.11 μm to 431.43 ± 61.92 μm (P = 0.005) after 24 months. The decreases in the mean logMAR of the BCVA, K_max and K_mean values, and corneal astigmatism were not statistically significant (P > 0.05) at the 24-month follow-up. Progression was halted in 29 eyes (96.6%); only 1 eye (3.3%) showed an increase in the K_max value of more than 2.0 D, which was indicative of treatment failure. In contrast, most other eyes showed a decrease in the K_max value although it was not statistically significant. There were no major complications in any of the patients during the study period.

CONCLUSION:

Standard CXL treatment was safe and stabilized both the visual acuity and tomographic parameters at the 2-year follow-up in eyes with advanced progressive keratoconus.

Collagen Cross- Linking for Paediatric Keratoconus

Background:

Since the late 1990s corneal crosslinking (CXL) has been proposed as a new treatment option which can stop progression of keratoconus with promising results in adults.

Objective:

Keratoconus presents a higher rate and faster progression in paediatric patients and for this reason prompt and effective treatment is essential. Due to its success in adult keratoconus patients, CXL has been recently applied to children in order to stop or slow progression of keratoconus in paediatric patients.

Conclusions:

This article will present an update of the literature on the topic of CXL in this age group.

Corneal collagen crosslinking for corneal ectasias: a review

PURPOSE

To review the published literature on corneal collagen crosslinking (CXL).

METHODS

Importance has been placed on seminal publications, systemic reviews, meta-analyses, and randomized controlled clinical trials. Where such evidence was not available, cohort studies, case-controlled studies, and case series with follow-up greater than 12 months were examined.

RESULTS

Corneal collagen crosslinking with riboflavin and ultraviolet A (UVA) 370 nm radiation appears to be capable of arresting the progression of ectatic corneal disorders, with most studies reporting significant improvements in visual, keratometric, and topographic measurements. Its mode of action at the molecular level is undetermined. Follow-up is limited to 5-10 years but suggests sustained stability and enhancement in corneal shape with time. Nearly all published long-term data and comparative studies are with epithelium-off techniques. Epithelium-on investigations suggest some efficacy but less than with epithelium-off treatments and long-term data are unavailable. Accelerated techniques with higher UVA fluencies and shorter treatments times, delivering the same UVA energy dosage, are the subject of recent investigation, with some laboratory and clinical studies suggesting reduced efficacy compared to the standard 3 mW/cm2 for 30 minutes irradiation procedure. Combined methodologies of CXL with techniques such as photorefractive keratectomy and intrastromal rings show promise but long-term follow-up is indicated. Sight-threatening complications of CXL are rare.

CONCLUSIONS

Studies of epithelium-off CXL with irradiation at 3 mW/cm2 for 30 minutes support its efficacy. Refinement in techniques may allow for safer and more rapid procedures with less patient discomfort but require further investigation.

Keratectasia After Presbyopia Treatment With INTRACOR

PURPOSE

To report a case of keratectasis of a patient underwent INTRACOR presbyopic treatment 5 years ago.

METHODS

Case Report.

RESULTS

Fifty-eight-year-old gentleman had presented with deteriorating vision in his left eye. He reported undergoing INTRACOR presbyopic treatment in that eye 5 years ago. At presentation, his best-corrected visual acuity was 20/40. Slit-lamp examination of the left eye showed an ectatic cornea with concentric corneal scars. Corneal topography revealed marked keratectasia, with significant anterior and posterior elevations. The area of maximal corneal thinning coincided with the site of maximal elevation. Patient was fitted with hybrid contact lenses as a temporary treatment option and his best-corrected visual acuity improved to 20/30.

CONCLUSIONS

INTRACOR is one of the newer modalilities to correct presbyopia. One must be aware of the complication such as corneal ectasia after this presbyopic treatment.

Corneal Cross-Linking (with a Partial Deepithelization) in Keratoconus with Five Years of Follow-Up

We performed a retrospective interventional case series including 80 eyes of 48 patients with keratoconus (KC) who were treated with modified corneal cross-linking (CXL) for KC (with a partial deepithelization in a pattern of stripes). The average follow-up was 5.8 years (with a minimum of 5 years). At the last follow-up visit, compared with preoperative values, there were no significant changes in spherical equivalent, average keratometry, corneal thickness, corneal hysteresis, or corneal resistance factor. The distance-corrected visual acuity was 20/39 preoperatively and 20/36 postoperatively (P = 0.3). The endothelial cell count decreased by 4.7% (P < 0.005). These findings suggest that this modified corneal CXL technique is a safe and effective alternative to halt the progression of KC up to five years after the procedure. However, some concerns remain as to whether this technique can affect in some degree the corneal endothelial cells.

Corneal collagen cross-linking (CXL) in thin corneas

Corneal collagen cross-linking (CXL) is a therapeutic procedure aiming at increasing the corneal stiffness in the keratoconus eyes by induction of cross-links within the extracellular matrix. It is achieved by ultraviolet-A (370 nm) irradiation of the cornea after saturation with the photosensitizer riboflavin. In the conventional CXL protocol, a minimum de-epithelialized corneal thickness of 400 μm is recommended to avoid potential irradiation damage to the corneal endothelium. In advanced keratoconus, however, stromal thickness is often lower than 400 μm, which limits the application of CXL in that category. Efforts have been undertaken to modify the conventional CXL procedure to be applicable in thin corneas. The current review discusses different techniques employed to achieve this end and their results. The overall safety and efficacy of the modified CXL protocols are good, as most of them managed to halt the progression of keratectasia without postoperative complications. However, the evidence of safety and efficacy in the use of modified CXL protocols is still limited to few studies with few patients involved. Controlled studies with long-term follow-up are required to confirm the safety and efficacy of the modified protocols.

A short-term study of corneal collagen cross-linking with hypo-osmolar riboflavin solution in keratoconic corneas

AIM

To report the 3mo outcomes of collagen cross-linking (CXL) with a hypo-osmolar riboflavin in thin corneas with the thinnest thickness less than 400 µm without epithelium.

METHODS

Eight eyes in 6 patients with age 26.2±4.8y were included in the study. All patients underwent CXL using a hypo-osmolar riboflavin solution after its de-epithelization. Best corrected visual acuity, manifest refraction, the thinnest corneal thickness, and endothelial cell density were evaluated before and 3mo after the procedure.

RESULTS

The mean thinnest thickness of the cornea was 408.5±29.0 µm before treatment and reduced to 369.8±24.8 µm after the removal of epithelium. With the application of the hypo-osmolar riboflavin solution, the thickness increased to 445.0±26.5 µm before CXL and recover to 412.5±22.7 µm at 3mo after treatment, P=0.659). Before surgery, the mean K-value of the apex of the keratoconus corneas was 57.6±4.0 diopters, and slightly decreased (54.7±4.9 diopters) after surgery (P=0.085). Mean best-corrected visual acuity was 0.55±0.23 logarithm of the minimal angle of resolution, and increased to 0.53±0.26 logarithm after surgery (P=0.879). The endothelial cell density was 2706.4±201.6 cells/mm(2) before treatment, and slightly decreased (2641.2±218.2 cells/mm(2)) at last fellow up (P=0.002).

CONCLUSION

Corneal collagen cross-linking with a hypo-osmolar riboflavin in thin corneas seems to be a promising treatment. Further study should be done to evaluate the safety and efficiency of CXL in thin corneas for the long-term.

Safety and efficacy of epithelium removal and transepithelial corneal collagen crosslinking for keratoconus

This review aims to assess the efficacy and safety of epithelial removal (ER) and transepithelial (TE) corneal collagen crosslinking (CXL) for the treatment of keratoconus. We used MEDLINE to identify all ER and TE CXL studies on keratoconic eyes (n≥20, follow-up ≥12 months). Ex vivo and studies for non-keratoconus indications or in conjunction with other procedures were excluded. Data on uncorrected (UDVA) and corrected (CDVA) distance visual acuity, refractive cylinder, maximum keratometry (Kmax), and adverse events were collected at the latest follow-up and 1 year. Only one randomised controlled trial (RCT) qualified inclusion. Forty-four ER and five TE studies were included. For logMAR UDVA, CDVA, mean spherical equivalent, refractive cylinder and Kmax, at latest follow-up 81, 85, 93, 62, and 93% ER studies vs 66.7, 80, 75, 33, and 40% TE studies reported improvement, respectively. Whereas at 1 year, 90, 59, and 91% ER studies vs 80, 50, and 25% TE studies reported improvement, respectively. The majority of studies showed reduced pachymetry in both groups. Treatment failure, retreatment rates, and conversion to transplantation were reported to be up to 33, 8.6, and 6.25%, respectively, in ER studies only. Stromal oedema, haze, keratitis, and scarring were only reported in ER studies, whereas endothelial cell counts remained variable in both groups. Both ER and TE studies showed improvement in visual acuity, refractive cylinder but Kmax worsened in most TE studies. Adverse events were reported more with ER studies. This review calls for more high quality ER and TE studies with comparable parameters for further assessment of safety and efficacy.

Keratoconus: tissue engineering and biomaterials

Keratoconus (KC) is a bilateral, asymmetric, corneal disorder that is characterized by progressive thinning, steepening, and potential scarring. The prevalence of KC is stated to be 1 in 2000 persons worldwide; however, numbers vary depending on size of the study and regions. KC appears more often in South Asian, Eastern Mediterranean, and North African populations. The cause remains unknown, although a variety of factors have been considered. Genetics, cellular, and mechanical changes have all been reported; however, most of these studies have proven inconclusive. Clearly, the major problem here, like with any other ocular disease, is quality of life and the threat of vision loss. While most KC cases progress until the third or fourth decade, it varies between individuals. Patients may experience periods of several months with significant changes followed by months or years of no change, followed by another period of rapid changes. Despite the major advancements, it is still uncertain how to treat KC at early stages and prevent vision impairment. There are currently limited tissue engineering techniques and/or "smart" biomaterials that can help arrest the progression of KC. This review will focus on current treatments and how biomaterials may hold promise for the future.

Sterile keratitis after combined riboflavin-UVA corneal collagen cross-linking for keratoconus

PURPOSE

To investigate patient risk factors and to look for potential causes of sterile infiltrates following an unexpected cluster of sterile keratitis after a routine collagen cross-linking (CXL) list.

METHODS

The records of all 148 cases of CXL were reviewed retrospectively. The equipment and solutions used and our clinic's standard operating procedure for CXL were reviewed. An in-vitro experiment to explore the variation in ultraviolet A (UVA) irradiance from fluctuations in the working distance of the UVA lamp was conducted.

RESULTS

The four patients who developed sterile infiltrates had steeper maximum corneal curvatures (68.0±7.3 D) and thinner pachymetry (389.9±49.0 μm) than the 144 who did not (57.0±8.2 D, P=0.05; 454.6±45.4 μm, P=0.08). A corneal curvature of >60 Dand a pachymetry of <425 μm were significant risk factors. All four affected cases obtained a complete resolution with topical antibiotics and steroids. The unaided VA and the maximum K improved from their pre-operative levels in three out of four patients. A 2-mm reduction in distance of the VEGA C.B.M. X-Linker from a treated surface increased irradiance to 3.5-3.7 mW/cm(2), which is above the threshold for endothelial toxicity.

CONCLUSION

Patients with thinner and steeper corneas are at an increased risk of developing sterile keratitis. The visual outcomes despite this complication are good.

Corneal collagen cross-linking: a review

The aim was to review the published literature on corneal collagen cross-linking. The emphasis was on the seminal publications, systemic reviews, meta-analyses and randomized controlled trials. Where such an evidence did not exist, selective large series cohort studies, case controlled studies and case series with follow-up preferably greater than 12 months were included. Riboflavin/Ultraviolet A (UVA) corneal collagen cross-linking appears to be the first treatment modality to halt the progression of keratoconus and other corneal ectatic disorders with improvement in visual, keratometric and topographic parameters documented by most investigators. Its precise mechanism of action at a molecular level is as yet not fully determined. Follow-up is limited to 4-6 years at present but suggests continued stability and improvement in corneal shape with time. Most published data are with epithelium-off techniques. Epithelium-on studies suggest some efficacy but less than with the epithelium-off procedures and long-term data are not currently available. The use of Riboflavin/UVA CXL for the management of infectious and non-infectious keratitis appears very promising. Its use in the management of bullous keratopathy is equivocal. Investigation of other methodologies for CXL are under investigation.

Safety and efficacy of epithelium-on corneal collagen cross-linking using a multifactorial approach to achieve proper stromal riboflavin saturation

Purpose. To evaluate the efficacy and safety of epithelium-on corneal collagen cross-linking (CXL) using a multifactorial approach to achieve proper stromal riboflavin saturation. Methods. This non-randomized retrospective study comprised 61 eyes with progressive keratoconus treated with epithelium-on CXL. Chemical epithelial penetration enhancement (benzalkonium chloride-containing local medication and hypotonic riboflavin solution), mechanical disruption of the superficial epithelium, and prolongation of the riboflavin-induction time until verification of stromal saturation were used before the UVA irradiation. Uncorrected and corrected distance visual acuity (UDVA, CDVA), refraction, corneal topography, and aberrometry were evaluated at baseline and at 1, 3, 6, and 12 months postoperative. Results. At 12-month, UDVA and CDVA improved significantly. None of the eyes lost lines of CDVA, while 27.4% of the eyes gained 2 or more lines. Mean spherical equivalent decreased by 0.74 D, and mean cylindrical reduction was 1.15 D. Irregularity index and asymmetry from Scheimpflug-based topography and Max-K at the location of cone from Placido-based topography showed a significant decrease. Higher-order-aberration data demonstrated a slight reduction in odd-order aberrations S 3, 5,7 (P = 0.04). Postoperative pain without other complications was recorded. Conclusion. Epithelium-on CXL with our novel protocol appeared to be safe and effective in the treatment of progressive keratoconus.

Corneal collagen cross-linking: an introduction and literature review

BACKGROUND

This literature review analyzes the scientific evidence available regarding corneal collagen cross-linking (CXL) as a treatment option for progressive keratectasia.

METHODS

A literature search was performed using dates from 1990 to August 2010 regarding CXL Specific areas of focus for the literature review include safety and efficacy of the procedure as a stand-alone treatment or when used in conjunction with Intacs® corneal implants (Addition Technology™) or photorefractive keratectomy (PRK).

RESULTS

A total of 50 clinical trials and studies were identified, 20 of which met the inclusion criteria. Results of the included literature support the conclusion that CXL is a safe and efficacious treatment for progressive keratectasia. The results of CXL alone have shown stabilization or improvement in the maximum keratometry readings, best-corrected visual acuity, uncorrected visual acuity, and spherical and cylinder refractive measurements. CXL has been shown to enhance the effects of Intacs and has been proven successful when used in conjunction with PRK.

CONCLUSION

CXL is an effective treatment for limiting the progression of keratectasia, thus reducing the need for penetrating keratoplasty. CXL has a similar side-effect profile and similar risk level as PRK.

The effect of standard and transepithelial ultraviolet collagen cross-linking on human corneal nerves: an ex vivo study

PURPOSE

To evaluate the early effect of standard and transepithelial collagen cross-linking on human corneal nerves in donor eyes by ex vivo confocal microscopy and acetylcholinesterase staining.

DESIGN

Experimental laboratory investigation.

METHODS

Eight human eye bank corneal buttons (mean age, 73.6 years) were included. Ultraviolet A collagen cross-linking was performed postmortem on 3 corneas with the standard protocol involving epithelial debridement and 4 corneas by the transepithelial approach. One cornea served as a control. Corneal nerves were evaluated using confocal microscopy and acetylcholinesterase histology.

RESULTS

Confocal microscopy demonstrated the absence of subbasal nerves in corneas treated by the standard technique. These nerves were preserved in corneas treated by the transepithelial approach. Stromal nerves were visible in both groups. Histology of corneas treated by the standard technique revealed localized swellings of the stromal nerves with disruption of axonal membrane and loss of axonal continuity within the treatment zone. These changes were absent in corneas treated by the transepithelial approach.

CONCLUSIONS

This study highlights the immediate effects of collagen cross-linking on the corneal nerves in an ex vivo model. The absence of subbasal nerves in the early phase of treatment appears to be attributable mainly to mechanical removal of epithelium, rather than ultraviolet light-induced damage. Localized swelling of the stromal nerves was the main difference between the 2 treatment protocols. Further research on laboratory animals would be necessary to verify these changes over a specified time course without the super-addition of postmortem changes.