Corneal melting after collagen cross-linking for keratoconus: a case report

Management of corneal melting after collagen cross-linking for keratoconus: a case report and a review of the literature

PURPOSE

We describe the management of a case of severe corneal melting after corneal cross-linking (CXL) treated with a staged approach using a conjunctival flap followed by deep anterior lamellar keratoplasty (DALK).

METHODS

A 12-year-old male developed severe corneal melting with pending perforation after an accelerated epithelium-off CXL protocol. We initially treated the patient with a conjunctival flap to prevent perforation. Three months later, we performed DALK to restore vision.

RESULTS

Conjunctival flap surgery allowed us to avoid corneal perforation and penetrating keratoplasty (PK) à chaud. Once the inflammation had resolved, we recessed the conjunctiva and performed DALK for optical purposes. Twelve months later, the graft was clear and the corrected visual acuity was 20/25 (Snellen). No complications occurred after surgery.

CONCLUSIONS

Although CXL is considered a safe procedure, in rare cases it can lead to serious complications, such as corneal haze, infectious and non-infectious keratitis, stromal melting and perforation. Corneal melting and perforation are usually managed by emergency PK. Herein we suggest a staged approach involving an emergency conjunctival flap followed by DALK at a later time that allowed us to avoid PK à chaud.

Collagen crosslinking impacts stromal wound healing and haze formation in a rabbit phototherapeutic keratectomy model

Purpose

The purpose of this study was to evaluate the elastic modulus, keratocyte-fibroblast-myocyte transformation, and haze formation of the corneal stroma following combined phototherapeutic keratectomy (PTK) and epithelium-off UV-A/riboflavin corneal collagen crosslinking (CXL) using an in vivo rabbit model.

Methods

Rabbits underwent PTK and CXL, PTK only, or CXL 35 days before PTK. Rebound tonometry, Fourier-domain optical coherence tomography, and ultrasound pachymetry were performed on days 7, 14, 21, 42, 70, and 90 post-operatively. Atomic force microscopy, histologic inflammation, and immunohistochemistry for α-smooth muscle actin (α-SMA) were assessed post-mortem.

Results

Stromal haze formation following simultaneous PTK and CXL was significantly greater than in corneas that received PTK only and persisted for more than 90 days. No significant difference in stromal haze was noted between groups receiving simultaneous CXL and PTK and those receiving CXL before PTK. Stromal inflammation did not differ between groups at any time point, although the intensity of α-SMA over the number of nuclei was significantly greater at day 21 between groups receiving simultaneous CXL and PTK and those receiving CXL before PTK. The elastic modulus was significantly greater in corneas receiving simultaneous CXL and PTK compared with those receiving PTK alone.

Conclusions

We showed that stromal haze formation and stromal stiffness is significantly increased following CXL, regardless of whether it is performed at or before the time of PTK. Further knowledge of the biophysical cues involved in determining corneal wound healing duration and outcomes will be important for understanding scarring following CXL and for the development of improved therapeutic options.

Severe Complications after Corneal Collagen Cross-Linking (CXL)

PURPOSE

To present a case series of rare and severe complications after corneal collagen cross-linking (CXL) of keratoconus patients.

METHODS

Single-center descriptive case series covering the period of 2012 to 2022 at the Department of Ophthalmology at the University Hospital, Zurich, Switzerland.

RESULTS

We present four eyes of four patients that showed severe unusual complications within the first month after CXL. Three patients had been treated with the classical epithelium-off "Dresden" protocol. One patient had been treated with the accelerated epithelium-off protocol. One patient presented with extensive corneal edema due to rubbing the eye after treatment. Two patients showed a bacterial infectious keratitis: one due to Streptococcus pneumoniae and the other due to Staphylococcus hominis, Micrococcus luteus, and Streptococcus epidermidis. The latter of the two patients exhibited extensive infectious crystalline keratopathy. The fourth patient showed a severe ulcerative lesion where no infectious cause could be found. Therefore, an autoimmune keratolytic process had to be suspected. Apart from the corneal edema, which resolved ad integrum, the other complications resulted in permanent corneal scarring and thinning. One patient needed an emergency amniotic transplant.

CONCLUSION

Severe complications after CXL remain rare. Most common causes are complications that are not directly associated with the treatment as such. Those indirect complications occur after the treatment during the healing course of the epithelium. Associations with bandage contact lenses, topical steroids, atopic disease, and inappropriate patient behavior are often suspected. Correctly performed corneal scrapings with repeated microbiological analysis and a detailed patient history are essential for establishing the correct diagnosis, especially in complicated cases that do not respond to a standard therapeutic regimen. This case series supports the efforts that are currently taken to improve the CXL technique in a way that postoperative complications are further reduced. A more efficient epithelium-on technique might be a step in that direction.

Acute corneal melt and perforation – A possible complication after riboflavin/UV-A crosslinking (CXL) in keratoconus

Purpose

To report two cases of acute corneal melting and perforation requiring emergency penetrating keratoplasty after corneal crosslinking (CXL) in advanced keratoconus.

Observations

Case 1 was a 34 and case 2 was a 16-year old male, both with progressive keratoconus, who underwent CXL (Dresden protocol). After riboflavin imbibition, patients had a minimal pachymetry of 337 μm and 347 μm, and therefore required stromal swelling by hypoosmolar riboflavin resulting in pachymetries of 470 μm and 422 μm, prior to the 30 minute UV-irradiation with 3mW/cm². In case 1, on the 7th postoperative day a 4mm linear perforation occurred. Extensive post-hoc examinations revealed no infectious cause. In case 2, a corneal melting developed within 24 hours, from which Staphylococcus aureus was cultured.

Conclusions and importance

Acute corneal melting and perforation may occur after CXL. Dysfunctional collagen metabolism, atopia, thin preoperative pachymetry and the use of hypoosmolar substances may have initiated this complication in our cases.

Controversy and Consideration of Refractive Surgery in Patients with Heritable Disorders of Connective Tissue

Heritable Disorders of Connective Tissue (HDCTs) are syndromes that disrupt connective tissue integrity. They include Osteogenesis Imperfecta (OI), Ehlers Danlos Syndrome (EDS), Marfan Syndrome (MFS), Loeys-Dietz Syndrome (LDS), Epidermolysis Bullosa (EB), Stickler Syndrome (STL), Wagner Syndrome, and Pseudoxanthoma Elasticum (PXE). Because many patients with HDCTs have ocular symptoms, commonly myopia, they will often present to the clinic seeking refractive surgery. Currently, corrective measures are limited, as the FDA contraindicates laser-assisted in-situ keratomileusis (LASIK) in EDS and discourages the procedure in OI and MFS due to a theoretically increased risk of post-LASIK ectasia, poor wound healing, poor refractive predictability, underlying keratoconus, and globe rupture. While these disorders present with a wide range of ocular manifestations that are associated with an increased risk of post-LASIK complications (e.g., thinned corneas, ocular fragility, keratoconus, glaucoma, ectopia lentis, retinal detachment, angioid streaks, and ocular surface disease), their occurrence and severity are highly variable among patients. Therefore, an HDCT diagnosis should not warrant an immediate disqualification for refractive surgery. Patients with minimal ocular manifestations can consider LASIK. In contrast, those with preoperative signs of corneal thinning and ocular fragility may find the combination of collagen cross-linking (CXL) with either photorefractive keratotomy (PRK), small incision lenticule extraction (SMILE) or a phakic intraocular lens (pIOL) implant to be more suitable options. However, evidence of refractive surgery performed on patients with HDCTs is limited, and surgeons must fully inform patients of the unknown risks and complications before proceeding. This paper serves as a guideline for future studies to evaluate refractive surgery outcomes in patients with HDCTs.

Infectious keratitis after corneal crosslinking: systematic review

Corneal crosslinking is a U.S. Food and Drug Administration--approved therapy to stiffen the cornea and prevent progression of corneal ectasia in patients with keratoconus. The standard procedure involves removal of the corneal epithelium (epithelial-off) prior to treatment. Variations to the standard procedure include accelerated crosslinking and transepithelial procedures. This study reviewed what is known regarding the risk for infection after epithelial-off crosslinking, the spectrum of pathogens, and clinical outcomes. 26 publications were identified. All eyes were fit with a bandage contact lens postoperatively. Available data indicate that the overall frequency of infectious keratitis after epithelium-off crosslinking is low. Bacterial infections are the most common, with a mean time of presentation of 4.8 days postoperatively. The use of steroids and bandage contact lenses in the immediate postoperative period and/or a history of atopic or herpetic disease were associated with infection. These patients require intense postoperative care with prophylactic antiviral therapy when appropriate.

Five-year results of a prospective, randomised, contralateral eye trial of corneal crosslinking for keratoconus

BACKGROUND

Few studies have evaluated corneal crosslinking (CXL) in a prospective, randomised fashion. This study aimed to determine the efficacy and safety of CXL to reduce the progression of keratoconus.

METHODS

Prospective, unmasked, randomised, contralateral eye controlled trial at a tertiary eye centre.

PARTICIPANTS

Individuals with bilateral progressive keratoconus. One eye from each subject was randomised to CXL and the contralateral, untreated eye acted as the control.

PRIMARY OUTCOME MEASURE

change in maximum keratometry.

SECONDARY OUTCOME MEASURES

uncorrected distance visual acuity, spectacle corrected distance visual acuity, spherical equivalent refraction, simulated keratometry, corneal astigmatism, minimum pachymetry and complications.

RESULTS

Thirty-eight individuals (mean age 21.1 ± 6.7 years) were enrolled with one eye treated with CXL. At 5 years, there was a mean decrease in maximum keratometry of treated eyes (-1.45 ± 2.25 D) compared to an increase among the controls (1.71 ± 2.46 D; p < 0.001). There were significant differences between the treated and control groups in the mean change of Steep SimK (-1.07 ± 1.22 vs. 0.96 ± 1.97 D; p < 0.001), Flat SimK (-0.61 ± 1.34 vs. 0.43 ± 1.12 D; p < 0.001), corneal astigmatism (-0.45 ± 1.31 vs. 0.63 ± 1.52 D; p < 0.01) and minimum pachymetry (-32.49 ± 26.32 vs. -13.57 ± 24.11 μm; p < 0.01). Complications included sterile infiltrates (n = 2), microbial keratitis (n = 1), persistent corneal haze/scarring at 5 years (n = 4) and loss of ≥2 lines of corrected distance visual acuity (n = 3).

CONCLUSIONS

CXL is an effective and relatively safe intervention to halt or reduce the progression of keratoconus in the majority of eyes for at least 5 years.

A new collagen scaffold for the improvement of corneal biomechanical properties in a rabbit model

Although collagen based materials are widely used in corneal tissue engineering with promising results. The usage of such materials for the improvement of corneal biomechanical properties is still unclear. In this study, we aimed to investigate a new Viscoll collagen-based membrane for the improvement of corneal biomechanical characteristics.The right eyes of 15 Chinchilla rabbits were implanted with the membrane via an intrastromal pocket, with the contralateral intact eyes as controls. At 7, 30, 90, and 180 days post-surgery, the rabbits underwent anterior segment optical coherence topography, clinical examination, and slit-lamp microscopy. Additionally, the corneal samples also underwent histological examination followed by the assessment of the biomechanical characteristics of four treated and non-treated corneas at 30, 90, and 180 days, including keratometry at 180 days, post operation. Data are presented as means ± confidence intervals with a 95% confidence level. All the operated corneas retained their transparency throughout the study. Implantation approximately doubled the central corneal thickness. Corneas became stronger by approximately 87% between 1 and 6 months after surgery (maximum fracture load, 13.3 ± 0.8 and 24.9 ± 1.4 N, respectively), and their elasticity increased by approximately 27% over the same time frame (maximum slope of the elastic region of the stress-strain curve, 11.5 ± 0.2 and 14.6 ± 1.4 N/mm respectively). We have thus proposed a new method to increase corneal thickness and strengthen the corneal tissues while preserving their transparency and demonstrated its safety and efficacy in a rabbit model over 6 months. This may be a suitable alternative to the existing corneal collagen crosslinking procedure.

Update on the genetics of keratoconus

In the past few years we have seen a great acceleration of discoveries in the field of keratoconus including new treatments, diagnostic tools, genomic and molecular determinants of disease risk. Recent genome-wide association studies (GWAS) of keratoconus cases and population wide studies of variation in central corneal thickness and in corneal biomechanical properties confirmed already identified genes and found many new susceptibility variants and biological pathways. Recent findings in genetic determinants of familial keratoconus revealed functionally important variants and established first mouse model of keratoconus. Latest transcriptomic and expression studies started assessing novel non-coding RNA targets in addition to identifying tissue specific effects of coding genes. First genomic insights into better prediction of treatment outcomes are bringing the advent of genomic medicine into keratoconus clinical practice.

Reduced fluence corneal cross-linking in mild to moderate keratoconus: One year-follow-up

PURPOSE

To evaluate the safety and efficacy of reduced fluence CXL (lower dose of UV-A irradiation) in mild to moderate keratoconus.

SETTING

Farabi Eye Hospital, Tehran, Iran.

DESIGN

Non-randomized prospective comparative interventional case series. Every eligible patient included in the study (mild to moderate progressive keratoconus) was randomly allocated to case (reduced fluence) and control (standard) groups, except for bilateral patients. In these patients the eye with more advanced disease was allocated to control group and the other eye was randomly assigned in either case or control group. Operators performing refraction and images and the data analyst were masked, but patients and physicians were not.

METHODS

Forty-six eyes of 38 patients were recruited. Group 1 received 7 min (fluence of 3.8 J/cm²), while group 2 received 10 min of 9 mW/cm² UV-A (fluence of 5.4 J/cm²). Visual, keratometric and biomechanical outcomes were compared between groups.

RESULTS

At last follow-up (mean12 months, range 6-24 months), there were no statistically significant differences in changes in uncorrected visual acuity, best corrected distance visual acuity, Kmax, Kmean, corneal hysteresis, corneal resistance factor, endothelial cell counts, demarcation line depth, and intraoperative pain scores between groups (all p-values < 0.05).

CONCLUSION

The results of this study show comparable one-year outcomes between 3.8 and 5.4 J/cm² accelerated CXL in mild to moderate keratoconus. Should the results of this study be confirmed in longer follow-ups, using a reduced fluence setting could be considered as an alternative to standard treatment in these patients.

Descemetocele

A corneal descemetocele, the anterior herniation of an intact Descemet membrane through an overlying stromal defect, is a rare, but serious outcome of progressive corneal ulceration and mandates urgent intervention owing to the imminent risk of perforation. Various ocular and systemic abnormalities that can lead to the formation of descemetocele include microbial keratitis, neurotrophic keratopathy, dry eye disorders, and corneal inflammation associated with immune-mediated disorders. The primary aim of management of a descemetocele remains prompt restoration of ocular integrity to prevent the rupture of the Descemet membrane and further complications. Medical therapy is instituted immediately while deciding on the most suitable operative modality for an individual case. Commonly available treatment options include therapeutic bandage contact lenses, tissue adhesives, amniotic membrane transplantation, corneal patch grafts, penetrating or lamellar keratoplasty, and conjunctival flaps. Infrequently, platelet-rich fibrin membrane grafting and umbilical cord patch transplantation have also been tried with success. The surgical strategy and the outcome are commonly determined by the size, location, and etiology of descemetoceles. Despite the availability of all these treatment options, ambiguity remains about management. We review the available literature on pathogenesis, causes, presentation, differential diagnoses, and management of this disorder and also discuss our experience.

Complications of accelerated corneal collagen cross-linking: review of 2025 eyes

PURPOSE

To evaluate the early- and late-stage complications of accelerated cross-linking (A-CXL) in a large case series and investigate the relationship of A-CXL complications with ocular and systemic conditions accompanying keratoconus.

METHODS

Retrospectively, records of 2025 eyes of 1184 patients diagnosed with keratoconus between March 2013 and 2020 who underwent A-CXL (18 mW/cm² for 5 min) treatment were reviewed. Comorbid ocular and systemic diseases other than keratoconus were recorded. In the postoperative follow-up, early and late complications and their association with accompanying diseases were examined.

RESULTS

The mean age of patients was 26.16 ± 6.05 (range 18-42), and the mean follow-up time was 3.40 ± 1.63 years (range 1-8 years). Vernal keratoconjunctivitis (3.7%) was the most common disease accompanying keratoconus. Less frequently, systemic allergic diseases (2.9%) and Down syndrome (2.3%) were observed. The most common complication in the early postoperative period was haze formation (9.1%), while failure of the treatment (4.2%) occurred in the late period. Other common complications were loss of two or more Snellen lines (2.4%) and delayed epithelial healing (1.8%). There was a significant relationship between vernal keratoconjunctivitis and delayed epithelial healing (p = 0.011). Statistically significant relationships were found between Down syndrome and haze formation (p < 0.001) and sterile infiltrate formation (p = 0.041).

CONCLUSION

Although A-CXL complication rates are low, vernal keratoconjunctivitis following A-CXL might increase the risk of delayed epithelial healing, and similarly corneal haze and sterile infiltrates might be observed more frequently in patients with Down syndrome.

Rapid keratitis and perforation after corneal collagen cross-linking

Purpose

To describe a case of rapid keratitis and corneal perforation after epithelium off collagen cross-linking.

Observations

We report a case of a 17-year-old male who underwent collagen cross-linking with the protocol and device approved by the United States Food and Drug Administration (FDA) that developed a corneal infiltrate 3 days after the procedure. He later developed corneal thinning and perforation on day 5 requiring the use of cyanoacrylate glue and a Kontur lens. Despite initial improvement in the infiltrate with fortified antibiotics he later had leakage of aqueous around the glue and a flat chamber requiring an emergent penetrating keratoplasty on postoperative day 16.

Conclusion and importance

While collagen cross-linking has been very effective for treating keratoconus and is being recommended more frequently since FDA approval in the United States, severe complications such as corneal perforation requiring early transplant can still occur.

Corneal Perforation After Corneal Cross-Linking in Keratoconus Associated With Potentially Pathogenic ZNF469 Mutations

PURPOSE

To report a case of bilateral and repetitive corneal perforations after corneal cross-linking (CXL) for keratoconus in a woman harboring potentially pathogenic variants in the ZNF469 gene and to characterize the keratoconus phenotype in this woman and her daughter who shared the same ZNF469 mutations.

METHODS

Clinical characterization of the proband and her daughter followed by sequencing of the genes associated with brittle cornea syndrome, ZNF469 and PRDM5, in both individuals.

RESULTS

An Ashkenazi Jewish woman in her sixth decade presented with diffuse corneal thinning and progressive steepening consistent with keratoconus. After CXL, epithelium-off in the first eye and epithelium-on in the second, she developed spontaneous corneal perforations in each eye. Her daughter in her fourth decade demonstrated a similar pattern of diffuse corneal thinning and progressive corneal steepening but did not undergo CXL and did not develop corneal perforation. Screening of the ZNF469 and PRDM5 genes revealed 3 missense ZNF469 variants (c.2035G>A, c.10244G>C, and c.11119A>G) in cis arrangement on 1 allele of ZNF469 in both proband and her daughter. Although the 3 variants share low (<0.01) global minor allele frequencies, each has significantly higher minor allele frequencies (0.01-0.03) in the Ashkenazi Jewish population, leading to uncertainty regarding a pathogenic role for the identified variants.

CONCLUSIONS

CXL may be associated with the development of corneal perforation in particular at-risk individuals with keratoconus. Identifying clinical and genetic risk factors, including screening of ZNF469 and PRDM5, may be useful in the prevention of significant complications after CXL.

Late-Onset Sterile Peripheral Ulcerative Keratitis Post-Corneal Collagen Crosslinking

PURPOSE

To report the incidence, characteristics, clinical presentations, risk factors, and the available treatment modalities of sterile peripheral ulcerative keratitis (PUK) post-corneal collagen crosslinking (CXL).

METHODS

This study is a retrospective study including 771 eyes of 474 patients operated for keratoconus or ectasia after LASIK between January 2010 and June 2017 at Beirut Eye & ENT Specialist hospital. The average follow-up period was 4.2 years with a minimum of 1 year post-CXL.

RESULTS

Eleven eyes (1.4%) of 8 patients developed late-onset PUK with or without corneal haze and sterile infiltrates. The complications occurred between 3 months and 6 years postoperatively. Their mean age of 39.6 ± 7.1 years was higher than the age of the noncomplicated patients 21.9 ± 8.8 years (P = 0.0001). Four affected patients had inflammatory and autoimmune conditions. Sex, presence of intrastromal ring segments, mean keratometry, and the thinnest pachymetry were found to be insignificantly different between groups, and photorefractive keratectomy was performed more in patients with keratitis. Duration of ultraviolet light exposure was related to sterile ulcerative keratitis development. All patients responded to steroid treatment, and only one had a relapse which resolved with topical cyclosporine 1% drops.

CONCLUSIONS

PUK is a rare but serious complication after CXL. Long-term follow-up is necessary to detect late-onset PUK. It is a treatable condition associated with older age and autoimmune conditions but has a good visual outcome.

Recurrent Peripheral Stromal Keratitis Following Corneal Collagen Cross-linking: A Case Report

Purpose

Corneal collagen cross-linking (CXL) has become the standard initial intervention in eyes with progressive keratoconus (KC) that have not undergone keratoplasty. The prolonged exposure of the de-epithelialized cornea predisposes it to adverse complications, such as microbial keratitis and melting. Herein, we report a case of bilateral recurrent peripheral stromal keratitis following CXL.

Case Report

We present a 29-year-old woman who complained of ocular redness and discomfort in both eyes for 4 months, and had undergone bilateral CXL 10 months before. The best spectacle corrected visual acuity (BSCVA) was 60/200 in the right and 80/200 in the left eye. Both eyes showed moderate conjunctival hyperemia, dilation, and engorgement of the perilimbal episcleral vessels. There was a peripheral corneal stromal infiltration with thinning, and an overlying epithelial defect in the right eye with a lucid interval from the limbus. She was treated with lubricating eye drops and ointments and topical corticosteroids every 4 hours for 2 weeks then slowly tapered off. Afterwards, she experienced multiple recurrences in both eyes, which were successfully managed with topical corticosteroids and lubricants. After 2 years, her BSCVA was 20/30 with -3.00-5.50 * 90 in the right eye and 20/40 with -4.00-4.50 * 90 in the left.

Conclusion

Although CXL is a safe method, studies with longer follow-ups are needed to investigate the risk of rare complications.

Updates on Managements for Keratoconus

Purpose

Keratoconus is a progressive disease of the cornea which can lead to blindness as irregular astigmatism increases. Currently, a variety of methods are available for the treatment of keratoconus, and in certain cases, it may be difficult to choose the most appropriate option. This article reviews available treatment modalities for keratoconus to provide the practitioner with practical and useful information for selecting the most suitable option for each individual patient.

Methods

To review treatment methods for different stages of keratoconus, PubMed (United States National Library of Medicine) and Scopus (Elsevier BV) databases were searched using the keywords “keratoconus”, “contact lens”, “cross-linking”, “Intacs”, “keratoplasty”, “gene therapy”, and “irregular astigmatism”, and related articles were reviewed based on disease assessment parameters and treatment methods.

Results

Various methods are available for the treatment of keratoconus: eyeglasses and contact lenses in the early stages, cross-linking for stabilizing disease progression, intrastromal corneal ring segments (ICRS) for reducing refractive errors or flattening the cornea, and penetrating keratoplasty (PK) and deep anterior lamellar keratoplasty (DALK), conductive keratoplasty, gene therapy and more recently, bowman layer transplantation (BL transplantation) in advanced stages of the disease. To achieve optimum results, it is essential to choose the best option for each individual patient.

Conclusions

A commonality of the reviewed papers was the advancement of novel diagnostic and treatment methods in ophthalmology, which can delay the need for corneal grafting. A better understanding of keratoconus treatment options can help enhance visual rehabilitation and prevent blindness in keratoconus patients.

Updates on corneal collagen cross-linking: Indications, techniques and clinical outcomes

Purpose

To review the historical background and basic principles of collagen cross-linking, to bring together the data regarding the outcomes and complications of collagen cross-linking and finally to explore the efficacy and safety of new variations of this technique.

Methods

A literature review was performed using PubMed and Scopus. The following keywords were used for literature search: cross linking, crosslinking, cross-linking, keratoconus, keratectasia.

Results

In contrast to traditional treatment modalities for keratoconus (KCN), this new technique addresses the progression of the disease. Several clinical studies have been conducted to assess the efficacy of corneal collagen cross-linking (CXL) in the last decade. The results were promising as collagen cross-linking showed significant improvement in visual acuity and keratometric values. Moreover, initial results show that it is a safe procedure with few reported complications.

Conclusion

CXL is an emerging treatment method in ophthalmology that offers the possibility to effectively treat progressive KCN.

Corneal Collagen Cross-Linking Complications

Corneal cross-linking was approved by United States Food and Drug Administration for the treatment of progressive keratoconus in April 2016. As this approach becomes more widely used for the treatment of keratoconus and post-laser in situ keratomileusis (LASIK) ectasia, the medical community is becoming more familiar with potential complications associated with this procedure. This article aims to review the reported complications of collagen cross-linking for the treatment of keratoconus and post-LASIK ectasia.

Persistent Epithelial Defects and Corneal Opacity After Collagen Cross-Linking With Substitution of Dextran (T-500) With Dextran Sulfate in Compounded Topical Riboflavin

PURPOSE

Collagen cross-linking (CXL) is a commonly performed procedure to prevent the progression of keratoconus. Riboflavin is an essential part of the procedure, which facilitates both the cross-linking process and protection of intraocular structures. Dextran can be added to riboflavin to create an isotonic solution. This case report highlights the importance of compounding riboflavin with the correct dextran solution.

METHODS

A retrospective case series.

RESULTS

Six eyes of 4 male patients with keratoconus aged from 20 to 38 years underwent CXL with substitution of 20% dextran (T-500) with 20% dextran sulfate in a compounded riboflavin 0.1% solution. Postoperatively, persistent corneal epithelial defects, stromal haze, and then scarring occurred. Corneal transplantation was performed for visual rehabilitation but was complicated by graft rejection followed by failure (n = 1 eye), dehiscence (n = 4), cataract (n = 2), post-laser ablation haze (n = 1), and steroid-induced glaucoma (n = 2). The visual outcome was <6/18 in all 6 cases because of irregular astigmatism and stromal haze. Thinning, vascularization, and scarring of the residual host tissue were noted.

CONCLUSIONS

Substitution of dextran (T-500) with dextran sulfate in riboflavin solutions during CXL results in loss of vision from permanent corneal opacity. Residual host changes may compromise the results of corneal transplantation.

Corneal Collagen Cross-Linking in the Management of Keratoconus in Canada: A Cost-Effectiveness Analysis

PURPOSE

To use patient-level microsimulation models to evaluate the comparative cost-effectiveness of early corneal cross-linking (CXL) and conventional management with penetrating keratoplasty (PKP) when indicated in managing keratoconus in Canada.

DESIGN

Cost-utility analysis using individual-based, state-transition microsimulation models.

PARTICIPANTS

Simulated cohorts of 100 000 individuals with keratoconus who entered each treatment arm at 25 years of age. Fellow eyes were modeled separately. Simulated individuals lived up to a maximum of 110 years.

METHODS

We developed 2 state-transition microsimulation models to reflect the natural history of keratoconus progression and the impact of conventional management with PKP versus CXL. We collected data from the published literature to inform model parameters. We used realistic parameters that maximized the potential costs and complications of CXL, while minimizing those associated with PKP. In each treatment arm, we allowed simulated individuals to move through health states in monthly cycles from diagnosis until death.

MAIN OUTCOME MEASURES

For each treatment strategy, we calculated the total cost and number of quality-adjusted life years (QALYs) gained. Costs were measured in Canadian dollars. Costs and QALYs were discounted at 5%, converting future costs and QALYs into present values. We used an incremental cost-effectiveness ratio (ICER = difference in lifetime costs/difference in lifetime health outcomes) to compare the cost-effectiveness of CXL versus conventional management with PKP.

RESULTS

Lifetime costs and QALYs for CXL were estimated to be Can$5530 (Can$4512, discounted) and 50.12 QALYs (16.42 QALYs, discounted). Lifetime costs and QALYs for conventional management with PKP were Can$2675 (Can$1508, discounted) and 48.93 QALYs (16.09 QALYs, discounted). The discounted ICER comparing CXL to conventional management was Can$9090/QALY gained. Sensitivity analyses revealed that in general, parameter variations did not influence the cost-effectiveness of CXL.

CONCLUSIONS

CXL is cost-effective compared with conventional management with PKP in the treatment of keratoconus. Our ICER of Can$9090/QALY falls well below the range of Can$20 000 to Can$100 000/QALY and below US$50 000/QALY, thresholds generally used to evaluate the cost-effectiveness of health interventions in Canada and the United States. This study provides strong economic evidence for the cost-effectiveness of early CXL in keratoconus.

Molecular and Histopathological Changes Associated with Keratoconus

Keratoconus (KC) is a corneal thinning disorder that leads to loss of visual acuity through ectasia, opacity, and irregular astigmatism. It is one of the leading indicators for corneal transplantation in the Western countries. KC usually starts at puberty and progresses until the third or fourth decade; however its progression differs among patients. In the keratoconic cornea, all layers except the endothelium have been shown to have histopathological structural changes. Despite numerous studies in the last several decades, the mechanisms of KC development and progression remain unclear. Both genetic and environmental factors may contribute to the pathogenesis of KC. Many previous articles have reviewed the genetic aspects of KC, but in this review we summarize the histopathological features of different layers of cornea and discuss the differentially expressed proteins in the KC-affected cornea. This summary will help emphasize the major molecular defects in KC and identify additional research areas related to KC, potentially opening up possibilities for novel methods of KC prevention and therapeutic intervention.

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 Melting after Collagen Cross-Linking for Keratoconus in a Thin Cornea of a Diabetic Patient Treated with Topical Nepafenac: A Case Report with a Literature Review

PURPOSE

To report the case of a 50-year-old woman with diabetes that presented with corneal melting and perforation 6 weeks after collagen cross-linking (CxL) for keratoconus (KC) and postoperative use of nepafenac eye drops, a nonsteroidal anti-inflammatory drug (NSAID).

METHODS

This is a case report of a patient with diabetes, KC and a thin cornea that had undergone left eye corneal CxL at a different hospital followed by postoperative use of nepafenac eye drops for 6 weeks.

RESULTS

The patient presented for the first time to our clinic with left corneal melting, perforation and iris prolapse 6 weeks after corneal CxL and topical nepafenac use. She was treated with a left eye tectonic penetrating keratoplasty, extracapsular cataract extraction, intraocular lens implantation and pupilloplasty.

CONCLUSIONS

The corneal melting and perforation in this patient was associated with multiple risk factors: (1) nepafenac eye drop use, (2) CxL in a cornea thinner than 400 µm and (3) diabetes. The recommended corneal thickness limits should be respected. Topical NSAIDs should be used with caution if used as postoperative treatment after corneal CxL and in patients with diabetes, epithelial defect or delayed healing, because of the possible increased risk for corneal melting when multiple risk factors are observed.

Corneal Collagen Cross-linking: A Review of Clinical Applications

Corneal collagen cross-linking (CXL) has been shown to slow down or stop the progression of keratoconus. In addition, CXL has been applied in cases of corneal ectasia. Recent reports of the use of CXL in cases of infectious keratitis have generated further interest in this treatment modality. This review discusses the principle, clinical uses, and complications associated with CXL.

Severe microbial keratitis and associated perforation after corneal crosslinking for keratoconus

PURPOSE

To report two cases of microbial keratitis with subsequent corneal perforation immediately following corneal collagen crosslinking (CXL).

METHODS

Retrospective case note review.

RESULTS

First case was a 19 year old female presented with staphylococcal corneal abscess 3 days post CXL procedure. Corneal perforation occurred during hospital admission and was successfully treated with corneal gluing. Microbial keratitis eventually resolved, with both topical and systemic antibiotics therapy, resulting in a vascularized corneal scar. Second case was an 18 year old male whom developed Methicillin Resistant Staphylococcus aureus (MRSA) corneal abscess 5 days after CXL procedure for progressive keratoconus. Corneal perforation occurred 48 h after presentation and patient underwent uneventful corneal gluing. Although infective keratitis was successfully treated with topical therapy, patient had visual outcome of count fingers due to scarring.

CONCLUSIONS

CXL has been widely used in the treatment of corneal ectatic conditions and complications, such as infective keratitis, are uncommon post procedure. We present two cases of severe microbial keratitis with subsequent corneal perforation within 7 days of CXL. The exact mechanism for the accelerated keratolysis process is unclear. Nonetheless, patients should be well-informed of such potentially devastating complication.

An overview of corneal collagen cross-linking (CXL)

Corneal collagen cross-linking (CXL) was first described over a decade ago and is now considered to be one of the most important surgical innovations of modern ophthalmology. Prior to its introduction, no interventions were available to arrest, or slow down ectatic disease progression, with corneal transplantation required in the majority of cases. Unlike earlier treatments of corneal ectasias that attempted to only improve the consequences of the disease, CXL aims to address the corneal biomechanical weakening itself. The long-term safety and efficacy of CXL have been established in several studies that have documented significant improvements in all outcome measures (visual acuity, spherical equivalent, astigmatism, and keratometric findings). The emerging combination of CXL with other interventions (termed 'CXL plus') optimizes the visual and topographic outcomes. This, along with the expansion of the techniques' indications for other clinical conditions, such as microbial keratitis, highlights the continuous improvement of the initial technique and confirms its wide acceptance. Overall, CXL has already demonstrated much promise and has several clinical indications, representing a clear example of recent advances in ocular therapy.

Corneal crosslinking with riboflavin and ultraviolet A. Part II. Clinical indications and results

Changes in the biomechanical properties of the human cornea play an important role in the pathogenesis of corneal ectatic diseases. A variety of conditions in primary acquired (keratoconus and pellucid marginal degeneration) or secondary induced (iatrogenic keratectasia after excimer refractive laser surgery) corneal ectatic disorders lead to reduced biomechanical resistance. Corneal collagen crosslinking (CXL) has emerged as a promising technique to slow or even to stop the progression of these corneal ectatic pathologies. In this procedure, riboflavin (vitamin B2) is administered in conjunction with ultraviolet A light (UVA, 365 nm). This interaction causes the formation of reactive oxygen species, leading to the formation of additional covalent bonds between collagen molecules, with consequent biomechanical stiffening of the cornea. Although this method is not yet accepted as an evidence-based medicine modality for the treatment of corneal primary or secondary ectasias, the results of prospective, randomized studies of CXL used in the treatment of these pathologic entities show significant changes in the properties of corneal tissue. This procedure is currently the only etiopathogenetic approach in ectatic eyes that can delay or stop the process of cornea destabilization, reducing the necessity for keratoplasty. Despite promising results, CXL is associated with issues that include long-term safety and duration of the stabilizing effect. Combination of CXL with vision-improving procedures, such as topography-guided custom ablation and implantation of intracorneal ring segments of phakic intraocular lenses, may expand the indications for this procedure.

Proteases, proteolysis and inflammatory molecules in the tears of people with keratoconus

PURPOSE

To investigate the expression of proteases, proteolytic activity and cytokines in the tear film of people with keratoconus.

METHODS

Basal tears from people with keratoconus, from individuals who had undergone corneal collagen cross-linking for the treatment of keratoconus, and from normal controls were collected using a capillary tube. Corneal curvature of each subject was mapped. The total protein in tears was estimated. Levels and activity of proteases in the tears were analysed using specific antibody arrays and activity assays.

RESULTS

The total tear protein level was significantly reduced in keratoconus (4.1 ± 0.9 mg/ml) compared with normals (6.7 ± 1.4 mg/ml) (p < 0.0001) or subjects who had undergone corneal collagen cross-linking (5.7 ± 2.3 mg/ml) (p < 0.005). Significantly (p < 0.05) increased tear expression of matrix metalloproteinases (MMP) -1, -3, -7, -13, interleukins (IL) -4, -5, -6, -8 and tumour necrosis factor (TNF) -α, -β were evident in keratoconus. Tear IL-6 was the only cytokine significantly (p < 0.05) increased in tears of keratoconus subjects compared with the collagen cross-linked group. No significant difference in tear proteases were observed between the normal and the cross-linked groups, although the expression of TNF-α was significantly (p < 0.05) increased in the cross-linked group compared with the controls. Elevated gelatinolytic (87.5 ± 33.6 versus 45.8 ± 24.6 FIU, p < 0.0001) and collagenolytic (6.1 ± 3.2 versus 3.6 ± 2.0 FIU, p < 0.05) activities were observed in tears from keratoconus compared with normal subjects. The activity of tear gelatinases (69.6 ± 22.2 FIU) and collagenases (5.7 ± 3.3 FIU) in the collagen cross-linked group was not significantly different compared with either keratoconus or normals.

CONCLUSION

Tears of people with keratoconus had 1.9 times higher levels of proteolytic activity and over expression of several MMPs and cytokines compared with tears from controls. Further investigations are required to study the possible implications of these changes and whether they can be used to monitor disease progression or determine the success of corneal collagen cross-linking.

Collagen cross-linking using riboflavin and ultraviolet-a for corneal thinning disorders: an evidence-based analysis

OBJECTIVE

The main objectives for this evidence-based analysis were to determine the safety and effectiveness of photochemical corneal collagen cross-linking with riboflavin (vitamin B(2)) and ultraviolet-A radiation, referred to as CXL, for the management of corneal thinning disease conditions. The comparative safety and effectiveness of corneal cross-linking with other minimally invasive treatments such as intrastromal corneal rings was also reviewed. The Medical Advisory Secretariat (MAS) evidence-based analysis was performed to support public financing decisions. SUBJECT OF THE EVIDENCE-BASED ANALYSIS: The primary treatment objective for corneal cross-linking is to increase the strength of the corneal stroma, thereby stabilizing the underlying disease process. At the present time, it is the only procedure that treats the underlying disease condition. The proposed advantages for corneal cross-linking are that the procedure is minimally invasive, safe and effective, and it can potentially delay or defer the need for a corneal transplant. In addition, corneal cross-linking does not adversely affect subsequent surgical approaches, if they are necessary, or interfere with corneal transplants. The evidence for these claims for corneal cross-linking in the management of corneal thinning disorders such as keratoconus will be the focus of this review. The specific research questions for the evidence review were as follows: TECHNICAL: How technically demanding is corneal cross-linking and what are the operative risks?

SAFETY

What is known about the broader safety profile of corneal cross-linking?Effectiveness - Corneal Surface Topographic Affects:What are the corneal surface remodeling effects of corneal cross-linking?Do these changes interfere with subsequent interventions, particularly corneal transplant known as penetrating keratoplasty (PKP)?Effectiveness -Visual Acuity:What impacts does the remodeling have on visual acuity?Are these impacts predictable, stable, adjustable and durable?Effectiveness - Refractive Outcomes: What impact does remodeling have on refractive outcomes?Effectiveness - Visual Quality (Symptoms): What impact does corneal cross-linking have on vision quality such as contrast vision, and decreased visual symptoms (halos, fluctuating vision)?Effectiveness - Contact lens tolerance: To what extent does contact lens intolerance improve after corneal cross-linking?Vision-Related QOL: What is the impact of corneal cross-linking on functional visual rehabilitation and quality of life?PATIENT SATISFACTION: Are patients satisfied with their vision following the procedure?Disease Process:What impact does corneal cross-linking have on the underling corneal thinning disease process?Does corneal cross-linking delay or defer the need for a corneal transplant?What is the comparative safety and effectiveness of corneal cross-linking compared with other minimally invasive treatments for corneal ectasia such as intrastromal corneal rings?

CLINICAL NEED

TARGET POPULATION AND CONDITION Corneal ectasia (thinning) disorders represent a range of disorders involving either primary disease conditions, such as keratoconus (KC) and pellucid marginal corneal degeneration, or secondary iatrogenic conditions, such as corneal thinning occurring after laser in situ keratomileusis (LASIK) refractive surgery. Corneal thinning is a disease that occurs when the normally round dome-shaped cornea progressively thins causing a cone-like bulge or forward protrusion in response to the normal pressure of the eye. The thinning occurs primarily in the stroma layers and is believed to be a breakdown in the collagen process. This bulging can lead to irregular astigmatism or shape of the cornea. Because the anterior part of the cornea is responsible for most of the focusing of the light on the retina, this can then result in loss of visual acuity. The reduced visual acuity can make even simple daily tasks, such as driving, watching television or reading, difficult to perform. Keratoconus is the most common form of corneal thinning disorder and involves a noninflammatory chronic disease process of progressive corneal thinning. Although the specific cause for the biomechanical alterations in the corneal stroma is unknown, there is a growing body of evidence suggesting that genetic factors may play an important role. Keratoconus is a rare disease (< 0.05% of the population) and is unique among chronic eye diseases because it has an early onset, with a median age of 25 years. Disease management for this condition follows a step-wise approach depending on disease severity. Contact lenses are the primary treatment of choice when there is irregular astigmatism associated with the disease. Patients are referred for corneal transplants as a last option when they can no longer tolerate contact lenses or when lenses no longer provide adequate vision. Keratoconus is one of the leading indications for corneal transplants and has been so for the last 3 decades. Despite the high success rate of corneal transplants (up to 20 years) there are reasons to defer it as long as possible. Patients with keratoconus are generally young and a longer-term graft survival of at least 30 or 40 years may be necessary. The surgery itself involves lengthy time off work and postsurgery, while potential complications include long-term steroid use, secondary cataracts, and glaucoma. After a corneal transplant, keratoconus may recur resulting in a need for subsequent interventions. Residual refractive errors and astigmatism can remain challenges after transplantation, and high refractive surgery and regraft rates in KC patients have been reported. Visual rehabilitation or recovery of visual acuity after transplant may be slow and/or unsatisfactory to patients.

DESCRIPTION OF TECHNOLOGY/THERAPY

Corneal cross-linking involves the use of riboflavin (vitamin B(2)) and ultraviolet-A (UVA) radiation. A UVA irradiation device known as the CXL® device (license number 77989) by ACCUTECH Medical Technologies Inc. has been licensed by Health Canada as a Class II device since September 19, 2008. An illumination device that emits homogeneous UVA, in combination with any generic form of riboflavin, is licensed by Health Canada for the indication to slow or stop the progression of corneal thinning caused by progressive keratectasia, iatrogenic keratectasia after laser-assisted in situ keratomileusis (LASIK) and pellucid marginal degeneration. The same device is named the UV-X® device by IROCMedical, with approvals in Argentina, the European Union and Australia. UVA devices all use light emitting diodes to generate UVA at a wavelength of 360-380 microns but vary in the number of diodes (5 to 25), focusing systems, working distance, beam diameter, beam uniformity and extent to which the operator can vary the parameters. In Ontario, CXL is currently offered at over 15 private eye clinics by refractive surgeons and ophthalmologists. The treatment is an outpatient procedure generally performed with topical anesthesia. The treatment consists of several well defined procedures. The epithelial cell layer is first removed, often using a blunt spatula in a 9.0 mm diameter under sterile conditions. This step is followed by the application of topical 0.1% riboflavin (vitamin B(2)) solution every 3 to 5 minutes for 25 minutes to ensure that the corneal stroma is fully penetrated. A solid-state UVA light source with a wavelength of 370 nm (maximum absorption of riboflavin) and an irradiance of 3 mW/cm(2) is used to irradiate the central cornea. Following treatment, a soft bandage lens is applied and prescriptions are given for oral pain medications, preservative-free tears, anti-inflammatory drops (preferably not nonsteroidal anti-inflammatory drugs, or NSAIDs) and antibiotic eye drops. Patients are recalled 1 week following the procedure to evaluate re-epithelialization and they are followed-up subsequently.

EVIDENCE-BASED ANALYSIS METHODS

A literature search was conducted on photochemical corneal collagen cross-linking with riboflavin (vitamin B(2)) and ultraviolet-A for the management of corneal thinning disorders using a search strategy with appropriate keywords and subject headings for CXL for literature published up until April 17, 2011. The literature search for this Health Technology Assessment (HTA) review was performed using the Cochrane Library, the Emergency Care Research Institute (ECRI) and the Centre for Reviews and Dissemination. The websites of several other health technology agencies were also reviewed, including the Canadian Agency for Drugs and Technologies in Health (CADTH) and the United Kingdom's National Institute for Clinical Excellence (NICE). The databases searched included OVID MEDLINE, MEDLINE IN-Process and other Non-Indexed Citations such as EMBASE. As the evidence review included an intervention for a rare condition, case series and case reports, particularly for complications and adverse events, were reviewed. A total of 316 citations were identified and all abstracts were reviewed by a single reviewer for eligibility. For those studies meeting the eligibility criteria, full-text articles were obtained. Reference lists were also examined for any additional relevant studies not identified through the search. (ABSTRACT TRUNCATED)