Microbial keratitis after corneal collagen crosslinking

Corneal ring infiltrate- far more than Acanthamoeba keratitis: review of pathophysiology, morphology, differential diagnosis and management

OBJECTIVE

Ring infiltrates usually accompany numerous infectious and sterile ocular disorders. Nevertheless, systemic conditions, drugs toxicity and contact lens wear may present with corneal ring infiltrate in substantial part. Considering its detrimental effect on vision, detailed knowledge on etiology, pathophysiology, differential diagnosis, and management should be considered essential for every ophthalmologist.

METHODS

The PUBMED database was searched for "corneal ring infiltrate" and "ring infiltrate" phrases, "sterile corneal infiltrate" and "corneal infiltrate". We analyzed articles written in English on risk factors, pathophysiology, clinical manifestation, morphological features, ancillary tests (anterior-segment optical coherence tomography, corneal scraping, in vivo confocal microscopy), differential diagnosis and management of corneal ring infiltrate.

RESULTS

Available literature depicts multifactorial origin of corneal ring infiltrate. Dual immunological pathophysiology, involving both antibodies-dependent and -independent complement activation, is underlined. Furthermore, we found that the worldwide most prevalent among non-infectious and infectious ring infiltrates are ring infiltrates related to contact-lens wear and bacterial keratitis respectively. Despite low incidence of Acanthamoeba keratitis, it manifests with corneal ring infiltrate with the highest proportion of the affected patients (one third). However, similar ring infiltrate might appear as a first sign of general diseases manifestation and require targeted treatment. Every corneal ring infiltrate with compromised epithelium should be scraped and treat as an infectious infiltrate until not proven otherwise. Of note, microbiological ulcer might also lead to immunological ring and therefore require anti-inflammatory treatment.

CONCLUSION

Corneal ring infiltrate might be triggered not only by ocular infectious and non-infectious factors, but also by systemic conditions. Clinical assessment is crucial for empirical diagnosis. Furthermore, treatment is targeted towards the underlying condition but should begin with anti-infectious regimen until not proven otherwise.

A review of the epithelial and stromal effects of corneal collagen crosslinking

Induced corneal collagen crosslinking and mechanical stiffening via ultraviolet-A photoactivation of riboflavin (UVA CXL) is now a common treatment for corneal ectasia and Keratoconus. Some effects of the procedure such as induced mechanical stiffening, corneal flattening, and cellular toxicity are well-known, but others remain more controversial. Authors report a variety of contradictory effects, and provide evidence based on individual results and observations. A full understanding of the effects of and mechanisms behind this procedure are essential to predicting its outcome. A growing interest in modifications to the standard UVA CXL protocol, such as transepithelial or accelerated UVA CXL, makes analyzing the literature as a whole more urgent. This review presents an analysis of both the agreed-upon and contradictory results reported and the various methods used to obtain them.

Rates of infectious keratitis and other ocular surface adverse events in corneal cross-linking for keratoconus and corneal ectasias performed in an office-based setting: a retrospective cohort study

BACKGROUND

This study aimed to compare the complication rates of epithelium-off corneal cross-linking (epi-off CXL) performed in an office-based setting with those of epi-off CXL performed in an operating room.

METHODS

A retrospective cohort study, comprising 501 consecutive epi-off CXL procedures, performed in a non-sterile procedure room without laminar flow ventilation at the ELZA Institute in Zurich, Switzerland, between November 2015 and October 2021, was conducted.

RESULTS

No cases of postoperative infectious keratitis were observed, while sterile infiltrates occurred in 10 out of 501 (2.00%) patients, all of whom responded well to topical steroid therapy. Delayed epithelialization (> 7 days) occurred in 14 out of 501 (2.79%) patients. No other adverse events were noted.

CONCLUSIONS

Office-based epi-off CXL does not appear to be associated with an increased risk of complications when compared to operating room settings.

A Case Series of Infectious Keratitis After Corneal Cross-linking

PURPOSE

To present the 7-year experience of a tertiary eye hospital while exploring possible risk factors and incidence of infectious keratitis in patients undergoing standard corneal cross-linking (CXL).

METHODS

This retrospective cohort study included patients with progressive keratoconus undergoing standard CXL in the Farabi Eye Hospital and all other patients who had undergone CXL in other facilities and were diagnosed as having infectious keratitis in the 7-year period of the study.

RESULTS

Among the total of 4,863 eyes that underwent CXL, 6 eyes developed infectious keratitis, yielding an incidence rate of 0.12%. Additionally, 13 eyes from 10 patients with a CXL history in other facilities who developed infectious keratitis were included. The mean age was 23.75 years, and 75% of patients were men and 25% were women. Gram-positive bacteria and Staphylococcus aureus were the most prevalent pathogens. Meibomian gland dysfunction, dry eye disease, or blepharitis were present in 12 patients. Medical treatment did not arrest the disease progress in 5 patients, which eventually required cases to undergo keratoplasty.

CONCLUSIONS

This study supports the need for proper patient selection by using a comprehensive medical history. It also highlights the imperative role of rigorous patient education and follow-up, particularly in the first postoperative week. Finally, the study emphasizes aggressive early therapy for patients with suspicious findings. [J Refract Surg. 2023;39(8):564-572.].

Effect of Corneal Collagen Cross-Linking on Subsequent Corneal Fungal Infection in Rats

Purpose

The purpose of this study was to determine whether corneal collagen cross-linking (CXL) alters fungal susceptibility and increases the severity of keratitis through macrophage activation in rats.

Methods

Four weeks following CXL pretreatment, the corneal epithelium of adult rats was removed and inoculated with Candida albicans (C. albicans; CXL + inoculation group). The non-CXL-pretreated corneas were also inoculated with C. albicans (inoculation group). Clinical scoring and histopathological examination were performed to determine the severity of fungal keratitis. Immunofluorescence and confocal microscopy imaging were applied to determine the effects of CXL treatment on corneal local macrophage content. Real-time polymerase chain reaction (RT-PCR) and Western blots were used to evaluate mRNA and protein expression. Flow cytometry assays were performed to detect M1- and M2-type macrophages.

Results

CXL pretreatment (CXL + inoculation) resulted in higher infection success rate and more severe fungal keratitis than inoculation alone (inoculation group). On days 1, 3, and 7 following fungal infection, the increase in macrophage infiltration and IL-1β, MMP-9, and VEGFA expression was greater in the CXL + inoculation group than in the inoculation group. Number of M1- and M2-type macrophages, M1 to M2 ratio, M1-type macrophage genes, inducible nitric oxide synthase (iNOS), and tumor necrosis factor (TNFα) expression were higher in the CXL + inoculation group compared with the inoculation group.

Conclusions

Our data demonstrate that CXL may increase the colonization of macrophages and activate more M1-type macrophages to increase fungal susceptibility and severity of keratitis.

Translational Relevance

This study may aid long-term risk assessment and treatment of the complications of CXL.

The research progress on the molecular mechanism of corneal cross-linking in keratoconus treatment

Keratoconus (KC) is a corneal anomaly that is manifested in a limited cone-like bulge with corneal thinning. Many molecules in the cornea change during the development of KC, including various components of the extracellular matrix, cytokines, cell connection, and cell adhesion-related proteins. Several treatment options are available, with corneal cross-linking (CXL) being the treatment of choice for early KC. However, postoperative complications have been reported in some CXL patients, mainly caused by corneal epithelial resection. Despite the fact that some novel approaches have helped to reduce some of the initial post-operative issues, their effectiveness seems to be inferior to that of the original CXL. To keep effectiveness while avoiding these negative effects, it is necessary to study the mechanism of CXL in KC treatment at the molecular level. This article provides a review of the molecular mechanism of CXL in the treatment of KC from four aspects: enzyme activity, signal transduction pathway, corneal-related proteins, and other KC-related molecules, further confirming the feasibility of CXL treatment of KC, providing new ideas for improving CXL.

Fungal Keratitis and Corneal Perforation as a Rare Complication of Corneal Collagen Cross-Linking Treatment

PURPOSE

The aim of this study was to report a case of fungal keratitis with subsequent corneal perforation after corneal collagen cross-linking (CXL) treatment performed for keratoconus.

CASE REPORT

A 20-year-old woman presented with redness and discharge in the left eye. She had a history of bilateral CXL procedure performed for keratoconus elsewhere 4 days earlier. The visual acuity was hand motion in the left eye. Slit-lamp examination revealed extended corneal melting with surrounding infiltrates. The patient was hospitalized, and corneal epithelial scraping samples were sent for microbiological assessment. In the meantime, empirical antibiotic therapy (fortified topical antibiotics: vancomycin 50 mg/mL, ceftazidime 50 mg/mL, and fluconazole 2 mg/mL q1 hour) was initiated. In direct microscopy of the corneal scraping, septate hyaline fungal hyphae were detected and topical fluconazole was switched to topical voriconazole (10 mg/mL). Three days after hospitalization, corneal melting progressed to perforation and corneal suturing with 10-0 monofilament was performed to reform the anterior chamber. Complete resolution of keratitis with residual scarring was noticed in 2 weeks. Three months later, penetrating keratoplasty was performed to obtain better visual acuity.

CONCLUSIONS

CXL with riboflavin has become a common procedure to prevent keratoconus progression by strengthening the biomechanical specialties of the cornea. Although the treatment itself has been used in the management of microbial keratitis and related corneal melting, fungal keratitis and corneal perforation after a CXL procedure for keratoconus might also be detected. Clinicians should be aware of this rare but devastating complication of CXL treatment and start prompt treatment when suspected.

Low-intensity low-frequency ultrasound mediates riboflavin delivery during corneal crosslinking

We employed the mechanical effect from 40 kHz ultrasound (US) to improve the delivery of riboflavin into corneal stroma for collagen crosslinking, which can benefit the treatment of keratoconus and other corneal ectasias. Experiments were conducted, first with porcine corneas ex vivo and then with New Zealand white rabbits in vivo, at varying mechanical index (MI) and sonication time. Results showed that 15 min of US applied on the cornea at MI = 0.8 in the presence of 0.5% of riboflavin solution enabled its delivery to deeper corneal stroma. Excessive heat was removed by a cooling setup to negate the thermal effect. The corneal absorption amount and penetration of riboflavin through cornea as detected by fluorotron, as well as the enhancement of corneal stiffness as measured by Young's modulus, were comparable to the conventional approach that requires complete corneal epithelium debridement. Histological analysis revealed minor exfoliation of superficial cell layers of corneal epithelium and loss of ZO-1 tight junctions immediately after US. Full recovery of the corneal epithelium and restoration of tight junctions occurred in 3-4 days. The study shows that low-intensity low-frequency ultrasound (LILF US) is a less invasive alternative to the conventional epithelium-off method for delivering riboflavin into the corneal stroma.

The Safety Profile of FDA-Approved Epithelium-Off Corneal Cross-Linking in a US Community-Based Healthcare System

Purpose

To determine the occurrence of early post-operative complications following FDA-approved epithelium-off corneal cross-linking in the United States.

Materials and Methods

This multicenter, retrospective cohort study identified patients who underwent epithelium-off (epi-off) corneal cross-linking (CXL) for keratoconus and post-refractive keratectasia within the Kaiser Permanente Northern California healthcare system between 2016 and 2018. Post-operative complications including delayed epithelial healing, infection, and loss of visual acuity were recorded.

Results

The study included 878 eyes of 654 patients. The mean age was 27±9.4 years (range 7–71). Five hundred ninety-nine patients (91.6%) had keratoconus while 55 had post-refractive corneal ectasia (8.4%). Forty-seven eyes had prolonged follow-up because of the occurrence of complications in the early post-operative period. The respective rates of delayed epithelial healing, and keratitis were 3.9% (95% CI 2.7–5.3%), and 1.5% (95% CI 0.8–2.5%). Four approaches for management of delayed epithelial healing were compared; epithelium healing duration was the longest in the repeat bandage contact lens (BCL) group (23.8 days) and the shortest in the antibiotic ointment group (14.3 days), with statistically significant differences (p < 0.05) in the healing time between these 2 groups.

Conclusion

The concern for early clinical complications after epi-off CXL often leads to delayed CXL intervention and further keratoconus progression with increased economic burdens. A large retrospective review of 878 eyes found that FDA-approved epi-off CXL protocol appears to be safe with low occurrence rates of early post-operative complications. The recommended management for delayed epithelial healing is using antibiotic ophthalmic ointment.

Photodynamic therapy for treatment of bacterial keratitis

Microbial keratitis is the main cause of corneal opacification and the fourth leading cause of blindness worldwide, with bacteria the major infectious agent. Recently, bacterial keratitis has become a serious threat due to routine use of antibiotics leading to selection of resistant and multidrug-resistant bacteria strains. New approaches for treatment of bacterial keratitis are necessary to outcome the increasing antibiotic resistance. Antimicrobial photodynamic therapy is based on three agents: photosensitizer, oxygen, and light radiation. This therapy has been successful for treatment of infections in different tissues and organs as well as against different type of infectious agents and no resistance development. Also, new photosensitizers are being developed that has increased the spectrum of therapeutic protocols for treatment of a number of infectious diseases. Thus, antimicrobial photodynamic therapy has an extraordinary potential for treatment of those bacterial keratitis cases that actually are not solved by traditional antibiotic therapy.

Polymicrobial keratitis after accelerated corneal collagen cross-linking in keratoconus: Case reports and literature review

PURPOSE

To report two cases of polymicrobial keratitis following corneal collagen cross-linking for keratoconus and to review the literature.

METHODS

Retrospective case note and literature review.

RESULTS

The first case involved a 27-year-old male who presented with amebic corneal ulcers 3 days after the collagen cross-linking procedure. Some gram-negative (gram-ve) cocci were found upon staining, and cysts were observed by confocal microscopy at 7 days after surgery. Acanthamoeba infection mixed with gram-ve organisms was diagnosed. In the second case, a 14-year male developed Staphylococcus aureus corneal infection with anterior chamber empyema 3 days after the collagen cross-linking procedure for keratoconus. Occasional gram-positive (gram + ve) cocci and gram-ve bacilli were observed under a microscope. The mixed keratitis in the two patients resolved after systemic and topical antibiotic therapy, but the infection ultimately resulted in corneal scarring. Follow-up keratoplasty was needed to improve vision acuity in both patients.

CONCLUSION

Although ultraviolet irradiation and the reactive oxygen released by riboflavin during collagen cross-linking have bactericidal effects, a lack of a corneal epithelial barrier, bandage contact lens usage, perioperative hygiene, and an abnormal immune state are risk factors for infectious keratitis after collagen cross-linking. Perioperative management of collagen cross-linking is important to prevent infection.

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Infectious keratitis after corneal crosslinking for keratoconus caused by levofloxacin-resistant microorganisms

Introduction

We present seven cases of infectious keratitis after corneal crosslinking (CXL) to attenuate keratoconus progression.

Methods

Of 524 consecutive patients who underwent CXL, 7 cases (4 males and 3 females; 21.5 ± 7.1 years) developed postoperative infectious keratitis were retrospectively reviewed. CXL was performed using the Dresden protocol or an accelerated protocol involving epithelial removal.

Results

All cases appeared normal on the day after surgery, but subsequently developed eye pain, blurred vision, corneal infiltration, inflammation of the anterior chamber, and ciliary injection on day 2 or 3. Methicillin-resistant Staphylococcus aureus was cultured from two eyes, methicillin-sensitive Staphylococcus aureus from two eyes, and Streptococcus pneumoniae from one eye. All detected bacteria were resistant to levofloxacin (LVFX). Five of the seven cases, especially four of the five severe cases with hypopyon, had a history of atopic dermatitis. All cases were observed after 2015.

Conclusions

Infectious keratitis after CXL caused by microbes resistant to LVFX is increasing. In addition to careful postoperative observation of the cornea, preoperative evaluation of bacteria within the conjunctival sac evident on nasal swab cultures may be useful to identify potentially problematic microbes and inform the selection of appropriate antibiotics.

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.

Foundational concepts in the biology of bacterial keratitis

Bacterial infections of the cornea, or bacterial keratitis (BK), are notorious for causing rapidly fulminant disease and permanent vision loss, even among treated patients. In the last sixty years, dramatic upward trajectories in the frequency of BK have been observed internationally, driven in large part by the commercialization of hydrogel contact lenses in the late 1960s. Despite this worsening burden of disease, current evidence-based therapies for BK - including broad-spectrum topical antibiotics and, if indicated, topical corticosteroids - fail to salvage vision in a substantial proportion of affected patients. Amid growing concerns of rapidly diminishing antibiotic utility, there has been renewed interest in urgently needed novel treatments that may improve clinical outcomes on an individual and public health level. Bridging the translational gap in the care of BK requires the identification of new therapeutic targets and rational treatment design, but neither of these aims can be achieved without understanding the complex biological processes that determine how bacterial corneal infections arise, progress, and resolve. In this chapter, we synthesize the current wealth of human and animal experimental data that now inform our understanding of basic BK pathophysiology, in context with modern concepts in ocular immunology and microbiology. By identifying the key molecular determinants of clinical disease, we explore how novel treatments can be developed and translated into routine patient care.

Crosslinking und Keratokonus

Ein Keratokonus führt zu einer progressiven Vorwölbung und Verdünnung der Hornhaut. Um dies aufzuhalten, kann ein Crosslinking durchgeführt werden. Dabei ist eine Behandlung nach dem „Dresdener Protokoll“ eine effektive und sichere Behandlungsmöglichkeit, aber auch zahlreiche neue Anwendungsprotokolle (akzeleriertes Crosslinking, transepitheliales Crosslinking) und sogar weitere Indikationen (refraktive Eingriffe, infektiöse Keratitis) wurden in den letzten Jahren veröffentlicht.

[Crosslinking and Keratoconus]

Keratoconus leads to a progressive protrusion and thinning of the cornea. In order to stop this, corneal crosslinking can be performed if the progression of the disease is proven. Crosslinking according to the "Dresden protocol" includes abrasion of the corneal epithelium, application of riboflavin eye drops and irradiation with UV-A light of an intensity of 3 mW/cm² for 30 minutes. The efficacy has been shown in several prospective randomized studies. One of the more recent developments is accelerated crosslinking, which allows a shorter irradiation time. On the other hand, the possibility of transepithelial crosslinking was presented, which does not require an abrasion of the cornea. This should reduce the occurrence of postoperative pain. The range of indications has also been expanded. Corneal crosslinking is used for post-LASIK keratectasia as well. It is also being considered for use in infectious keratitis. Topographically controlled crosslinking can likewise be used to try to positively influence the refractive power of the cornea. The risks of crosslinking include the occurrence of pain, haze or scarring, endothelial cell damage and, rarely, the occurrence of keratitis.

Microbial Keratitis After Corneal Collagen Cross-Linking for Corneal Ectasia

PURPOSE

The aim of this study was to report the clinical profile and microbiological of patients with microbial keratitis post accelerated corneal collagen cross-linking (CXL).

METHODS

A retrospective case series of all patients diagnosed with microbial keratitis post-CXL who attended the Sydney Eye Hospital, Australia from January 1, 2012 to December 31, 2019 were included. Patients were identified from hospital coding and pathology data. Data were extracted from patients' medical records.

RESULTS

Eleven eyes from 10 patients with a mean age of 29 ± 11 years (range 16-48) were included. The median time of infection after CXL surgery was 4 days [interquartile range (IQR) 3-83]. Median initial and final Visual acuity at presentation were 1.3 logMAR (IQR 1-2.0) and 0.8 logMAR (IQR 0.6-1.2), respectively. The culture positivity rate was 92%, identifying 13 isolates, predominately made up of coagulase-negative Staphylococcus (n = 6, 50%) and Staphylococcus aureus (n = 3, 25%). The median epithelial healing time was 30 days (IQR 15-53).

CONCLUSIONS

Post-CXL microbial keratitis was predominately associated with gram-positive bacteria and in some cases delayed epithelialization. Microbial keratitis post-CXL may lead to moderate to poor patient outcomes.

Outcomes of Corneal Topography among Progressive Keratoconus Patients 12 months following Corneal Collagen Cross-Linking

Purpose

This study aimed to assess the overall and specific topographic changes among patients who underwent corneal collagen cross-linking (CXL) due to progressive keratoconus.

Methods

This retrospective case series study was conducted at a single-arm hospital in King Abdulaziz Medical City, Riyadh. All progressive keratoconus patients who underwent CXL between January 2017 and December 2018 were included consecutively. The epi-off crosslinking technique (Dresden protocol) was applied in all patients. The topographic values were measured preoperatively and 12 months postoperatively. Patients with a history of a previous corneal procedure, corneal trauma, or any corneal scarring were excluded.

Results

Among our population (29 eyes of 24 patients), 58.6% of eyes were for male patients, and the mean age of the population was 27.76 ± 4.21 years. Based on the topography results, the mean values of corneal thickness at central 3 mm decreased from 473.45 ± 38 µm to 465.72 ± 41.78 µm following CXL (Z = −1.93, 95% confidence interval [CI] = 0.048–0.057, p= 0.053). Clinically significant astigmatism measurements were present in 28 (96.6%) eyes before CXL compared to 26 (89.7%) eyes after CXL. The mean values of astigmatism among the patients were 3.37 ± 2.25 diopters before and 3.67 ± 2.61 diopters after CXL (Z = −1696, 95% confidence interval [CI] = 0.085–0.096, p = 0.09). After CXL, the mean values of the front elevation at the apex changed from 33.90 ± 20.13 µm to 36.10 ± 21.09 µm (Z = −2.792, 95% [CI] = 0.003–0.006, p = 0.005). The mean values of the back elevation at the apex changed from 68.4 ± 35.66 µm to 69.90 ± 35.89 µm (Z = −0.934, 95% CI = 0.343–0.366, p = 0.35).

Conclusion

The topographic corneal parameters improved significantly in the patients with corneal ectasia after CXL. These results revealed the safety and efficacy of CXL in stabilizing keratoconus progression among Saudi patients at 1 year of follow-up.

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.

Alternaria keratitis after corneal crosslinking

Purpose

To report a case of fungal keratitis after corneal collagen crosslinking (CXL) surgery.

Observations

We report a case of fungal keratitis after CXL for post-refractive surgery ectasia. The patient presented 12 days after surgery with a corneal ulcer that was culture positive for Alternaria species of fungus. She subsequently developed a bacterial superinfection. The keratitis resolved with medical therapy, although the patient required a penetrating keratoplasty (PKP) due to central corneal scarring.

Conclusions and Importance

To our knowledge, this is the first case of fungal keratitis as a complication after CXL in the United States and the first case of Alternaria infection after CXL using the Dresden protocol. Infectious keratitis is a rare but serious complication of CXL, and we suggest continued innovation of operative techniques that may reduce the risk of infectious keratitis.

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.

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.

Corneal crosslinking without epithelial removal

PURPOSE

To evaluate the effect of riboflavin-ultraviolet (UV)-A corneal crosslinking (CXL) without epithelial removal on ectatic corneal disease.

SETTING

Woolfson Eye Institute, Atlanta, Georgia, USA.

DESIGN

Prospective observational study.

METHODS

Patients were treated with a new riboflavin formulation without epithelial removal, then exposed to UV light (365 nm) at 4 mW/cm² with on-off cycling for 30 minutes. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, maximum corneal curvature (maximum keratometry [Kmax]), total higher-order aberrations (HOAs), and coma were measured at 3, 6, 12, and 24 months postoperatively. Progression was defined as an increase of more than 1 diopter (D) in Kmax and loss of more than 1 line of CDVA.

RESULTS

Five hundred twelve eyes of 308 patients with keratoconus or forme fruste keratoconus and 80 eyes of 55 patients with ectasia after laser in situ keratomileusis (LASIK) were treated with the new riboflavin formulation without epithelial removal; 229 patients received bilateral treatments, 95 of which were simultaneous. The mean UDVA and CDVA improved by 1 to 1.5 Snellen lines at 1 and 2 years postoperatively (P < .0001). Mean Kmax decreased by 0.48 D at 2 years postoperatively (P = .0002). Mean total HOAs and coma decreased by 36% (P < .0001) and 37% (P = .0002), respectively, at 2 years postoperatively. Kmax decreased more than 1 D in three times as many eyes as it increased more than 1 D (P < .0001). No eyes progressed, and there was no loss of effect between 1 and 2 years postoperatively. No vision-threatening events were observed. Pain typically resolved within 24 hours, and visual acuity returned to preoperative levels in 1 to 2 days.

CONCLUSION

Epithelium-on CXL using this new protocol halted the progression of keratoconus and ectasia after LASIK. It was safer and provided more rapid visual recovery than CXL with epithelial removal, allowing routine bilateral, simultaneous treatment.

Evaluation of the Effectiveness of Cross-Linking Combined With Photorefractive Keratectomy for Treatment of Keratoconus

PURPOSE

To evaluate the effectiveness and safety of combined epithelium-off cross-linking (CXL) with photorefractive keratectomy (CXL Plus) for correction of the myopic and astigmatic components of keratoconus.

METHODS

Seventy-nine eyes of 46 patients who underwent CXL Plus were enrolled in this retrospective, multicenter, noncomparative clinical study. Uncorrected distance visual acuity, corrected distance visual acuity, refraction, keratometry, and pachymetry measurements were recorded preoperatively and at 3, 6, 12, and 18 months during follow-up.

RESULTS

The mean (±SD) preoperative uncorrected distance visual acuity and corrected distance visual acuity were 1.00 ± 0.22 logarithm of the minimum angle of resolution (logMAR) and 0.62 ± 0.38 logMAR, respectively, and improved to 0.71 ± 0.36 logMAR and 0.32 ± 0.18 logMAR postoperatively. The mean k value, mean corneal thickness at the thinnest location, and mean myopic and astigmatic components decreased from 46.58 ± 0.97 D, 473 ± 29 μm, 3.65 ± 1.72 D, and 1.83 ± 0.69 D preoperatively to 43.79 ± 1.17 D, 431 ± 38 μm, 1.02 ± 0.78 D, and 1.15 ± 0.26 D, respectively, during follow-up. Eleven eyes had delayed epithelial healing, 2 had stromal opacities, 1 had primary herpes simplex keratitis, and 5 showed progression of keratoconus.

CONCLUSIONS

CXL Plus improved the refractive status of keratoconus during 18 months of follow-up, despite its potential early postoperative complications of delayed epithelial healing and corneal haze. CXL Plus reduced the myopic component more than the astigmatic component of keratoconus. However, the safety and stability of the procedure were offset by longer-term postoperative complications and a high rate of postoperative progression of keratoconus.

Collagen cross-linking impact on keratoconus extracellular matrix

Background

Keratoconus (KC) is a common multifactorial ectatic corneal disease with unknown onset. KC most commonly appears in adolescence and affects approximately 1:400 people worldwide. Treatment options, for advanced KC cases, are collagen cross-linking (CXL) and corneal transplants. CXL is a new KC treatment that helps arrest the disease. Unfortunately, only a fraction of KC patients will qualify for CXL treatment. Our goal, in this study, was to begin to understand how CXL affects the corneal microenvironment and pave the way towards a more patient-driven CXL treatment.

Methods

Primary human corneal fibroblasts from healthy and KC donors were plated on transwell polycarbonate membranes and stimulated by a stable vitamin C. At 4 weeks, riboflavin was added followed by UVA irradiation. Transmission Electron Microscopy (TEM) and western blots were used to assess the effect of CXL on the extracellular matrix (ECM) and the resident cells, pre- and post CXL.

Results

Data shows CXL improved lamellar organization showing more organized collagen fibrils decorated with proteoglycans (PGs). The distribution of the collagen fibrils and interfibrillar spacing was also visibly improved, post-CXL. Lumican, mimecan, and decorin were the dominant PGs and were significantly upregulated in post-CXL cultures. ECM degradation proteins, matrix metalloproteinases (MMPs), MMP-1, -3, and -9, but not MMP-2, were significantly downregulated post-CXL. TIMP-1 and -2 were not modulated by CXL.

Conclusion

The unknown effects of CXL on the human corneal microenvironment have hampered our ability to make CXL available to all KC patients. Our current study provides a deeper understanding on CXL activity, using our unique 3D in vitro model.

Influence of standard corneal cross-linking in keratoconus patients on macular profile

Purpose

To determine the effect of corneal cross-linking (CXL) on retinal structure and function.

Methods

The current study was conducted on 42 eyes of 21 patients with keratoconus (KCN) who were candidates for CXL due to disease progression. The Optovue optical coherence tomography (OCT) (Optovue Inc., Fremont, USA) from macula and multifocal electroretinography (mERG) were performed on all patients prior to surgery and at 1- and 6- month follow-up. Structural and functional parameters of macula including retinal thickness in OCT, and amplitude and latency of electroretinogram were compared between eyes that underwent surgery and control fellow eyes during the study period.

Results

A statistically significant increase in central foveal, foveal, parafoveal, and perifoveal thickness was observed at 1-month follow-up. The changes were non-significant at 6 months. Although a statistically significant reduction in amplitude and increase in latency in both rings 2 and 3 were observed at 1 month in mERG, only amplitude changes in ring 2 remained significant at 6 months.

Conclusion

Transient anatomical and functional alterations following CXL were observed in the current study.

Microbial Keratitis After Accelerated Corneal Collagen Cross-Linking in Keratoconus

PURPOSE

To assess the pattern of microbial keratitis after accelerated corneal collagen cross-linkage (aCXL) in patients with keratoconus.

METHOD

The medical records of cases of keratoconus that underwent aCXL from June 2014 to May 2017 were reviewed. Cases that developed microbial keratitis after aCXL were included in the study. The clinical, microbiological profile and the treatment outcomes were evaluated.

RESULTS

Of 532 eyes that underwent aCXL, 7 cases developed microbial keratitis during the study period. Median age at presentation was 11 years (range 8-17). Association with vernal keratoconjunctivitis was noted in 57.1% of cases (n = 4/7). The median time at the onset of infection was 3 days after aCXL (range 1-4). Microbiological reports revealed mixed infection in 3 cases [coagulase-negative Staphylococcus (CoNS) + Aspergillus fumigatus, Staphylococcus aureus and Mucor spp., Staph. aureus and Acanthamoeba], Staph. aureus in 2 cases, and CoNS and Alternaria spp. in 1 case each. Resistance to fourth-generation fluoroquinolones was noted in 83.3% of cases of bacterial keratitis (n = 5/6). All cases were initially managed with empirical antibiotic treatment that was later tailored based on microbiological reports. One case eventually required therapeutic penetrating keratoplasty for corneal perforation. At 6 months, the corrected distance visual acuity was >6/60 in 3 cases while 4 cases had corrected distance visual acuity <6/60.

CONCLUSIONS

Microbial keratitis after aCXL is rare; however, the infection tends to be severe with high preponderance of mixed infection and resistance to fourth-generation fluoroquinolones.

[Corneal collagen cross-linking in the treatment of infectious keratitis and corneal ulcers]

In recent years, collagen cross-linking (CXL) of the cornea has acquired a new usage - in the treatment of infectious keratitis and corneal ulcers. This review was aimed at compiling the previously published data and assessing the effectiveness of the method.

Current perspectives on corneal collagen crosslinking (CXL)

Corneal collagen crosslinking has revolutionized the treatment of keratoconus and post-refractive corneal ectasia in the past decade. Corneal crosslinking with riboflavin and ultraviolet A is proposed to halt the progression of keratectasia. In the original "Conventional Dresden Protocol" (C-CXL), the epithelium is removed prior to the crosslinking process to facilitate better absorption of riboflavin into the corneal stroma. Studies analyzing its short- and long-term outcomes revealed that although there are inconsistencies as to the effectiveness of this technique, the advantages prevail over the disadvantages. Therefore, corneal crosslinking (CXL) is widely used in current practice to treat keratoconus. In an attempt to improve the visual and topographical outcomes of C-CXL and to minimize time-related discomfort and endothelial-related side effects, various modifications such as accelerated crosslinking and transepithelial crosslinking methods have been introduced. The comparison of outcomes of these modified techniques with C-CXL has also returned contradictory results. Hence, it is difficult to clearly identify an optimal procedure that can overcome issues associated with the CXL. This review provides an up-to-date analysis on clinical and laboratory findings of these popular crosslinking protocols used in the treatment of keratoconus. It is evident from this review that in general, these modified techniques have succeeded in minimizing the immediate complications of the C-CXL technique. However, there were contradictory viewpoints regarding their effectiveness when compared with the conventional technique. Therefore, these modified techniques need to be further investigated to arrive at an optimal treatment option for keratoconus.

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.

Bilateral corneal perforation due to MRSA keratitis in a crosslinking patient

Introduction: The cornea may become infected and perforated after epithelium-on collagen crosslinking. Case presentation: A healthy 33-year-old male who underwent corneal collagen crosslinking in both eyes developed a purulent keratitis and bilateral corneal perforations, requiring bilateral penetrating keratoplasties. He was exposed to methicillin resistant staphylococcus aureus (MRSA) by a family member with a tracheostomy and was treated with MRSA-directed antibiotics. After prolonged recovery and treatment of his infection, he had acceptable but limited uncorrected visual acuity, with excellent corrected visual acuity. Conclusion: While epithelium-on crosslinking is commonly thought to be associated with a lower risk of postoperative infection, this case illustrates that even epithelium-on treatment may present the patient with a risk of infection. Patients in higher risk groups who are exposed to infectious disease may be more predisposed.

Fungal keratitis: study of increasing trend and common determinants

Fungal keratitis is one of the leading cause of ocular morbidity. Fungal keratitis possesses a clinical challenge due to its slow pathologic process, overlapping features, diagnostic difficulty, and potential complications. Its increasing trend can be attributed to the use of contact lens, non-judiciary corticosteroid, and vegetative trauma. Early diagnosis and treatment is the cornerstone for its effective control. Knowledge of pathological course and clinical characteristics of fungal keratitis will definitely add in early diagnosis and treatment, with reduction in ocular morbidity. This review article explores the risk factor of fungal keratitis, its clinical course and management strategy.

Efficacy of transepithelial corneal collagen crosslinking for keratoconus: 12-month follow-up

Purpose

To evaluate the efficacy of transepithelial corneal collagen crosslinking (TE-CXL) in patients with progressive keratoconus.

Patients and methods

This is a prospective interventional consecutive study carried out on 30 eyes of 18 patients with progressive keratoconus who underwent TE-CLX using both ParaCel™ (riboflavin 0.25%, hydroxy propyl methyl cellulose, NaCl, ethylenediaminetetraacetic acid [EDTA], Tris, and benzalkonium chloride) and vibeX-Xtra (riboflavin 0.22%, phosphate-buffered saline solution). The procedure was carried out at Ebsar Eye Center in Egypt in the period from 2012 to 2014. The follow-up visits were scheduled on days 1, 3, 6, and 12 months after treatment.

Results

There were statistically significant improvements (P<0.001) in the mean best-corrected visual acuity (0.54±0.22 preoperatively vs 0.61±0.19 at 12 months postoperatively), the mean manifest refraction spherical equivalent (MRSE; −6.16±3.90 diopters [D] preoperatively and −5.91±3.72 D at 12 months postoperatively), and the mean preoperative corneal astigmatism (−3.39±2.11 D preoperatively and −2.46±2.60 D at 12 months postoperatively).

Conclusion

TE-CXL could halt the progression of keratoconus in adult patients. TE-CXL resulted in a statistically significant improvement in best-corrected visual acuity, manifest refraction, refractive and corneal astigmatism and K values in keratoconus patients at the 12-month follow-up. Larger sample sizes and longer follow-ups are required in order to make meaningful conclusions.

Chlorin e6 mediated photodynamic inactivation for multidrug resistant Pseudomonas aeruginosa keratitis in mice in vivo

Following corneal epithelium scratches, mouse corneas were infected with the multidrug resistant (MDR) P. aeruginosa strain PA54. 24 hours later, 0% (for control group), 0.01%, 0.05% or 0.1% Chlorin e6 (Ce6), a second generation photosensitizer derived from chlorophyll, was combined with red light, for photodynamic inactivation (PDI). 1 hour or 2 days later, entire mouse eyes were enucleated and homogenized for counting colony forming units (CFU) of P. aeruginosa. For comparison, 0.1% Ce6 mediated PDI was started at 12 hours post infection, and 0.005% methylene blue mediated PDI 24 hours post infection. Clinical scores of corneal manifestation were recorded daily. Compared to the control, CFU 1 hour after PDI started 24 hours post infection in the 0.01% Ce6 and 0.05% Ce6 groups were significantly lower (more than one log₁₀ reduction), the CFU 2 days post PDI higher in the 0.1% Ce6 group, clinical score lower in the 0.1% Ce6 group at 1 day post PDI. These findings suggest that PDI with Ce6 and red light has a transient efficacy in killing MDR-PA in vivo, and repetitive PDI treatments are required to fully resolve the infection. Before its clinical application, the paradoxical bacterial regrowth post PDI has to be further studied.

Sterile corneal infiltrates after corneal collagen cross-linking: evaluation of risk factors

PURPOSE

To evaluate possible risk factors leading to sterile corneal infiltrates following corneal collagen cross-linking (CXL).

METHODS

A total of 588 eyes of 459 patients treated with Epi-off (n = 461) or Epi-on (n = 127) CXL were retrospectively evaluated. Risk factors, including preoperative blepharitis and vernal conjunctivitis, the postoperative use of topical non-steroidal anti-inflammatory drugs (NSAIDs), as well as Kmax and pachymetry measurements, were assessed. In vivo confocal microscopy (IVCM) and anterior segment optical coherence tomography (AS-OCT) analyses were performed in patients with sterile infiltrates.

RESULTS

Sterile infiltrates developed in 19 cases (3.2%). No patients in the Epi-on group developed sterile infiltrates. The evaluation of acceleration of the CXL procedure as a risk factor revealed no specific difference in the incidence of infiltrates among four different Epi-off groups (3 mW/cm² -30 min, 9 mW/cm² -10 min, 18 mW/cm² -5 min, 30 mW/cm² -4 min procedures; p > 0.05, all). Blepharitis, vernal conjunctivitis, Kmax and pachymetry were not identified as risk factors (p > 0.05). Postoperative use of NSAIDs was a significant contributor (p = 0.007), and it increased the chance of sterile infiltrates 4.09 times (95% CI, 1.463-11.428). In vivo confocal microscopy (IVCM) showed non-specific inflammation with dendritic cells at the epithelium and at Bowman's layer. In AS-OCT, a hyper-reflective band at the level of the anterior stroma to a depth of 100-140 μm was observed.

CONCLUSION

The evaluation of the risk factors such as blepharitis, the use of NSAIDs, vernal conjunctivitis, the duration of CXL procedure and amount of light intensity showed that epithelial damage is possibly the common pathway in the pathogenesis, as no sterile infiltrates in Epi-on CXL occurred, and the postoperative use of NSAIDs increased the risk of developing sterile infiltrates about four times.

Therapeutic and inducing effect of corneal crosslinking on infectious keratitis

The corneal crosslinking (CXL) with riboflavin and ultraviolet-A (UVA) is a new therapy method to successfully treat infectious keratitis in clinical practice. However, there are rare reports on the complications of CXL such as the secondary keratitis. The diverse clinical outcomes on keratitis have highlighted the necessity to further evaluate the efficacy and complications of CXL. We reviewed the positive and negative reports on UVA/riboflavin related with keratitis and provided our opinion on the therapeutic and side effect of UVA/riboflavin crosslinking on keratitis.

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.

One-year Outcomes of Pachymetry and Epithelium Thicknesses after Accelerated (45 mW/cm(2)) Transepithelial Corneal Collagen Cross-linking for Keratoconus Patients

The thickness of corneal pachymetry and the epithelium after accelerated (45 mW/cm(2)) transepithelial corneal collagen cross-linking (CXL) for keratoconus were assessed in this prospective case series study. Twenty-eight patients were treated for keratoconus. The mean Kmax was 56.18 ± 7.90. The thinnest point, as assessed by optical coherence tomography (OCT), was 443.18 ± 39.75 μm. Accelerated transepithelial CXL was performed, and corrected distance visual acuity (CDVA), corneal topography, and OCT were recorded at 1 week postoperatively as well as at 1, 3, 6, and 12 months. The surgery was uneventful in all eyes. Postoperative epithelial edema was observed and faded in 3 days. The postoperative Kmax was 54.56 ± 8.81, 55.78 ± 8.11, 56.37 ± 8.71, 55.80 ± 7.92, and 55.47 ± 8.24 at 1 week, 1 month, 3 months, 6 months, and 12 months, respectively (all, P > 0.05). The thinnest postoperative corneal point, 439.04 ± 44.99 μm, was observed at 12 months (P = 0.109). The epithelial thickness decreased during the first postoperative week then showed a gradual recovery. Postoperative pachymetry thickness showed no significant changes for up to 12 months. Postoperative epithelial thickness decreased temporarily, then stabilized at month 12. Accelerated transepithelial CXL was shown to be effective and safe for the treatment of keratoconus.

Potential Effects of Corneal Cross-Linking upon the Limbus

Corneal cross-linking is nowadays the most used strategy for the treatment of keratoconus and recently it has been exploited for an increasing number of different corneal pathologies, from other ectatic disorders to keratitis. The safety of this technique has been widely assessed, but clinical complications still occur. The potential effects of cross-linking treatment upon the limbus are incompletely understood; it is important therefore to investigate the effect of UV exposure upon the limbal niche, particularly as UV is known to be mutagenic to cellular DNA and the limbus is where ocular surface tumors can develop. The risk of early induction of ocular surface cancer is undoubtedly rare and has to date not been published other than in one case after cross-linking. Nevertheless it is important to further assess, understand, and reduce where possible any potential risk. The aim of this review is to summarize all the reported cases of a pathological consequence for the limbal cells, possibly induced by cross-linking UV exposure, the studies done in vitro or ex vivo, the theoretical bases for the risks due to UV exposure, and which aspects of the clinical treatment may produce higher risk, along with what possible mechanisms could be utilized to protect the limbus and the delicate stem cells present within it.

Corneal Changes After Collagen Crosslinking for Keratoconus Using Dual Scheimpflug Imaging

Purpose:

To evaluate corneal changes after collagen crosslinking (CXL) therapy for keratoconus (KCN) using the Galilei dual Scheimpflug analyzer.

Methods:

This prospective, nonrandomized clinical study included 35 eyes of 32 keratoconus patients who had undergone CXL. The eyes were saturated with riboflavin solution and were subjected for 30 minutes to ultraviolet-A (UV-A) light with irradiance of 3 mW/cm². Effectiveness of the treatment was assessed by measuring uncorrected visual acuity (UCVA), best-corrected visual acuity (BCVA), manifest cylinder/sphere, keratometry, pachymetry, posterior and anterior elevations by the Galilei dual Scheimpflug analyzer. Prior to treatment and 8 months after therapy, Scheimpflug analysis was performed using the Galilei system. The four sets of data including keratometry values, pachymetry, elevation parameters and surface indices were statistically analyzed and compared.

Results:

Mean patient age was 22.3 ± 3.8 years and mean postoperative follow-up was 8.1 ± 3.2 months. There was a significant increase in UCVA (0.54 ± 0.35 Log MAR preoperatively to 0.49 ± 0.34 LogMAR postoperatively, P = 0.01) and BCVA (0.21 ± 0.19 Log MAR preoperatively to 0.16 ± 0.17 LogMAR postoperatively, P = 0.01). Mean cycloplegic spherical equivalent refractive error was −4.13 ± 2.65 Diopter (D) preoperatively and − 4.67 ± 2.96 D postoperatively (P < 0.001). During the follow-up period, no significant difference was observed in pachymetric and elevation data postoperatively.

Conclusion:

Corneal stabilization could be achieved by collagen crosslinking therapy for keratoconus in terms of corneal thickness, keratometry values, elevation parameters and surface indices.