PACK-CXL: Corneal Cross-linking for Treatment of Infectious Keratitis

Enhancing Rose Bengal penetration in ex vivo human corneas using iontophoresis

Aim: Rose Bengal photodynamic antimicrobial therapy (RB-PDAT) has poor corneal penetration, limiting its efficacy against acanthamoeba keratitis (AK). Iontophoresis enhances corneal permeation of charged molecules, piquing interest in its effects on RB in ex vivo human corneas.Methods: Five donor whole globes each underwent iontophoresis with RB, soaking in RB, or were soaked in normal saline (controls). RB penetration and corneal thickness was assessed using confocal microscopy.Results: Iontophoresis increased RB penetration compared with soaking (177 ± 9.5 μm vs. 100 ± 5.7 μm, p < 0.001), with no significant differences in corneal thickness between groups (460 ± 87 μm vs. 407 ± 69 μm, p = 0.432).Conclusion: Iontophoresis significantly improves RB penetration and its use in PDAT could offer a novel therapy for acanthamoeba keratitis. Further studies are needed to validate clinical efficacy.

Photoactivated Chromophore for Keratitis-Corneal Cross-linking (PACK-CXL)-A Scoping Review Based on Preclinical Studies

Purpose

Photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) stabilizes the corneal stroma and eliminates microorganisms. Numerous PACK-CXL protocols, using different energy sources and chromophores, have been applied in preclinical studies, including live animal studies, with various experimental designs and endpoints. So far, a systematic mapping of the applied protocols and consistency across studies seems lacking but is essential to guide future research.

Methods

The scoping review protocol was in line with the JBI Manual for Evidence Synthesis. Electronic databases were searched (Embase, MEDLINE, Scopus, Web of Science) to identify eligible records, followed by a two-step selection process (title and abstract screening, full text screening) for record inclusion. We extracted information on (1) different PACK-CXL protocol characteristics; (2) infectious pathogens tested; (3) study designs and experimental settings; and (4) endpoints used to determine antimicrobial and tissue stabilizing effects. The information was charted in frequency maps.

Results

The searches yielded 3654 unique records, 233 of which met the inclusion criteria. With 103 heterogeneous endpoints, the researchers investigated a wide range of PACK-CXL protocols. The tested microorganisms reflected pathogens commonly associated with infectious keratitis. Bacterial solutions and infectious keratitis rabbit models were the most widely used models to study the antimicrobial effects of PACK-CXL.

Conclusions

If preclinical PACK-CXL studies are to guide future translational research, further cross-disciplinary efforts are needed to establish, promote, and facilitate acceptance of common endpoints relevant to PACK-CXL.

Translational Relevance

Systematic mapping of PACK-CXL protocols in preclinical studies guides future translational research.

How does atmospheric pressure cold helium plasma affect the biomechanical behaviour on alkali-lesioned corneas?

BACKGROUND

Melting corneal ulcers are a serious condition that affects a great number of animals and people around the world and it is characterised by a progressive weakening of the tissue leading to possible severe ophthalmic complications, such as visual impairment or blindness. This disease is routinely treated with medical therapy and keratoplasty, and recently also with alternative regenerative therapies, such as cross-linking, amniotic membrane transplant, and laser. Plasma medicine is another recent example of regenerative treatment that showed promising results in reducing the microbial load of corneal tissue together with maintaining its cellular vitality. Since the effect of helium plasma application on corneal mechanical viscoelasticity has not yet been investigated, the aim of this study is first to evaluate it on ex vivo porcine corneas for different exposition times and then to compare the results with previous data on cross-linking treatment.

RESULTS

94 ex vivo porcine corneas divided into 16 populations (healthy or injured, fresh or cultured and treated or not with plasma or cross-linking) were analysed. For each population, a biomechanical analysis was performed by uniaxial stress-relaxation tests, and a statistical analysis was carried out considering the characteristic mechanical parameters. In terms of equilibrium normalised stress, no statistically significant difference resulted when the healthy corneas were compared with lesioned plasma-treated ones, independently of treatment time, contrary to what was obtained about the cross-linking treated corneas which exhibited more intense relaxation phenomena.

CONCLUSIONS

In this study, the influence of the Helium plasma treatment was observed on the viscoelasticity of porcine corneas ex vivo, by restoring in lesioned tissue a degree of relaxation similar to the one of the native tissue, even after only 2 min of application. Therefore, the obtained results suggest that plasma treatment is a promising new regenerative ophthalmic therapy for melting corneal ulcers, laying the groundwork for further studies to correlate the mechanical findings with corneal histology and ultrastructural anatomy after plasma treatment.

Collagen cross-linking beyond corneal ectasia: A comprehensive review

The history of corneal cross-linking (CXL) dates back to 2003 when some German scientists investigated possible treatments to harden the corneal structure to increase its resistance in ectatic corneal diseases. Nowadays, CXL is considered the most effective therapy in ectatic corneal diseases due to its proven efficacy in hardening the cornea, thus halting the development of the disease. Since 2003, CXL applications have dramatically expanded and have been implemented in several other areas such as infectious keratitis, corneal edema, and before performing keratoplasty for various purposes. Moreover, several irradiation patterns are being studied to correct refractive errors, taking into account the corneal refractive changes that occur after the procedure. Currently, scleral cross-linking is also being investigated as a potential therapy in cases of progressive myopia and glaucoma. In this article, we provide a comprehensive overview of the available applications of cross-linking in nonectatic ocular conditions and highlight the possible future indications of this procedure.

The novel role of lymphatic vessels in the pathogenesis of ocular diseases

Historically, the eye has been considered as an organ free of lymphatic vessels. In recent years, however, it became evident, that lymphatic vessels or lymphatic-like vessels contribute to several ocular pathologies at various peri- and intraocular locations. The aim of this review is to outline the pathogenetic role of ocular lymphatics, the respective molecular mechanisms and to discuss current and future therapeutic options based thereon. We will give an overview on the vascular anatomy of the healthy ocular surface and the molecular mechanisms contributing to corneal (lymph)angiogenic privilege. In addition, we present (i) current insights into the cellular and molecular mechanisms occurring during pathological neovascularization of the cornea triggered e.g. by inflammation or trauma, (ii) the role of lymphatic vessels in different ocular surface pathologies such as dry eye disease, corneal graft rejection, ocular graft versus host disease, allergy, and pterygium, (iii) the involvement of lymphatic vessels in ocular tumors and metastasis, and (iv) the novel role of the lymphatic-like structure of Schlemm's canal in glaucoma. Identification of the underlying molecular mechanisms and of novel modulators of lymphangiogenesis will contribute to the development of new therapeutic targets for the treatment of ocular diseases associated with pathological lymphangiogenesis in the future. The preclinical data presented here outline novel therapeutic concepts for promoting transplant survival, inhibiting metastasis of ocular tumors, reducing inflammation of the ocular surface, and treating glaucoma. Initial data from clinical trials suggest first success of novel treatment strategies to promote transplant survival based on pretransplant corneal lymphangioregression.

Repeated sessions of PACK-CXL WA for the treatment of resistant bacterial keratitis: a retrospective study

OBJECTIVE

The aim of this work is to evaluate the safety and efficacy of repeated sessions of photo-activated chromophore for keratitis-cross linking (PACK-CXL) window absorption (WA) for the treatment of resistant bacterial keratitis (BK).

PATIENTS AND METHODS

This is a retrospective clinical cohort study. Thirty eyes with clinically suspected and lab-confirmed bacterial keratitis, resistant to appropriate antibiotic therapy- which was modified by sensitivity reports- for 2 weeks with failure of epithelialization for 4 weeks after the standard anti-microbial therapy (SAT) together with one setting of PACK-CXL WA were included. If after the first session of PACK-CXL, there is a start of improvement in the form of reduction of the size of corneal ulcer and stromal infiltrates together with the start of epithelialization on clinical examination and AS-OCT, another session of PACK-CXL WA was performed after one week, and so on, till the complete healing and resolution of bacterial keratitis and confirmation by negative bacterial culture. Identification of the micro-organisms was done by lab study before and after treatment. Corneal healing was evaluated by corneal examination and anterior segment OCT (AS-OCT).

RESULTS

Thirty eyes of 30 patients were recruited in this study. They were 16 males and 14 females, their mean age was 44.3 ± 5.38 years. The mean ulcer size was 3.96 ± 1.87 (mm³), while the mean size of stromal infiltrates was 4.52 ± 2.24 (mm3). PACK-CXL WA treatment was performed an average of 2.87 times for the 30 eyes. Complete healing and resolution (Successful treatment) was observed in 27 eyes (90%) of cases and failure of epithelialization was observed only in 3 eyes (10%). Complete corneal healing was reported in the second month postoperatively in 90% of eyes.

CONCLUSION AND RECOMMENDATION

PACK-CXL WA may be a promising, non-invasive treatment option for resistant bacterial keratitis. It may have a synergistic effect with standard antimicrobial treatment (SAT). Also, it can overcome the antibiotics resistance that has become rapidly spreading worldwide. Repeated sessions of PACK-CXL WA may be more effective for the treatment of resistant bacterial keratitis till complete epithelialization and resolution of BK than a single session with few complications. However, further prospective and comparative studies to support the results are needed.

How Modifications of Corneal Cross-Linking Protocols Influence Corneal Resistance to Enzymatic Digestion and Treatment Depth

Purpose

The purpose of this study was to determine the effects of the Photoactivated Chromophore for Keratitis Corneal Cross-Linking (PACK-CXL) protocol modifications on corneal resistance to enzymatic digestion and treatment depth.

Methods

Eight hundred one ex vivo porcine eyes were randomly divided into groups of 12 to 86 corneas, treated with various epi-off PACK-CXL modifications, including acceleration (30 > 2 minutes, 5.4 J/cm2), increased fluence (5.4 > 32.4 J/cm2), deuterium oxide (D2O) supplementation, different carrier types (dextran versus hydroxypropyl methylcellulose [HPMC]), increased riboflavin concentration (0.1 > 0.4%), and riboflavin replenishment during irradiation (yes/no). Control group eyes did not receive PACK-CXL. A pepsin digestion assay was used to determine corneal resistance to enzymatic digestion. A phalloidin fluorescent imaging assay was used to determine the PACK-CXL treatment effect depth. Differences between groups were evaluated using a linear model and a derivative method, respectively.

Results

PACK-CXL significantly increased corneal resistance to enzymatic digestion compared to no treatment (P < 0.03). When compared to a 10 minute, 5.4 J/cm2 PACK-CXL protocol, fluences of 16.2 J/cm2 and higher increased corneal resistance to enzymatic digestion by 1.5- to 2-fold (P < 0.001). Other protocol modifications did not significantly change corneal resistance. A 16.2 J/cm2 fluence also increased collagen compaction in the anterior stroma, whereas omitting riboflavin replenishment during irradiation increased PACK-CXL treatment depth.

Conclusions

Increasing fluence will likely optimize PACK-CXL treatment effectiveness. Treatment acceleration reduces treatment duration without compromising effectiveness.

Translational Relevance

The generated data help to optimize clinical PACK-CXL settings and direct future research efforts.

Photoactivated Chromophore Corneal Collagen Cross-Linking for Infectious Keratitis (PACK-CXL)-A Comprehensive Review of Diagnostic and Prognostic Factors Involved in Therapeutic Indications and Contraindications

Infectious keratitis is a severe infection of the eye, which requires urgent care in order to prevent permanent complications. Typical cases are usually diagnosed clinically, whereas severe cases also require additional tools, such as direct microscopy, corneal cultures, molecular techniques, or ophthalmic imaging. The initial treatment is empirical, based on the suspected etiology, and is later adjusted as needed. It ranges from topical administration of active substances to oral drugs, or to complex surgeries in advanced situations. A novel alternative is represented by Photoactivated Chromophore Corneal Collagen Cross-Linking (PACK-CXL), which is widely known as a minimally invasive therapy for corneal degenerations. The purpose of this review is to identify the main diagnostic and prognostic factors which further outline the indications and contraindications of PACK-CXL in infectious keratitis. Given the predominantly positive outcomes in the medical literature, we ponder whether this is a promising treatment modality, which should be further evaluated in a systematic, evidence-based manner in order to develop a clear treatment protocol for successful future results, especially in carefully selected cases.

Corneal cross-linking guards against infectious keratitis: an experimental model

BACKGROUND

PACK-CXL (photo-activated chromophore for keratitis-corneal cross-linking) is an alternative option in treatment of corneal infections. It inhibits corneal melting by increasing the stromal resistance, besides the microbicidal effect of photo-activated riboflavin.

METHODS

Corneal infection with Pseudomonas aeruginosa and Staph aureus bacteria was induced in 20 eyes of 10 rabbits after 6 weeks of corneal cross-linking in half of the eyes, while the other acted as control group. Clinical and corneal histopathological examination was done to evaluate the extent of inflammation, ulceration, organism penetration, and depth of corneal stromal affection.

RESULTS

The control eyes developed severe inflammation compared to the cross-linked eyes. Corneal melting occurred in 6 eyes in the control versus none in cross-linked group. Histopathological examination showed that the inflammation was confined to the superficial part of the stroma with localization of the inflammation in the cross-linked eyes in contrast to the control eyes that showed deep infiltration.

CONCLUSION

PACK-CXL provides infection localization through increasing the corneal rigidity and resistance to enzymatic digestion, even in the absence of the riboflavin microbicidal role. So, early PACK-CXL is worth to be considered in the IK treatment algorithm.

Features of the clinical picture of keratitis in horses with different forms of the course of the disease

Background

Keratitis is a common cause of eye diseases in horses, often resulting in complete loss of vision.

Aim

The purpose of this article is to study the features of the clinical picture of primary and secondary keratitis in horses, depending on the form of the course of the disease.

Methods

The study was conducted in 2019 at 22 private horse breeding farms. The study involved 80 horses with keratitis, which were divided into two equal groups depending on the diagnosis of primary or secondary keratitis.

Results

The effectiveness of the therapies was compared 1, 3, and 6 months after the start of treatment. Following a 1-month therapy, only a minority of horses with primary keratitis had their eye functions fully restored, the number of horses with macula was two times higher (p ≤ 0.05), the number of horses with nebula was seven times higher (p ≤ 0.001), and leukomas were reported in most of the cases ( p ≤ 0.0001).

Conclusion

The effectiveness of the therapy for keratitis is directly related to the peculiarities of treatment and adherence to the regimen.

Recurrent corneal erosion

Recurrent corneal erosion (RCE) is a common recurrent disease caused by abnormal adhesion of the corneal epithelium to the basement membrane. Previous corneal trauma is the most common cause of this disease. Corneal dystrophies, such as dystrophy of the epithelial basement membrane, Meesmann dystrophy, ReisBcklers dystrophy, lattice dystrophy and granular dystrophies, are also involved in the pathogenesis of recurrent corneal erosion. The main diagnostic methods for recurrent corneal erosion are slit-lamp examination and taking of medical history. Detectable RCE changes range from small corneal irregularities (such as epithelial microcysts) to large areas of loose epithelium or epithelial defects detecting by fluorescein staining. Areas of irregular epithelium with grayish inclusions or microcysts and a fingerprint pattern or a map-like defects are also revealed. The main goal of treatment is to relieve pain, stimulate re-epithelialization, and fully restore the adhesion of the basement membrane and epithelium. Lubricants and matrix proteinase inhibitors are prescribed as first-line therapy, and blood derivatives can be used as second-line therapy. When conservative therapy fails, surgical procedures are used (excimer laser phototherapeutic keratectomy, Bowmans membrane polishing with diamond drill, anterior stromal puncture, corneal collagen cross-linking).

Recent Advances in Photodynamic Therapy against Fungal Keratitis

Fungal keratitis is a serious clinical infection on the cornea caused by fungi and is one of the leading causes of blindness in Asian countries. The treatment options are currently limited to a few antifungal agents. With the increasing incidence of drug-resistant infections, many patients fail to respond to antibiotics. Riboflavin-mediated corneal crosslinking (similar to photodynamic therapy (PDT)) for corneal ectasia was approved in the US in the early 2000s. Current evidence suggests that PDT could have the potential to inhibit fungal biofilm formation and overcome drug resistance by using riboflavin and rose bengal as photosensitizers. However, only a few clinical trials have been initiated in anti-fungal keratitis PDT treatment. Moreover, the removal of the corneal epithelium and repeated application of riboflavin and rose bengal are required to improve drug penetration before and during PDT. Thus, an improvement in trans-corneal drug delivery is mandatory for a successful and efficient treatment. In this article, we review the studies published to date using PDT against fungal keratitis and aim to enhance the understanding and awareness of this research area. The potential of modifying photosensitizers using nanotechnology to improve the efficacy of PDT on fungal keratitis is also briefly reviewed.

Genipin in an Ex Vivo Corneal Model of Bacterial and Fungal Keratitis

Purpose

To determine whether genipin (a natural crosslinker) could reduce the colonization and proliferation of bacteria and fungi in an ex vivo model of corneal infection.

Methods

This study, using an ex vivo model of bacterial and fungal keratitis, investigated the antimicrobial efficacy of genipin crosslinking. Excised corneoscleral buttons were wounded by scalpel incision and subsequently infected with Staphylococcus aureus, Pseudomonas aeruginosa, or Candida albicans. After inoculation, corneas were treated with genipin for 24 hours at 37°C. Histologic examinations were carried out, and the number of viable colony-forming units (CFU)/cornea was determined.

Results

Genipin exerts bactericidal action against S. aureus and P. aeruginosa, as well as fungicidal action against C. albicans and significantly reduced the CFU compared to contralateral eyes that received saline treatment (P < 0.05).

Conclusions

These data identify genipin as a novel ocular antimicrobial agent that has the potential to be incorporated into the therapeutic armamentarium against microbial keratitis.

Translational Relevance

This study provided evidence for the antimicrobial and antifungal properties of genipin as an alternative crosslinker that could be used in the management of infectious keratitis.

Long-term results of corneal collagen crosslinking for recurrent corneal erosion

BACKGROUND: Recurrent corneal erosion (RCE) is characterized by excacerbation and remission episodes, reduced patients quality of life affecting their daily and professional activities. In case of conservative therapy inefficacy surgical procedures are used (Bowmans membrane polishing with diamond drill, excimer laser phototherapeutic keratectomy, anterior stromal puncture, and amniotic membrane transplantation). All methods have their advantages and weak points, as well as a certain percent of recurrence. In this regard the use of corneal collagen cross-linking is of the interest as an alternative method of the RCE surgical treatment. MATERIALS AND METHODS: 18 patients (20 eyes) with RCE without central corneal stroma scars, aged from 30 to 66 (average 49,5 10,6, all women), after conservative treatment failure (more than 6 months) underwent cross-linking according to the Dresden protocol with the UVX device, version 1000, by IROC INNOCROSS (Switzerland). RESULTS: All patients were asymptomatic and had no recurrence during the observation period (from 1 to 6 years, in average 2,6 1,6). There was a slight but statistically significant BCVA improvement (from 0,93 0,09 at baseline to 0,97 0,07 after intervention). CONCLUSIONS: Crosslinking may be an additional and effective treatment in a number of RCE cases when there is no central corneal stromal scars present. To reduce stromal keratocytes alteration during the procedure modified protocols may be used.

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.

Photoactivated Chromophore for Keratitis-Corneal Collagen Cross-Linking (PACK-CXL) Improves Outcomes of Treatment-Resistant Infectious Keratitis

Purpose

To investigate the efficacy of photoactivated chromophore corneal collagen cross-linking (PACK)-CXL in the management of treatment-resistant infectious keratitis.

Design

Observational cohort study.

Participants

Forty-two eyes from 41 patients with treatment-resistant infectious keratitis.

Methods

Eyes underwent PACK-CXL treatment with the Dresden modified protocol in addition to standard antimicrobial therapy. The primary endpoint was the size of the corneal ulcer. Descriptive statistics, Wilcoxon rank test, McNemar test and Spearman correlation coefficient were used for statistical analysis, and p values lower than 0.05 were considered statistically significant.

Results

Success rate at third postoperative month was of 90.5%. Statistical analyses showed a significant effect of (PACK)‑CXL with standard antimicrobial therapy to reduce corneal ulcer size (p=0.031).

Conclusion

As adjuvant therapy to standard antimicrobial treatment, PACK-CXL improves the outcomes in patients with treatment-resistant corneal ulcers.

High fluence PACK-CXL as adjuvant treatment for advanced Acanthamoeba keratitis

Purpose

To describe the outcome of adjuvant high fluence photoactivated chromophore for infectious keratitis cross-linking (PACK-CXL) used to treat an advanced form of refractory Acanthamoeba keratitis (AK) diagnosed several months after initial presentation.

Observations

An otherwise healthy 24-year old female presented with a severe unilateral keratitis. The diagnosis eluded clinicians for several months and when finally confirmed as AK, anti-amoebic therapy was instated and only appeared to be effective after addition of high fluence PACK-CXL.

Conclusion and importance

In this case of advanced AK, high fluence PACK-CXL treatment given adjuvant to pharmacologic anti-amoebic therapy resulted in lasting pain relief, re-epithelization and eradication of the Acanthamoeba parasite. Given adjuvant to anti-amoebic pharmacotherapy, high fluence PACK-CXL might be a useful method for treating typically refractory advanced AK.

UV light crosslinking regresses mature corneal blood and lymphatic vessels and promotes subsequent high-risk corneal transplant survival

Immunologic graft rejection is the main complication after corneal transplant into pathologically prevascularized so-called high-risk eyes. The aim of this study was to evaluate whether ultraviolet (UV) light crosslinking can regress pathologic corneal blood and lymphatic vessels and thereby improve subsequent graft survival. Using the murine model of suture-induced corneal neovascularization, we found that corneal crosslinking with UVA light and riboflavin regressed both preexisting blood and lymphatic vessels significantly via induction of apoptosis in vascular endothelial cells. In addition, macrophages and CD45⁺ cell counts were significantly reduced. Consistently, corneal crosslinking reduced keratocyte density and corneal thickness without affecting corneal nonvascular endothelial cells, iris, and lens depending on the crosslinking duration. Furthermore, using the murine model of corneal transplant, long-term graft survival was significantly promoted (P < .05) and CD4⁺ CD25⁺ FoxP3⁺ T regulatory cells were upregulated (P < .01) in high-risk eyes preoperatively treated with crosslinking. Our results suggest UV light crosslinking as a novel method to regress both pathologic corneal blood and lymphatic vessels and to reduce CD45⁺ inflammatory cells. Furthermore, this study demonstrates for the first time that preoperative corneal crosslinking in prevascularized high-risk eyes can significantly improve subsequent graft survival and may become a promising novel therapy in the clinic.

Bilateral Non-tuberculous Mycobacterial Keratitis After Small Incision Lenticule Extraction

PURPOSE

To report a case of bilateral non-tuberculous mycobacterial keratitis after small incision lenticule extraction (SMILE) that was successfully treated with oral and topical fortified antibiotics.

METHODS

Case report and literature review.

RESULTS

An otherwise healthy 21-year-old woman presented with culture-proven bilateral Mycobacterium abscessus keratitis 8 days after undergoing SMILE, showing multiple white stromal infiltrates in the interface in both eyes. Progressive, diffuse flap edema followed by pocket abscess, exudation in the anterior chamber, granulation tissue formation in the pocket, intrastromal neovascularization, and eventually partial resolution of corneal opacity were noted after topical and oral antibiotic treatment for 6 months. Her corrected distance visual acuity was 20/32 and 20/50 in the right and left eyes, respectively, 12 months after initial presentation.

CONCLUSIONS

This is the first report of successful medical management of bilateral non-tuberculous mycobacterial keratitis after SMILE. The manifestations are different from and even more difficult to treat than those of keratitis after LASIK. [J Refract Surg. 2018;34(9):633-636.].

Changes in interleukin-6 tear concentration and clinical outcome in moderate-to-severe bacterial corneal ulcers after corneal collagen cross-linking

We aimed to evaluate interleukin-6 (IL-6) tear concentration and clinical outcome in patients with moderate-to-severe bacterial corneal ulcers post corneal collagen cross-linking (CXL) therapy. This pre-post designed study involving 21 moderate-to-severe corneal ulcer patients who underwent CXL therapy. Patients with infectious corneal ulcer were given CXL therapy as adjunctive treatment after 5d of broadspectrum antibiotic treatment. Patients with moderate to severe infectious bacterial corneal ulcers were included in this study. Tear sampling was performed before CXL therapy, using sterile Schimer paper from conjunctival inferior fornix. CXL therapy was performed in accordance with the CXL Dresden protocol. Data recording and tear sampling were then performed at day 1 and day 7 after CXL therapy. Data recording included, presence of conjunctival hyperemia, visual analogue scale (VAS), size of corneal defects, and decemetocele. There was a decrease in IL-6 tear concentration by day 7 after CXL therapy (P=0.001). IL-6 concentration at 1h after therapy (2274.67±2120.46 pg/mL) tended to be lower than before therapy (4330.09±3169.70 pg/mL), but the difference was not statistically significant (P=0.821). The size of corneal defects decreased significantly post CXL (P=0.007). The logMAR visual acuity before and after CXL therapy was not found to be significantly different (P=0.277). There was a significant decrease in VAS values (P=0.018) and blepharospasm (P=0.011) pre and post CXL. There was no significant decrease in conjunctival hyperemia pre and post CXL (P=0.293). There was significant reduction in IL-6 tear concentration and clinical improvement in moderate-to-severe bacterial corneal ulcers which underwent CXL therapy.

Simultaneous Noncentered Photoactivated Chromophore for Keratitis-Corneal Collagen Cross-Linking and Penetrating Keratoplasty for Treatment of Severe Marginal Fusarium spp. Keratitis: A Description of a New Surgical Technique

The purpose of this article is to describe the use of simultaneous noncentered photoactivated chromophore for keratitis-corneal collagen cross-linking (PACK-CXL) combined with penetrating keratoplasty in the treatment of a severe marginal Fusarium spp. keratitis case with imminent corneal perforation. It is a retrospective case report study; it was performed by collecting clinical data, images, video, and postoperative evaluations. The clinical control of the infection was accomplished, despite difficulties in obtaining antifungal medications due to the patient's extremely poor socioeconomic status and essentially nonexistent health insurance. We can conclude that combining simultaneous decentered PACK-CXL with centered penetrating keratoplasty appears to be a safe and effective way of treating patients with fungal marginal keratitis with corneal perforation, in which regular penetrating keratoplasty alone would leave fungal elements in the receptor corneal tissue, which would predispose to infection of the graft.

Standard, transepithelial and iontophoresis corneal cross-linking: clinical analysis of three surgical techniques

BACKGROUND

To evaluate the clinical results of standard, transepithelial (TE) and iontophoresis (I) corneal cross-linking (CXL), in patients with progressive keratoconus.

METHODS

Thirty eyes of 30 patients with progressive keratoconus treated by CXL (10 by standard-CXL, 10 by TE-CXL and 10 by I-TE-CXL) with 12 months of follow-up. Pre- and postoperative ophthalmologic testing were: uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive examination (spherical error, spherical equivalent), corneal topography (corneal astigmatism, simulated maximum, minimum and average keratometry), aberrometry (coma and spherical aberration), pachymetry and endothelial cell density.

RESULTS

In all groups, UDVA and CDVA improved significantly after treatment. Furthermore, a significant improvement in spherical error, spherical equivalent, topographic and aberrometric outcomes was observed in 3 groups at 1 year posttreatment. No significant variations were recorded in corneal thickness and endothelial cellular density.

CONCLUSION

Our results showed efficacy, clinical and refractive stability after standard-CXL, TE-CXL and iontophoresis-CXL.

Corneal Cross-Linking Has No Effect on Matrix Metalloproteinase 9 and 13 Levels During Fungal Keratitis on the Early Stage

The aim of our study was to investigate matrix metalloproteinases, MMP-9 and MMP-13 levels, in the rabbit model of Fusarium and Candida keratitis treated by corneal cross-linking (PACK-CXL). Rabbit corneas were inoculated with fungal inoculum for keratitis. Each group divided into four subgroups, including un-treated group, PACK-CXL group, voriconazole group and PACK-CXL plus voriconazole group. PACK-CXL was applied with 0.25% riboflavin in accelerated Dresden protocol, and 0.1% voriconazole drops were administered. All corneal buttons excised at tenth day after ophthalmological examination. Fungal cell counts and Scheiber scores were determined in all groups. Corneal tissue MMP mRNA levels were evaluated quantitative reverse transcriptase PCR. The difference in MMP-9 and MMP-13 levels at all groups was not statistically significant (p > 0.05). PACK-CXL with 0.25% riboflavin either alone or combined with antifungal drops was unable to provide decline in inflammatory findings in both macroscopic and microscopic levels similar to medical antifungal treatment.

Patient selection for corneal collagen cross-linking: an updated review

Corneal cross-linking (CXL) is an option that in the last decade has demonstrated its efficacy and safety in halting the progression of keratoconus (KCN) and other corneal ectasias. Its indication has been extended beyond the classic definition that required evidence of KCN progression, especially in the presence of some risk factors for a possible progression (particularly the younger age). However, the results can be still somewhat variable today. There are several protocols, each with its own advantages and disadvantages. Some predictors of CXL outcome have been identified. We will review the current knowledge on patient selection for CXL, its indications, and options in special cases (such as thin corneas).

Corneal collagen cross-linking. A review of its clinical applications

OBJECTIVE

To perform a literature review of the current clinical applications of corneal collagen cross-linking.

METHODS

An exhaustive literature search was made, including the main biomedical databases, and encompassing all years since the introduction of cross-linking in ophthalmology practice.

RESULTS

Corneal collagen cross-linking using UVA irradiation and riboflavin is a surgical technique that is currently being optimised, and is supported by a good amount of pre-clinical and clinical studies. These papers found show the beneficial effect of the surgery on preventing the progression of corneal ectasia, especially keratoconus, but also on pellucid marginal degeneration and keratectasia after refractive surgery. The effect of cross-linking on avoiding the occurrence of iatrogenic keratectasia when combined with a photo-ablative procedure is less clear to date. Additionally, it appears that cross-linking may have a considerable beneficial effect on controlling corneal infection caused by fungi, bacteria and amoebae. However, its effect on viral keratitis can be detrimental. The benefit on bullous keratopathy seems to be rather transient.

CONCLUSIONS

Corneal collagen cross-linking may be used with relative safety and efficacy in patients with progressive keratoconus. Its use could also be considered in patients with other corneal ectasias or with corneal infections of non-viral origin. Currently, there is still a need for more studies as regards its effect on preventing iatrogenic keratectasia.

Challenges of corneal infections

INTRODUCTION

Ocular infections remain an important cause of blindness worldwide and represent a challenging public health concern. In this regard, microbial keratitis due to fungal, bacterial, or viral infection can result in significant vision loss secondary to corneal scarring or surface irregularity. Left untreated corneal perforation and endophthalmitis can result, leading to loss of the eye. Rigorously studied animal models of disease pathogenesis have provided novel information that suggests new modes of treatment that may be efficacious clinically and emerging clinical data is supportive of some of these discoveries.

AREAS COVERED

This review focuses on advances in our understanding of disease pathogenesis in animal models and clinical studies and how these relate to improved clinical treatment. We also discuss a novel approach to treatment of microbial keratitis due to infection with these bacterial pathogens using PACK-CXL and recommend increased basic and clinical studies to address and refine the efficacy of this procedure.

EXPERT COMMENTARY

Because resistance to antibiotics has developed over time to these bacterial pathogens, caution must be exercised in treatment. Attractive novel modes of treatment that hold new promise for further investigation include lipid based therapy, as well as use of small molecules that bind deleterious specific host responsive molecules and use of microRNA based therapies.

PACK-CXL: Corneal cross-linking in infectious keratitis

Background

Corneal cross-linking (CXL) using ultraviolet light-A (UV-A) and riboflavin is a technique developed in the 1990’s to treat corneal ectatic disorders such as keratoconus. It soon became the new gold standard in multiple countries around the world to halt the progression of this disorder, with good long-term outcomes in keratometry reading and visual acuity. The original Dresden treatment protocol was also later on used to stabilize iatrogenic corneal ectasia appearing after laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). CXL efficiently strengthened the cornea but was also shown to kill most of the keratocytes within the corneal stroma, later on repopulated by those cells.

Review

Ultraviolet-light has long been known for its microbicidal effect, and thus CXL postulated to be able to sterilize the cornea from infectious pathogens. This cytotoxic effect led to the first clinical trials using CXL to treat advanced infectious melting corneal keratitis. Patients treated with this technique showed, in the majority of cases, a stabilization of the melting process and were able to avoid emergent à chaud keratoplasty. Following those primary favorable results, CXL was used to treat beginning bacterial keratitis as a first-line treatment without any adjunctive antibiotics with positive results for most patients. In order to distinguish the use of CXL for infectious keratitis treatment from its use for corneal ectatic disorders, a new term was proposed at the 9th CXL congress in Dublin to rename its use in infections as photoactivated chromophore for infectious keratitis -corneal collagen cross-linking (PACK-CXL).

Conclusion

PACK-CXL is now more frequently used to treat infections from various infectious origins. The original Dresden protocol is still used for this purpose. Careful modifications of this protocol could improve the efficiency of this technique in specific clinical situations regarding certain types of pathogens.

[Efficacy of corneal cross-linking for the treatment of keratoconus]

Keratoconus (KC) is a complex disease whose pathophysiology is only partially understood. The priority in management is to halt the progression of corneal deformation as soon as possible in the course of KC disease. Corneal cross-linking (CXL) is at present the only dedicated treatment for this purpose. Its biochemical mechanism of action leads to changes in the viscoelastic properties of the cornea induced by matrix bonding and renewal of keratocytes. The effect of CXL is difficult to quantify when measured in in-vivo conditions because of a lack of consistent tools adapted for clinical practice. Nevertheless, a large amount of evidence has been collected so far confirming the positive action of CXL on corneal structural reinforcement, and numerous studies have demonstrated significant efficacy in halting progression of KC with long-term follow-up. Published studies, however, are of relatively low scientific power given the great heterogeneity of the disease and the numerous associated biases in evaluation. The purpose of this paper is to summarize the consistent evidence of efficacy of CXL and to justify its role in our therapeutic armamentarium for management of progressive KC.

Collagen cross-linking: when and how? A review of the state of the art of the technique and new perspectives

Since the late 1990s corneal crosslinking (CXL) has been proposed as a new possibility to stop progression of keratoconus or secondary corneal ectasia, with the promising aim to prevent progressive visual loss due to the evolution of the pathology and to delay or avoid invasive surgical procedures such as corneal transplantation. The possibility of strengthening corneal tissue by means of a photochemical reaction of corneal collagen by the combined action of Riboflavin and ultraviolet A irradiation (UVA), radically modified the conservative management of progressive corneal ectasia. This is a review of the state of the art of CXL, reporting basic and clinical evidence. The paper describes basic principles, advantages and limits of different CXL techniques and possible future evolution of the procedure.