Anterior segment optical coherence tomography in evaluation of severe fungal keratitis infections treated by corneal crosslinking

Role of Anterior Segment Optical Coherence Tomography in Staging and Evaluation of Treatment Response in Infectious Keratitis

PURPOSE

The aim of this study was to evaluate the role of anterior segment optical coherence tomography during follow-up of infectious keratitis and to assess response to treatment.

METHODS

This was a prospective, consecutive, observational clinical series of cases. Twenty-three eyes of 23 patients with clinically proven fungal keratitis were included in the study. The patients received medical treatment according to clinical diagnosis, and follow-up was performed weekly. Slit-lamp examination and photography, and anterior segment optical coherence tomography were performed at initial and follow-up visits until corneal healing occurred. The main outcome measures included infiltrate depth, width, and density; central corneal thickness; minimal corneal thickness; corneal thickness at the site of the lesion; and stromal thickness at the center of the lesion.

RESULTS

Twenty-three eyes of 23 patients (17 men and 6 women), mean age 42.5 ± 19 (8-66) years, were clinically diagnosed with fungal keratitis. Localization was central in 14 cases and paracentral/peripheral in 9 cases. Healing time was 6 to 12 weeks. Minimal corneal thickness, corneal thickness at the site of lesion, and stromal thickness at the center of lesion, and also infiltrate width and depth changed significantly from the first visit to the healing stage at the last follow-up (0.009, 0.001, 0.007, 0.001, and <0.001, respectively).

CONCLUSIONS

In cases of fungal keratitis, anterior segment optical coherence tomography can provide the clinician with a quantitative assessment of a number of corneal parameters that can be used to determine effectiveness of therapy and confirm complete healing of the lesions that cannot be achieved by clinical evaluation.

CLINICAL TRIAL REGISTRATION

The study was registered in Clinical Trials.gov with NCT04969640.

Therapeutic non-ectasia applications of cornea cross-linking

Corneal cross-linking is a photopolymerization technique traditionally used to strengthen corneal tissue. Corneal cross-linking utilizes riboflavin (vitamin B2) as a photosensitizer and ultraviolet-A light (UVA) to create strong covalent bonds within the corneal stroma, increasing tissue stiffness. Multiple studies have demonstrated corneal cross-linking's effectiveness in treating corneal ectasia, a progressive, degenerative, and non-inflammatory thinning disorder, as quantified by key tomographic, refractive, and visual parameters. Since its introduction two decades ago, corneal cross-linking has surpassed its original application in halting corneal ectatic disease and its application has expanded into several other areas. Corneal cross-linking also possesses antibacterial, antienzymolytic and antioedematous properties, and has since become a tool in treating microbial keratitis, correcting refractive error, preventing iatrogenic ectasia, stabilising bullous keratopathy and controlling post keratoplasty ametropia. This review provides an overview of the current evidence base for the therapeutic non-ectasia applications of cornea cross-linking and looks at future developments in the field.

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.

The Value of Anterior Segment Optical Coherence Tomography in Different Types of Corneal Infections: An Update

Anterior segment optical coherence tomography (AS-OCT) is a modality that uses low-coherence interferometry to visualize and assess anterior segment ocular features, offering several advantages of being a sterile and noncontact modality that generates high-resolution cross-sectional images of the tissues. The qualitative and quantitative information provided by AS-OCT may be extremely useful for the clinician in the assessment of a wide spectrum of corneal infections, guiding in the management and follow-up of these patients. In clinical practice, infections are routinely evaluated with slit-lamp biomicroscopy, an examination and imaging modality that is limited by the physical characteristics of light. As a consequence, the depth of pathology and the eventually associated corneal edema cannot be accurately measured with the slit-lamp. Therefore, it represents a limit for the clinician, as in vivo information about corneal diseases and the response to treatment is limited. Resolution of corneal infection is characterized by an early reduction in corneal edema, followed by a later reduction in infiltration: both parameters can be routinely measured with standardized serial images by AS-OCT.

Safety and efficacy of UV application for superficial infections in humans: A systematic review and meta-analysis

BACKGROUND

Ultraviolet (UV) light is naturally antimicrobial, but risks associated with UV overexposure have limited its clinical application. This systematic review evaluates the safety and efficacy of UV light treatment of superficial human infections.

METHODS

MEDLINE, Embase, Cochrane CENTRAL, ANZCTR and US National Library of Medicine were searched (March 25, 2020). Clinical studies applying UV light (200-400 nm) for superficial infections and non-clinical studies evaluating the antimicrobial effects of UV light on human samples were included. Randomised controlled trials (RCTs) and non- RCTs were appraised using the Cochrane risk of bias and the ROBINS-I tools, respectively.

RESULTS

Eleven RCTs, seven non-RCTs, 24 case studies, and 11 in vitro studies were included. Most clinical studies (34/42) evaluated UVA treatment for microbial keratitis (MK) using cross-linking (UVA-CXL) methods. Six clinical studies assessed UVC; one, UVB; and one, broadband UV for chronic skin infections. Pooled data analysis showed no difference in the time to wound resolution with UVA-CXL relative to standard treatment (mean difference [MD]: -18.20 [95% CI: -39.04 to 2.65] days; p = 0.09). Adverse event incidence was similar to control for UVA-CXL in MK (RR: 0.70 [95%CI: 0.32-1.79]; 5 RCTs) and UVC in skin infections (RR: 0.63 [95%CI: 0.25-1.54]; 2 RCTs).

CONCLUSION

Alone or as an adjunct to standard therapy, UV light shows promise as a safe and effective treatment for a wide range of infections. Applications of UV light as an anti-infective agent are deserving of further evaluation, especially in the context of growing antibiotic resistance.

REGISTRATION

PROSPERO registration number CRD42020176510.

Corneal cross-linking as a treatment for corneal dystrophy with secondary bacterial infection in a Friesian horse

Corneal cross-linking should be considered as treatment option in Friesian horses with infectious keratitis and corneal dystrophy. Optical coherence tomography, giving information of corneal structure, can help for diagnosis and monitoring.

Anterior-Segment Optical Coherence Tomography-Guided Measurement Of A Melting Ulcer For Follow-Up Of Corneoscleral Thinning Progression

Purpose

To evaluate the feasibility of using anterior-segment optical coherence tomography (AS-OCT) for three-dimensional assessment of corneoscleral thinning progression in ulcers after pterygium removal.

Methods

A patient with corneoscleral melting after pterygium removal surgery and mitomycin C treatment was evaluated using AS-OCT imaging of the corneoscleral ulcer at five consecutive time points, up to 2 years. AS-OCT scans of 8.3×5.6 mm (15°×10°) containing 41 B-scans spaced 139 µm apart were performed monthly for 4 months and then at 2 years following pterygium removal. A single B-scan was comprised of 768 A-scans. Ten B-scans of the same position were averaged in a single AS-OCT image. The area of ulcer’s section (AUS) was measured in seven fixed landmarks through a horizontally aligned plane in order to provide an estimation of the three-dimensional size of the lesion.

Results

The AUS in the two superior locations increased during the follow-up period to an average of 114% at 2 years compared to the initial visit. In the other five locations (three midline and two inferior), the AUS decreased and was on average 64% in the midline and 29% in the inferior locations at 24 months.

Conclusion

AS-OCT provided a readily available assessment of the lesion’s three-dimensional size during repeated follow-ups and identification of localized areas at higher risk for perforation. This method may potentially be useful for corneal surface pathologies requiring repeated follow-ups and may aid in decision-making regarding corneal thickness based on an accurate measurement.

Photoactivated chromophore for infectious keratitis - Corneal cross-linking (PACK-CXL): A systematic review and meta-analysis

PURPOSE

To examine the efficacy of adjuvant photoactivated chromophore for infectious keratitis-corneal cross-linking (PACK-CXL) for the treatment of infectious keratitis (IK).

METHODS

Electronic databases, including MEDLINE, EMBASE and Cochrane Central, were searched for articles related to PACK-CXL. All clinical studies, including randomized controlled trials (RCTs), non-randomized controlled studies, case series and case reports, were included. A meta-analysis was further performed when there were sufficient similarities in the included RCTs. Primary outcome measure was time to complete corneal healing and secondary outcome measures included size of epithelial defect and infiltrate, corrected-distance-visual-acuity (CDVA), and adverse events.

RESULTS

Forty-six eligible studies (including four RCTs) with 435 patients were included. When compared to standard antimicrobial treatment (SAT) alone, adjuvant PACK-CXL resulted in shorter mean time to complete corneal healing (-7.44 days; 95% CI, -10.71 to -4.16) and quicker resolution of the infiltrate at 7 days (-5.49 mm²; 95% CI, -7.44 to -3.54) and at 14-30 days (-5.27 mm²; 95% CI, -9.12 to -1.41). There was no significant difference in the size of epithelial defect, CDVA and risk of adverse events. Evidence on the use of PACK-CXL in acanthamoeba and mixed IK was insufficient.

CONCLUSIONS

Our study demonstrates that adjuvant PACK-CXL expedites the healing of IK when compared to SAT alone (low-quality evidence). Further adequately powered, high-quality RCTs are required to fully ascertain the therapeutic effect of PACK-CXL.

Appearance of herpes simplex keratitis on anterior segment optical coherence tomography

PURPOSE

To describe the anterior segment AS-OCT findings of herpetic simplex keratitis.

METHODS

Forty-two eyes of 42 patients with proven herpetic keratitis of varying severity were included in this prospective, observational, non-comparative case series study. All subjects underwent ophthalmologic examination and AS-OCT imaging.

RESULTS

Twenty-five of the 42 eyes (59.5%) had sub-epithelial infiltrates. In 11 of these cases, the overlying epithelium appeared intact, but in 14 cases, hydropic changes, heaping, and defects were observed. Seventeen eyes (40.5%) showed stromal involvement: six cases with scar at presentation and one case associated with uveitis. Stromal infiltrates were also seen, in ten cases, as a diffuse or local lentiform or spindle-shaped hyper-reflective area in the stroma.

CONCLUSION

Herpetic keratouveitis has characteristic features on AS-OCT images. This study demonstrates that herpetic keratitis also has characteristic AS-OCT features, including sub-epithelial infiltration and specific stromal hyper-reflective patterns. These features are not unique to herpetic keratitis, but AS-OCT imaging may provide useful supplementary information for diagnosing and monitoring herpetic keratitis.

[Corneal collagen cross-linking to treat infectious keratitis]

Infectious keratitis are a frequent cause of ocular morbidity. Today, new treatments are necessary to combat the emergence of antibiotic resistant germs. Corneal collagen cross-linking has been suggested to treat corneal infectious (PACK-CXL). Its action would be both antimicrobial and protective for the cornea, increasing its biochemical resistence to proteolytic enzymes. In vivo, PACK-CXL might demonstrate good efficacy against bacterial keratitis, contrary to herpetic keratitis for which it is contraindicated. For fungal or amoebic keratitis, results are uncertain regarding its safety and efficacy. The purpose of this paper is to clarify the use of corneal collagen cross-linking to treat infectious keratitis.

Anterior segment optical coherence tomography for evaluation of cornea and ocular surface

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple. Several devices and technologies allow to explore and manage patients better. Optical coherence tomography (OCT) technology has evolved over the years, and hence a detailed evaluation of anterior segment (AS) structures such as cornea, conjunctiva, tear meniscus, anterior chamber, iris, and crystalline lens has been possible in a noncontact and safe procedure. The purpose of this special issue is to present and update in the evaluation of cornea and ocular surface, and this paper reviews a description of the AS-OCT, presenting the technology and common clinical uses of OCT in the management of diseases involving cornea and ocular surface to provide an updated information of the clinical recommendations of this technique in eye care practice.

Recent advances in diagnosis and management of Mycotic Keratitis

Mycotic keratitis is a major cause of corneal blindness, especially in tropical and subtropical countries. The prognosis is markedly worse compared to bacterial keratitis. Delayed diagnosis and scarcity of effective antifungal agents are the major factors for poor outcome. Over the last decade, considerable progress has been made to rapidly diagnose cases with mycotic keratitis and increase the efficacy of treatment. This review article discusses the recent advances in diagnosis and management of mycotic keratitis with a brief discussion on rare and emerging organisms. A MEDLINE search was carried out for articles in English language, with the keywords, mycotic keratitis, fungal keratitis, emerging or atypical fungal pathogens in mycotic keratitis, investigations in mycotic keratitis, polymerase chain reaction in mycotic keratitis, confocal microscopy, treatment of mycotic keratitis, newer therapy for mycotic keratitis. All relevant articles were included in this review. Considering the limited studies available on newer diagnostic and therapeutic modalities in mycotic keratitis, case series as well as case reports were also included if felt important.

Corneal cross-linking in the treatment of corneal ulcers

PURPOSE OF REVIEW

New treatments for corneal ulcers are needed to address challenges with antibiotic resistance, cost, and specificity requiring timely pathogen identification. This review assesses the evidence regarding safety and efficacy of corneal cross-linking (CXL) as an adjunct or stand-alone treatment.

RECENT FINDINGS

To date approximately 200 clinical cases of CXL used with various types of infectious keratitis have been reported in about 30 publications. Most employed the CXL protocol developed for keratoconus as an adjunct to antibiotics for resistant ulcers, and a number of cases resolved after this intervention. However, a few studies raised concerns about resurgence and perforation when CXL was utilized with deep fungal infections. The infiltrate depth is an important consideration, because the standard CXL treatment is cytotoxic (to keratocytes) to a depth of approximately 200-300 μm and 50% of the energy is absorbed within the first 100 μm. CXL was used successfully as a monotherapy in approximately 16 eyes with early bacterial or shallow fungal infections.

SUMMARY

Further work is needed to develop optimized CXL protocols for treatment of corneal ulcers, define the appropriate conditions for use, and determine the safety and efficacy relative to standard antibiotic treatments.

Photoactivated Chromophore for Moderate to Severe Infectious Keratitis as an Adjunct Therapy: A Randomized Controlled Trial

PURPOSE

To evaluate the efficacy of photoactivated chromophore for infectious keratitis (PACK-CXL) in the treatment of patients with moderate to severe infectious keratitis as adjunct therapy to the topical medication treatment.

DESIGN

Randomized clinical trial.

METHODS

Thirty eyes from 30 patients with moderate to severe infectious keratitis were randomized to receive either standard treatment plus PACK-CXL (n = 15) or standard treatment alone (control group, n = 15). The primary outcome was the sizes of stromal infiltrates measured on slit-lamp photographs 30 days after treatment. The secondary outcomes were the sizes of epithelial defects, the complication rates, and best pinhole-corrected visual acuity (BPVA).

RESULTS

The median (interquartile range [IQR]) sizes of stromal infiltrates at day 30 were 5.0 mm(2) (0-23.0 mm(2)) in the PACK-CXL group and 10.6 mm(2) (1.1-16.3 mm(2)) in the control group (median difference 0, 95% CI -7.0 to 0, P = .66). The median (IQR) sizes of epithelial defects were 0.7 mm(2) (0-6.3 mm(2)) and 4.6 mm(2) (0-10.2 mm(2)) in the PACK-CXL group and control group, respectively (median difference -3.0, 95% CI -0.8 to 0, P = .41). The complication rates and BPVA after treatment were comparable between groups.

CONCLUSIONS

Standard treatment combined with PACK-CXL did not provide any advantageous effect over standard treatment alone in moderate to severe infectious keratitis over a 30-day period.

Current and Future Applications of Photoactivated Chromophore for Keratitis-Corneal Collagen Cross-Linking (PACK-CXL): An Overview of the Different Treatments Proposed

PURPOSE

To review the application of the PACK-CXL and to identify different treatment protocols according to the pathogens associated with keratitis.

METHODS

A systematic review of 21 articles. The primary outcome was the healing of a corneal ulcer, defined as epithelization, blocking corneal melting. The secondary end-point was the recovery of visual acuity.

RESULTS

We studied a total of 145 eyes. Infectious keratitis was associated with bacteria in 80 eyes (55.55%), fungus in 24 eyes (16.67%), and protozoa in 13 (8.97%). In 26 (18%), the microbiological culture was negative or not performed. The mean time of re-epithelization was 25.70±29.83days (1-180). A total of 27 patients needed corneal transplantation. The overall probability of blocking corneal melting was 84.13%. Three different protocols for each group of pathogens have been proposed.

CONCLUSION

PACK-CXL still has a limit in its spread. In the future, we hope that each pathogen will be treated with the most efficient and least invasive protocols available.

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.

Corneal collagen cross-linking for infectious keratitis: an update of clinical studies

Collagen cross-linking (CXL) with ultraviolet light-activated riboflavin is a corneal surface procedure developed for the treatment of keratoconus and corneal ectasia. With the known microbicidal and corneal stiffening effects of ultraviolet irradiation and photoactivated riboflavin, it has recently been introduced for the management of infectious keratitis, especially for ulcers resistant to antimicrobial therapy or associated with corneal melting. Various authors have attempted to use CXL as an adjunctive, salvage or even as the sole treatment for infectious corneal ulcers. The aim of this review was to provide a summary of the clinical studies in the literature. It is worth noting that there is still no consensus on the treatment protocol of CXL against infectious keratitis. The disparities in outcome measures, treatment protocol and study design can confound the interpretation and hamper the generalization of the study results. Based on current evidence, the role of CXL in infectious keratitis remained unclear despite the reported success in some clinical cases. Further investigations are warranted concerning the efficacy and safety of treating infectious keratitis with CXL.