Corneal biopsy in microbial keratitis

Diagnosis of Acanthamoeba Keratitis: Past, Present and Future

Acanthamoeba keratitis (AK) is a painful and sight-threatening parasitic corneal infection. In recent years, the incidence of AK has increased. Timely and accurate diagnosis is crucial during the management of AK, as delayed diagnosis often results in poor clinical outcomes. Currently, AK diagnosis is primarily achieved through a combination of clinical suspicion, microbiological investigations and corneal imaging. Historically, corneal scraping for microbiological culture has been considered to be the gold standard. Despite its technical ease, accessibility and cost-effectiveness, the long diagnostic turnaround time and variably low sensitivity of microbiological culture limit its use as a sole diagnostic test for AK in clinical practice. In this review, we aim to provide a comprehensive overview of the diagnostic modalities that are currently used to diagnose AK, including microscopy with staining, culture, corneal biopsy, in vivo confocal microscopy, polymerase chain reaction and anterior segment optical coherence tomography. We also highlight emerging techniques, such as next-generation sequencing and artificial intelligence-assisted models, which have the potential to transform the diagnostic landscape of AK.

Role of corneal biopsy in the management of infectious keratitis

PURPOSE OF REVIEW

The aim of this study was to review the existing literature and investigate the role of microbiologic culture and histopathologic examination of corneal biopsies in the management of infectious keratitis.

RECENT FINDINGS

Corneal biopsy continues to be a significantly useful tool in the diagnosis and tailored management of infectious keratitis. Several techniques can be employed for tissue collection, handling and processing to optimize diagnostic yield and maximize safety, including emerging femtosecond laser-assisted biopsy.

SUMMARY

Corneal opacities represent a significant cause of global blindness, and infectious keratitis is the most common cause. Organism identification in progressive infectious keratitis is essential for proper management. However, microbiological culture alone has a high rate of false-negative results. Records from the Bascom Palmer Eye Institute were retrospectively searched for patients between 1 January 2015, and 31 December 2019, who underwent corneal biopsy, therapeutic keratoplasty or endothelial graft removal for infectious keratitis and had specimens bisected and submitted for evaluation with both microbiologic culture and histopathologic examination. Detection of bacteria, fungus and mycobacteria was not statistically different between culture and histopathology. Microbiology and histopathology are complementary methods for the identification of causative microorganisms in corneal specimens with presumed infectious keratitis.

Resistant Microbial Keratitis in South Nile Delta, Egypt: Influence of Regional Risk Factors

PURPOSE

This study was conducted in an attempt to identify the regional, geographic, climatic, socioeconomic, and other risk factors for microbial keratitis in south Nile Delta, Egypt.

METHODS

This is a prospective cross-sectional study that was carried out on 340 eyes of 340 patients with microbial keratitis attending at the outpatient clinic of Ophthalmology Department of Menoufia University Hospital during a period of three years between March 2010 and March 2013.

RESULTS

Epidemiological factors, lines of management, and follow-up results were recorded and statistically analyzed and there were regional variations in the prevalence, risk factors, and outcome in resistant corneal ulcers.

CONCLUSION

Higher incidence of affections and complications has appeared in farmers, rural area residents, and illiterates which are considered the main predisposing factors for ulcer resistance. According to culture results, bacterial organisms (especially Staphylococcus aureus) were the main cause of resistant corneal ulcers.

Microbiologic and histopathologic assessment of corneal biopsies in the evaluation of microbial keratitis

PURPOSE

To investigate the utility of corneal biopsy in the evaluation of infectious keratitis; to compare results of culture and histopathologic examination of the same specimens; to investigate potential factors related to positive biopsy results.

DESIGN

Retrospective, observational case series.

METHODS

We reviewed medical records for all patients who underwent corneal biopsy because of infectious keratitis at the Jules Stein Eye Institute from June 1989 through June 2009. In general, biopsy specimens were both cultured and examined histopathologically. Lesion size, lesion progression, and interval from presentation to biopsy were analyzed as possible predictors of positive biopsies.

RESULTS

Organisms were identified in 20 of 48 (42%) consecutive biopsies (positive cultures in 9 of 47 cases [19%]; positive histopathologic examination in 19 of 47 cases [40%]). Culture and histopathologic results were concordant in 30 of 46 biopsies (65%) for which both techniques were performed; 10 of the 16 discordant cases were culture-negative/histopathology-positive, while the remaining 6 had positive but discordant results for the 2 techniques (cultures all showed bacteria; histopathologic examination showed fungi or cysts consistent with Acanthamoeba sp.). Corneal biopsy revealed microorganisms in 12 of 27 patients (44%) with negative cultures of corneal scrapings obtained at presentation. None of the potential risk factors was statistically associated with positive biopsies.

CONCLUSIONS

Corneal biopsy can be useful for identifying the cause of infectious keratitis in selected cases. Culture and histopathologic examination can provide complementary information, but discordant results may occur. Acanthamoebic and fungal infections are more likely to be identified by histopathologic examination.

Successful treatment of Paecilomyces lilacinus endophthalmitis after foreign body trauma to the cornea

PURPOSE

To report the successful treatment of a patient with Paecilomyces lilacinus endophthalmitis infection after foreign body (FB) trauma to the cornea.

METHODS

A 30-year-old man presented to us with a corneal abscess and iritis 2 months after removal of a metal corneal FB. Initial corneal biopsy culture was negative. Treatment with topical 5% natamycin, 0.9% fortified gentamycin, and 5% cephalothin hourly was commenced. As a result of developing signs of endophthalmitis, two more biopsies were taken, a week apart, from the vitreous and anterior chamber, successively. The last biopsy yielded positive microbiologic results of the specious Paecilomyces lilacinus. Intravitreal injection of 50 microg/0.5 mL of amphotericin was administered during the vitreal biopsy. Soon after isolating the specious Paecilomyces lilacinus, the following treatment was administered: 200 mg of itraconazole bd by mouth, 5% topical natamycin every hour, 2 mg/mL of topical fluconazole every 2 hours, three anterior chamber injections of 0.35 mL of 0.1% fluconazole and two amphotericin B injections to the anterior chamber of 50 microg/0.5 mL each.

RESULTS

There appeared to be no sign of infection 6 months after initial treatment. A large, dense scar existed in the medial part of the cornea only. The pupil was secluded. The patient's visual acuity was 6/21. The eye was comfortable and all topical antifungal medication was ceased.

Corneal biopsy in the management of progressive microbial keratitis

PURPOSE

To study the indications and role of diagnostic corneal biopsy in the management of patients with progressive microbial keratitis.

METHODS

The records of 33 consecutive patients who underwent a diagnostic corneal biopsy from January 1, 1986, to December 31, 1998, were reviewed. The indication for corneal biopsy was progressive infectious keratitis despite intensive broad-spectrum topical antimicrobial therapy, or progressive stromal infiltration inaccessible to corneal scrapings. Microbiologic evaluation of all corneal biopsies was performed, and 11 of the 33 biopsies were also examined histopathologically.

RESULTS

A microorganism was isolated from 27 (82%) of the 33 corneal biopsies. Of the six patients with a negative biopsy, a penetrating keratoplasty was performed in five patients and the pathogen was identified by examination of the corneal button. In one patient no microorganism was identified; however, the infection resolved with topical antimicrobial therapy. The most common risk factor for keratitis was foreign body exposure or corneal abrasion (14 patients). A solid stromal infiltrate was the most common pattern of corneal involvement. Corneal biopsy revealed previously unidentified microorganisms that led to a change in antimicrobial therapy in 24 (89%) of the 27 patients and confirmed prior culture results in the remaining 3 patients. Microbiologic evaluation of the corneal biopsy was more sensitive than histopathologic examination. Acanthamoeba was the most commonly isolated pathogen (five cases), followed by Propionibacterium acnes and Fusarium (four cases each). Gram-positive organisms were isolated in 16 patients. Only five of the 27 patients with a positive corneal biopsy required a penetrating keratoplasty, in contrast to five of the six patients with a negative corneal biopsy (P =.005). During the 13-year period of the study, only three corneal biopsies were performed in the last 6 years.

CONCLUSIONS

Microbiologic evaluation of a diagnostic corneal biopsy contributed significantly to the diagnosis, treatment, and outcome of patients with progressive infectious keratitis.

Investigation of microbial keratitis: an audit from 1988-1992

An audit was performed of the investigation of 263 cases of microbial keratitis severe enough to be admitted to the Manchester Royal Eye Hospital over the 5-year period, 1988-1992. A pathogen isolation rate of 37% was noted during the first year which increased to 79% (p < 0.05) by the final year of audit. In late 1991 a new method of inoculating enrichment broths was introduced, which also contributed by increasing the yield from corneal scrapes. The audit process resulted in the development of and adherence to our investigation protocol, improved communication between Manchester Royal Eye Hospital and the microbiology laboratory, the implementation of a new investigatory method, and a significantly improved microbial isolation rate.

Corneal virulence, cytopathic effect on human keratocytes and genetic characterization of Acanthamoeba

Acanthamoeba keratitis is a sight-threatening complication of corneal trauma or contact lens wear. Although the majority of corneal isolates of Acanthamoeba belong to Group II in the Pussard-Pons classification based on cyst morphology, they have been placed in at least six species and their genetic relatedness is uncertain. The aim of this study was to determine the virulence of, and the relationship among, strains derived from the cornea, the nasal mucosa, and other environmental sources. To assess virulence, 10(4) trophozoites of each strain were incubated with monolayers of human corneal fibroblasts. By day 7, 12 of 29 strains tested had induced significant cytopathic changes. In addition, inocula of 10(4) cysts or trophozoites with 10(6) Corynebacterium xerosis were injected into the corneas of Porton rats; 11 amoebic strains induced infection within 7 days. The correlation between the virulence of trophozoites in vitro and in vivo was 86%. Using allozyme electrophoresis, 23 Acanthamoeba strains clustered into 5 major phylogenic divisions. Three divisions contained one or more strains that were virulent in the rat cornea. Virulent Pussard-Pons Group II strains clustered tightly to a fixed allelic difference of 13.6%. The eight corneal isolates clustered to 33%, dividing into three lineages. Five avirulent nasal isolates were strongly differentiated from other Group II strains. The results were not in accord with species designations based primarily on morphological criteria. These data suggest that particular subsets of Acanthamoeba strains are virulent in the human cornea.