Diagnosis of fungal keratitis: current options

Microbiological study of infectious keratitis at Ho Chi Minh City Eye Hospital

BACKGROUND

Infectious keratitis remains a significant cause of vision impairment worldwide, particularly in developing countries like Vietnam, where socio-economic factors and environmental conditions contribute to its prevalence.

PURPOSES

This study aims to investigate the epidemiology, risk factors, and microbiological causes of infectious keratitis at Ho Chi Minh City Eye Hospital, Vietnam, from August 2019 to January 2020.

METHODS

A descriptive study of 56 cases was analyzed using microbiological tests, including smear microscopy, culture, and RT-PCR.

RESULTS

Bacterial and fungal pathogens were the most common causes of infection, each responsible for approximately 35.71% of cases, with 17.86% exhibiting polymicrobial infections. Risk factors for infectious keratitis included trauma, systemic conditions like diabetes, and ocular conditions such as previous herpetic keratitis. Furthermore, RT-PCR was found to be more sensitive than traditional culture methods in detecting bacterial pathogens.

CONCLUSION

These findings underscore the importance of timely intervention and improved diagnostic methods to mitigate the burden of infectious keratitis in Vietnam.

Ultrasound-Enhanced Transcorneal Drug Delivery for Treatment of Fungal Keratitis

PURPOSE

Transcorneal drug delivery is hindered by ocular physical and biochemical properties, such as tear production, the epithelial layer of the cornea, and blinking. The aim of this study was to determine whether ultrasound can be applied to increase the transcorneal drug delivery of natamycin used in the treatment of fungal keratitis without dangerously overheating the surrounding ocular tissues.

METHODS

To verify the safety of various sets of ultrasound parameters, modeling studies were conducted using OnScale, an ultrasonic wave modeling software. Ultrasound parameters determined optimal for ocular tissue safety were used in a laboratory setting in a jacketed Franz diffusion cell setup. Histological images of the cross-section of the corneas used in experiments were examined for cell damage under a microscope.

RESULTS

Increases in transcorneal drug delivery were seen in every treatment parameter combination when compared with the sham treatment. The highest increase was 4.0 times for 5 minutes of pulsed ultrasound at a 25% duty cycle and a frequency of 400 kHz and an intensity of 0.5 W/cm 2 with statistical significance ( P < 0.001). Histological analysis revealed structural damage only in the corneal epithelium, with most damage being at the epithelial surface.

CONCLUSIONS

This study suggests that ultrasound is a safe, effective, and minimally invasive treatment method for enhancing the transcorneal drug delivery of natamycin. Further research is needed into the long-term effects of ultrasound parameters used in this study on human ocular tissues.

Fungi of the human eye: Culture to mycobiome

The focus of the current review is multi-fold and compares the diversity and abundance of fungi on the ocular surface by the conventional culture-based method with the more sensitive, high throughput, culture-independent NGS method. The aim is to highlight the existence of a core ocular mycobiome and explore the transition of the ocular fungal microbiota from the normal eye to the diseased eye. PubMed, Google Scholar and Medline were used to search for publications and reviews related to cultivable fungi and the mycobiome of the normal and diseased eye. The conventional cultivable approach and the NGS approach confirm that the eye has its own mycobiome and several confounding factors (age, gender, ethnicity etc.) influence the mycobiome. Further, dysbiosis in the mycobiome appears to be associated with ocular diseases and thus impacts the health of the human eye. Considering that the mycobiome of the eye is influenced by several confounding factors and also varies with respect to the disease status of the eye there is a need to extensively explore the mycobiome under different physiological conditions, different ethnicities, geographical regions etc. Such studies would unravel the diversity and abundance of the mycobiomes and contribute to our understanding of ocular health. Research focused on ocular mycobiomes may eventually help to build a targeted and individualized treatment.

Fungal Keratitis in Northern Thailand: Spectrum of Agents, Risk Factors and Putative Virulence Factors

Fungal keratitis (FK) is a serious ocular infection that can result in various degrees of vision loss, including blindness. The aim of the study was to identify and retrospectively review all FK cases diagnosed between August 2012 and December 2020 at a tertiary care hospital in northern Thailand with a specific focus on epidemiologic features, including season, patient sex and age, the spectrum of pathogens, and presence of certain putative virulence factors. Of 1237 patients with corneal ulcers, 294 (23.8%) were confirmed by direct microscopic examination and/or fungal culture. For the positive cases, direct examinations of Calcofluor white (CW) stains and KOH mounts were found in 97.3% (286/294) and 76.5% (225/294), respectively (p < 0.05). Of the cases diagnosed by microscopy and culture, fungi were isolated in 152 (51.7%), with Fusarium spp. being the most frequently identified (n = 69, 45.5%) followed by dematiaceous fungi (n = 45, 29.6%) and Aspergillus spp. (n = 18, 11.8%). The incidence of FK was higher in the rainy season of July to October. The mean age was 54.4 ± 14.4 (SD) years, with a range of 9–88 years. Males (75.8%) were affected significantly more than females (24.2%) (p < 0.05). Of 294 patients, 132 (44.9%) were middle-aged adults (41–60 years) and 107 (36.4%) were older than 60 years. Trauma to the eye by soil or vegetative matter were the most common preceding factors (188/294; 64.0%). We assessed two virulence factors. First, 142 of the 152 culture-positive FK cases were due to molds, indicating that hyphal morphogenesis is extremely important in disease. We also demonstrated that fungal melanization occurs in the molds during the course of FK by applying a melanin-specific monoclonal antibody (MAb) that labeled fungal elements in corneal samples of patients, and melanin particles derived from the hyphae were also recovered after treatment of the samples with proteolytic enzymes, denaturant and hot concentrated acid. In summary, we demonstrate that northern Thailand has a high rate of FK that is influenced by season and males engaged in outside activities are at highest risk for disease. Moulds are significantly more commonly responsible for FK, in part due to their capacity to form hyphae and melanins. Future studies will examine models of fungal corneal interactions and assess additional factors of virulence, such as secreted enzymes, to more deeply decipher the pathogenesis of FK.

Impact of Iontophoresis and PACK-CXL Corneal Concentrations of Antifungals in an In Vivo Model

PURPOSE

To investigate voriconazole (VRZ) penetration and fungal load in the cornea after applying VRZ therapy with various treatment combinations in a fungal keratitis model.

METHODS

Fifty-four eyes of 27 young albino rabbits were provided for this experimental study. Twelve corneas were inoculated with Candida albicans, 12 corneas were inoculated with Fusarium solani, and 6 eyes were selected as controls. Infected corneas received various treatment combinations including VRZ 1% drop therapy alone, VRZ 1% plus amphotericin B 1% drop combination therapy, iontophoretic VRZ therapy, and VRZ 1% drop therapy after corneal cross-linking. Fungal load was measured by log reduction, and VRZ levels were quantified by liquid chromatography-tandem mass spectrometry.

RESULTS

Iontophoresis-assisted VRZ application showed the highest antifungal activity against F. solani keratitis (4-log reduction) and C. albicans keratitis (5-log reduction) compared with other treatment applications. VRZ levels were also found to be the highest in corneas that received iontophoretic VRZ treatment (3.6313 ± 0.0990 ppb for F.solani keratitis and 1.7001 ± 0.0065 ppb for C. albicans keratitis) compared with other treatment applications.

CONCLUSIONS

Iontophoresis seems to provide the highest VRZ concentration and highest antifungal activity in the cornea compared with other treatment applications for C. albicans and F. solani keratitis.

Early deep anterior lamellar keratoplasty for fungal keratitis poorly responsive to medical treatment

PurposeTo investigate the efficacy of early therapeutic deep anterior lamellar keratoplasty (DALK) in eradicating fungal keratitis that is poorly responsive to medical treatment.Patients and methodsTwenty-three eyes (23 patients) underwent early therapeutic DALK within 15 to 50 days from the onset of symptoms. The adopted eligibility criteria for early DALK included the following: active fungal keratitis affecting the optical zone with ulcer confined in the 6.00 mm central cornea; deeper than 150 μm but not exceeding 300 μm; and poorly responsive to medical treatment.ResultsThe big bubble technique was accomplished in 74% (17) of eyes, whereas manual dissection was performed in the remaining 26% (6) of eyes. Histopathological examination did not show any sign of fungal colonization in the peripheral and deep stromal lamellae in any case. All grafts were transparent postoperatively, and no recurrence of infection occurred. Median best spectacle corrected visual acuity significantly improved from 2.0 (1.0 interquartile range) logMAR to 0.1 (0.1 interquartile range) logMAR (P<0.01). The mean follow-up was 32±10 months. Neither episode of rejection nor graft failure was noted during the follow-up period.ConclusionEarly DALK could represent a safe therapeutic approach to eradicate fungal keratitis that affects the optical zone and is poorly responsive to medical treatment.

Bipolaris oryzae, a novel fungal opportunist causing keratitis

We report a case of mycotic keratitis caused by Bipolaris oryzae with predisposing trauma from a foreign body. The fungus was identified by sequencing the internal transcribed spacer region, translation elongation factor 1α (TEF1) gene, and partial glyceraldehyde-3-phosphate dehydrogenase (GPDH) gene, and the species identity was confirmed on the basis of its characteristic conidial phenotype. The patient was treated with surgical intervention and antifungal agents, including intravenous fluconazole (FLC), oral itraconazole, topical 0.15% amphotericin B eye drops, and 0.5% FLC eye drops. To our knowledge, this is the first report of mycotic keratitis caused by B. oryzae worldwide.

A case of fungal keratitis and onychomycosis simultaneously infected by Trichophyton species

BACKGROUND

Fungal keratitis is difficult to treat that can result in corneal blindness requiring penetrating keratoplasty and in fungal endothalmitis. We report a case of fungal keratitis and onychomycosis simultaneously infected by Trichophyton.

CASE PRESENTATION

A 77-year old male presented with ocular pain, conjunctival injection, and severe loss of vision in his left eye. His best corrected visual acuity was hand movements in the left eye, and slit-lamp examination showed a corneal ulcer with feathery margin and hypopyon. Bacterial and fungal smear/culture showed no organism, and there was no improvement in spite of treatment with topical fortified 5% cefazolin and 2% tobramycin. Trichophyton species was identified by repeated cultures. We found onychomycosis on the patient's foot, where the same fungal species were identified. Regimen was changed to topical itraconazole and systemic intravenous itraconazole. No clinical improvement was observed, so therapeutic penetrating keratoplasty and cryotherapy was done with continuation of antifungal therapy. The graft was clear at postoperative 1 month and no evidence of recurrence was found.

CONCLUSION

It is important to identify the pathogen of keratitis because early identification of pathogen causing keratitis provides the appropriate treatment in early phase of keratitis. It is necessary to search for other fungal skin infections such as onychomycosis and athelete's foot considering the fungal keratitis following skin infection. In addition, fungal skin infection including onychomycosis should be treated for prevention of fungal keratitis as soon as possible.

Spectrum of fungal keratitis: clinicopathologic study of 44 cases

AIM

To determine the causative agents of fungal keratitis and study the predisposing factors over a period of ten years in a single tertiary care hospital.

METHODS

A retrospective analysis of fungal corneal ulcers was done from 2003-2012. Patients' clinical data were noted from the file records. Correlation of histopathological diagnosis was done with the report on fungal culture.

RESULTS

Mycotic keratitis was established in 44 cases by a positive fungal culture. Direct microscopic examination of potassium hydroxide (KOH) mounts revealed fungal elements in 39 cases while 40 cases showed fungus on Gram stained smears. Males (54.55%) were more commonly affected than the females (45.45%). The age ranged from 18 to 82 years. Most common age group to be involved was 41-60 years. Predisposing risk factors were seen in 34 (77.27%) cases. Most common findings on clinical examination were anterior chamber reaction and conjunctival injection seen in all the cases. Other common findings were stromal infiltration and hypopyon seen in 20 (45.45%) and 18 (40.91%) cases respectively. On histopathological examination the fungus was typed, as aspergillus in 34 cases while no definite typing was possible in 10 cases. The predominant isolate was aspergillus flavus (59.09%) followed by fusarium (15.91%). Mixed fungal and bacterial infection was seen in 3 (6.82%) cases.

CONCLUSION

Although culture is the gold standard for definitive diagnosis of fungal keratitis, direct microscopic examination of corneal scrapings or histomorphological evaluation of biopsies allow a rapid preliminary diagnosis. Early administration of antifungal treatment helps in preventing dreadful complications.