Fungal keratitis is a severe microbial keratitis where poor results are common compared to bacterial and viral keratitis and, in some cases, can lead to blindness. It can be caused by more than 100 different fungal species, but 95% of the cases are caused by filamentous fungi (Fusarium spp and Aspergillus spp) or yeast fungi (Candida spp) (Brown et al. 2021).
Although fungal keratitis occurs worldwide, epidemiological differences are influenced by the climate and level of economic development in the country (Mahmoudi et al. 2018). It is more common in tropical and subtropical regions, where most infections are caused by filamentous fungi, and the main risk factor is ocular trauma with plant matter (Thomas and Kaliamurthy 2013; Mahmoudi et al. 2018). However, in temperate and developed countries, the main pathogen is yeast, in relation with the use of contact lenses (Mahmoudi et al. 2018; Hoffman, Burton, and Leck 2021).
Treatment of fungal keratitis remains a challenge for ophthalmologists because of the poor corneal penetration, limited spectrum of action, and surface toxicity of topical antifungal drugs (Konar et al. 2020). Surgical techniques, such as lamellar keratoplasty or penetrating keratoplasty, can be effective and may be required, but the success rate of this surgical technique is limited by the risk of reinfection and graft rejection (Konar et al. 2020). An alternative to the poor corneal penetration of antifungal agents is the intrastromal injection of these drugs, which increases the drug concentration at the infection site (Sun et al. 2018).
However, in those cases where the fungus enters the anterior chamber after corneal perforation, there is no standard treatment, and the anatomical and visual prognoses are very poor.
This study aimed to describe a case of fungal keratitis treated with intrastormal and intracameral injections of caspofungin and amphotericin B. To the best of our knowledge, this is the first case to describe this treatment.
An 18-year-old Caucasian woman with history of soft contact lens wear was referred to our ophthalmology department after one month of poor clinical evolution of infectious keratitis in her left eye (LE) treated with hourly antimicrobial fortified eye drops (vancomycin 5%, ceftazidime 5% and voriconazole 1%).
On initial examination, her best corrected visual acuity (BCVA) was hand motion in the LE. Slit-lamp revealed ciliary injection, full-thickness corneal infiltrate with satellite lesions, positive Seidel test, significant fibrinous anterior chamber (AC) reaction, and athalamia. The infiltrate penetrated the AC reaching the iris and anterior lens capsule. Fungal keratitis was suspected because of the appearance of the cornea and the poor outcomes after one month of treatment. Microbiologic examination of corneal scrapings showed yeast cells in direct smear, but the fungus did not grow in culture media, so it was no possible to perform yeast isolation or antifungal drugs susceptibility testing.
The corneal perforation was immediately sealed with cyanoacrylate tissue adhesive (Figure 1), and intracameral and intrastromal voriconazole 50 μg/0.1 ml was injected. Systemic voriconazole 200 mg every 12 hours, hourly topical voriconazole 1% and natamycin 5%, and ceftazidime 5% every 6 hours were added.
The next day, the patient underwent therapeutic penetrating keratoplasty (TPK) plus AC washout with intracameral alteplase, and intracameral and intrastromal injections of voriconazole 50 μg/0.1 ml. Oral voriconazole and topical treatment was continued, and oral prednisolone 30 mg/day and topical dexamethasone every 8 hours were also added to avoid graft rejection. Histopathological examination of the removed cornea with Grocott’s methenamine silver (GMS) stain demonstrated the presence of fungal organisms in the tissue.
Intracameral and intrastromal voriconazole 50 μg/0.1 ml was reinjected every 48 hours twice, however, a white corneal endothelial plaque appeared. On suspicion of fungal resistance to voriconazole after graft reinfection, a new AC washout with intracameral alteplase was performed, and the treatment was changed. Oral, intracameral and intrastromal voriconazole were discontinued. Instead, intravenous liposomal amphotericin B (3 mg/kg every 24 hours for 7 days) and a combination of intrastromal and intracameral injections of caspofungin 250 μg/0.1 ml and amphotericin B (AmB) 20 μg/0.1 ml were administered. Subsequently, an intrastromal and intracameral combination of caspofungin 250 μg/0.1 ml and AmB 20 μg/0.1ml injections were administered every 48 hours 6 times until infection was clinically controlled. The intrastromal and intracameral antifungals where prepared by the pharmacy department of our hospital.
After three months, there were no signs of active infection, but there was scarring of the TPK graft and residual fibrin in the AC. In addition, the patient developed a cataract and an angle-closure glaucoma secondary to iridocorneal synechiae. BCVA was counting fingers and intraocular pressure (IOP) was 24 mmHg so an optical penetrating keratoplasty (OPK) plus AC washout with intracameral alteplase and synechiolisis were performed. BCVA improved to 20/200 after surgery but IOP elevated to 40 mmHg, so topical dorzolamide and timolol were administrated and IOP was normalized. One year later, a cataract surgery was performed with excellent visual and anatomical outcomes and BCVA achieved was 20/20 (Figure 2). IOP was 21 mmHg after cataract surgery so topical hypotensives were continued. Currently the patient continues with the same treatment with controlled pressure and no optic nerve damage.
Fungal keratitis is a challenge for the ophthalmologist due to the ability of the fungus to penetrate the cornea and pass through the intact Descemet’s membrane to the anterior chamber, and the poor corneal penetration of antifungal agents. In addition, there are no standard protocols for the management of this cases.
In our hospital, the management of fungal keratitis (Figure 3), it is initially treated with topical voriconazole 1% every hour. In case of poor response topical natamycin 5% every hour is added. Topical natamycin 5% is not always available in our country, so in these cases it is replaced by topical chlorhexidine 0,2% every hour.
For cases not responding to topical treatment, intrastromal injections of voriconazole 50 µg/0.1 mL and oral voriconazole 200mg twice day are added. If fungus has penetrated Descemet´s membrane, intracameral injections of voriconazole 50 µg/0.1 mL are performed. Intrastromal and intracameral injections of voriconazole are repeated every 48 hours if necessary, depending on the clinical evolution.
If despite the previous treatment it has poor response or in case of corneal thinning with high risk of perforation or perforation, therapeutic keratoplasty is performed. Deep anterior lamellar keratoplasty (DALK) plus intrastromal voriconazole 50 µg/0.1 mL is performed when the infiltrate does not involve the posterior 150-200 µm of the stroma. When the infiltrate reaches the posterior 150-200 µm of the stroma a TPK is performed plus AC washout with intracameral alteplase and intracameral and intrastromal injections of voriconazole.
In our case, there was a therapeutic failure of intrastromal and intracameral voriconazole after performing the TPK with graft reinfection. So, on suspicion of fungal resistance to voriconazole, antifungal drug was changed. The patient underwent intrastromal and intracameral combination of caspofungin and AmB injections associated with intravenous liposomal AmB. To the best of our knowledge, no published studies have reported the outcomes of this therapy.
The use of systemic antifungal agents in fungal keratitis is controversial. They are not routinely recommended because of the poor bioavailability in AC and the systemic side effects (Dong and Krebs 2022), particularly nephrotoxicity (Yoon et al. 2007). This, however, is a common practice in severe cases that present ulcers >5 mm, involvement of >50% stromal depth, recalcitrant infections, bilateral infections, when associated with scleritis, with limbal involvement or endophthalmitis, paediatric cases, post keratoplasty infections and in cases of impending perforation/perforated ulcers (Sahay et al. 2019; Sharma et al. 2019; Raj et al. 2021). Systemic antifungal therapy with liposomal AmB (3 mg/kg every 24 hours for 7 days) was administrated to our patient. The liposomal formulation was found to be associated with less nephrotoxic and infusion-related reactions compared to conventional AmB (Botero Aguirre and Restrepo Hamid 2015; Stone et al. 2016).
For intrastromal and intracameral injections, AmB plus caspofungin were combined. In vitro studies have shown a positive interaction with this drug combination, but further studies will need to validated this results in vivo (Arikan et al. 2002; Barchiesi et al. 2007).
There has been only one report of intrastromal caspofungin and none of intracameral caspofungin; therefore, the ideal dose for intrastromal and intracameral use remains undetermined. Neoh et al (Neoh et al. 2011) reported a case of Alternaria keratitis treated with 500 μg/0.1 ml of intrastromal caspofungin, while we used 250 μg/0.1 ml dose of intrastromal and intracameral caspofungin according to previous publications of intravitreal injections for fungal endophthalmitis (Danielescu, Cantemir, and Chiselita 2017). No adverse effects were observed in either case, but we have not found previous publications with a larger sample that confirm these results and guide us to decide the correct dose.
About intrastromal AmB for fungal keratitis there have been some reports. Qu et al (Qu, Li, and Xie 2014) reported a study in rabbit corneas, where they determined that intrastromal injection of AmB 10 μg/0.1 ml where effective and safe, while at concentrations between 20 μg/0.1 ml and 30 μg/0.1 ml presented side effects such as severe inflammation, severe corneal edema, corneal epithelial erosion, and severe corneal neovascularization. However, Nada et al (Nada, Al-Aswad, and El-Haig 2017) reported 41 patients treated with intrastromal AmB 20 μg/0.1 ml and no toxic effects of intrastromal injection were reported. In our case, we also used 20 μg/0.1 ml dose and no side effects were observed.
About intracameral AmB, in vitro study showed to be toxic to corneal endothelial cells (Wang et al. 1996). Foster et al (Foster et al. 1958) found that injection of as much as 50 µg of AmB did not cause corneal or lens toxicity in rabbit eyes. Kaushik et al (Kaushik et al. 2001) describes three cases of Aspergillus flavus keratitis treated with doses between 7.5-10 µg in 0.1 mL and no clinical evidence of corneal or lenticular toxicity in any patient. Kuriakose et al (Kuriakose et al. 2002) reported four cases of deep fungal keratitis with endothelial plaque that underwent intracameral injections of AmB 5 µg in 0.1 mL. Three of the four patients had a complete resolution of the infection and did not present more effects than pain and AC reaction that improved in the following 24 hours, although one patient perforated and required evisceration. Yilmaz et al (Yilmaz, Ture, and Maden 2007) also used 5 µg in 0.1 mL in 14 eyes with successful resolution of the infection. According to some reports, the recommended dose of intracameral AmB is 10-30 µg in 0.1 to 0.2 mL (Hu et al. 2016). In this case 20 μg/0.1 ml of AmB was intracamerally injected with no observed adverse effects.
The outcomes of this case report showed a good evolution after the injection of intracameral and intrastromal combination of caspofungin and AmB. Despite this, it is important to note that the patient had corneal scarring after the resolution of the infection and developed a white cataract and angle-closure glaucoma secondary to iridocorneal synechiae. In our opinion corneal scarring was most likely related to the secondary inflammation accompanying infection, but it could have been caused by the intrastromal injections. No long-term corneal side effects were observed because of the OPK performed three months after caspofungin and AmB injections, but no signs of corneal decompensation were observed between the TPK and OPK. Cataract and glaucoma are typical in these cases of fungal keratitis due AC inflammatory reaction, but could be related to intracameral drug toxicity and/or injection trauma, as has already been described by other authors (Yilmaz, Ture, and Maden 2007; Hu et al. 2016; Sharma et al. 2019). Other adverse effects described in relation with intracameral injections are post injection pain, AC reaction, secondary infection and bleeding (Dong and Krebs 2022).
In conclusion, this case report describes an off-label use of intrastromal and intracameral injections of caspofungin and amphotericin B. This therapy appears to be effective and safe and might be considered as an alternative treatment for drug-resistant fungal keratitis. However, randomized controlled trials are necessary to confirm the effectiveness, safety, and determine the appropriate concentration of these drugs.
DECLARATION OF CONFLICTING INTERESTS
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
STATEMENT OF CONSENT
We confirm that the patient’s consent statement has been obtained to publish this case and these images.