Development and Assessment of a Simulator for in Vivo Confocal Microscopy in Fungal and Acanthamoeba Keratitis

Impact of implementation of polymerase chain reaction on diagnosis, treatment, and clinical course of Acanthamoeba keratitis

PURPOSE

Acanthamoeba keratitis (AK) is a painful and possibly sight-threatening ocular infection. While the correct diagnosis and specific treatment in the early stages significantly improve the prognosis, the disease is often misdiagnosed and in clinical examination confused with other forms of keratitis. Polymerase chain reaction (PCR) for the detection of AK was first introduced in our institution in December 2013 to improve the timely diagnosis of AK. The aim of this study was to assess the impact of implementation of Acanthamoeba PCR on the diagnosis and treatment of the disease in a German tertiary referral center.

PATIENTS AND METHODS

Patients treated for Acanthamoeba keratitis between 1st of January 1993 and 31st of December 2021 in the Department of Ophthalmology of the University Hospital Duesseldorf were identified retrospectively via in-house registries. Evaluated parameters include age, sex, initial diagnosis, method of correct diagnosis, duration of symptoms until correct diagnosis, contact lens use, visual acuity, and clinical findings as well as medical and surgical therapy by keratoplasty (pKP). In order to assess the impact of implementation of Acanthamoeba PCR, the cases were divided into two groups (before (pre-PCR group) and after PCR implementation (PCR group).

RESULTS

Seventy-five patients with Acanthamoeba keratitis were included (69.3% female, median age 37 years). Eighty-four percent (63/75) of all patients were contact lens wearers. Until PCR was available, 58 patients with Acanthamoeba keratitis were diagnosed either clinically (n = 28), by histology (n = 21), culture (n = 6), or confocal microscopy (n = 2) with a median duration until diagnosis of 68 (18; 109) days. After PCR implementation, in 17 patients, the diagnosis was established with PCR in 94% (n = 16) and median duration until diagnosis was significantly shorter with 15 (10; 30.5) days. A longer duration until correct diagnosis correlated with a worse initial visual acuity (p = 0.0019, r = 0.363). The number of pKP performed was significantly lower in the PCR group (5/17; 29.4%) than in the pre-PCR group (35/58; 60.3%) (p = 0.025).

CONCLUSIONS

The choice of diagnostic method and especially the application of PCR have a significant impact on the time to diagnosis and on the clinical findings at the time of confirmation of diagnosis and the need for penetrating keratoplasty. In contact lens-associated keratitis, the first crucial step is to take AK into consideration and perform a PCR test as timely confirmation of diagnosis of AK is imperative to prevent long-term ocular morbidity.

Clinical Observation of Corneal Endothelial Plaques With Fungal and Bacterial Keratitis by Anterior Segment Optical Coherence Tomography and In Vivo Confocal Microscopy

PURPOSE

Endothelial plaque is an important sign of fungal keratitis and is related to diagnosis, surgical indications, and prognosis. However, bacterial keratitis sometimes involves fibrin formation on the back corneal surface, similar to endothelial plaques. Because corneal infiltration interferes with precise observation of the posterior corneal plaque, distinguishing pathogens with a slitlamp is difficult. We hope to assist clinicians in early diagnosis and timely treatment by observing the connection state of endothelial plaques and the corneal endothelium through anterior segment optical coherence tomography (AS-OCT) and the different forms of endothelial plaques in infectious keratopathy through in vivo confocal microscopy (IVCM).

METHODS

We analyzed 52 patients in the Eye Hospital of the First Affiliated Hospital of Harbin Medical University who were clearly diagnosed with fungal or bacterial keratitis with endothelial plaques. All patients underwent AS-OCT and IVCM on admission.

RESULTS

According to the smear, IVCM, or fungal and bacterial culture results, the patients were diagnosed with fungal (28 patients) or bacterial keratitis (24 patients). AS-OCT in 25 patients diagnosed with fungal keratitis revealed that the corneal endothelium-endothelial plaque boundary was unclear and wavy, and 24 patients had unclear cell boundaries and a large number of compactly distributed inflammatory cells in the endothelial layer according to IVCM. AS-OCT in 23 patients diagnosed with bacterial keratitis revealed clear corneal endothelium-endothelial plaque boundaries, and insufficient endothelial cell boundaries with a large number of visible and scattered inflammatory cell structures were observed through IVCM in 22 patients.

CONCLUSIONS

Corneal endothelial plaque detection by AS-OCT and IVCM can be used for early diagnosis of infectious keratitis.

Outcomes of Severe Fungal Keratitis Using in vivo Confocal Microscopy and Early Therapeutic Penetrating Keratoplasty

Purpose

The purpose of this study was to assess the impact of early diagnosis using in vivo confocal microscopy and early therapeutic penetrating keratoplasty (TPK) on the outcomes of severe cases of fungal keratitis.

Methods

This retrospective single-center study included 38 patients (40 eyes) with fungal keratitis who presented between December 2013 and February 2020. Preoperative, intraoperative, and postoperative parameters were recorded to assess the role of early correct diagnosis and early surgical therapy on visual acuity outcome and enucleation rate during follow-up.

Results

The mean patient age was 51 years (71% females). The initial external diagnosis was correct in 20 cases (50%). The mean time from symptom onset until admission to our department was 46.8 ± 68.0 (median 28.5) days. The mean time to correct diagnosis after admission to our department was 1 day with in vivo confocal microscopy (IVCM). IVCM was performed in 38 cases, of which 36 (sensitivity: 94.7%) were positive for fungal infection. Twenty-seven out of 40 (67.5%) eyes received a TPK 4.2 ± 3.9 days after admission, with a mean graft size of 8.9 ± 1.9 mm. Three eyes (7.5%) were enucleated. The corrected distance visual acuity of the entire study population increased from 2.0 ± 1.2 LogMAR to 0.96 ± 1.17 LogMAR.

Conclusion

In vivo confocal microscopy is a powerful tool for the early detection of fungal organisms in infectious keratitis. An early TPK with a large graft helps to eradicate the infection timely and results in a favorable visual acuity outcome and lower enucleation rate, especially when treating filamentous fungi.

The use of in vivo confocal microscopy in fungal keratitis - Progress and challenges

Fungal keratitis (FK) is a serious and sight-threatening corneal infection with global reach. The need for prompt diagnosis is paramount, as a delay in initiation of treatment could lead to irreversible vision loss. Current "gold standard" diagnostic methods, namely corneal smear and culture, have limitations due to diagnostic insensitivity and their time-consuming nature. PCR is a newer, complementary method used in the diagnosis of fungal keratitis, whose results are also sample-dependent. In vivo confocal microscopy (IVCM) is a promising complementary diagnostic method of increasing importance as it allows non-invasive real-time direct visualization of potential fungal pathogens and manifesting infection directly in the patient's cornea. In numerous articles and case reports, FK diagnosis by IVCM has been evaluated, and different features, approaches, sensitivity/specificity, and limitations have been noted. Here, we provide an up-to-date, comprehensive review of the current literature and present the authors' combined recommendations for fungal identification in IVCM images, while also looking to the future of FK assessment by IVCM using artificial intelligence methods.

Establishment of an Acanthamoeba keratitis mouse model confirmed by amoebic DNA amplification

Acanthamoeba castellanii, the causative agent of Acanthamoeba keratitis (AK), occurs mainly in contact lens users with poor eye hygiene. The findings of many in vitro studies of AK, as well as the testing of therapeutic drugs, need validation in in vivo experiments. BALB/c mice were used in this study to establish in vivo AK model. A. castellanii cell suspensions (equal mixtures of trophozoites and cysts) were loaded onto 2-mm contact lens pieces and inserted into mouse eyes that were scratched using an ophthalmic surgical blade under anesthesia and the eyelids of the mice were sutured. The AK signs were grossly observed and PCR was performed using P-FLA primers to amplify the Acanthamoeba 18S-rRNA gene from mouse ocular tissue. The experimental AK mouse model was characterized by typical hazy blurring and melting of the mouse cornea established on day 1 post-inoculation. AK was induced with at least 0.3 × 10⁵ A. castellanii cells (optimal number, 5 × 10⁴), and the infection persisted for two months. The PCR products amplified from the extracted mouse eye DNA confirmed the development of Acanthamoeba-induced keratitis during the infection periods. In conclusion, the present AK mouse model may serve as an important in vivo model for the development of various therapeutic drugs against AK.