Prospective Study of the Diagnostic Accuracy of the In Vivo Laser Scanning Confocal Microscope for Severe Microbial Keratitis

Abstract

PurposeTo determine the diagnostic accuracy of in vivo confocal microscopy (IVCM) for moderate to severe microbial keratitis (MK).DesignDouble-masked prospective cohort study.ParticipantsConsecutive patients presenting to Aravind Eye Hospital, Madurai, India, between February 2012 and February 2013 with MK (diameter ≥3 mm, excluding descemetocele, perforation, or herpetic keratitis).MethodsFollowing examination, the corneal ulcer was scanned by IVCM (HRT3/RCM, Heidelberg Engineering, Heidelberg, Germany). Images were graded for the presence or absence of fungal hyphae or Acanthamoeba cysts by the confocal microscopist who performed the scan (masked to microbial diagnosis) and 4 other experienced confocal graders (masked to clinical features and microbiology). The regrading of the shuffled image set was performed by 3 graders, 3 weeks later. Corneal-scrape samples were collected for microscopy and culture.Main Outcome MeasuresThe main outcome measures were sensitivity, specificity, and positive and negative predictive values of IVCM compared with those of a reference standard of positive culture or light microscopy. Sensitivities and specificities for multiple graders were pooled and 95% confidence intervals calculated using a bivariate random-effects regression model.ResultsThe study enrolled 239 patients with MK. Fungal infection was detected in 176 (74%) and Acanthamoeba in 17 (7%) by microbiological methods. IVCM had an overall pooled (5 graders) sensitivity of 85.7% (95% confidence interval [CI]: 82.2%–88.6%) and pooled specificity of 81.4% (95% CI: 76.0%–85.9%) for fungal filament detection. For Acanthamoeba, the pooled sensitivity was 88.2% (95% CI: 76.2%–94.6%) and pooled specificity was 98.2% (95% CI: 94.9%–99.3%). Intergrader agreement was good: κ was 0.88 for definite fungus; κ was 0.72 for definite Acanthamoeba. Intragrader repeatability was high for both definite fungus (κ: 0.88–0.95) and definite Acanthamoeba classification (κ: 0.63–0.90). IVCM images from 11 patients were considered by all 5 graders to have a specific organism present (10 fungus, 1 Acanthamoeba) but had negative results via culture and light microscopy.ConclusionsLaser scanning IVCM performed with experienced confocal graders has high sensitivity, specificity, and test reproducibility for detecting fungal filaments and Acanthamoeba cysts in moderate to large corneal ulcers in India. This imaging modality was particularly useful for detecting organisms in deep ulcers in which culture and light microscopy results were negative.

In vivo confocal microscopy of the inflamed anterior segment: A review of clinical and research applications

“…Using slit scanning IVCM, Kanavi et al reported a sensitivity of 94% and specificity of 78% for the diagnosis of fungal keratitis by experienced observers. In a large prospective study, Chidambaram et al pooled five graders of varying levels of experience (2‐5 years) and reported a sensitivity of 85.7% and specificity of 81.4% for the diagnosis of fungal keratitis using laser scanning IVCM. Interestingly, having access to a clinical image of the ulcer resulted in a greater sensitivity for fungal detection (89.8% sensitivity) .…”

“…In a large prospective study, Chidambaram et al pooled five graders of varying levels of experience (2‐5 years) and reported a sensitivity of 85.7% and specificity of 81.4% for the diagnosis of fungal keratitis using laser scanning IVCM. Interestingly, having access to a clinical image of the ulcer resulted in a greater sensitivity for fungal detection (89.8% sensitivity) . A subsequent retrospective reliability study by Kheirkhah et al assessed the effect of observer experience on diagnostic accuracy and showed that the level of experience had a significant impact on sensitivity (71.4% and 42.9% for experienced and inexperienced observers, respectively) but not on specificity (89.6% and 87.5% for experienced and inexperienced observers, respectively) …”

“…Despite their relatively low sensitivity (less than 11%), these features were pathognomonic of the disease. 33 Chidambaram et al 39 pooled five graders of varying levels of experience (2-5 years) and reported a sensitivity of 88.2% and a specificity of 98.2% for the diagnosis of acanthamoeba keratitis using laser scanning IVCM. Hau et al 36 noted that the longer the duration of acanthamoeba keratitis, the higher the likelihood that a correct diagnosis was made by the observers in grading the IVCM images.…”

Anterior segment optical coherence tomography: its application in clinical practice and experimental models of disease

“…In vivo confocal microscopy is a technique that can be used to visualise specific cellular components of the cornea and limbus, including epithelial and endothelial cell number and morphology, sensory nerves, keratocytes, infiltrating inflammatory cells and resident immune cells . In addition, due to the high image resolution and en face , non‐invasive image acquisition mode, in vivo corneal confocal microscopy is often applied clinically to identify causative agents in infective keratitis, including fungal filaments and acanthamoeba cysts to guide appropriate therapy. In animal models, in vivo corneal confocal microscopy has been used to quantify basal epithelial cell density and nerve density in the mouse cornea .…”

Mikrobielle Keratitis, Teil 1: allgemeine Aspekte und bakterielle Keratitiden

“…Die In-vivo-Konfokalmikroskopie (IVCM) ist heutzutage aus dem Pool der diagnostischen Methoden zum Nachweis einer mikrobiellen Keratitis nicht mehr wegzudenken. Sie ermöglicht eine schnelle, nichtinvasive, atraumatische, detaillierte Darstellung der einzelnen Hornhautschichten auf zellulärer Ebene in Echtzeit [14,24,25]. In erfahrenen Händen können mit diesen Methoden frühzeitig wertvolle Hinweise über die einzelnen Erreger gewonnen werden.…”