Diagnostic accuracy of microbial keratitis with in vivo scanning laser confocal microscopy

Scott Hau (1) , John Dart (1) , Minna Vesaluoma (1) , Dipak Parmar (2) , Ilse Claerhout (3) , Kanom Bibi (1) , Frank Larkin (1)

1 Moorfields Eye Hospital
2 Dept of Ophthalmology, Whipps Cross Hospital, London, UK, E11 1NR
3 Ghent University Hospital

Aims To determine the accuracy of diagnosing microbial keratitis by masked medical and non-medical observers using the Heidelberg Retina Tomograph II / Rostock Cornea Module in vivo confocal microscope. Methods Confocal images were selected for 62 eyes with culture or biopsy proven infections. The cases comprised of 26 Acanthamoeba, 12 fungus, 3 Microsporidia, 2 Nocardia, and 19 bacterial infections (controls). The reference standard for comparison was a positive tissue diagnosis. These images were assessed on two separate occasions by 4 observers who were masked to the tissue diagnosis. Diagnostic accuracy indices, Kappa (κ) statistic and percentage agreement values were calculated. The Spearman correlation coefficient (rs) was calculated for the number of correct diagnoses versus duration of disease. Results The highest sensitivity and specificity values were 55.8% and 84.2%, and the lowest sensitivity and specificity values were 27.9% and 42.1%. The highest positive and negative likelihood ratios were 2.94 and 0.59, respectively. Agreement values were: fair to moderate (κ, 0.22-0.44) for reference standard versus observer diagnosis, moderate to good in intra-observer variability (repeatability, κ, 0.56-0.88), and poor to moderate in inter-observer variability (reproducibility, κ, 0.15-0.47). The correct diagnosis was associated with duration of disease for Acanthamoeba keratitis (rs = 0.60, p = 0.001). Conclusions The diagnostic accuracy of microbial keratitis by confocal microscopy is dependent on observer experience. Intra-observer repeatability was better than inter-observer reproducibility. Difficulty in distinguishing host cells from pathogenic organisms limits the value of confocal microscopy as a stand-alone tool in diagnosing microbial keratitis.

Mots clés: Cornea; Imaging; Diagnostic tests/Investigation

Scott Hau, John Dart, Minna Vesaluoma, Dipak Parmar, Ilse Claerhout, et al.. Diagnostic accuracy of microbial keratitis with in vivo scanning laser confocal microscopy. British Journal of Ophthalmology, 2010, 94 (8), pp.982. ⟨10.1136/bjo.2009.175083⟩. ⟨hal-00557354⟩