Microscopy of biofilms on intraocular lenses

PURPOSE. Recent scanning electron microscope (SEM) studies of intraocular lenses (lOL's), removed from non-infected patients at Moorfields Eye Hospital, have shown that a bacterial biofilm was present on 14/27 lenses examined- However the processing and dehydration necessary to image biofilms by SEM does not give a realistic picture of biofilm structure. We tested two techniques, Hoffinan Modulation Contrast Light Microscopy, and Atomic Force Microscopy (AFM), to image biofilms on freshly removed lOL's. METHODS. Intraocular lenses were collected in sterile saline, following removal from patients in theatre at Moorfields Eye Hospital. For light microscopy, lenses were taken to CAMR, Salisbury, and imaged on a glass slide with no cover slip, and no staining, using Hoffinan Modulation Contrast optics mounted on a Nikon Labophot microscope with long working distance water immersion lenses. For AFM, lenses were taken to Portsmouth, and imaged directly on removal from the sterile saline using a TopoMetrix Discoverer AFM. RESULTS. Light microscopy gave a good overview of the presence of biofilm on the lOL's at a low magnification (x20, x40). AFM gave a much higher magnification view of small areas of the biofilm, imaging single bacterial cells. We also analysed the AFM images to determine biofilm thickness, and the percentage of the IOL covered. CONCLUSIONS. The two methods tested gave complementary information about the lenses examined, one imaging at high power and one at a lower magnification. The Hoffinan optics enabled us to have an overview of the whole lens and to determine the presence and extent of biofilm contamination, whereas the AFM proved to be an attractive non-invasive technique, which gave detailed information about biofilm height, and percentage coverage of the IOL. The main advantage of both techniques was that they enabled the study of bacterial biofilms in their natural, fully hydrated state.