Digitalization of a Wide Field Contact Specular Microscope

Objectives: Non-contact specular microscopes (SM) have a very small field of observation (usually 0.1 mm2). This constitutes a major limitation when accurate and extended assessment of the corneal endothelium is needed, for instance during clinical trials or difficult diagnosis. Previous contact SM had the advantage of a wide field thanks to the use of an applanating cone but none of the old commercial devices passed the stage of digitalization. This paper aims at upgrading a wide field contact SM with a digital camera and dedicated software in order to combine wide field with the advantages of non-contact SM.Materials and methods: The digital device was composed of an acquisition unit consisting in a contact Konan Specular SP5500 equipped with a digital camera Canon EOS 6D and a Linux-based computer. Image processing uses segmentation algorithms (Gestalt theory and watershed with markers).Results: The device acquired wide field (0.5 mm2) highly contrasted images. The software provided cell boundaries and statistics: endothelial cell density, coefficient of variation of cell area and percentage of hexagonality. Contact SM images significantly increased the sampling of endothelial cells and consequently the reliability of endothelial quality analysis.Conclusion: The digital contact SM is not destined to compete with commercial non-contact SM but is an exceptional device for reference centers. It will allow obtaining accurate and reproducible endothelial qualification for specific studies.