Since the introduction of specular microscopy clinically into eye banks in the 1970s,1–3 this imaging technology has been primarily limited to imaging of the central corneal endothelium for determination of endothelial cell density (ECD), morphology (coefficient of variation and % of hexagonal cells), and detection of disease at a more magnified view than afforded by slit-lamp examination. Confocal microscopy,4 available clinically for patients, accomplishing not only endothelial imaging but cross-sectional imaging across the entire cornea, was never commercially available in eye banking.
This limitation has now changed with the introduction in 2015 of a “confocal image–like” wide-field ex vivo dual imaging microscope (CellChek® D+®; Konan Medical, Irvine, CA).5 This image atlas is the first major effort to demonstrate the capabilities of this instrument and the potential for its uses complementing slit-lamp biomicroscopy, conventional specular microscopy, and optical coherence tomography imaging. To our knowledge, this new technology is the first multi-imaging system for donor corneas. As defined by the manufacturer, it uses a specular microscopy mode (Specular mode), an Enhanced mode, and a Finder mode to better image and evaluate the cornea ex vivo.5 According to the manufacturer, the Specular mode has an expanded viewing area of 750,000 μm2.5 With the larger viewing field, the microscope allows users to visualize all the corneal layers in a cross-sectional view across the entire cornea.6 For endothelial imaging and determination of ECD, an option to sample and analyze 4 different areas of the central and midperipheral endothelium is possible. The average ECD can then be determined with a potential area of analysis of 480,000 μm2, allowing for an 8.5× larger analysis field compared to its predecessor, the Konan EB-10.6 The dual imaging microscope also allows for a 10-degree greater tilt to better account for the curvature of the cornea when analyzing samples (Figs. 1–4).5
Beyond the advancements associated with specular microscopy, the Enhanced mode provides confocal image–like or “scanning electron microscopy–like” imaging of all corneal layers such as imaging from the irregular surface of the epithelium, endothelium, and interface of lamellar dissection of the donor for Descemet stripping automated endothelial keratoplasty with a 3-dimensional effect, a limitation of conventional specular microscopy.5 With its introduction in 2015, these capabilities are now being explored by eye banks and corneal surgeons as to its utility with both normal and disease states affecting these layers. Because the Enhanced mode enables seeing the surface of the outer epithelium, the apical surface of the endothelium and the interface of lamellar dissection, total corneal thickness, or graft thickness can also be measured. Once the Enhanced mode image is captured, a composite image can display the Enhanced mode and Specular mode images over each other to better define the cornea's pathology.
The Finder mode (low magnification) allows users to see the overall appearance of the entire donor cornea with reference location indication. This new view provides the ability to scan the donor cornea and determine the areas of interest for further analysis by switching to the high-magnification view. This mode also allows users to determine the diameter of the cornea or clear zone and the lengths and areas of any area of interest on the cornea using donor feature measurement tools.5
The newly introduced wide-field ex vivo dual imaging microscope has provided an imaging tool whose contribution to the tissue evaluation process remains to be fully explored and has not yet become part of the standard operating procedure of the eye bank. It is the hope of the coeditors and contributors of this atlas that the images from this instrument, as they complement the images from other existing technologies, will stimulate establishment of specific guidelines and procedures for incorporation of this new imaging technology into standard operating procedure to further enhance tissue evaluation for the 21st century eye bank, assuring the highest tissue quality and inclusion of more tissues which may have been eliminated based on slit-lamp examination alone.
1. Bourne WM, Kaufman HE. Specular microscopy of human corneal endothelium in vivo. Am J Ophthalmol. 1976;81:319–323.
2. Laing RA, Sandstrom MM, Leibowitz HM. In vivo photomicrography of the corneal endothelium. Arch Ophthalmol. 1975;93:143–145.
3. Maurice DM. A scanning slit optical microscope. Invest Ophthalmol. 1974;13:1033–1037.
4. Guthoff RF, Zhivov A, Stachs O. In vivo confocal microscopy, an inner vision of the cornea: a major review. Clin Exp Ophthalmol. 2009;37:100–117.
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6. Tran KD, Clover J, Odell K, et al. Comparison of endothelial cell measurements by two eye bank specular microscopes. Int J Eye Banking. 2016;4:1–8.