The corneal specular microscope is a reflected-light microscope that projects light onto the cornea and images the light reflected from an optical interface of the corneal tissue, most typically the interface between the corneal endothelium and the aqueous humor. Depending on the instrument used, the projected light can be in the form of a stationary slit, a moving slit, or a moving spot and the optical design can either be non-confocal or confocal. Although specular microscopes have been used primarily to evaluate the corneal endothelium, the corneal epithelium and stroma as well as the crystalline lens can also be visualized and evaluated.
The young normal corneal endothelium above as seen by specular microscopy, shows a quasi-regular array of hexagonal cells all having nearly the same size. With aging, trauma, and corneal disease, this regularity is lost. The goal of endothelial specular micrsocopy is to enable the status of the endothelium to be obtained by visual observation and morphometric analysis of the endothelial image. In general, the more the endothelial image varies from the normal appearance shown in the above figure, the more comporomized the endothelium, and the less able is the endothelium to provide its necessary functions that maintain corneal clarity. Although observation of the corneal endothelium by specular reflection dates back to the early part of this century1-3 and observation of excized, non-moveable, rabbit corneas was accomplished4-6 it was not until a suitable instrument was developed by Laing in 19757,8 that clinical specular microscopy became a viable method. This original clinical specular microscope gave clinical photomicrographs having sufficient resolution to demonstrate individual cell boundaries and to distinguish numerous intracellular structures. From this early instrument the technique of clinical specular microscopy, as we know it today, was launched. Over the past 20 years there has been a continual improvement in the available technology that has resulted in instruments that are easy to use and that give superior image quality as compared to the early instruments. |
References: 1. Guillstrand A. Ber Versamml Ophthalmol Dtsch Ges. 1911;37:374. 2. Vogt A. Albrecht von Graefe"s Arrch Klin Exp Ophthalmol. 1920;101:123-144. 3. Vogt A. Atlas Des Spaltlampmicroskopie Des Lebender Auges. Berlin: Springer-Verlag; 1921. 4. Maurice D. Cellular membrane activity in the corneal endothelium of the intact eye. Experientia. 1968;24:1094. 5. Hoefle F, Maurice D, Sibley R. Human corneal donor material. A method of examination before keratoplasty. Arch Ophthalmol. 1970;84:741. 6. Leibowitz H, Laing R, Sandstrom M. Corneal endothelium. The effect of air in the anterior chamber. Arch Ophthalmol. 1974;92:227. 7. Laing R, Sandstrom M, Berrospi A, Leibowitz H. Changes in the corneal endothelium as a function of age. Exp Eye Res. 1976;22:587. 8. Laing R, Sandstrom M, Berrospi A, Leibowitz H. Morphological changes in corneal endothelial cells after penetrating keratoplasty. Amer J Ophthalmol. 1976;82:459. |
