Imaging Dynamic Events in Living Tissue using Water Immersion Objectives

Abstract The use of water immersion objectives can provide a significant benefit to research involving the study of dynamic events in living tissue. Optical and quantitative imaging techniques like Confocal, Differential Interference Contrast (DIC), and Epi-fluorescence microscopy are dependent on the ability of high magnification, high numerical aperture immersion objectives to provide a high resolution image. The need to image the specimen not only at the surface next to the cover glass, but deeper down to 200 microns or more, can be greatly assisted by the use of highly corrected water immersion objectives. With oil immersion objectives, the deeper into the specimen and aqueous media one images, the more spherical aberration occurs. Spherical aberration is the main optical problem in imaging living cells with oil immersion, and spherical aberration increases proportionately with depth into the aqueous media and cellular material. The destructive effect of spherical aberration is seen as a loss of intensity and contrast, inability to collect and resolve small spatial frequencies, and reduced accuracy of reproduction in an optical system, all in direct proportion to the distance from the cover glass. It is possible to compensate mathematically for these distortions and extend resolution with deconvolution or image restoration software. These methods require accurate measurement of the point-spread function; if resolution varies with depth, then measurements must be taken at different depths, which complicates the process.