Introduction

This special issue of Optics Express focuses on a number of exciting new applications in biology and medicine utilizing nonlinear microscopy and reflected light confocal optical microscopy.

A number of papers in this issue focuses on the deep tissue penetration capability of these techniques. In the area of embryology, Mohler and White present a paper on using two-photon microscopy to monitor c. elegans embryo development. This study provides an excellent demonstration of the potential of noninvasive long-term microscopic imaging in the elucidation of developmental biology problems. Masters has presented two papers on using reflected light confocal microscopy to characterize ocular tissues. One paper deals with the localization of cataract in human lens. The second paper focuses on characterizing corneal structure with subcellular resolution. These papers demonstrate the power of 3D microscopy to understand and diagnose ocular diseases. Finally, So et al. presents a paper on the use of two-photon microscopy to resolve dermal and subcutaneous structures. The ability of two-photon imaging to retrieve structural information in turbid tissues opens new opportunities in the diagnosis of cancer and the design of tissue regenerative devices.

While reflected light confocal microscopy and two-photon fluorescence microscopy are finding an ever wider range of applications, the future of microscopy lies in the continuous technological innovations. Squier et al. demonstrates a 3D resolved imaging technique based on third harmonic generation. Intrinsic nonlinear optical properties of cells and tissues can be used to provide image contrast in the absence of fluorescence probes. The demonstration that fluorescence labeling can be sometime eliminated points out another important way to minimize specimen perturbation.

I would like to thank all the authors for the excellent submissions received for this special issue.