Resolution in the ApoTome and the confocal laser scanning microscope: comparison

The essential feature of the confocal laser scanning microscope (cLSM) is the generation of optical sections by the removal of out-of-focus light. About ten years ago, structured illumination microscopy (SIM) was introduced as an alternative method for obtaining optical sections from biological specimens. Here we compare the resolution of the ApoTome (commercial SIM by Zeiss) to that achieved by a cLSM (Zeiss LSM 510). If fluorescent beads are used as test objects, then the ApoTome will achieve a lower axial resolution than the cLSM. In contrast to that, its lateral resolution scores slightly better. If subresolution homogeneous fluorescent layers are used as test objects, then the ApoTome will achieve a higher axial resolution than the cLSM. The ApoTome's axial resolution is homogeneous over the field-of-view while that of the cLSM changes markedly. Finally, the anisotropy of the ApoTome's resolution was found to be negligible for standard applications while its capability to resolve fine structures within stained tissue slices is limited to one or two cell layers and thus worse than in the cLSM.