Spectral domain optical coherence tomography (SDOCT) is a noninvasive, cross-sectional imaging technique that measures depth resolved reflectance of tissue by Fourier transforming the spectral interferogram with the scanning of the reference avoided. Interferometric synthetic aperture microscopy (ISAM) is an optical microscopy computed-imaging technique for measuring the optical properties of biological tissues, which can overcome the compromise between depth of focus and transverse resolution. This paper describes the principle of SDOCT and ISAM, which multiplexes raw acquisitions to provide quantitatively meaningful data with reliable spatially invariant resolution at all depths. A mathematical model for a coherent microscope with a planar scanning geometry and spectral detection was described. The two-dimensional fast Fourier transform (FFT) of spectral data in the transverse directions was calculated. Then the nonuniform ISAM resampling and filtering was implemented to yield the scattering potential within the scalar model. Inverse FFT was used to obtain the ISAM reconstruction. One scatterer, multiple scatterers, and noisy simulations were implemented by use of ISAM to catch spatially invariant resolution. ISAM images were compared to those obtained using standard optical coherence tomography (OCT) methods. The high quality of the results validates the rationality of the founded model and that diffraction limited resolution can be achieved outside the focal plane.