Modeling of PSF for refractive index variation in fluorescence microscopy

In fluorescence microscopy, thickness of the specimen is significant compared to the depth of focus of a high numerical aperture (N_a) lens of the imaging system. An aberration is introduced when there is a variation in refractive index in the specimen. Aberrations decrease the resolution and contrast of the image. Deconvolution is a method used to restore the image computationally, and for a successful deconvolution an accurate knowledge of the imaging system's point spread function (PSF) is a must. Here, we derive an appropriate model to obtain shift varying PSF for a thick specimen. Deconvolution results obtained for such a specimen are significantly better compared to those obtained using the standard Gibson and Lanni PSF model.