  Optical microscopy offers a unique insight of biological structures with a
sub-micrometer resolution and a minimum invasiveness. However, the
inhomogeneities of the specimen itself can induce multiple scattering of light
and optical aberrations which limit the observation to depths close to the
surface. To predict quantitatively the penetration depth in microscopy, we
theoretically derive the single-to-multiple scattering ratio in reflection.
From this key quantity, the multiple scattering limit is deduced for various
microscopic imaging techniques such as confocal microscopy, optical coherence
tomography and related methods.
