An optical system for examination of biological tissue includes a light source, a light detector, optics and electronics. The light source generates a light beam, transmitted to the biological tissue, spaced apart from the source. The light detector is located away (i.e., in a non-contact position) from the examined biological tissue and is constructed to detect light that has migrated in the examined tissue. The electronics controls the light source and the light detector, and a system separates the reflected photons (e.g., directly reflected or scattered from the surface or superficial photons) from the photons that have migrated in the examined tissue. The system prevents detection of the “noise” photons by the light detector or, after detection, eliminates the “noise” photons in the detected optical data used for tissue examination.