Label-free contrast enhancement for translucent cell imaging by purposefully displacing the detector

A method for imaging vertebrate translucent retinal structures includes imaging a translucent retinal structure at a first imaging plane in the retina with a light source focused at such first imaging plane, and detecting reflected light with a non-confocal off-axis detector, wherein the detector is axially displaced from a plane conjugate to the first imaging plane to a plane conjugate to a reflective layer deeper in the retina along a path of illumination from the light source. The method may employ scanning ophthalmic instruments, and enables an enhancement in contrast and collected intensity by axially displacing the image detector away from the object of interest to positions closer to conjugate to layers of strong retinal reflection, like the photoreceptors or the interface between the choroid and the sclera, that act as a diffusive screen. This improvement was found using a model that describes the source of the contrast in offset aperture and split-detector ophthalmoscopy by emphasizing the role of cellular refractive index change within the plane of illumination.