Any structure, normal or abnormal, present in the fundus oculi will be visible if certain basic criteria are satisfied: (1) the illuminating light must reach the structure in question; (2) the structure must react with this light either absorbing or reflecting it or both; and (3) in this light the surrounding structures must react sufficiently differently to the one under consideration. Structures will be invisible under the following conditions: (1) if the light does not reach them; (2) if they do not react with the light—so-called transparent; and (3) if the reaction of the surrounding structures is so similar that no differentiation is possible.
Spectral reflectance photography has opened new vistas of investigation in both clinical and basic ophthalmology. The basic principle underlying this methodology depends upon the reaction of various structures in the fundus with light of specific wavelengths and the photographic recording of the resulting interactions. Highly
BEHRENDT T, DUANE TD. Investigation of Fundus Oculi With Spectral Reflectance PhotographyI. Depth and Integrity of Fundal Structures. Arch Ophthalmol. 1966;75(3):375-379. doi:10.1001/archopht.1966.00970050377012