Fundus reflectance--historical and present ideas.

In 1851 Helmholtz introduced the ophthalmoscope. The instrument allowed the observation of light reflected at the fundus. The development of this device was one of the major advancements in ophthalmology. Yet ophthalmoscopy allows only qualitative observation of the eye. Since 1950 attempts were made to address the challenging, quantitative assessment of the amount of light reflected by the fundus. At first, only comparative measurements were possible, applied in the study of macular and visual pigments. With improvements in light detecting techniques, and with the advent of microprocessors, the measurement of spectral and spatial distribution of the reflectance became feasible. This led to the development of models that explained the observed wavelength dependence and the directional behavior of light reflected from the fovea. The models allowed a quantitative assessment of many parameters on absorption and reflection by structures in the human eye. This paper provides a review of both the experimental and theoretical progress, and summarizes the results of fundamental and clinical research using fundus reflectometry.