The use of spectral imaging for the diagnosis of retinal disease

Empirical collections of retinal images gathered over the years form the basis of many retinal interventions. Identification of the diseased retina requires understanding of abnormal patterns and colors in the retina. Quantification of the clinician's interpretation of pathological changes in morphology and color is the subject of this presentation. In particular, various hyperspectral imaging techniques which map wavelength-resolved reflectivity across a two dimensional scene offer considerable promise as a new clinical tool. Quantification of retinal images could permit both early detection as well as monitoring of the effectiveness of therapy. The authors discuss hyperspectral imaging methods using external illumination from a filtered tungsten lamp, projected in non-imaging mode by a standard ophthalmic fundus camera. This device also enables convenient image relay from the retina to a hyperspectral imaging system. Light gathered by the fundus camera originates from backscattering caused by the retina, choroid, and sclera. Both wavelength-dependent scattering and wavelength-dependent absorption determine the spectrum of light emerging from an area element of the retina. Furthermore, the high level of turbidity in the retina and choroid imply that photons do not sample properties in a locality. Instead, photons migrate between elements to some extent. The effects of photon migration on sampling volume is discussed.