Hyperspectral fundus light scattering measurements

Abstract

Abstract: : Purpose: To characterize the light scattering characteristics of the fundus as a function of wavelength and to construct a bidirectional reflectance distribution function (BRDF) or light scattering function of retinal tissue Methods: Enucleated swine eyes are illuminated with a scanning monochromator coupled into a probe placed into the eye through the pars plana. The illuminated retina is then imaged using a modified fundus camera. The monochromator is calibrated with a spectralon target prior to measurement. The measurement system and lens/cornea transmittance are calibrated by illuminating a spectralon target inserted into the vitreous and placed above the retina. Care is taken to record the geometry of the illumination and imaged beams so the angles of incidence and scatter could be reconstructed to 5º accuracy. Areas shadowed by large blood vessels can be used to estimate the multiply scattered background illumination levels. Results: Spectra from areas relatively free of blood vessels are averaged. From a collection of measurements the BRDF light scattering function has been measured over several steradians of illumination and scatter angles. The light scattering function changes abruptly for wavelengths longer than 620 nm as light penetrates through the melanin pigmented retinal pigment epithelium and diffuses into and back out of the choroid. Conclusions: Retinal light scattering functions will enable more precise models of light diffusion in the retina and can be applied to image enhancement and deblurring techniques for fundus photography, confocal imaging and OCT.

Keywords: retina • imaging/image analysis: non–clinical • optical properties