title: In vitro multispectral diffuse reflectance measurements of the porcine fundus.
abstract: OBJECTIVE
  To quantify the reflectance of the swine fundus as a function of illumination angle and wavelength using a novel technique of intravitreal illumination.
  
  
  METHODS
  Enucleated swine eyes were illuminated with a scanning monochromator coupled to a fiber-optic probe placed in the vitreous at several locations. Intravitreal illumination was used to reduce the effects of extraneous reflections and scatter from the anterior structures of the eye, including glints from the internal limiting membrane and blood vessels. Intravitreal illumination provided different light paths and additional information to apply to retinal reflectance modeling. A 25-mm(2) region of the illuminated fundus was imaged while the angle of illumination was varied over a maximum range of 22 degrees . Multispectral images from areas free of large blood vessels were acquired. The diffusely reflected intensity was integrated over the pupil with a solid angle of 0.028 steradians. The spectral reflectance function was calculated for multiple illumination angles.
  
  
  RESULTS
  Multispectral fundus image sets were obtained for two enucleated swine eyes by using intravitreal illumination. The fundus spectral reflectance function showed decreasing reflectance with increasing illumination angle, rapid changes in the 430- to 480-nm range, and a fairly consistent reflectance decrease for 480 to 700 nm.
  
  
  CONCLUSIONS
  Variations in fundus spectral reflectance with change in the illumination angle were found to deviate from Lambertian behavior, varying from Lambertian by 5% across the spectrum in one sample and 20% in a second sample. Intravitreal illumination resulted in markedly decreased extraneous reflections.
authors.affiliation: Optical Sciences Center, University of Arizona, Tucson.
authors.forename: David A
authors.initials: DA
authors.lastname: Salyer
authors.forename: Karen
authors.initials: K
authors.lastname: Twietmeyer
authors.forename: Neil
authors.initials: N
authors.lastname: Beaudry
authors.forename: Sreenivasa
authors.initials: S
authors.lastname: Basavanthappa
authors.forename: Robert I
authors.initials: RI
authors.lastname: Park
authors.forename: Russell
authors.initials: R
authors.lastname: Chipman
mesh_terms: D000818:Animals; D005654:Fundus Oculi; D008027:Light; D009412:Nerve Fibers / Q000502:physiology*; D012160:Retina / Q000502:physiology* / Q000528:radiation effects; D012542:Scattering, Radiation; D013552:Swine