title: Retinal oximetry using intravitreal illumination.
abstract: OBJECTIVE
  To demonstrate spectroscopic retinal oximetry measurements on arteries and veins in swine using intravitreal illumination. Retinal arterial and venous saturations are measured for a range of inspired O2 levels after pars plana vitrectomy.
  
  
  METHODS
  Pars plana vitrectomy and intravitreal manipulations were performed on two female American Yorkshire domestic swine. Light from a scanning monochromator was coupled into a fiberoptic intraocular illuminator inserted into the vitreous. The retinal vessels were illuminated obliquely, minimizing vessel glints. Multispectral images of the retinal vasculature were obtained as the swine's arterial blood oxygen saturation was decreased from 100% to 67% in decrements of approximately 10%. Retinal vessel spectra were used to calculate oxygen saturation in selected arteries and veins. Arterial oxygen saturations were calibrated using blood gas analysis on blood drawn from a Swan-Ganz catheter placed in the femoral artery.
  
  
  RESULTS
  Oblique illumination of retinal vessels using an intravitreal fiberoptic illuminator provided a substantial reduction in the central vessel glint usually seen in fundus images, thus simplifying the analysis of spectral data. The vessel shadows were displaced from the vessel image simplifying the light paths in the eye. Using a full spectral analysis simplified by the light path reductions, we calculated retinal vessel saturations. The reduction of glint allowed for increased accuracy in measuring retinal vessel spectral optical density. Abnormally low retinal venous oxygen saturations were observed shortly after pars plana vitrectomy.
  
  
  CONCLUSIONS
  Retinal oximetry using intravitreal illumination has been demonstrated. As a research tool, intravitreal illumination addresses several difficulties encountered when performing retinal oximetry with transcorneal illumination.
authors.affiliation: Optical Sciences Center, University of Arizona, Tucson, Arizona 85721, USA. salyer@optics.arizona.edu
authors.forename: David A
authors.initials: DA
authors.lastname: Salyer
authors.forename: Neil
authors.initials: N
authors.lastname: Beaudry
authors.forename: Sreenivasa
authors.initials: S
authors.lastname: Basavanthappa
authors.forename: Karen
authors.initials: K
authors.lastname: Twietmeyer
authors.forename: Mohammad
authors.initials: M
authors.lastname: Eskandari
authors.forename: Kurt R
authors.initials: KR
authors.lastname: Denninghoff
authors.forename: Russell A
authors.initials: RA
authors.lastname: Chipman
authors.forename: Robert I
authors.initials: RI
authors.lastname: Park
mesh_terms: D000818:Animals; D005260:Female; D005336:Fiber Optic Technology; D008962:Models, Theoretical; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D010775:Photic Stimulation / Q000379:methods; D012160:Retina / Q000378:metabolism*; D012161:Retinal Artery / Q000378:metabolism; D012169:Retinal Vein / Q000378:metabolism; D013552:Swine; D014822:Vitreous Body
chemical_list: D010100:Oxygen