THE INFLUENCE OF INTRAOCULAR-PRESSURE AND SYSTEMIC OXYGEN-TENSION ON THE INTRAVASCULAR PO(2) OF THE PIG RETINA AS MEASURED WITH PHOSPHORESCENCE IMAGING

The intravascular-oxygen tension (pO(2)) of the pig retina was determi ned hy measuring the phosphorescence lifetime of an intravenously inje cted dye. Pseudocolor images of the intravascular retinal pO(2) were o btained. The method is noninvasive except for the application of the d ye. The measurement system was adapted to a fundus camera. The systemi c arterial oxygen pressure (PaO2) as well as the intraocular pressure (IOP) were altered. In the measurements the pO(2) of the choriocapilla ris was close to the systemic PaO2. Under normoxia, the retinal veins showed a lower pO(2) of about 40 mm Hg. We found evidence of an autore gulation of the retinochoroidal pO(2). The retina and the optic nerve head showed an autoregulation of the intravascular pO(2) at low IOP, h ut were more sensitive to a moderate elevation of the IOP about 40 mm Hg, as compared to the choroidal pO(2). The pO(2) of the choriocapilla ris seemed to change little until the considerably high IOP value of a bout 50 mm Hg was attained. This behavior is due to either the high pe rfusion reserve capacity of the choroid or to autoregulation. Although our experiments refer to the perfusion of the pig eye, the results pr ovide indirect evidence that even during a glaucoma attack the human c horoid might be able to maintain a reasonable oxygen supply to the ret ina, whereas the intravascular pO(2) of the retinal vessels and of the optic nerve head decrease strongly. The adaptation to a fundus camera Facilitates a future clinical application if a nontoxic dye can de de veloped. (C) 1997 by Elsevier Science Inc. All lights reserved.