RETINAL ARTERY AND VEIN PRESSURES IN THE DOG AND THEIR RELATIONSHIP TO AORTIC, INTRAOCULAR, AND CEREBROSPINAL-FLUID PRESSURES

The relationship between retinal arterial (P-ra) and aortic (P-a) pres sures is unknown, and the relationship between retinal vein (P-IV) pre ssure and intraocular pressure (IOP) is not clear. Also unclear is the effect of cerebrospinal fluid pressure (CSFp) upon retinal venous pre ssure. We aimed to measure the relationships among P-ra, P-IV, P-a, IO P, and CSFp. Dogs were anesthetized while IOP, CSFp, and P-a were moni tored. Pipettes with 2.5-mu m diameter tips, connected to a servonulli ng pressure transducer, were used to record pressures from the retinal arteries and veins. Across a range of IOP (16-22 mmHg), CSFp (0-21 mm Hg), and P-a (23-195 mmHg) the P-ra = 0.72 P-a + 4.3 (r = 0.99, n = 61 , P < 0.01), which suggests that the relationship between P-ra and P-a is linear over a broad range of systemic blood pressures. The correla tion coefficient between P-IV and IOP was greater than 0.96 (P < 0.01) at all venous sites and whether IOP was greater than or less than CSF p. The transmural pressure varied along the retinal vein from 1.3 +/- 0.3 mmHg (+/-95% CI, n = 30) at 1 disk diameter from the optic disk ri m to 0.3 +/- 0.2 mmHg (n = 66) at the optic disk, with a 0.9-mmHg/mm p ressure gradient. These are the first measurements demonstrating a ret inal vein transmural pressure close to zero. (C) 1997 Academic Press.