Retinal Artery and Vein Pressures in the Dog and Their Relationship to Aortic, Intraocular, and Cerebrospinal Fluid Pressures

Abstract

The relationship between retinal arterial (Pra) and aortic (Pa) pressures is unknown, and the relationship between retinal vein (Prv) pressure and intraocular pressure (IOP) is not clear. Also unclear is the effect of cerebrospinal fluid pressure (CSFp) upon retinal venous pressure. We aimed to measure the relationships among Pra, Prv, Pa, IOP, and CSFp. Dogs were anesthetized while IOP, CSFp, and Pawere monitored. Pipettes with 2.5-μm diameter tips, connected to a servonulling pressure transducer, were used to record pressures from the retinal arteries and veins. Across a range of IOP (16–22 mmHg), CSFp(0–21 mmHg), and Pa(23–195 mmHg) the Pra= 0.72 Pa+ 4.3 (r= 0.99,n= 61,P< 0.01), which suggests that the relationship between Praand Pais linear over a broad range of systemic blood pressures. The correlation coefficient between Prvand IOP was greater than 0.96 (P< 0.01) at all venous sites and whether IOP was greater than or less than CSFp. 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 rim to 0.3 ± 0.2 mmHg (n= 66) at the optic disk, with a 0.9-mmHg/mm pressure gradient. These are the first measurements demonstrating a retinal vein transmural pressure close to zero.