The Pressure Dependency of Aqueous Humor Formation in the Anesthetized Cat

Abstract

In cats anesthetized with pentobarbital Na, a highly significant correlation was found between the rate of aqueous humor production and eye arterial perfusion pressure (blood pressure minus intraocular pressure). The filtration coefficient for water was 0.312 μl min^––1 mm Hg^––1. This value is not significantly different from those reported earlier for enucleated, arterially perfused eyes of the same species.

Fluid Transport across the Isolated Porcine Ciliary Epithelium

“…The relative contribution of these forces to the production of aqueous humor is still an open question, although most researchers accept a contribution from both. [1][2][3][4] Only three studies have measured the actual spontaneous movement of fluid, which occurs secondary to active transport mechanisms, across the isolated ciliary epithelium. [5][6][7] All quantified a fluid transport rate that was many times less than the generally accepted rate of in vivo aqueous formation.…”

“…One obvious consideration is that hydrostatic pressure may be an important driving force in vivo by inducing ultrafiltration, as previously proposed. [1][2][3][4][5] Alternatively, it is also possible that in the isolated preparation, without blood supply, the rate of active transport decreases. This may be due to a partial collapse of the ciliary processes in the divided chambers, and/or the possibility that the blood circulation provides hormones or other paracrine agents that stimulate active ionic transport, which are obviously not present in the in vitro bathing solutions.…”

Fluid Transport across the Isolated Porcine Ciliary Epithelium

“…The relative contribution of these forces to the production of aqueous humor is still an open question, although most researchers accept a contribution from both. [1][2][3][4] Only three studies have measured the actual spontaneous movement of fluid, which occurs secondary to active transport mechanisms, across the isolated ciliary epithelium. [5][6][7] All quantified a fluid transport rate that was many times less than the generally accepted rate of in vivo aqueous formation.…”

“…One obvious consideration is that hydrostatic pressure may be an important driving force in vivo by inducing ultrafiltration, as previously proposed. [1][2][3][4][5] Alternatively, it is also possible that in the isolated preparation, without blood supply, the rate of active transport decreases. This may be due to a partial collapse of the ciliary processes in the divided chambers, and/or the possibility that the blood circulation provides hormones or other paracrine agents that stimulate active ionic transport, which are obviously not present in the in vitro bathing solutions.…”

Fluid Transport across the Isolated Porcine Ciliary Epithelium

“…The relative contribution of these forces to the production of aqueous humor is still an open question, although most researchers accept a contribution from both. [1][2][3][4] Only three studies have measured the actual spontaneous movement of fluid, which occurs secondary to active transport mechanisms, across the isolated ciliary epithelium. [5][6][7] All quantified a fluid transport rate that was many times less than the generally accepted rate of in vivo aqueous formation.…”

“…One obvious consideration is that hydrostatic pressure may be an important driving force in vivo by inducing ultrafiltration, as previously proposed. [1][2][3][4][5] Alternatively, it is also possible that in the isolated preparation, without blood supply, the rate of active transport decreases. This may be due to a partial collapse of the ciliary processes in the divided chambers, and/or the possibility that the blood circulation provides hormones or other paracrine agents that stimulate active ionic transport, which are obviously not present in the in vitro bathing solutions.…”

Fluid Transport across the Isolated Porcine Ciliary Epithelium

“…The relative contribution of these forces to the production of aqueous humor is still an open question, although most researchers accept a contribution from both. [1][2][3][4] Only three studies have measured the actual spontaneous movement of fluid, which occurs secondary to active transport mechanisms, across the isolated ciliary epithelium. [5][6][7] All quantified a fluid transport rate that was many times less than the generally accepted rate of in vivo aqueous formation.…”

“…One obvious consideration is that hydrostatic pressure may be an important driving force in vivo by inducing ultrafiltration, as previously proposed. [1][2][3][4][5] Alternatively, it is also possible that in the isolated preparation, without blood supply, the rate of active transport decreases. This may be due to a partial collapse of the ciliary processes in the divided chambers, and/or the possibility that the blood circulation provides hormones or other paracrine agents that stimulate active ionic transport, which are obviously not present in the in vitro bathing solutions.…”