The bulk drainage of aqueous humour into the general circulation and into the orbital tissues was studied with ¹³¹I-labelled albumin and red dextran (molecular weight 40,000) in rabbits with and without cyclodilaysis.

In animals at a normal intraocular pressure of about 20 mm Hg and without an artificial cleft between the anterior chamber and the suprachoroid the rate of aqueous bulk flow into the general circulation was 3.99 ± 0.55 μl/min. There seemed to be some outflow also through other routes ending up in the episcleral tissues in the limbus region but less than 0.11 ± 0.02 μl/min was drained in that way.

Even in dead eyes maintained at an intraocular pressure of 14 mm Hg only negligible quantities of labelled anterior chamber fluid passed into the tissues with bulk flow.

In acute experiments in living animals, after a cleft had been opened between the anterior chamber and the suprachoroid without damaging the sclera, the rate of aqueous production was 5.64 ± 0.65 μl/min. On an average 54% of the aqueous humour was drained into the suprachoroid from where great amounts penetrated the sclera in part by way of perivascular spaces in part directly through the scleral substance. Before the cleft was produced the facility of outflow was 0.237 ± 0.038 μl/min per mm Hg, afterwards it was on an average 0.505 ± 0.092 μl/min per mm Hg higher.